Document 70OmyO43jgKQvRr0mvopmGxno

GDOD[JOD[rJ Vinyl chloride monomer... What you should know s are o for ; This survey of the VCM (vinyl chloride monomer) industry, commercial developments, chemistry, commercial processes and new developments indicates that VCM can remain competitive with rising crude costs R. W. McPherson, C. M. Starks and G. J. Fryar, Continental Oil Co,, Ponca City, Okla. Development of the vinyl chloride monomer (VCM) industry has been closely interrelated with the polyvinyl chloride (PVC) industry. Effectively 96 percent of the VCM production goes into the manufacture of PVC. Therefore, technological advances in one area have significant impacts upon the other, producing a domino effect. This, in conjunction with increasingly tighter en vironmental regulations, has insured a continuing evolu tion of VCM technology. It is timely to review the state of the art. INDUSTRY PROFILE The commercial significance of vinyl chloride monomer (VCM) can be highlighted by the statistical ranking of the 19th largest chemical commodity in the United States. Turning our vierw upstream, we realize the significance VCM plays in wedding the petrochemical and chloroalkali industries. Fig. 1 schematically depicts the U.S. market integration surrounding VCM. Pondering the posture individual companies present to the market (Table 1), one can muse as to the motivational forces behind their respective business strategics. It holds that, if 96 percent of the VCM demand in this country is derived from PVC, then VCM's future is inescapably tied to that of PVC's. Within the scope of known-unknowns, one basic fact attests to its longevity. On an energy-equivalent basis, PVC is one of the most energy-efficient construction materials available (Table 2). This follows even after weighing the socioeconomics of health and environment. Looking at the two principal components of the PVC 1 ' v -a tr Cj Rg. 1--Shows the U.S. market integration surrounding vinyl chloride industry. Hydrocarbon PROCEsstNG March 1979 Export Tj , ' *i,, ' 7TTT tc- >.*..... 75 COLOR!TE 019612 VINYL CHLORIDE MONOMER market, flexible or plasticized products, of which fabric for automobile interiors and electrical wiring insulation are examples, and rigid products, including sewer and water pipes, electrical conduits and shoe soles, we find the rigid aggregate growing at 9 percent per year, as opposed to the flexible area which is increasing at a rate of approximately 5 percent. Within the past few years, the rigid aggregate has surpassed the size of the flexible market which can be witnessed by the creeping seasonal response the VCM industry has to construction, the major end-use outlet for rigid products. Wood PVC Steel Aluminum Copper Fig. 2--Relative energy content of various construction materials. TABLE 1--Nameplate capacities (MM pounds) Borden. .. ....... Conoco.......... Diamond.. Dow.. Ethyl .. . B. F. Goodrich , .. ICI ....................... Monochem. PPG ... Shell.... Stauffer. .. PVC 550 550 None None 175 1,100 None None None None 420 VCM 300 700 1,000 2,250 300 1,100 300 300 900 1,540 170 Ethylene None 650 None 4,800 None 350 None None None 2,700 None Chlorine None None 2,500 8,400 500 250 300 None 2,900 200 780 TABLE 2--Commercial types of VCM technology I. High Purity Acetylene Feedstock II. Dilute or Mixed Gas Feedstock III. Balanced Ethylene Feedstock A. Air-Based Oxychlorination B. Oxygen-Based Oxychlorination Developer/Licensor Dow......................................... Ethyl, ICI, Solvay.................................... B. t. Goodrich......................................... Kureha.......................... Mitsui Toatsu................ , .. Monsanto.......................................... PPG.................... Rhone Poulenc...................... Stauffer....................... Tokuyama Soda..................................... ToyoSoda................................... Hoechst........... . ICI................... Technology Basic Oxychlorination III A Ml A III A,B II III B Ml A,B III B III A III A,B III A III A 1 1" Over the course of the past ten years, VCM has be come a major item of international commerce, with the United States the architect of this business. Between 1975 and 1977, eight percent of the VCM produced was carried ofTshore, making it third only to styrene nionomci and toluene in the generation of trade dollars bv a chemi cal commodity. This factor has tended to fill in the valley in demand brought about by construction. More signifi cantly, it has permitted the VCM industry to consistcnth operate near capacity levels by exporting domestic suipluses into the world arena. Looking at the global VCM market, we view forces at work changing the disposition of trade. Beginning within the past five years, Europe as a whole has swung from a net importer to cxportei of VCM. With ten billion pounds of VCM rapaciu integrated to where there is less than IS percent merchantly derived PVC demand, producers are now chal lenging U.S. material for a share of the remaining world exports. Japan, whose five billion pound VCM industry wa-. built to serve the whole of the Asian-South Pacific market, first in PVC and then later in VCM. has witnessed a major influx of U.S. and now European monomer pro ducers into their domain. The present situation in the U.S. is manifested b\ cheaper feedstocks, vis-a-vis energy, and an undervalued currency that together are able to offset logistical cost* and remain competitive in the consuming markets. Eventually, merging energy parity and emission cost pass throughs will leave U.S. VCM no more competitive than that of any other nation. We conclude, therefore, that exports will continue as developing third world markets seek to establish a plastics industry in advance of petro chemicals. Conversely, the major market imbalances of the past have gone by the wayside, and market growth will come from the domestic sector. Fig. 3 depicts the longer term outlook for VCM. In making our projections, we assume that the growing capital commitment required to make VCM will not force PVC to become uncompeti tive with alternative products. Secondly, we foresee no major technological innovation on the horizon that could radically alter the economics of production. We do see. however, technological improvements of degree that di rectionally level out the inflationary trend of plant con struction. Within the U.S., we project a 700 to 1.000 MM lb. per year grass roots plant will be required every two years to meet demand. It is within the scope of this time frame that innovation will be tested, COMMERCIAL DEVELOPMENT VCM was first produced commercially in the early 1900s via reaction of HCI and acetylene derived from calcium carbide. VCM usage in the manufacture of syn thetic rubber accelerated dramatically during and after World War II. This increased demand prompted searches for more economical hydrocarbon feedstocks. Acetylene was recovered from refining steps, and new technology was developed to produce acetylene specifically from hydrocarbon cracking. Ethylene became plentiful in the early 1950s. Direct chlorination processes to produce 1,2-dichloroethane (EDC) from chlorine and ethylene were developed in 76 March 1979 Hydrocarbon Processing COLORITE 019613 conjunction with EDC cracking technology to yield VCM This process yielded byproduct HC1 and did not pro liferate immediately, except in conjunction with acety lene-based technology which needed HC1 to produce VCM, In the U.S., ethylene production from abundant sup plies of low cost LEG began to predominate. In Europe, ethylene prices also continued to drop, though not to the same degree since higher priced naphtha and gas oil were the primary feedstocks. Therefore, while European producers continued to use acetylene-based VCM tech nology, American companies moved rapidly to ethylenebased technology. With the startup in 1958 of the first large scale oxychlorination process to yield EDC from HC1 and ethylene, a new era in VCM technology began. This "balanced" process allowed production of VCM from two commodity chemicals, chlorine and ethylene, without voluminous byproduct HC1. VINYL CHLORIDE CHEMISTRY Large scale production of vinyl chloride was first done by addition of hydrogen chloride to acetylene: Fi8. 3--U.S. vinyl chloride nameplate capacity versus demand Hydrochlorination of acetylene Catalyst HC1 + HC = CH -------------* HC2 = CHC1 (1) However, much lower costs for production of ethylene than acetylene and the discovery that 1,2-dichloroethane (EDC) thermally decomposes to vinyl chloride in excel lent yield led to the following reaction sequence as the predominant manufacturing method for VCM: Direct chlorination of ethylene CHS = CH2 + CL -- CICHjCHjCl EDC cracking to VCM Heat C1CH2CH2C1 ----* CHS = CHC1 + HC1 This method was especially advantageous for those producers having a use for the HC1 by product, particu larly so if acetylene were available; since then, a bal anced VCM process with no coproducts could be op erated. Later, the discovery that oxychlorination technology could be applied to ethylene to give 1,2-dichloroethane in high selectivity now allowed a completely balanced process based only on ethylene and chlorine as feedstocks. Oxychlorination of ethylene Catalyst CH2 = CH2 + 2HC1 + 1 /20j ------------- - CICHjCHjCl + HjO At present, about 92 percent of the vinyl chloride pro duced in the United States is from plants that use the balanced process based on ethylene via chlorination, oxychlorination, and thermal cracking of EDC.1 These three separate steps are described in greater detail below. Additionally, the hydrochlorination of acetylene is also discussed below since plants using this chemistry are still in operation. Moreover, some recent crude oil cracking technology may narrow the cost gap between acetylene and ethylene with consequent revival of interest in VCM from acetylene. Some chemistry on direct preparation of VCM from ethane is also briefly outlined. Direct chlorination of ethylene. Direct chlorination of ethylene to 1,2-dichloroethane is almost always conducted in a liquid phase reactor by intimately mixing ethylene and chlorine in liquid EDC. Ferric chloride, a highly efficient and selective catalyst for this reaction, is normally used in commercial processes. Amides, such as n,ndimethylformamide, have been reported to increase PVC selectivity.1 Oxygen, frequently present as an impurity in chlorine, likewise increases EDC selectivity in direct chlorination of ethylene by inhibition of free radical re actions that give 1,1,2-trichloroethane. Direct chlorination reactions may be run rich in either ethylene or chlorine, depending on the methods available to the plant for handling offgases from this reactor. Con version of the lean component is usually 100 percent, and selectivity to EDC is greater than 99 percent. 1,2-Dichloroethane, as it comes from the direct chlori nation reactor, is frequently of sufficient purity for crack ing, except that it may contain ferric chloride, which would lead to rapid fouling of the cracking reactor. To avoid expensive purification of this already pure EDC, one may remove FeCf, by adsorption on activated carbon3 or other solids.4 Alternately, one may operate the direct chlorinator at the boiling point of EDC, taking pure EDC overhead and using the heat of reaction to supply the heat for vaporization.5'6,7,8 Oxychlorination of ethylene to EDC. Ethylene oxy chlorination is normally conducted at temperatures of 225-325 C and at pressures of one to 15 atmospheres. Catalysts for this reaction almost always contain copper chloride and sodium or potassium chloride deposited on alumina or other suitable support. The detailed mech- Hydrocarbon Processing March 1979 77 COLORITE 019614 VINYL CHLORIDE MONOMER anism of the catalyst's activity is not known, but it is recognized that cupric chloride is the active chlorinating agent. The cuprous chloride produced is rapidly recon verted to CuCl; under the reaction conditions, but the presence of some cuprous chloride is thought to be advantageous because it complexes with ethylene, bring ing it into contact with CuCla for a long enough time for chlorination to occur. The sodium or potassium chloride serves to increase EDC selectivity, mostly by inhibiting formation of ethyl chloride. Other catalyst components, such as rare earth metal chlorides, sulfate salts, ferric chloride and numerous other additives, have been de scribed in the patent literature. Good temperature control of the highly exothermic oxy reaction is a key element in successful production of 1,2-dichIoroethane. Temperatures higher than about 325C lead to increased byproduct formation, mostly through increased dehydrochlorination of EDC to vinyl chloride followed by additional oxychlorination to give products having high levels of chlorine substitution. High temperatures also increase the amount of ethylene burned to carbon monoxide and carbon dioxide. Of equal im portance, high temperatures deactivate the catalyst by highly accelerated coking and consequent powdering of the catalyst units and by increased sublimation of copper, chloride away from the catalyst. Temperature control in fluidized bed reactors is main tained by the excellent intermixing of the catalyst par ticles and by use of internal cooling surfaces.1<' Tempera ture control in fixed bed reactors is more difficult since "hot spots" tend to develop. To keep the hot spot temperature below below 325 C, yet get maximum utilization from the reactor, it is common practice to pack the reactor tubes with active catalyst and inert diluent mixtures in proportions of each so adjusted as to have low catalyst activity at the inlet, steadily in creasing to maximum activity at the outlet. This grading of the catalyst activity flattens the temperature profile, allowing for good temperature control with high produc tivity. For example, one patent8 indicates the use of four zones with 93 percent, 85 percent, 40 percent, and 0 percent, respectively, of the active catalyst pellets replaced by inert graphite. As an alternate to using inert materials in the catalyst bed, catalysts, each with higher levels of CuCl2 and consequently of increasing reactivity, are sometimes used. Fluid bed oxychlorination of ethylene, operated under good control, results in 94-97 percent ethylene conver sion, 95-97 percent HC1 conversion, and EDC selectivities in the range of 94-96 percent. Fixed bed oxychlorinations are normally run with excess ethylene relative to HC1, resulting in 93-97 percent ethylene conversion, 94-95 percent HC1 conversions, and EDC selectivities of 93-95 percent. These data do not include recovery of excess ethylene in subsequent reaction steps. Excess ethyl ene in vent gases from oxychlorination is normally con verted to EDC by direct chlorination with chlorine,11-11 although, if oxygen is used rather than air, the excess ethylene may be recycled directly back to oxychlorination. Byproducts of ethylene oxychlorination are vinyl chlo ride, ethyl chloride, 1,1-dichloroethane, vinylidene chlo ride, cis- and tranr-I,2-dichloroethylenes, trichloroethyl ene, chloroform, carbon tetrachloride, methyl chlondc. methylene chloride, chloral and high boiling compound-. All of these byproducts present problems in one was oi another, such that their production needs to be minimized to lower raw material costs, to lessen the difficulties ol preparing pure EDC, and to prevent fouling in tin cracking reactor. Chloral, in particular, needs to be 11 moved since it polymerizes readily in strong acids to give solids which clog and foul operating lines ami controls. One must also take care to see that the feeds to oxychlorination are pure. Normally, the only problem is with low levels (0.1 to 0.5 percent) of acetylene present in the HC1 from cracking of EDC. Acetylene in the Iced leads to the formation of considerable highly chlorinated byproducts and tars. Selective hydrogenation of this acetylene to ethylene and ethane is practiced by many companies.15 Oxychlorination with oxygen instead of air. Use of oxygen instead of air for ethylene oxychlorination has received much attention.14"19 The outstanding benefits from using oxygen are avoidance of expensive facilities to recover EDC, ethylene and other chemicals from tinlarge nitrogen vent gas stream; a large reduction in tiltquantity of offgases that will probably need to be in cinerated ; and the ability to use ethylene as a diluent foi oxychlorination, a procedure said to improve heat transfei in tubular reactors. purification of EDC for cracking. Great care must be taken to ensure that EDC used for cracking to vinyl chloride is of high purity, normally greater than 99.5 peicent, since cracking is exceedingly susceptible to inhibition and fouling by trace amounts of impurities. Additionally, the EDC must be bone dry to prevent excessive corrosion downstream of the cracker. For these purposes, one must consider removal from EDC of byproducts from three sources: EDC from direct chlorination, EDC from oxy chlorination, and EDC recovered from the cracking step (see below). EDC from direct chlorination is usually quite pure, greater than 99.5 percent; and, except for the FeCU present, it needs little further purification. As mentioned previously, ferric chloride may be removed by adsorption on a solid, or the EDC may be distilled away from FeClj in a boiling reactor. Alternatively, the ferric chlo ride may be removed by washing with water, usually in conjunction with oxy-EDC. 1,2-Dichloroethane from oxychlorination contains a variety of impurities as listed previously. EDC from this source is usually washed with water and then with caustic solution to remove chloral and other water extractablc impurities.20 Low boiling impurities and water are taken overhead in a first (light ends) distillation column, and then pure dry EDC is taken overhead in a second (heavy ends) column. EDC recovered from the cracking step contains an j j I 78 March 1979 Hydrocarbon Processing COLOR!TE 019615 appreciable number of impurities, of which two, chloroprene and trichloroethylene, are not readily removable by distillation, necessitating the use of other treatments. Chloroprene, if not altered by chemical treatment, con centrates in the light ends column where it can polymerize to solid or rubbery materials which seriously foul and upset this column. Trichloroethylene forms an azeotrope with EDC, boiling very close to EDC. If it is not removed in some way, it accumulates in the EDC, leading to re duced cracking rates and increased fouling. Both impuri ties may be removed by subjecting the recycle EDC stream to chlorination prior to distillation.1153 Treatments with HC121'26 and by hydrogenation27 have also been patented as methods for removal of chloroprene. Cracking of 1,2-dichloroethane to vinyl chloride. At temperatures in the range of 425-550 C, and near at mospheric pressure EDC undergoes clean thermal dehydrochlorination (cracking) to yield vinyl chloride and hydrogen cloride: Heat C1CHSCH,C1 --------- 1 CH2 = CHC1 + HC1 The mechanism of this reaction has been extensively investigated28 and shown to involve a sequence of free radical intermediates. Use of pressure up to 25 to 30 atmospheres during cracking at temperatures of 500-550 C provides better heat transfer, reduced equipment size and easier separa tion of HC1 from the product by fractional distillation. EDC conversion levels are normally maintained in the range of 50 to 60 percent at residence times of 2 to 30 seconds, with selectivities of VCM ranging from 96 to 99* percent. Some byproducts generated during crack ing act as inhibitors to the free radical sequence so that increasing severity leads to smaller and smaller increases in EDC conversion with correspondingly increasing levels of byproducts. Various materials, such as chlorine, bro mine, or oxygen have been shown to be initiators for EDC cracking.28 Recently, however, exclusion of oxygen is claimed to result in considerable reduction of fouling on the cracker tube walls.20 A rather spectacular claim has been made that use of nitromethane as an initiator provides EDC conversion levels of up to 92.5 percent at 480 C.80 An important processing requirement in EDC cracking is rapid cooling or quenching of the re action mixture. If cooling is done too slowly, substantial yield losses to heavy ends and tars result.25,80,81 Byproducts from the cracking reaction include acetyl ene, ethylene, methyl chloride, butadiene, vinyl acetylene, benzene, chloroprene, vinylidene chloride, 1,1-dichloroethane, chloroform,, carbon tetrachloride, 1,1,1-trichloroethane and other compounds. Most of these impurities remain in the unconverted EDC fraction and are re moved when this stream is distilled. Ethylene and acety lene codistill with the HC1 and are thus routed back to oxychlorination (after optional hydrogenation of the acetylene to ethylene). Methyl chloride and butadiene more or less codistill with the vinyl chloride, depending on the efficiency of the VCM fractional distillation sys tem. Addidon of chlorine or carbon tetrachloride to the cracker feed is claimed to suppress methyl chloride for mation.88 Removal of butadiene, a contaminant which can interfere with polymerization of VCM, has been done by treatment with chlorine,31 anhydrous HO,37 or selective hydrogenation.30 HCI addition to acetylene. Recent development of a new crude oil cracking process27 using very high tem perature steam (2,000 C) as a heat transfer fluid pro duces substantial yield of acetylene along with ethylene Under some economic and geographic conditions, the use of this cracking process may be advantageous and may, thereby, provide acetylene for vinyl chloride pro duction. Typical conditions of hydrogen chloride addition to acetylene are total pressures on the order of five to 15 atmospheres, temperatures of 150 to 180 C, and use of a mercuric chloridc-on-carbon catalyst.88 With stoichio metric quantities of reactants, essentially 100 percent con version is observed with VCM selectivities on the ordei of 98 percent. It is notable that ethylene does not react under these conditions, thereby allowing the use of mixed ethylene-acetylene streams as feeds. Ethylene, easily re covered from the vinyl chloride product by fractional distillation, is then chlorinated to yield 1,2-dichloroethane Other catalysts have been shown to be effective foi addition of HCI to acetylene, but HgCI2 is vastly supe rior.58 However, in addition to the general toxicity prob lems involved in working with mercury-containing substances, HgCl2 has appreciable volatility under the above reaction conditions leading to a need for consideiable care and control in operation of the reactor. In fixed bed operations, HgCl2 vaporizes from the hot spot of the reactors, condenses at cooler locations downstream and results in continuous movement of the hot spot downstream with eventual loss of catalytic activity. This loss is minimized by periodic reversal of flow through the reactor. Ethane-based vinyl chloride processes. A number of patents dealing with chemistry for conversion of ethane to EDC and/or VCM have been published in recent years.10-11 Most of these reactions involve high tempera ture oxychlorinations, such as CuCl2 Catalyst CHjCH3 + HCI + O, ------------ / 350-450 C CH2 = CHC1 + 2H20 However, these processes suffer from a number of dis advantages, the most important of which includes low selectivities, low conversions and difficult operating con ditions such as CuCl2 sublimation. One reaction system based on ethane, called the "TRANSCAT" process, has been developed on a large pilot plant scale but is not yet in commercial practice.15*13 The chemistry of this process is a complex series of re actions, generally involving chlorination, dehydrochlorination and oxychlorination. A mixture of'ethane, eth ylene, ethyl chloride, chlorine and HCI are fed to a melt of cupric oxychloride and potassium chloride, yielding vinyl chloride, water, and cuprous chloride as the main products. The cuprous chloride-potassium chloride prod uct is taken to an oxidation reactor where the cupric oxychloride is regenerated by treatment with air. Vinyl chloride is separated from the organic product and puri- Hydrocarbon Processing March 1979 79 COLOR!TE 019616 VINYL CHLORIDE MONOMER TABLE 3--Cun nt VCM technology sources fied by fractional distillation. Removal of about 0.4 per cent butane plus butenes present in the main VCM cut represents a very difficult separation.45 Ethyl chloride and ethylene can be recycled into the feed. Chlorine values in the chlorinated byproducts can be recovered by incineration and then feeding these gases to the cuprous chloride oxidative regenerator reactor. Disposal Of byproducts. Disposal of byproducts pre sents special problems for vinyl chloride manufacturing plants, since a variety of gaseous organic liquid, and acqueous streams must be handled, each with its own particular problems. Vent gas streams from various units may contain small amounts of HCI, chlorine, ethylene, vinyl chloride, methane and carbon monoxide. These streams may some times be treated by scrubbing, chemical treatment, sorption, or other methods to recover some chemicals when economically justified. Otherwise, the common cleanup technique is either incineration or catalytic com bustion followed by recovery of HCI from the vent gases. Two organic byproduct streams are produced. The light ends contain mainly ethyl chloride, cis- and trans1,2-dichloroethylenc. chloroform and carbon tetrachloride. The heavy ends or "tars" contain mostly 1,1,2-trichIoroethane, lesser concentrations of tetrachloroethanes, chlori nated butanes, chlorinated aromatics and a large number of other compounds present in small amounts. These streams are normally fractionated to recover useful com ponents, the others incinerated to recover chlorine values either as aqueous or anhydrous HCI. Process water streams are steam stripped to remove volatile organics followed by neutralization and then treatment in an activated sludge system to remove non volatile organics in the water.46 COMMERCIAL PROCESSES Broadly speaking, there are three types of VCM pro cesses in commercial use today. These are categorized as acetylene, ethylene, or mixed gas based on feedstock re quirement. Within the "ethylene-type" plants, further classification is desirable to distinguish the type of oxychlorination technology used, i.e., oxygen versus air feed stock (see Table 2). Over 90 percent of the world's listed 35 billion lb. per year VCM capacity currently is based upon the balanced ethylene feedstock route. Of this, just under 90 percent uses air-based oxychlorination. How ever, of the projected worldwide plant startups for the period 1979-1981, approximately 30 percent of the 7.7 billion lbs. per year VCM will be derived from oxygenbased oxychlorination. Other existing producers will un doubtedly be evaluating the conversion of present airbased plants to the use of oxygen during this time frame. Table 3 presents a summary of the technology sources in use today. It is thought that the technology currently licensed by ICI and Solvay is similar to the process normally attributed to Ethyl. Therefore, all are listed under Ethyl's technology. It is interesting to note that several plants exist where the oxychlorination process Existing VCM, Technology Source Plants MM Lbs./Yr. 1. B. F. Goodrich, .. 2. Hoechst/BFG* .. 3. Stauffer/BFG* 4. Stauffer............... 5. Ethyl, Solvay, ICI . 6. Dow..................... 7. PPG . . . 8. Rhone-Poulene... 9. Monsanto........... 10. Toyo Soda ........ 11. Tokuyama Soda .. 12. Mitsui Toatsu 13. Kureha................. 14. Miscellaneous... . 18 II 5 19 14 7 5 5 4 3 2 3 2 10 5,840 4,290 2,360 6,390 5,000 3,040 1,700 1,330 1,110 400 660 610 410 2,400 107 35,540 Planned (1979-1981) VCM, Plants MM Lbs./Yr. 4 2,160 2 580 ---- 2 350 1 260 3 1,050 3 1,780 1 500 1 250 1 330 -- ----1 90 ---- 1 330 20 7,680 `Oxychlorination process provided by BFG of one licensor, B. F. Goodrich, has been combined with direct chlorination and VCM technologies of others, i.e.. Hoechst and Stauffer. Table 4 presents a tabulation of worldwide VCM producers. This summary was prepared from scores of literature sources, some of which were contradictory. However, the authors have exercised their best judgment in the absence of specific information from the listed licensors. The reader is referred to Leonard,14 Gomi,5C or Sittig55 for details of the acetylene and mixed gas routes to VCM. The technology discussion herein will be limited to the balanced ethylene feedstock route used overwhelming]} today. Although each of the major technology licensors has many patents, none has complete coverage of each step of his process. As a result, the sequence and type of operating steps tend to be very similar from process to process. The basic differences stem from the oxychlorina tion technology and the types of impurities appearing in the crude EDC. The licensor, therefore, provides process know-how primarily, as opposed to patent position. As a result, published literature by major licensors is under standably very sparse and highly simplified, with certain exceptions.16'17 **19 TYPICAL VCM PROCESS The typical VCM process combines direct and oxy chlorination (oxy) processes to provide 1,2-dichloroethane (EDC) feedstock for the EDC pyrolysis unit (see Fig. 4). The direct chlorination process relative to oxy is char acterized by low capital investment, low operating costs and high purity product. However, HCI generated from the EDC pyrolysis unit dictates the use of an oxy unit. With the current pyrolysis yield of approximately 0.55 mol VCM per mol EDC fed, and the HCI yield of 1 mol per mol VCM, the oxy unit size is set at approximately 0.5 mol EDC per mol of VCM desired. This sets the direct chlorination unit size at approximately 0.5 mol EDC per mol VCM. The combined EDC streams are caustic treated to re- 80 March 1979 Hydrocarbon Processing COLORITE 019617 Fig. 4--Typical vinyl chloride monomer block/flow diagram. Direct chtoriMbon Reactor Reactor Reactor OiycMorifiatiort Reactor Reactor eoc putfcwtioft 5 Schematic of the Stauffer vinyl chloride monomer process. Hydrocarbon Processing March 1979 VCM purttaation 81 COLOR!TE 019618 TABLE A--VCM plants--worldwide--(cont'd) Optra tor Location Procats Startup Year** Licensor Engineer/ Contractor VCM Capacity, MM Lhi/Tr4* Italy Amc Montedison Rumianca Sud SARP Sincat Sotoic Sir Consorzio industries Ravenna Brindisi Porto Marghera Caglitri Cijtian Termini Imersee Priolo Rayamtno Porto Torres Asaht Penn Chiba VCM Chisso Oenkt Kagaku Japanese Geon Ktnegafuehi Kanegdfuchi Kashima VCM Kureha Mitsubishi-Monsanto Mitsui Toatsu Nissan Ryo-Nichi Co., Ltd. Sanyo Monomer Shunan Petrxhemicals Sumitomo Sun Arrow Chemical Toyo Gosei Toyo Soda Chiba Chiba Mimmote Chiba Takaoka Takasaga Takasaga Kashima Nishiki Yokkaichi Nagoya Osaka Chiba Mizushima Mizushima Tokuyama Niitiama Tokuyama Tokushima Tokuyama City Yokkaichi Keru Korea Pacific Korea Pacific Yeo-Su Uisan Libya GnOl Mexico Pemex Morocco SNEP Abu Kammash Pajaritos Pajaritos Mohammadia Norway Norsk Hydro Raines Peru Sociedad Paramonga LTDA Paramonga Poland PoHroex-Cekop Wioctawek Portugal CNP Sines Rumania Industrial Import :! State Authority ti/mnieu Vilcea Rimmcu Vilcea South Africa Africa Explosives and Chemicals / SasOlburg \ Sasolburg A/-/M/A/0 M/A/0 E/-/D t/A/O AC/-/0 E/A/B M/-/D E/A/B E/A/B E/A/B M/-/D At/A/- AE/A/O E/A/6 AE/A/O E/A/B AE/A/O A/-/E/A/B E/A/O M/-/D E/A/B E/A/B E/A/B E/A/B E/A/O E/0/B Planned e/o/b E/-/D A/-/- 1971 ms 1970 ms 1976 1967 1971 1967 1969 1970 1970 1964 1970 1964 1970 1968 1970 1970 1969 1967 1966 (1979) (1980) 1978 1976 1978 (1979) (1981) 1968 1978 Stauffer BFG BFG PPG PPG Ethyl Solvay Sir PPG Stauffer Toyo Soda Denkj Kagaku Japanese Geon Stauffer Stauffer BFG Kureha Monsanto Mitsui Toatsu Mitsui Toatsu Toyi Soda BFG BFG Tokuyama Soda Stauffer Tokuyama Soda Toyo Gosei Toyo Soda Toyo Soda Dow Dow BFG, Hoechst Monsanto BFG Stauffer BFG, Hoechst Vulcan PPG Dow Mitsui Toatsu ICI, Solvay Tenneco Opt, Se/as Solvay Euteco Sumitomo Sumitomo Kanegafuchi Chiyoda Toyo Engineering Toyo Engineering Fluor/Daelim Procon f. Uhde, Salzgitter Lummus Bulele Krebs Badger Petiocarbon, Davy-Powergas Klock Toyo Engineering Humphries & Glasgow Crawford-Russel 165 400 400 350 350 (110, 290 UG 310 99 350 220 (330) 257 331 331 265 130 no 130 73 440 238 440 180 220 88 UQ 220 (330> 132 (136* 155 440 59 660 17 (4501 (330- 88 350 60 440 Spain Monsanto Rio Rodano Vimcior Dow Sweden Kamanobel Switzerland Lonza Taiwan Formosa Plastic Chung Tai (7) Turkey Petkim Petkim United Kingdom British Petroleum Tarragona Tarragona Tarragona Tarragona Huelva Martonell Huelva Stenungsund Lalden Kaohuung Toufen Yarimca izmit Aliaga-lsmir Bagian Bay, Wales E/A/B E/A/B A/-/E/A/B E/O/B/ E/'/b AE/A/O (1980) 1970 (1981) 1967 Monsanto Monsanto Monsanto MRhoonnsea'nPtorogil Solvay Dow Stauffer 1973 (1981) 1971 Stauffer Mitsui Toatsu Solvay ICI, Solvay BFG McKee, CTIP McKee, CTIP Lurgi Humphreys and Glasgow CTIP 176-330 (250) 220 <5001 265 (770) 180 44 530 (530) 119 (257) 573 ICI Hjithouse Runcorn A/-/* Solvay Solvay C. F. Braun C, F. Braun USSR Techmashimport Venezuela Petroplas Yugeelevia Ork. Kem. Ind Hemlltka Ind. Otm/lna Djerjinsk Gorki Gorki Kalush Volgograd Zima El Ttbitzo Skopje Pancevo KRK E/A/B E/A/6 E/A/B 1970 1974 (1979) 1977 (1979) (1981) Rhone-Piogil Stauffer Rhone-Progil BFG, Hoechst Kureha BFG, Hoechst BFG Rhone-Progil Stauffer Dow Speichim Speichim Speichim F. Uhde Chiyoda F. Uhde Foster Wheeler 66 73 68 550 145 (595) U0 110 (220) (440) * Information tabulated from many sources. In eases (several) of contradictory reports, authors have exercised their best judgment ** Parentheses denote that plant is thought to be in engineering and/or construction stage and his not reached an operational status. kgend: Hydrocarbon Feedstock (E)thylene (A)cetylene (M)ixed Gas / Oxy Basis (A)ir (O)xygen / Process (Balanced (O)xy (D)irect 82 March 1979 Hydrocarbon Processing COLOR!TE 019619 VINYL CHLORIDE MONOMER TABLE 4--VCM plants--worldwide Operator United States ICI America Conoco Chemicals Dow Ethyl Corp B. F. Goodrich PPG Shell Chemical Stauffer Diamond Shamrock Algeria Sonatrach Dow Quimica Elect roclor Iciaru Belgium BASF Umburgse (LVM) Solvic Brazil Copamo Petroquim Camacan TechnoeompJekt Dow Shawinigan Chile Petroquimica Dow/ENAP China Technical Import Corp Petroquimica Columbiana Czechoslovakia Chemopettot Chemrckezavody W Piecka Finland Pekema Oy AKZO Chomie emc/dsm Daufac Rhone-Poulenc Sofvic PCUK/Shell Chemie East Germany Industrie Anlagen Impart West Germany Alusuisse Huls BASF Solvay Dynamit Nobel Hoechst Knapsack, AG Wacker ICI Greece Ethyl Hallas Holland AKZO Hoechst Shell? Hungary Chemokomptex Bososodi Vegyi Kombinat India CAP India National Organic Chemistry fran Abadan Petrochemical Iran-Japan J.V, Iraq State Israel Eiectrochemici! Induitries _ Location Baton Rouge. Louisiana lake Charles. Louisiana Freeport, Tetas Oyster Creek, Texas Piaquemine, Louisiana Baton Rouge. Louisiana Calvert City, Kentucky Geismar, Louisiana Lake Charles, Louisiana Lake Charles, Louisiana Guayanilla Puerto Rico Deer Park, Texas Norco, Louisiana Long Beach. California Geismar, Louisiana Piaquemme, Louisiana Deer Park, Texas Skikda Bahia Bianca Capitan, Bermudei Bahia Blanca Boforry Anvers Feluy Tessenderlo Jemeppe-Sur Eiclor Bahia Blanca Camacan Burgas Oevnya Sarnia, Ontario Fort Saskatchewan V&rennes, Quebec Shawinigan, Quebec Concepcion Concepcion Peking Neratorice Novaky, Slovakia Porvoo GonfreviUe Le Havre Ottmarsheim iarrie Lavera St. Auban St. Fons * Tavaux FosSurMer Schkopau Wilhelmshaven Mari Ludwigshaven Rheinberg lufsdorf Gendorf Knapsack Vlisstngen Knapsack Knapsack Burghausen Burghausen Wilhelmshaven Thessalomka Botlek Botlek (Expansion) Vlisstngen Pernis Berente Berente Kazincbarcika Madias Bombay Abadan Bandar Basra Haifa Akko Process E/A/B E/A/B E/A/O E/A/0 A/-/ E/O/B E/O/B E/O/B E/A/B/ E/A/B E/A/B E/A/B E/O/B E/A/B E/O/B E/A/B A/-/D E/A/B E/A/B E/A/B E/A/B E/A/B E/O/B E/A/B A/A/O E/A/O E/A/B e/a/b M/-/D Startup Year** 1968 1968 1969 1978 1964 I960 (1980) 1971 1972 1957 (1980! 1978 (1979) 1967 1972 1976 1968 1972 (1979) (1979) (1979) 1967 1969 1978 1973 1972 1972 1971 BFG Stauffer Dow Dow Oqw Ethyl Ethyl BFG PPG PPG PPG Stauffer Stauffer Stauffer Stauffer PPG Stauffer, BFG Mitsui Toatsu DICoIw BFG )CI Stauffer BFG Hoechst, BFG Hoechst, BFG Ethyl Soway, iCl BFG BFG PPG Dow Dow BFG BFG Dow B. F. Goodrich Stauffer Stauffer BFG. Hoechst Solvay Engineer/ Contractor Ford. Bacon & Davis R. M, Parsons Fluor R M Parsons R. M. Parsons C. F Braun R M. Parsons Brown and Root Lummus, Badger, Brown & Root Toyo Engineering Chemico Badger BASF Badger Badger Solvay McKee. CTIP Badger Badger/Promon Techmp/TPl Badger Fish Engineering F Uhde R. M Parsons, Voest, Alpine F. Uhde E/A/B M/./D E/A/B E/A/B e/a/b AE/-/D AE/-/D e/a/b E/A/O E/A/O EA/A/0 E/A/O E/A/B E/VO e/a/b e/a/b e/a/b E/-/D A/-/E/A/B E/A/B E/A/B 1967 1970 1965 (1980) (1979) 1973 1966 1972 1963 1971 (1980) 1971 (1979) (1981) 1978 1967 1969 (1979) (1980) (1979) Stauffer, BfG, Hoechst Rhone-Progil Rhone*Progil BFG, Hoechst Solvay, Ethyl BFG Hoechst Rhone* Progil Rhone-Progi! Solvay Badger F. Uhde Huls Stauffer Solvay Stauffer, BFG BFG, Hoechst BFG, Hoechst BFG BFG Staufier/Staulter Wacker ICI Ethyl Stauffer/BFG Hoechst Solvay C. F. Braun Uhde Badger, Uhde Badger, Uhde Badger, Knapsack R. M. Parsons R. M. Parsons Fluor Comprimo*Lurgi AKZO Engineering Hoechst BFG, Hoechst BFG, Hoechst BFG Shell, BASF BFG Toyo Soda Stauffer Monsanto Uhde Badger Badger Badger, Lummus Hitachi lummus, Thyxsen VCM Capacity, MM Lbs/Yr' 300 7ZO0O0 700 1,150 30Q 150 1,050 300 400 (I,000> 500 840 700 175 330 (1,000,' 1,000 (88) no 73 287 ? 240 (1,100' 440 440 550 220 (286' (330' (33Q> ? ($60 i 126 1? 35 35 176 265 240 m 795 291 440 440 (440) (440) (660) 700-770 160-320 440 130 375 220 (440) 220 330 176 350 (68Q) 33 660 (330) (350) 79 350 350 33 45 130 (330) 145 29 (220) Hydrocarbon Processing March 1979 83 COLORXTE 019620 VINYL CHLORIDE MONOMER Fig. 6--Modifications used in the Stauffer oxygen-based oxychlorination process. move HC1 and certain clorinated byproducts which otherwise would hinder fractionation or pyrolysis. The "clean" EDC is subjected to distillation steps in which water and other light components are removed, as well as heavy components typically labeled tars. The dry product EDC, generally of 99.5 percent or greater purity, is thermally cracked to yield HC1 and VCM in an EDC carrier stream. Further distillation equipment separates EDC and HC1 for recycle and yields product VCM for final treating. The typical VCM plant includes VCM treating, offgas treating, light ends/tars handling and waste treating facili ties. It will also include incineration units for reclaiming waste chlorinated hydrocarbons from offgas or liquid streams.1 heat is removed by generation of steam on the shell side of each reactor. The final reactor effluent is cooled to condense EDC, and the offgas is contacted/reacted with chlorine to recover ethylene as additional EDC. The offgas stream is cooled versus cooling water and refrig eration to further condense EDC before exiting the pro cess. Residual ethylene concentration in the vent gas is reportedly as low as 10 ppm.61 Stauffer also offers an oxygen-based oxy process (Fig. 6) in which the main reactor offgas, following condensa tion of EDC, is compressed and recycled to the first oxy reactor. An excess of ethylene is used to maximize HC1 conversion and minimize byproducts. A small slipstream from the ethylene-rich recycle is purged to an ethylene recovery unit for control of inerts. Stauffer technology.60 '1 In the Stauffer direct chlori nation process (see Fig. 5), ethylene and chlorine are reacted, in the liquid phase and under controlled condi tions, to yield a crude product which analyzes 99.7 per cent EDC. The reactor product is then combined with the crude oxy EDC, washed and distilled to remove water, light ends and heavy ends. Pure EDC is preheated in the economizer of the pyrolysis furnace and then vaporized with steam. EDC vapor is then heated to dissociation temperature in the furnace tubes to yield a mixture of vinyl chloride and hydrogen chloride. Conditions are controlled to maintain EDC conversion at 50 to 55 percent. Following a quench and condensation step, HC1, VCM, and uncracked EDC are separated by distillation. Hydrogen chloride gas is sent to the oxy section. Unreacted EDC is recycled to purification. The oxy section combines recycle HC1 with fresh ethyl ene and air in tubular fixed-bed catalytic reactors. The ethylene and air are fed in excess of stoichiometric re quirements to assure high HC1 conversion.*1 Reaction Ethyl integrated VCM process.61 Gaseous chlorine and ethylene are introduced into a direct chlorination reactor in which they combine to form EDC. The very high purity EDC product can be sent directly to (or, after degassing, can bypass) the EDC purification system (see Fig. 7). Air and gaseous ethylene and HC1 are introduced into an oxychlorination reactor in which EDC is produced at an elevated pressure and temperature in the presence of a fluidized catalyst. The reaction products are neutralized and partially condensed to recover EDC which is first sent to a drying column and then to the EDC purification system. A portion of the vent gas, consisting primarily of nitrogen and carbon dioxide is recycled to the reactor for added safety. The purified EDC stream which contains recycled EDC as well as the EDC from direct and oxychlorina tion is vaporized and introduced into a furnace. At least half of the EDC stream is cracked to HC1 and VCM. The reaction products are cooled rapidly, partially con densed, and then sent to the VCM purification system. 84 March 1979 Hydrocarbon Processing COLOR!TE 019621 Oirect chtorinmion Oxyehlorinalion Recycle gas Vent gas Fig. 7--Ethyl Corp.'s integrated vinyl chloride monomer process. HC1 and VCM are separated by fractional distillation from the unconverted EDC and small amounts of by products. The EDC, containing the byproducts, is re cycled to the EDC purification system. Mitsui Toatsu Chemicals technology.08 The MTC technology utilizes a boiling liquid process for the direct chlorination reaction. Reaction heat is dissipated with the gaseous EDC exit stream which is condensed externally and sent to purification. The oxychlorination process is characterized by the use of oxygen feedstock and a fluidized bed reactor. The reactor effluent gases are quench cooled with circulating EDC followed by caustic neutralization. The neutralized gas is cooled to condense EDC and water. Uncondensed gases, primarily ethylene, are recycled back to the oxy reactor. A small stream is vented from the recycle gas to allow purging of inerts. EDC liquid is phase separated from water and dehydrated before joining the EDC streams in the purification system. A conventional EDC purification system splits crude EDC into light ends, heavy residue and pure EDC. The latter is cracked to yield VCM which is purified in a manner similar to that described in the Stauffer technology (see Fig. 8). PPG technology.0" The EDC production technology appears very similar to that described for Mitsui Toatsu, particularly in the use of oxygen feedstock and fluidized bed reaction for oxychlorination. However, PPG does not indicate use of a dehydrator to dry crude oxy EDC prior to purification. Also, PPG uses three rather than two towers to obtain the HC1-VCM-EDC separation. B. F. Goodrich technology.07- 70 Goodrich direct chlori nation uses conventional water-cooled technology similar to that shown for Stauffer. The air-based, fluidized bed oxychlorination technology is similar to that shown for Ethyl. Goodrich also utilizes an absorber-stripper system on the oxy vent gas stream to minimize hydrocarbon losses. Goodrich, in conjunction with Badger, Inc., offers complete technology for waste treating of VCM plant effluent streams. Toyo Soda technology.ss-07 This technology appears very similar to that offered by Stauffer. The principal differences are in the use of an absorber-stripper on the oxy vent gas effluent (as with Goodrich) and the de hydration of crude EDC prior to purification. As with other oxychlorination processes, steam generation is used to remove reaction heat. Phone-Poulenc technology os-fl Rhone-Poulenc offers two processes, Chloe I and Chloe II. The former is of a special nature07 to yield concurrently significant quantities of other chlorinated hydrocarbons such as trichloroethyl ene and trichloroethane. The Chloe II process is "true" VCM technology using air-based, fluidized bed oxychlo rination in combination with boiling liquid direct chlo rination. Monsanto technology.T: This process appears very simi lar to that offered by Stauffer. Hydrocarbon Processing March 1979 85 COLORITE 019622 VINYL CHLORIDE MONOMER Wreet eMortnation ftaactor OxreMorfMM Quench column Caustic ecrubbar B)C piatBcaMon CPC pmtyito VCN purification Fig. 8--Mitsui Toatsu uses these modifications in their vinyl chloride monomer process DOW technology. Dow's technology has not been pub is utilized to purify all EDC processed in the purification licized. It has been used only by Dow and its foreign train. affiliates. Increased activity by EPA (U.S. Environmental Pro NEW DEVELOPMENTS tection Agency) and state agencies in regulating hydro- Although it is believed that several VCM producers currently use boiling liquid reactors for direct chlorina tion, Stauffer has developed a unique application of this concept.*0 Their approach, "High Temperature Chlorina tion," in effect uses the reactor as a reboiler for the con ventional EDC purification system (see Fig. 9) Purified EDC is withdrawn as a side stream from the tower, and any light components formed are removed overhead. Normal feed to the tower consists of treated EDC from oxy and recycle. Small amounts of the normal heavy ends or tars are purged from the base of the reactor. This ap plication eliminates approximately 100,000 lbs. per hour of 150 psig steam consumption for a one billion lb. per year VCM plant, A similar energy savings is achieved in reduction of cooling water usage relative to a conven f tional reactor and light ends tower. B. F. Goodrich7* abo offers a boiling liquid process in which the heat of reaction Flg. 9--Stauffer high temperature chlorination and ethylene dichloride purification schematic. 86 March 1979 Hydrocarbon Processing COLORXTE 019623 carbon emissions are likely to stimulate further new developments, particularly in oxychlorination processes. These will range from development of new oxygen-based technology to various add-on systems for cleaning up oxy vent gas. The latter may include catalytic oxidation, in cineration (of oxygen-based oxy vent gas), solvent absorp tion, combined refrigeration and absorption techniques and/or other combinations. Several companies not active as VCM producers are involved in developing these add-on systems. It is expected that companies will continue to devote considerable effort to the development of cracking pro moters and inhibitors of side reactions in pyrolysis chem istry. Current cracking practices limit EDC conversion to 50-60 percent. Considerable energy and cost savings could be achieved through increased conversion levels without concurrent losses of EDC to undesirable side reactions. EPA regulations. EPA's "Standard Support and Envi ronmental Impact Statement: Emission Standard for Vinyl Chloride,"1 presented the following regulations: Emissions from all point sources except oxychlorina tion would be reduced to 10 ppm VCM by volume Emissions from the oxychlorination reactor would be reduced to 0.02 lb. VCM per 100 lbs. EDC product from the oxy process Preventable relief valve discharges would not be permitted Fugitive emissions would be minimized by requiring enclosure of the emission sources and collection of the emissions. EPA estimated typical VCM plant emissions in 1974 as follows: Lbs./VCM/ 100 Lbs. Source VCM Fugitive 0.1215 EDC Finishing Column 0.05 VCM Finishing Column 0.24 Oxy Process 0.0364 Process Water 0.0007 Total 0.4479 The regulations were predicated upon reduction of such emissions by 94 percent using best available technology. Compliance testing of these installations was begun in the last quarter of 1978. Additional EPA and state actions were initiated in mid-1977 to reduce hydrocarbon emissions from VCM plants in non-attainment regions, i.e., much of the Gulf Coast. EDC production is reported to account for 28 percent of the hydrocarbon emissions in the southern Louisiana and East Texas AQCRs.** These actions were directed primarily against oxychlorination vent gas from air-based units. The amount of hydrocarbon reduction sought varies from region to region. No published guide lines are currently available to reference. The net effect of these various regulations has been to increase substantially the scope of add-on technology in VCM plants, such as: Installation of primary and redundant incineration facilities for VCM point (ex oxy) source and collected fugitive emissions Installation of HC1 scrubbing and neutralization oi recovery units in conjunction with the incinerators Installation of closed process sewers, collection sys tems and larger or redundant waste water strippers Replacement of single mechanical seals on pumps and agitators with double mechanical seals. (In some cases, conventional pumps were replaced with canned ot magnetic drive pumps) Leak detection systems and portable monitors Enclosed sampling and analytical systems Vapor recovery systems for VCM loading/unloading and equipment clearing. The EPA report estimated a maximum capital impact of $0.8 to $1.9 MM (1975 dollars) for a "model" 700 MM lb. per year VCM plant. Recent cost estimates in dicate the true impact for these items is nearer $15 MM based on 1978 dollars. Addition of hydrocarbon compli ance (proposed regulations) may add another $2-$5 MM. EPA also has proposed further reductions in VCM emissions.5 Under consideration at present are regulations which will reduce allowable emissions from 10 ppm to 5 ppm for all point sources, including oxy vent gas. EPA further plans to prohibit emission increases within 8 kilometers of an existing source due to construction of a new emission source. This will effectively prevent expan sion of existing facilities or construction of new plants in the vicinity of existing plants. The proposed oxy vent gas regulation will also dictate substantial capital expendi tures for add-on facilities and^ possibly the conversion of air-based to oxygen-based plants to facilitate incineration of tail gases. ECONOMICS Table 5 presents a 1981 manufacturing cost buildup for a typical 700 MM lb. per year grass roots VCM plant. Raw materials total 12 cents per lb. VCM or 54 percent of the required FOB plant selling price. Capitalrelated costs amount to 6.8 cents per lb. VCM or 32 percent. Utilities are only 6.7 percent of the total VCM cost. In perspective, the 1972-1973 reported VCM selling price67 was only 4-5 cents per lb. By 1981, the capitalrelated unit costs alone will exceed this by 50 percent. The obvious major factor in VCM pricing is raw ma terials cost. Although chlorine price is expected to double between 1973 and 1981, the impact of ethylene price will be even greater (three cents per lb. versus 17 cents per lb.). The real culprit, of course, is crude oil cost. During the late 1960s and early 1970s, plants using inexpensive LNG feedstocks were significant contributors to the low cost U.S. ethylene supply picture. The energy crisis rap idly reversed the low cost feedstock trend. LNG scarcity Hydrocarbon Processing March 1979 87 COLORITE 019624 VINYL CHLORIDE MONOMER dictated construction of naphtha and/or gas oil crackers for present and future ethylene production. This tied VCM prices irreversibly to crude oil prices through ethylene, fuel and power (particularly via its impact on chlorine). ACKNOWLEDGMENTS The authors gratefully acknowledge contributions by A B. Stryker, Jr., of Stauffer and H. H, Wall of Eutyl and permission by their companies to use the information presented on their respective processes, LITERATURE CITED * U.S. Environmental Protection Agency Report No, EPA-45Q/2-75*009} Research Triangle Park, N-C., (1975). * Leach, H. S., (to Monsanto Chemical Co.) U.S. Intent 3,338,982 (1967), B. F. Goodrich Co., British Patent 1,233,238 (1971). * Campbell, R. G., (to Stauffer Chemical Co.), U.S. Patent 4,000,205 (1976) * Benedict, D., (to Union Carbide), U.S. Patent 2,929,852 (I960). 4 Di Fiore, L., and Calcagno, B., (to Soc. Ital. Resine), U.S. Patent 3,911,036 (1975). T Tsao, U., (to I.umipu* Co.), U.S. Patent 3,917,727 (1975). * Kurtz, B. D., and Omelian, A., (to Allied Chemical Co.), U.S. Patent 3,941,568 (1976). 4 Vulcan Materials, British Patent 980,983 (1965). 44 Van Antwerp, A. E., Harpring, J. W., Sterbenr, R, G-, and Kang, T. L., (to B. F. Goodrich), U.S. Patent 3,488,398 (1970). 11 Severino, F T., (to Stauffer Chemical Co.) U.S. Patent 4,046 822 (1977) 44Stauffer Chemical Co., British Patent 1,230,607 (1971). 14 B. F. Goodrich Co., Belgium Patent 660,413 (1966). ** Kita, H., (to Mitsui Toattu Chemical), Japanese Patent 46-43367 (1971). u Miyauchi, K., (to Mitsui Toatsu Chemical), British Patent 1, 189,815 (1970). " Takahashi, T., (to Mitsui Toatsu Chemical), Japanese Patent 45-32406 (1970). If Mitsui Toatsu Chemical, Japanese Patent 46-33010 (1971). u PPG Industries, French Patent 2,080,666 (1971). 14 Muen, A. P., (to PPG Industries), British Patent 1,220,394 (1971). 44 Ahlstrocn, Jr., R. C., (to Dow Chemical Co.), U-S- Patent 3,966,30(< (1976). ** Strini, J. C., and Costes, J. R., (to Rhone-Progil), U.S- Patent 3,935,286 (1976). About the authors Robert W. McPherson is products manager, Continental Oil Co.t Houston. He is responsible for the worldwide profit performance of Conoco's chlo rinated hydrocarbons and their strategic development. Mr. McPherson received his B.S. from Cornell University. Charles M. Starks is director of ex ploratory research, Continental Oil Co.t Ponca City, Ohio. Dr. Starks received his BJS. from the University of Okla homa and his PhD. from Massachusetts Institute of Technology. 1 t 3a ^3 yi Garvin J. Fryar is supervising process engineer with Continental Oil Co., Ponca City, Okla, He is responsible for the supervision of process designsf technical consulting and economics for chemicals processes. Mr. Fryar received W* BJS. in chemical engineering from ^he University of New Mexico. TABLE 5--Estimated 1981 VCM manufacturing cost lb*/Lb VCM Raw Materials Chlorine . Ethylene................................................ Catalyst and chemicals .. Utilities ............ 0.64 0.49 Total variable ... Labor... , Miscellaneous. ,. Total fixed... . ......... Total manufacturing cost.. Capital charges and depreciation ............. Selling price FOB plant............................... //Unit 5.6 17.1 Cost, */Lb/ VCM 3.53 MS 0.39 1.42 13.79 1.18 0.98 2.16 15.95 5.85 21 79 % 16 2 38 8 1.8 65 63.3 54 45 9.9 73 2 26,8 100.0 Baaet: 1. 700 MM Pounds/Year Balanced VCM Plant. 2.1981 Startup 3. Grass Roots Investment f 140 MM 4. Light and heavy ends incinerated; recovered HCl sold as muriatic add to break even on incineration costs 5 Fifteen percent DCF rate o( return to cover interest charges and profit, 6. Unit values are generalized and are not specific to a particular lisensor or technology s Smalley, E. W., Kurtz, B. ., and Bandyopadhyay, B., (to Allied Chem ical Corp.). VS. Patent 4,060,460 (1977). 44 Knapsack Co-, British Patent 1,266,676 (1972). 54 Solvay et de, French Patent 1,602,522 (1971). .............................. ........ ' " ` " "" ' (1969) * UICUUI, r.,, \\\J VLIUHD Il\CUl ,l,<r?t (1973). 34 Barton, D. H R , J Chem. Soc., 148 (1949). 44 Young, D. P., (to B. P, Chemicals, Ltd.), U.S. Patent 3,896,182 (1975) * Mitsui Chemical Industries, Japanese Patent 42-2292) (1967), ...................... ........ ,329 (1969). ** Keating H. J., (to Monsanto Chemical Co.), U.S. Patent 3,125,607 (1964), **Gause, E. M., (to Monsanto Chemical Co.), U.S. Patent 3,142,709 (1964). * McDonald, D. W., (to Monsanto Chemical Co.), U.S. Patent 3,125 608 (1964). 47 Gomi, S., Eighth World Petroleum Congress, Proceedings 4, 371 (1971) " Kureha Chemical Industries, British Patent 977,578 (1964), British Patent 1,068,793 (1967). * Barton, D. H., and Mugdan. M., 7. Soc Chem, lnd, (London), 69. 75 (1950); Patat, F,, and Weidlieh, P., Hdv. Ckim. Acta., 32, 783 (1949). 40 Gordon, R. D , and Starks, C M., (to Continental Oil Co.), U.S. Pateni 4.046,823 (1977). 41 Kuck, M. A., (to Stauffer Chemical Co.), U.S. Patent 3,987,118 (1976) 42 Winstein, N. J., (to Princeton Chemical Research, Inc.), U.S. Patent 3.5"5*1,55006 (1970J. 44 Kurtz, B. E., Smalley, E. W., ^Sommernun^ W. E., and Van Atu, J, R , (to Allied Chemical Corp.), U.S. Patent 3,987,119 (1976). 44 Gordon, Tv H., and Kuimn mcrle, H. F., (to Owens-Illinois, Inc.), U.S Patent 4,042,639' (1972). 41 Riegel, H., (to Ltimmus Co.), U.S. Patent 3,796,641 (1974). 44 Riegcl, H., (to Lummus Co.), U.S. Patent 3,557,229 (1971). 41 Riegel H., (to Lummus Co.), U.S. Patent 3,937,744 (1976) ^Szc, M, C., (to Lummus Co.), U.S. Patent 3,949,010 (1976). "Tsao, U.; (to Lummus Co.), U.S. Patent 3,963,5M (1976). "Tsao, U., (to Lummus Co.), U.S. Patent 3,992,460 (1976). 41 Riegel, H., (to Lummus Co.), U.S. Patent 3,935,288 (1976). uTao, U., (to Lummus Co.), U.S. fctent 3,985,816 (1976) 44 Minot, J. D., Chcm. Eng. Progr., 69, (8), 71 (1973). ** Leonard, E. D., Vinyl end Diene Monomers (Pori 3), John Wiley and Sons, Inc., New York, 1971. 44 Sittig, M., Vinyl Chloride and PVC Manufacture, Noyes Data Corp., 1978 "Gomi, SM "Japan't New Vinyl Chloride Process (Kuteka).*' Hydrocarbon Processing, Vol, 43, No. 11, November 1964. *T Rosencweig, M. D., /'Vinyl Process Has Wide Range of By-Products,*' (Rhone-Progil), Chemical Engineering, Vol 78, No. 24, Oct. 18, 1971. 44 Robert, J.f and Bcrgier. A. "Rhone-Progil New Processes for the Manu facture of Vinyl Chloride Monomer and Chlorinated Solvents from Ethyl ene,** 164th A.C.S. National Meeting, New York, Aug, 27-Sept. 1, 1972 ** Buckley, J. A., "Process Flow Sbeet/Vinyl Chloride via Direct Chlorinatom and Osychlorination/* Chemical Engineering, Vol. 73, No. 24, Nov. 21, 44 Private Communication from A. B. Stryker, Jr., Stauffer Chemical Co Nov. 29, 1978. * Reich, Peter, "Air or Oxygen for VCM?** Hyydrocmrbon Processing. March, 1976, pp. 85-. 44 Private Communication from H. H. Wall, Ethyl Cop., Nov. 28, 1978. 44 Vinyl Chloride, "Hydrocarbon Processing, Nov., 1975. 44 EPA-450/3-73-006-C, Vol. 3, November, 1974. 44 Federal Register, June 2, 1977. 44 EPA-600/2-76-053, March, 1976. "Keane, DavidIP., et al, "Vinyl Chloride: How, Where, Who--Future/' Hydrocarbon Processing, February, 1973. "Vinyl Chloride--Mitsui Toatsu Chemicals/* Hydrocmrbon Processing, No vember 1971. "Vinyl Chloride--PPG Industries, Inc./* Hydrocarbon Processing, Novem ber 1975. 44 "Vinyl Chloride--B, F. Goodrich Chemkal Co., Hydrocarbon Processing. November J975. ^Vinyi Chloride--Rhome-Poulenc S.A./* Hydrocarbon Processing, Novem ber 1975. "l975DyI Cfafc*ide^(Moni*nto Co,),*' Hydrocmrbon Processing, November " Private cotnmnieations from J. S. Benson B. F, Goodrich Chemical Co Jan. 5, 1979. m 88 March 1979 Hydrocarbon Processing COLORITE 019625 Alloy selection for VCM plants Data aids engineers in selecting alloys for critical equipment in direct chlorination, xychlorination and EDC pyrolysis sections of vinyl chloride monomer plants C. M. Schillmoller, VDM Div., The Ore & Chemical Corp., Houston Design conditions, alloy selection and operating ex perience are all part of the proprietary package offered by various VCM process licensors. Therefore, of neces sity, this article will be limited to the three separate operating steps that all "balanced ethylene feedstock" plants have in common: direct chlorination, oxychlorination and EDC pyrolysis. We will look into the cor rosive effects of chlorine and hydrogen chloride gases as well as that of hydrochloric acid. Aspects of alloy se lection are based on published information of various processes, knowledge of corrosion and privileged infor mation on actual sales of large quantities of high-nickel (Editor's note. Alloys 200, 201, 400, 600, 800 and 825 referred to in this article correspond to the VDM trade names shown in Table I with which the author has the most recent experience in vinyl chloride monomer plants.) alloys for VCM plants in Europe, Japan and the USA. T'he data presented, within the limited scope of this article, are intended only for guideline purposes, without any guarantee of performance. SELECTING ALLOYS Nickel and high-nickel alloys are among the few me tallic materials having useful resistance to dry chlorine, hydrogen chloride and hydrochloric acid. These alloys are not new to the chlor-alkali industry, being more or less standard selections in caustic, brine and salt processing. We will, in turn, deal with each of the three chief corrosive environments encountered in VCM processes. Table 1 provides a brief description of alloys commonly in use, their ASTM specifications and the tradenames under which they are known. Chlorine. Gaseous chlorine at low temperatures and in the absence of moisture is not severely corrosive and is commonly handled by carbon steel. Usually a more re sistant material such as Alloy 400 is specified for critical parts such as valve trim, instrumentation and orifice plates in chlorine pipe lines. In contrast, wet chlorine is extremely corrosive on steel and nickel alloys, and re quires Hastelloy* C or titanium. At elevated temper atures, corrosion rates on steel increase with temperature. The upper limit of usefulness is around 400 F when the protective effects of the corrosion products disap pear. Ferric chloride vaporizes at 420 F. Fig. 1 provides a guide to the selection of various alloys in dry chlorine. The surface coating of chlorides tend to provide protection up to a temperature level TABLE 1--Alloys commonly used in VCM plants Mittrfali Rtftrtnct In tost Nicktl Nicktl . Uw Carbon Niditl .. Alloy 200 ................................... Alloy 201 Nlckal-uppar alltyi Niditl-Cnpptr Alloy....................................................... Alloy 400 illoy* Nieke-Chromium-lfttn Alloy___ wt1, J^Chromium Alloy.................. ,, nckeMroA-CftrotaiuRi-Molybdonuni-Copptr Alloy........ Alloy 600 Alloy 800 Alloy 825 HI 95.6 09.6 61 76 32 42 Ntln*l CoJRptttltJoft, % Cr mo Co 31 15 21 21 3 2.3 ASTM ASMS t0 VDM C--ipirtblt Ft fiutibtr WflAlw In4s mm* product* 161*163 161-163 161-163 161-163 VUM-Ntdit! 200 VDM-NicM 201 Nicktl 200 Nickel 201 1.5 163-165 163- I5S NICORROS 400 Monel 400 8 163-168 163*168 NICROFER 600 lucoocl 600 46 163-407 163*407 NICROFER 800 Incoloy 800 30 163-423 163-423 NICR0FIR t?5 Incotoy 825 SICftortR art ntiitend tirdemjrki or Varamifta Danticht MataUwaritt AG Garmany. Monti, Incsntl. Intoloy art raaisttrtd tradamarks id Tkt IMtrntiaiial Nitktl Co. nantnoy is i rajiittrtd tradamirk si Cabot-Stallrte Division Hydrocarbon Processing March 1979 89 COLORITE 019626 ALLOY SELECTION Fig. 2--Hydrogen chloride. Alloy selection guide. at which melting, vaporization or decomposition removes such films. The corrosion rate appears proportional to the vapor pressure of the metal chlorides. The common design parameter for tubing, valve trim and internals is 0.003 in. per year (IPY) maximum corrosion rate, while for vessels and pipe an upper corrosion rate of 0.020 IPY is frequently adopted with a corrosion allow ance of to in. Alloy 200 and Alloy 600 are the most commonly used alloys for reactors, coils and agitators in the 500 to 1000 F range. Hydrogen chloride. Dry HC1 behaves in a similar man ner as chlorine, and carbon steel can suffice up to 450 F above which Alloy 200 is usually specified. Fig. 2 provides a guide to the selection of various alloys in dry HC1 gas and the design parameters of 0.003 IPY and 0.020 IPY upper corrosion rates for certain com ponents are shown. The presence of moisture does not appreciably increase corrosion rates above the dewpoint over that by dry gas. It must be pointed out that there are many variables, and even small amounts of addition agents to control catalyst activity, may exert an influence on the tenacity and vapor pressure of the protective corrosion scales. Therefore, absolute corrosion rates for different temper atures in chlorine and HCI systems are difficult to pre dict. Even so it is felt that Figs. 1 and 2 are sufficiently accurate to serve as a guide. These figures should be checked against actual experience of each of the different VCM processes. The performance of Alloy 200 in dry as well as wet hydrogen chloride gas has been consistently good. In cyclic operating conditions, particularly in the presence of air or oxygen, Alloy 600 and Alloy 825 offer good all round resistance. It is prudent to assume that Types 304 and 316 stainless steels would foe subject to chloride stress corrosion cracking conditions during shutdown in spite of various precautions that may be taken. Fig. 3--Hydrochloric acid. Alloy selection guide (Basis: 0.020 IPY max. corrosion rate). Hydrochloric acid. HCI is a typical reducing arid through its entire concentration range. Its strongly acidic character is harmful to steel. Alloy 200 and Alloy 400 be have similarly and find application at ambient temperature up to 20 percent concentration and at higher temper ature below 5 percent concentration. Fig. 3 shorn isocorrosion lines for 0.020 IPY which is generally con sidered the upper design limit of an alloy selection. The graph immediately delineates the conditions suitable for handling with Alloy 400 and those where Hastelloy B is required. It should be noted that in most cases in which hydro chloric acid is formed as a result of hydrolysis of chlo- 90 March 1979 Hydrocarbon Processing COLORITE 019627 rides or chlorinated hydrocarbons such as EDC, the acid concentrations are less than .5 percent and both Alloy 200 and Alloy 400 can withstand such conditions satis factorily at temperatures up to 400 F. Also in hydrogen chloride gaseous processes when cooling takes place near the dewpoint of HC1 (that is below 260 F) it is prudent to assume that because of the hygroscopic nature of the chloride on steel that HC1 might condense with resultant high corrosion rates. In applications where 18-8 Cr-Ni stainless steel is used at elevated temperatures such condensation can lead to chloride stress cracking. Alloy 800 is highly resistant to chloride stress corrosion cracking while Alloy 600 and Alloy 825 are immune to this phenomena in this applica tion. Even though with special precautions a system can be kept dry during operation, adequate consideration must also be given to protect equipment during shut down and when starting up the unit. Purging with inert dry gas prior or during shutdown is helpful in sustain ing a dry atmosphere. Alternately one can maintain temperatures above the dewpoint. Also, sludges present in the system absorb chlorides and must be kept dry otherwise aqueous HC1 acid is formed from moisture pick-up. Alloy 400 is widely used for handling dilute HC1 acid in waterwash solutions and for heat-exchanger tubes in the EDC purification. Fig. A--Principal VCM process steps. VCM PROCESS COMPARISON The typical VCM process combines direct chlorination and oxychlorination processes to provide ethylene di chloride (EDC) feedstock to the pyrolysis unit. Because of the large amount of hydrogen chloride generated in the cracking of EDC, plant economies dictate the need for an oxy unit. The sequence and three principal operating steps are quite similar from process to process and are shown in Fig. 4. It is not the writer's intention to make a detailed analysis of the entire alloy selection for the various licensed processes, but instead, to com ment on the basis of previously provided corrosion data, on alloy considerations applicable to each of the three principal steps. Direct chlorination. Ethylene is reacted with dry chlorine in the presence of a catalyst, to produce ethylene di chloride. The catalyst usually is a ferric chloride. Liquid EDC is used as a reaction medium to insure intimate mixing. Conventional water cooling removes the exo thermic heat of reaction. Temperatures are controlled at 130 F to 150 F. The EDC produced is usually treated for removal of ferric chloride carry-over. In a number of systems lately, the reaction is carried out at the EDC boiling point (approximately 230 F) taking pure EDC overhead and using the heat required to vaporize part of the reactor content, to control the temperature. Fig. 5 shows the direct chlorination pro cess. It is necessary to insure a dry chlorine feedstock and to properly control the temperature by thorough mixing of the reactants to prevent hot spots and runaway tem peratures. With such operating control conditions, car bon steel can be safely used for the reactor and auxiliary equipment. As can be seen from Fig. 1, a suitable corrosion allowance may need to be applied depending Fig. 5--Direct chlorination. on temperature and experience. Further, proper shut down procedures should be employed keeping the unit dry or free from chlorine to prevent attack by wet residual chlorine on the steel when the unit is not in operation. Oxychlorination. Ethylene is reacted with dry hydrogen chloride and oxygen in the presence of a catalyst to produce EDC and water. The catalyst usually is im- Hydrocarbon Processing March 1979 91 COLOR!TE 019628 ALLOY SELECTION pregnated with copper chloride. The oxychlorination process can be carried out either in a fluid bed of catalyst or in tubular fixed bed catalytic reactors. Fur ther, the reaction of ethylene and HC1 can take place either with air or oxygen. Both process systems are shown in Fig. 6. Fluid bed. Reaction with a fluidized catalyst generally takes place at 435 F to 450 F and atmospheric pres sure. The reaction is highly exothermic and the tem perature is controlled by good intermixing of reactants and catalyst and by the use of internal cooling sur faces. A carbon steel reactor can be used. Referring to Fig. 2, we can expect corrosion rates in the order of 0.010 IPY which means a corrosion allowance of '/a in. or 3/16 in. should be applied. For internals, where corrosion can occur on both sides of the metal, where velocity effects may interfere with protective scales or where a corrosion allowance is not practical or inter feres with the rate of heat transfer, a corrosion resistant alloy is commonly specified. Good service with Alloy 600 and Alloy 825 has been ob tained when used for the sparging equipment to intro- High nickel alloys are often restricted to locations in critical equipment Less expensive materials are then selected as soon as allowed by process conditions. duce the gases in the fluid bed, and for pipe, nozzles and fittings inside the reactor. These alloys are not susceptible to chloride stress corrosion cracking if hy drolysis takes place during shutdown. Occasionally a problem is experienced from the combined effect of corrosion and erosion by the catalyst which removes the protective corrosion products on steel. Also, accu mulation of catalyst on the bottom of the reactor can cause localized attack and should be avoided. Because of the carbon steel reactor construction, it is definitely necessary to control temperatures below 500 F. Proper shutdown procedures to prevent corrosion on steel by dilute hydrochloric acid, when the unit is not in oper ation, is of course most desirable. Fixed bed. Reaction in a fixed-bed catalyst reactor is carried out at temperatures of 450 F to 600 F and pressures from atmospheric up to 200 psi. The catalyst is contained in a number of vertical tubes held in a tubesheet at top and bottom. Reaction heat is removed by the generation of steam on the shell side of the re actor. It is more difficult to control temperatures uni formly than in the fluidized bed, and occasional hot spots tend to develop on the tubes. As can be seen from Fig. 2 operating conditions re quire corrosion-resistant alloys. Both Alloy 200 and 600 are preferred alloy selections. Usually Alloy 200 is used for the reactor tubes and has given excellent perfor mance. The tubesheets and heads of the reactor are clad with nickel on steel. The reactor shell which is exposed to water and steam is made of carbon steel. When three or four reactors are required, nickel is also used for the interconnecting piping. Temperatures should be controlled no higher than 600 F to prevent by-product formation and deactivation of the catalyst. Also, when localized hot spots occur on the Alloy 200 tubes we have observed intergranular embrittlement on some tubes. Alloy 201, which has a low carbon level, is resistant to such intergranular attack. Oxygen versus air. The use of oxygen instead of air in the oxychlorination process improves operating ef ficiency and product yield. It permits operation at a lower temperature. Even though alloy selection is not affected by this, from a metals standpoint substantially less quantity of alloy is required as the equipment tends to be more compact and smaller. Also capital savings are possible for not having to separate EDC, ethylene and other chemicals from a large nitrogen vent gas stream and burning the vent gas. EDC pyrolysis. Ethylene dichloride is vaporized and thermally cracked to vinyl chloride yielding volumous by-product hydrogen chloride. Cracking is carried out in a fired furnace at a temperature of 900 F to 1000 F and at an elevated pressure of about 400 psi. The re action products are cooled rapidly, partially condensed and then sent to a VCM purification system where HC1 and VCM are distilled from the unreacted EDC and small amounts of by-products. The cracking pro cess is susceptible to inhibition and fouling by trace amounts of impurities and therefore the crude EDC is purified and the light and heavy ends removed--both of which contain chlorinated waste products. Further, to prevent excessive hydrochloric add corrosion here and 92 March 1979 Hydrocarbon Processing COLORITE 019629 downstream of the cracker, it is necessary that the crude EDC is washed, neutralized with caustic, and dried. The pure EDC is preheated in an economizer and then vaporized in a steam heated kettle-type re boiler, See Fig. 7 for the EDC pyrolysis process system. For alloy selection of the pyrolysis furnace tubing we are guided by the fact that hydrogen chloride is formed in the thermal decomposition of EDC, that the furnace requires periodic decoking and that during shutdown About the author C. M. "Dick" Schillmoller ta respontible for the technical marketing ac tivities for VDM in the USA. VDM is a member of Metallgesellschaft Group. He is located in Houston, Texas. Be fore returning to the United States in March, 1978 he had 19 years with In ternational Nickel in the USA, Aus tralia and Europe followed by n period conditions hydrolysis of hydrogen chloride is likely to occur. Alloy 600 is the preferred alloy section for this application and has consistently given good reliable per formance. In recent years, Alloy 800 has been used with of management consulting in Brussels, Belgium. Schillmoller holds a degree in chemical engineering. He is the author of over S00 techni cal papers dealing with corrosion and high temperature material problems in the process industries, and has success. It is prudent to assume that the 18-8 Cr*Ni type of stainless steels are subject to chloride stress corrosion cracking below the dew point and during shut lectured at Stanford and the University of California. He is well known to the petroleum/petrochemical industry and serves on a number of technical committees. down. One company reported that they had used 5 Cr-'/j moly steel without excessive corrosion when in required to maintain such coatings and prevent damage suring a bone-dry feed to the unit and taking the usual at joints. special shutdown and start-up precautions of gas-blanket ing and keeping the unit dry. Alloy 600 is often speci TECHNOLOGY TRENDS fied for the cooling coil where halogen corrosion is the No major changes in the use of established materials of greatest. Also Alloy 600 solid or as clad plate has been construction is foreseen. Brief mention has already been used for batch polymerizer reactors in an aqueous me made of a trend towards higher temperature direct chlori dium in the presence of a catalyst and suspending agents, nation using the reactor as a reboiler to remove the heavy producing PVC resin. ends. Also a substantial share of new plants appears to In the purification system, corrosion can be very se utilize oxygen instead of air in the oxychlorination step. vere because of the hydrolysis of hydrogen chloride and This approach discharges fewer chlorinated hydrocarbons of various organic chlorides. This can occur at temper with the vent gases into the atmosphere. For this reason atures of 260 F and downwards forming dilute hydro and also to increase existing plant capacity, some VCM chloric acid. It is extremely difficult to insure a bone- plant oxychlorinators are being converted from air to dry system, that is, zero free water and below 10 ppm oxygen. of total dissolved water. Inadvertent moisture pick-up Emission control standards are getting more severe, from sources such as leakage at water coolers and steam forcing the scrubbing and neutralization of HC1, use of I heaters and intrusion of humidity at flanges and seals is always a possibility. Also entrained water is frequently waste water strippers to remove volatile organics, en closing and collecting emissions for incineration. Cor carried along in the distillation process. Carbon steel rosion in parts of this equipment can be very severe and in dry systems usually corrodes less than 0.002 IPY the rate of attack is not always predictable; some of while in the presence of water, dilute HC1 acid is formed the previously mentioned alloy selection guidelines do and corrosion rates are approximately 0.010 to 0.160 apply. I IPY depending on the temperature and concentration. Conclusion. For economic considerations, special high- In the presence of 2 percent hydrochloric acid, carbon nickel alloys are often restricted to critical locations from steel corrosion often exceeds one inch per year. where one downgrades to less expensive materials as I From Fig. 3 we can see that Alloy 400, in most cases, soon as process conditions permit. During the final de would be the desired economical choice of alloy. It has sign, the limitations of each material selected must be been used in industry to resist a wide variety of chlori scrutinized as well as the means used to minimize cor nated hydrocarbons and solvents. Hastelloy B finds use rosion by control of process conditions. For example, for critical components such as valve trim and pump what will be done to control exothermic reactions, ve impellers. Corrosion of steel equipment tends to be the locity/impingement effects, moisture content, pH/acidic greatest in reboilers, the bottom section of distillation conditions, impurities, sludges and acid concentrations? columns, bubble caps, plates, condensers, water separa We have the tools available to do this and particularly in tors, valves, pumps and fittings. chlorine and HC1 processes we should not overlook proper It should be pointed out that titanium is not a suitable selection in dilute hydrochloric acid, because of its strong start-up and shutdown procedures, since severe corrosive attack may take place while the unit is not in operation. reducing nature. Where titanium is used, it has provided useful life under mild conditions with a pH above 1.5. For economic reasons, various coatings and liners are frequently considered and used as an alternate to alloy. The following applications have been reported: a gunnite lined pretreater, glass-lined vessels, polypropylene-lined steel piping, Saran and Kynar-lined pipe, glass-coated pumps, various coatings in accumulators. Even though attractive from a first-cost standpoint, special care is REFERENCES 1 "Vinyl Chloride," Hydrocarbon Procuring, November, 1975, pp. 214-216. 1 Buckley, J, A-, "Process Flowsheet Vinyl Chloride via Direct Chlorination and Oxychlorination," Chemical Engineering, November 21, i960. * Reich, P-, "Air or Oxygen for VCM," Hydrocarbon Processing March. 1976, pp. 85-89. 4 "Resistance of Nickel and High-Nickel Alloys to Corrosion by Hydro chloric Acid, Hydrogen Chlorine and Chlorine,'1 INOO Corrosion Engi neering Bulletin CEB-3, July 1975. * "Resistance to Corrosion, Huntington Alloys Technical Brochure, Novem ber, 1970. * Schillmoller, C. M-, and Mason, J. F., "What to do about Corroding Isomerization Units," Petroleum Refiner, July, 1958. 7 CUd, G- P., "Effects of Moisture on Corrosion in Petrochemical Environ ments," Chemical Engineering Progress, October, i960. | Hydrocarbon Processing March 1979 93 COLOR!TE 019630