Document YjaqrwGN12DEw4qeZjk1KB0BN

Industrially Significant Organic Chemicals Part 3 ^^S^'-j^C^SSSSSA; GEORGE T. AUSTIN. Washington State University* This third part of our series covers 14 chemicals, in cluding chloroethane (vinyl chloride), which ranks sev enth in sales among the top 100 organics and is manufac tured by 12 U.S. companies. In 1970. seven U.S. firms (American Chemical. Dow, Du Pont. Hercules, Pittsburgh Plate Glass. Martin Mari etta. and Ethyl Corp.) made 678 million lb priced at 6c/lb. The current price is about 8e/lb. Chloroethane (Ethyl Chloride) Three-quarters of ethyl chloride production is used for the manufacture of tetraethyl lead, a use whose future is uncertain. Ethyl cellulose consumes about 10%: other uses, such as refrigerants, anaesthetics and other ethyla tions are trivial, even when considered all together. Ethyl chloride can be made from ethyl alcohol (al though this is not the preferred method), from ethylene and HO (about 88% of production), and (along with a mixture of byproducts) from the light- or heat-catalyzed chlorination of ethane or ethane/methane mixtures: ZaCI, C,HsOH + HC1 CjHjCI + H,0 98% yield CHjCH. + Ha C,H4a c,h. + ci, -- c,H,a + ho C.H. + CH, + CL --P*"*0--. ^* 4 ' 100-200'C CjHjCHm) + 01,0(13%) + 2HO To nwot aw auewf. MO Ckano Eng, Jan. 21.1970. a 132. . . ... CHEMICAL ENGJNEERING/MARCH nIlH -; . >> ,- r Chloroethylene (Vinyl Chloride) Chemical principles indicate that the reaction, CH,CH, + CL -- CHjCHCI + HC1. offers a desirable way to make vinyl chloride. Yields from this reaction are low. however, and it has not been commercialized. Be cause the product vinyl chloride is in such great demand, research toward making this reaction economically at tractive would seem promising. Three commercial feedstocks yield vinyl chloride: naphtha, ethylene or acetylene. Oxychlorination, hydro chlorination, dehydrochlorination and combinations of these reactions all are used commercially. The fine qualities of polyvinyl chloride plastic have brought about enormous demand for the monomer, and its production rate has been expanding at 10%/yr. It alone now accounts for nearly 15% of U.S. chlorine pro duction. Because its price is low, the processes for its production must be efficient in their use of both energy and materials. The usual procedure is to form dichloroethane (DCE). then dcchlorinate DCE to vinyl chloride either by ther mal cracking or the use of strong NaOH. Competition 87 ." V'! ' ' 24831001 vo-:^ ORGANIC CHEMICALS. PART 3 ... in licensing the processes is keen. While there are impor tant differences in handling heal and managing catalysts, temperatures, and yields, there are essentially four proc essing systems: acetylene hydrochlorination, balanced acetylene-ethylene chlorination, oxychlorination. and single-step chlorination and cracking. From acetylene: HjK'L on cbjn.mil IICOH + MCI W |40'C CHXHCI Since ethylene costs approximately half as much as acetylene, considerable chemical manipulation can be justified to allow substituting ethylene for acetylene, so this process appears to be disappearing. From balanced acetylene-ethylene: While no new plants using this process are being built, it represents a major step forward and solves two problems: (I) reducing the amount of acetylene consumed, and thus the feedstock costs, and (2) using byproduccd HCL Thermal cracking of the intermediate DCE must not proceed beyond 50%. or too many heavy ends are formed. CHXH, + Cl, -- CIIXKHX1 CHXICTIXI CtlXHCI + HC1 pumice auN HCCH + MCI -- CIIXIICI From cthvlcne by oxychlorination: This process uses an ethylene and chlorine feedstock for a normal chlorination to DCF., plus oxychlorination of ethylene and HCI to DCE bv means of the HCI formed on decomposition of the DCE: CIIXH. + Cl, -- CHX1CHX1 CHXH. + 2IIC1 + '/.O,-- ClljCTCHjCl + 11,0 4JO-5WC CHXICHXI-------- ----* CHXHCI + HCI pumkc cauty*t M Single-step chlorination and cracking (Transcat): Eth ane is cheaper and more readily available as a feedstock than either ethylene or acetylene. There has been devel oped through the pilot plant stages a new process using a molten salt bath, in which such feedstock is cracked to ethylene, and in which chlorination, oxychlorination and dehydrochlorination of DCE all occur simulta neously. Copper oxychloride acts as an oxygen carrier in this process, and functions also in the HCI recovery process: CuXI, + O, -- 2CuO CuCL CuXI, +' Cl. -- 2CuCI. CuXI, + 2110 + '/.Cl. -- 2CuCL + H,0 Vinyl chloride is produced at high purity, and with an overall yield of 80 mol% based on ethane and 90 mol% based on chlorine. Feeds can contain ethane, ethylene, mixed ethylene, chlorination products, and HCI in various mixtures, permitting recovery of values from such mate rials. Changing the reaction conditions permits the pri mary product to be vinyl chloride, chloromethancs, trichloro-ethylene or pcrchlorocthylcne. Currently, the balanced oxychlorination process domi nates the production of vinyl chloride, and it has several variations, involving fixed and fluid beds and different methods of heating and separation, all of which are economically and technically important None of the processes is totally byproduct-free, but some are very good. Feedstock problems make the question of which process will dominate the future highly uncertain: eth ane. ethylene (from naphtha)'and acetylene are all in short supply. All the vinyl chloride goes into polymers. . In 1970. ten U.S. firms (Allied Chemical. American Chemical, Goodrich. Conoco Chemical. DiamondShamrock. Dow, Tcnncco. Monochcm, Pittsburgh Plate Glass, and Ethyl Corp.) made 4.04 X 10" lb for a price ofaround 4f/lb. Production of4Jt X I0*lbat4%t/tbhas MARCH It, 1974/CHEMICAL ENGINEERING ^1^ been predicted for 1973. The price is currently quoted at 5e/lb. Chloroform This is an old product, which can be made in several ways, but the only significant quantity is made through chlorination of methane. Since this reaction produces a range of chlorinated compounds, depending on the ratio of chlorine to methane and the reaction conditions, methyl chloride, methylene chloride, chloroform and carbon tetrachloride are manufactured together. The flow diagram for making chloromethane (methyl chloride) suffices for all four products. Two-stage chlorination gives the maximum yield of chloroform: CH, + Cl, - mixed products including CHCt, Some chloroform is also made from acetone and bleaching powder: (CHJ,CO + 6CaCtOCl H,0 2CHO, + (CHjCOOljCa + Ca(OH), + 3CaCl, + 6H,0 The yield is about 88%. Ethyl alcohol or acetaldehyde or mixtures of these can also be converted with bleaching powder, but the process appears to be uneconomical in most cases. Most chloroform (55%) is used in making dichlorodifluoromethane, the principal refrigerant fluid in home air conditioners: 30% goes into fluorocarbon resins, such as polytetrafluoroethane, TFE, and FEP. There are also many small uses: it is an ingredient in liniment, cough syrup and perfume; it is a denaturant, and a solvent extractant in the manufacture of penicillin, steroids, vita mins, and nicotine: it is used in dye application; and it is used as propellant for aerosols, freezing-point depres sant for carbon tetrachloride, and fumigating agent for grain. In 1970, six U.S. manufacturers (Allied Chemical, Diamond-Shamrock, Dow, Du Pont, Vulcan Materials, and Stauffer) made 2.4 x 10* lb, which sold at 16e/lb. It is currently quoted at 17l/^/lb. Chloromethane (Methyl Chloride) Chloromethane is made either by the chlorination of methane or the hydrochlorination of methanol. By anal ogy with the oxychlorination of similar hydrocarbons, the reaction of methane with HC1 and oxygen should be feasible, but yields are not sufficiently good to make this process attractive for methyl chloride at this time. The hydrochloric acid byproduced by direct chlorina tion of methane can be used up as formed, by reacting it with excess methanot: CH4 + Cl, -- CH,C1 + HQ + (mixed products) alumina _ CH,OH + HO CH,a + h,o Either fluidized or fixed-bed catalysts are used with alumina gel or Cu2Clj and ZnCl, on active carbon or pumice, as well as H,P04 on active carbon. The yield with alumina is about 95% on methanol. When methyl . chloride is desired from the direct chlorination reaction. ; the, C1j/CH4 ratio should be below stoichiometric and ^th^.yield per pass minimal. Even with low C1,/CH4 .ratids, however, polychloro compounds are formed, and the methyl chloride yield docs not exceed 40%. Unless a market for methylene chloride, chloroform and carbon tetrachloride exists, production of methyl chloride by the direct chlorination of methane is not practical. Chloromethane's primary use (58% of production) is in the manufacture of methyl silicones. The manufacture of tetramethyl lead consumes 16%, th manufacture of M 24831003