Document gbkBbLz6aEx3075qeR3Gop7r3

/.* 'T^ax^ueu and CAcmtca& STRIPPING OF VINYL CHLORIDE MONOMER FROM RESINS IN AQUEOUS SLURRIES AND FROM DRY RESIN POWDERS R. K. S. Chan, M. Langsam, J. T. Barr*, P. L. T. Brian, J. T. Cheng, D. H. Francke, R. E. Grandin, E. H. Hollister, D. Pesuit, F. L. Riddle, C. H. Worman, G. J. Mantell* *W111 Present Paper Air Products & Chemicals, Inc. P. 0. Box 538 Allentown, Pennsylvania 18105 I. INTRODUCTION The unreacted monomer remaining In polyvinyl chloride can be a source of worker exposure and environmental emissions in polymerization plants, and is, of course, the only source of vinyl chloride released durinq a fabrication process or present in the final product. Because of the very strict requirement imposed by OSHA, serious efforts have been expended during the last year by polymer producers to reduce this residual monomer to the lowest possible concentrations. This paper will report on some of the steps which can be utilized for this purpose in production of resin by the suspension process. Our work still is in proqress and many of the conclusions presented here are preliminary. VVC 000020429 aru/ (Yicmicafi II. DESCRIPTION OF THE PROCESS Approximately 70% of the polyvinyl chloride produced In the United States is made by the batch suspension process. This amounted to nearly four billion pounds in 1974. A simplified flow diagram for a typical suspension plant is shown in Flqure 1. Monomer and Initiator are dispersed in water by means of agitation and suspending agents and polymerized at an appro priate temperature to give the desired molecular weight. The reaction cycle is terminaled when the rate becomes uneconomical to maintain, or earlier if enhanced porosity is desired. Conversion is normally between 83% and 90% at this point. Most of the unreacted monomer is recovered and recycled to the process, but the last few tenths of a percent historically has been left in the slurry because It is difficult to remove. It Is this residual monomer which is now of primary concern. _. Monomer Is usually 'recovered by vacuum stripping of the reaction slurry, either in the polymerization reactor or in a special stripping vessel. The monomer so obtained Is compressed and condensed for re-use. The parameters of the stripping cycle, time, temperature and pressure are controlled to optimize equipment and monomer utilization. After stripping, the polymer slurry is transferred to open equipment, and any remaining free monomer eventually enters the environment. The amount and location of this release depends on the amount of residual monomer, the physical nature of the polymer particles and processing conditions to which the resin is exposed. Blends of several batches of polymer are mixed In slurry tanks and pumped to centrifuges for partial dewatering. Drying Is done In either cocurrent rotary kiln driers or fluid bed driers. Dried resin is collected and con veyed pneumatically to storage or packaging. Resin may be transferred several times and stored for a few days to a few weeks before It finally reaches the fabricator and is blended with necessary additives and processed Into finished goods. During each of these stages there Is further loss of monomer content, dependent upon time, temperature, partial pressure of monomer over the resin, and properties of resin particles. vvc OOOOZO^30 sSrfi\ 'T^iodicfc anc/ (Ytemtcafo III. MONOMER LOSSES DURING MANUFACTURE OF RESIN Monomer concentrations decrease approximately exponentially with time. This exponential decay is seen in every condition to which resins are subjected, but rates may be quite different under varying conditions. For example, the half life of monomer concentration will be on the order of two or three days for general purpose resin stored in paper bags, six to eight hours for well aerated resins at ambient conditions, or a few minutes for resins at very high temperatures. Thus, while it is possible to produce a final product with very low vinyl content by treat ment during the last stages of processing, it is more effective in terms of preventing exposure and release to the atmosphere to remove as much monomer as possible during the stripping process. Figure 2 shows a typical curve relating losses.of monomer In resins, water and vapor phases as a function of time during a plant stripping operation. The slurry temperature during this run was 170F (77C) and pressure was 8 psia. The data in Fiqure 2 were obtained from a plant slurry batch of a Type B resin, described later in Table III, taken to about 85% conversion and transferred to an evacuated stripper. During transfer the pressure in the stripper rose to about 40 psig in about two minutes. With the pump capacity and steam input then available, a period of approximately 15 minutes was required to reach the specified temperature and vacuum. Under these conditions, about 50 ppm of monomer remains in this medium porosity resin at the end of one hour total resident time in the stripper. Under comparable conditions a lower porosity qcneral purpose Type A resin (Table III) will have a higher residual monomer content at this point. Let us follow the monomer content of a Type A non-porous qeneral purpose resin as it moves through the steps downstream of the stripping process. Table I lists these processing steps and approximate average losses of VCM at each step. These concentrations, however, are relatively high com pared with our most recent data. The table shows that the greatest absolute loss of monomer downstream of the stripper occurs in the blending step; it shows a reduction of approximately 60%. A further 60% loss is also shown in the drying step; with a more porous resin, this can be as high as 80%. Resins with lower initial residual vinyl chloride show a lower absolute rate of loss. For example, if initial content of VCM were 500 ppm instead of 2,000 ppm, the driving force would be less and the final concentration under the same conditions would be 50 to 75 ppm or 10-15% of the starting concentration rather than the 5% shown in Table I. -3VN/C -/X- and &cfm'ca/j IV. STRIPPING PROCESS The primary variables which have been identified in a plant strippinq operation are time, temperature, pressure and resin properties. Stripping should be carried out for as long a time as practical at high temperature and at as low a pressure as practical to achieve maximum reduction in VCM levels. Better results are obtained on highly porous resins of small primary particle diameter. For convenience in the discussions which follow, we have defined three consecutive staqes in the strippinq process. Figure 3 and Table II show the changes in monomer content, pressure, and temperature which occur in these stages when a batch of slurry is dropped from a reactor into an evacuated stripper. As noted earlier, there is a very rapid increase In pressure, generally risinq to about 40 psiq in the first few minutes, followed by a slower fall to the operating pressure. Operating temperature is reached at about the same time. This is de fined as Stage I and generally results in a monomer reduction from approximately 18% in the solid to about 2-4% depending upon conditions of the drop. In Stage II residual monomer has dropped to about 500 ppm. The last Stage III is where residual monomer is below 500 ppm and where rates of VCM removal are at their lowest values. Table II summarizes approximate monomer losses during the three strippinq staqes. About 80-85% of unreacted VCM Is lost in Stage I in a few minutes. We have not studied Stage I strippinq. We believe, however, that improved rates of monomer removal can be achieved in Stage I by any method that speeds transfer of slurry and monomer vapor, for example, large drop lines, high pumping capacity and use of a gas holder. In Stage II the point at which our monomer stripping studies generally begin, there is a slower rate of monomer removal. About 15% of unreacted monomer is removed. We have established that higher temperatures, higher porosities, and increased liquid/vapor interface via boiling favor more rapid removal of monomer in Stage II. Adequate pumping capacity and steam input into the strippinq system is desirable and necessary to maintain temperature and vacuum. It may be.of interest to comment on some factors which do not appear important in the stripping process. Within limits of agitation ranaes normally available, the degree of agitation does not seem to effect stripping rate. We must assume, therefore, that turnover rates in the slurry were adequate to produce optimum stripping in our plant equipment. In addition, we have found no marked discontinuities in stripping rates in temperatures approaching the normal qlass transition temperature for PVC homopolymer (70-8CrC). -4- VVC 000020^32 .t/i'i 'T^Kx/licT^ ant/ (Yiptmcafa V There are process variables that do play an important role in the reactor prior to dropping the slurry batch. Batches which have been polymerized passed the optimum cut-off point result in lowered resin porosity and slower strippinq. We have found that batches which have been cooled for scheduling reasons not only require lonqer time for heatinq to stripping temperatures but also appear to give slower stripping rates. One general ization discussed later in greater detail is that low molecular weight resins polymerized at higher temperatures are generally less porous and require lonqer strippinq times than higher molecular weight resins manufactured with similar recipes at lower temperature. -5- VVC 000020433 'T^ux/ucU atut {Ytemicafa V. EXPERIMENTAL Resins, equipment and experimental procedures used in this work are described in the following sections. A. Experimental Procedures and Materials Five resin types used in this study and important property ranaes are described in Table III. Resins A and B are general purpose resins made in recipes which contain a conventional colloid stabilizer. Resin Type C, made in laboratory or plant reactors, in the absence of the conventional polymeric colloid stabilizer does not contain a pericellular membrane. Resin C is measurably more porous than A and B and the primary particle structure can be easily identified using a scanninq electron microscope. Other resins of Table HI are copolymer resins containing either vinyl acetate or propylene. B. Laboratory Studies Resins, Type A, B, and C, used In the laboratory stripping experiments were prepared in a gallon reactor uslnq coimerclal recipes. Resin slurries after polymerization were cooled, vented and stored In gallon widemouth glass jars. Aliquot portions were taken at Intervals over a period of weeks. No significant losses of monomer occurred in the solid phase during this period. Laboratory stripping was conducted in a one-liter, three-necked glass flask fitted with a Friedricks condenser. Stirrinq was supplied by a magnetic stir bar. The slurry mixture from the master batch and added water were mixed, heated rapidly by immersion into a pre-heated fivegallon oil bath. The overall water/resin ratio was approximately 2 to 1. Compressed nitrogen at 5 psi or steam at atmospheric pressure were used in sparging experiments. The water/polymer mixture was sampled prior to strippinq to determine VCM content in resin. At completion of each stripping experiment a second sample was removed to determine VCM content of resin and in some cases, resin porosity. C. Plant Studies A 10,000 gallon stripper equipped with vacuum and high pressure steam was used in plant stripping. The stripper was fitted with an agitator located just above the steam inlet port near the bottom of the stripper. The procedure for dropping the charge from reactor to stripper was described earlier. Initial samples for analysis and zero time were taken when the pressure rise in the stripper had reached Its maximum value before falling. Analytical samples were removed using a "sampler" of special design located at the bottom of the stripping vessels. This attachment allowed separate collection of slurry and water phases under conditions where no monomer losses occurred. The sampler and analytical procedures will be described in a separate publication. VVC 000020434 -6- ancS C/icmica^A 0. Analytical Procedures Analysis for VCM in PVC solid was conducted using a solution of the resin in tetrahydrofuran and a gas chromatograph. Impurities in the solvent were removed previously by a passage through a column of basic alumina with or without activated carbon. Gas chromatoaraphs were fitted with flame ionization detectors and used nitrogen or helium as_ carrier gas. Column packing was either Porapak Qand Chromasorb W^H) . Concentrations of monomer in solid and liquid phases are expressed in parts per million (PPM) by weight. Concentrations in the gas phase are expressed in mole fraction. oooo*0 -7- T^oductl ant/ VI. INFLUENCE OF VARIABLES ON REMOVAL OF VCM IN THE STRIPPING PROCESS The strippinq operation is the most effective and safest step for removal of unreacted VCM from PVC resin. The following sections report on labora tory and manufacturing plant work designed to establish Important process variables and their quantitative effects. A. Variables of Time, Temperature and Pressure in Stripping As noted earlier from Figure 2 there is a loss of monomer at a con tinually decreasing rate with time during a typical plant stripping operation during Stages II and III. Time is an Important variable, and under any given set of conditions, the more extended the stripping the lower is residual monomer in resin and.aqueous phases. In the following sections, primary emphasis is given to removal of monomer from the solid resin phase. Figure 4 is a semi-log plot of residual monomer In a Type B resin as a function of time at two temperatures in a plant strippinq study. Slurry and vapor temperatures for the two runs appear In Table IV. From these data a 20F (UC) Increase In slurry temperature produced an Increase in rate of removal in Stage II of approximately two times at the 2,000 to 3,000 ppm VCM level and an increase of three times at 200 and 300 ppm In Stage III. Laboratory scouting experiments were carried out with the medium porosity resin Type B to determine influence of temperature on stripping rate In Stages II and III. The master batch slurry contained about 35,000 ppm in polymer solids. Figure 5 is a semi-log plot of data obtained in the temperature range of 50-77C (122-170F). In a 15-minute stripping period an increase of 25C (45F) decreases residual VCM In the resin by almost two orders of magnitude. We note that at a temperature of approximately 170F (77C) residual monomer content in this medium porous resin was about 200 ppm after 15 minutes of vacuum stripping. Temperature has a profound effect on removal of VCM In Stages II and III. For com parison, plant data for a Type B resin are also plotted In Figure 5. At 77C rates of VCM removal from the two systems are fairly close con sidering significant differences in procedures, equipment and times to reach strippinq temperature. -8- 00002*36 A- /--\ hi 'T^ux/ucft atu/ (VtciTttcafd Influences of stripping pressure and steam sparging in laboratory stripping studies are shown in Figure 6. Percentage monomer losses from resin is plotted as a function of temperature at a fixed stripping time of 15 minutes. There is a distinct advantage to using vacuum and a further advantage for vacuum plus steam as opposed to operating at atmospheric pressure. Remarkable Increases in rate of VCM removal are noted at approximately 203F (95C) under atmospheric stripping con ditions and at approximately 158F (70C) in vacuum stripping with steam. Vie associate these rate increases with the onset of "pseudo boiling" or nucleation of a high liquid to vapor interface. The importance of this Interface to promote rapid stripping is discussed below. B. Surface Area for Evaporation Type B resin was stripped under atmospheric conditions In laboratory equipment using nitrogen sparging to determine Influence of a qaseous phase in slurry stripping. Figure 7 shows that a nitrogen sweep slightly above the surface Is without effect. The accelerating effect of nitrogen sparging into the liquid is temperature dependent and is greater as stripping temperature Is increased. Apparently the liquidvapor barrier for VCM removal under these laboratory conditions becomes more important as rate of removal from the solid phase is accelerated. C. Particle Structure Particle micro-structure has an Important influence on rate of VCM removal during stripping. Figure 8 is a graphical plot of VCM removal from general purpose non-porous resin "A" and general purpose medium porosity resin "B" in plant strippers. Table V summarizes slurry and vapor temperature data for these two runs. Data show that the more porous resin "B" loses monomer at a rate of about 1.5 to 1.8 times faster than resin A at VCM levels between 200 and 2,000 ppm. Laboratory studies established influence of resin porosity on stripping rates under atmospheric conditions. Figure 9 and Table VI summarize results usinq master batch slurries containing resins Type A, B, and C stripped at temperatures between 60C (140F) and 100C (212F) for 15 minutes. We noted again an abrupt increase In rate at a temperature close to but measurably below the boiling point of water. Figure 10 is a plot relating resin porosities of A, B and C to residual VCM content after 15 minutes of stripping at 100OQ. For purpose of comparison, data from resins Type A and B plant runs (Figure 8) are plotted also in Figure 10. Response of stripping rate to resin porosity is remarkably similar in these laboratory and plant strippings. An increase of one unit of IPTU of resin porosity in the range measured increases stripping rate by about 15% in Stage III. -9vvc 000020437 fa Tfuxtucti un</ C4emica& An unexpected effect on resin porosity was produced by rapid stripping in Staqes II and III In laboratory work. Table VII summarizes stripping conditions and resultant particle porosities as measured by the procedure of Carleton and MlshuckO). Rapid removal of monomer from a PVC slurry containing 4.5% residual VCM in Type D resin markedly increased plasticizer absorption from a value of about 26 to values as high as 31. This phenomenon may be related to the process of producing "blotter" resins where liquid vinyl chloride monomer is removed from resin at low con version forming a highly porous structure and sometimes referred to as the "popcorn" effect. Work is underway to establish the influence of temperature, pressure and unreacted monomer on resin porosity In Stage I stripping. -10- VVC 0000,20*38 /\ ant/ C/icmtcaf V11. MODEL FOR STRIPPING VCM FROM A SOLID PVC AQUEOUS SLURRY A model for removal of VCM from a PVC particle suspended In an aqueous medium in contact with a vapor phase Is shown In Figure 11. From this model, equations relating rates of removal from the three phases as a function of operating variables and polymer properties were developed. The model assumes that there are four barriers for removal of monomer from a suspended particle in an aqueous medium. There are two boundary layers above and below the solid/liquid and liquid/vapor interfaces. Among these, the vapor side boundary layer above the liquid/vapor inter face is believed to be of no great importance and for practical purposes can be disregarded. Calculations using the correlation In Reference 8 show convincingly that the liquid side boundary resistance at the solid/ liquid interface is also negligible. This leaves two boundary layers as important: one on the solid side of the solid/liquid interface and one at the liquid, side of the liquid/vapor interface. PVC particles have a micro-porous structure as discussed in a number of papers(**3,45). Particle diameters in our model relate to primary particles or aggregates of them shown In Figure 11 rather than the diameter of the particle measured by typical screen analysis. Concentrations of VCM in solid, liquid and vapor phases are expressed in terms of concentration or VCM partial pressures. Their relationships during a typical stripping operation are shown in Figure 2 for a particular stripping experiment. These are expressed in the model as Cs, X|_> and PycM* respectively. Mass transfer coefficients of VCM at the barriers for the remaining two important boundary layers are given a K$[_ and K|_y. The model envisions a driving force which is measured as a deviation of VCM con centration from equilibrium in two adjacent phases, rt Is necessary, therefore, to measure Henry Law constants for solutions of VCM at equilibrium in the liquid, solid and vapor phases. From a consideration of the model, mass balance equations relating rates of losses in solid, liquid and vapor phases, have been formulated in terms of mass transfer coefficients, pumpinq capacity, reactor dimensions, the amount of slurry charged and the vapor pressure of water at the temperature of stripping. We are currently in the process of determining the mass transfer coefficients by a computer assisted curve fitting procedure. In addition, we are determining Henry's Law constants H5L and H|_y at a variety of temperatures. Experimental values obtained for a Stage III slurry at 170F (77C) are as follows: For Solid/Liquid Interface: = = .08 .01 For Vapor/Liquid Interface: H^y = VCM = (1.00 .05) x 1011 S- x g. mole - 0.024 .001 psi/ppm -11- VVC 000 A -li 7$<k/ucU arvt C/te*rttCt/4 This liquid/vapor Henry's law constant is nearly identical with the value obtained usinq Berens's VCM water solubility datav5/ and a vapor pressure of 10,200 mm Hg at 76C; H^y - 9.71 x lQlO dyne-cm/g.mole. The solid/liquid constant is somewhat lower than the 76QC value calculated from Berens's liquid/vapor and solid/vapor data, usinq the relation, = Msy/H^; H$l = 0.10. -12- WC 000020440 /\ A------ \ '7~^IC*/uc7a ant/ {Yiemtem .*.1 V r11. STRIPPING OF VCM FROM PVC SOLIDS When freshly manufactured PVC resins are "stripped" In a small fluid bed type drier, rates of monomer removal in general resemble rates obtained on monomer slurry stripping. Figure 12 is a plot of residual monomer con tent obtained with resin Type B and resin Type E-2 as a function of time in fluid bed strippinq. Percentage losses from both resins were essentially identical over a 24-hour period. Linder these conditions, approximately 50X of contained residual monomer was removed in about 2-3 hours at 115F (46C). Very rapid removal of residual monomer from resins Is achieved by mixing in an intensive mixer under vacuum at temperatures between 130 and 200OF {55 and 930C). Figure 13 is a plot of residual monomer content of a propylene copolymer resin Type E-l at various temperatures for 9 minutes in an intensive mixer. At approximately 170F (76C) 50% of the original monomer content was removed and 90% at 200F. Extensive studies conducted in our laboratories 'and in others as well show that in typical compounding operations of this type rapid and nearly complete monomer removal can be achieved at high temperatures with no resin discoloration and no loss of thermal stability. Influence of drying temperature in a commercial rotary drier In manufacture of Type A resin is summarized in Table VIII. As expected, increasing the air inlet temperature in the range of 220 to 280F (105 to 138C) had a marked effect on the residual monomer content. -13- VVC 000020447 A`i 'ffitx/acZi am/ (Vtemi'ca/j IX. DISCUSSION OF RESULTS Reduction of monomer content in both aqueous and powder stripping work (Figures 2 and 12) show continuing rate losses with time. The curves are similar to those reported by Berens(^) for PVC powders at 90C. He interpreted reduced monomer losses with time to arise from a lowerinq of monomer diffusion rates inside particles as monomer content is reduced and in later stages to the presence of glass particles. Since our glassy particle contents were in the range of 0% to 2%, we do not believe that glassy particles played a dominant role in our work. This aspect will be quantified in later studies. We note no discontinuity in Figure 13 for VCM loss in the region of the second order transition temperature of PVC, 160-175F (70-80C). Hopfenberq and Stannett report a number of examples where no discon tinuities in diffusion coefficients were noted in the region of the glass transition temperature for a number of polymers and a number of penetrating gases.(7) The increase in monomer removal rate in atmospheric stripping at 90-95C in Figures 6 and 9 we associate with the on-set of bubble nucleation. Rate controlling processes for VCM In Stages I, II and III of aqueous slurry stripping appear to differ. In Stage I, extremely large amounts of monomer are lost in very short periods of time. It is likely that this process occurs by direct formation of bubbles at the solid/liquid inter face which move directly to the slurry liquid/vapor interface. Quantitative effects of resin porosity, temperature and pumping capacity remain to be established. The special on-line sampler will make this possible. Stage II rates are influenced markedly by temperature, by boiling or nitrogen sparqinq and by resin porosity. Present work on our model will establish quantitatively the relative importance of the two important barriers at the solid/liquid and liquid/vapor interfaces. Our work suggests that both are playing a role. It is clear, however, that a boiling or rapid degassing condition in Stage II is necessary to promote optimum rate of VCM removal. Staqe III stripping rates appear to be more dependent upon the solid/liquid interface and on diffusion rates inside resin particles. The very rapid losses of VCM in Stage I and rapid increases in rates at about 90C in atmospheric stripping suggests that pseudo boilinq or degassinq occurs below the normal boilinq point of water. How bubbles form and how they are influenced by primary particle diameter, pore size and pore distribution remain to be established. -14- 0000*0^2 v vc Ai 'T^ux/ucti (ttu/ {Vsc-mica/^ ACKNOWLEDGEMENTS We wish to express our appreciation to many persons in the Analytical Department of Air Products and Chemicals, Inc. and to many members of the industry who have shared so generously their knowledge toward the solution of a problem affecting the health and safety of our employees and theirs. It is in this same spirit that we have elected to share our preliminary findings with others in this progress report. We are continuing our work and will be reporting additional findings in the future. OOOO20443 ei 'T^ux/lictl i!>u/ C/temica/4 REFERENCES 1. Carleton, L. T. and Mlshuck, E., Jour.Appl.Polymer Science, 8, 1221-1255 (1964). 2. Chan, R. K. S. and Beale, J., Polymer Jour., 3[, No. 6, 690-697 (1972). 3. Glass, J. E. and Fields, J. W., Jour.Appl .Polymer Science, 1_6, 2269 (1972). 4. Treqan, R. and Bonnema.yre, A., Revue Plastlques Modernes, 23 (7), 3 (1971). 5. Berens, A. R.,r ACS Polymer Reprints, 15_ (2), 197 (1974). 6. Berens, A. R., ACS Polymer Reprints, 1_5 (2), 203 (1974). 7. Hopfenberg, H. B. and Stannett, V., Chaoter 9, Physics of Glassy Polymers, R. N. Haward ed, Wiley, New York, 1973. 8. Brian, P. L. T., Hales, H. B. and Sherwood, T. K., A.l.Ch.E. Journal, 1_5, No. 5, 727-733 (1969). -16- OOQOZO^ vvt VCL CONDENSER FIG. 1. TYPICAL SUSPENSION PROCESS POLYVINYL CHLORIDE PLANT FLOW DIAGRAM X-J Oz 3 CO CL i2~ (x/) oooo 2.0^ SjNjO FIG. 2. VCM CONCENTRATION IN SOLID, LIQUID AND VAPOR PHASES AS A FUNCTION OF TIME DURING PLANT STRIPPING VVC 000020446 \ /A 'T^ioa.'itctl afuS C/tetMtca/^ TABLE I APPROXIMATE MONOMER LOSSES AFTER STRIPPING IN MANUFACTURE OF RESIN TYPE A Process Step Leaving Stripper Slurry Blending Centrifuging Drying Storage Shipping VCM Content (PPM) End Step 2,000 800 720 290 215 105 Percent Loss in Step ~- 60 10 60 40 50 VVC 000024<t7 Changes of Temperatures, Pressure and VCM Content in Resin with Time. TEMPERATURE -45 180 -- 30 160 -15 140 -0 120 -15 100 FIG. 3. TIME (N MINUTES STAGES OF PLANT SLURRY STRIPPING VVC 000020448 -ZA- A- TABLE II LOSSES OF MONOMER IN THREE STAGES OF STRIPPING OF BATCH FROM SLURRY OF 10,000 LBS. MONOMER*CHARGE* STAGE PPM of VCM In Resin Initial Final Pounds Lost** I II III 180,000 30,000 1,275 30,000 500 251 500 1 4 *Approx1mate Conversion = 85% Approximate Weight Ratios of Monomer In Vapor, Liquid and Solid Phases are 1:100:1000 during stripping. 0X ov 7~Mjic?4 aru/ C4emicai TABLE III PVC HOMOPOLYMER AND COPOLYMER RESIN TYPES USED IN THIS STUDY Resin Composition Description IPTU* Range % Accessible Porosity** Inherent Viscosity dl/qm A PVC ' General Purpose 19-21 10-11 0.88-0.92 Low Porosity B PVC General Purpose 26-28 17-18 0.94-0.98 Medium Porosity C PVC Specialty No Pericellular Membrane High Porosity D Vinyl Acetate Copolymer -- 30-32 -- 25 - 26 22 0.80-0.88 0.46-0.50 E-l Propylene Copolymer -- 16-20 8.5- 10 0.70-0.76 E-2 Propylene Copolymer 16-20 0.57-0.63 Irreversible Plasticizer Take Up By Method Reference (1) **By Mercury Porosimeter According to Reference (2) . ,.r oooc^o TIME IN MINUTES FIG. 4. EFFECT OF STRIPPING TEMPERATURE ON VCM LOSS IN TYPE B RESIN 00002^ VY C . ....crul t fictm'ca/j- TABLE IV TEMPERATURES OF SLURRY AND VAPOR FOR RESIN TYPE B IN PLANT STRIPPING STUDY* Sampling Point* Time (Minutes) High Temperature Run Slurry Temp. Vapor Temp. F F Low Temperature Run Slurry Temp. Vapor Temp. F F 1 0 136 136 2 15 170 170 132 130 152 150 3 30 168 172 151 152 4 45 168 172 150 154 5 60 170 172 150 156 *See Figure 4 i ooooz^2 VMC TIME IN MINUTES FIG. 5. LABORATORY VERSUS PLANT SLURRY STRIPPING OF TYPE B RESIN AND TEMPERATURE EFFECTS VVC 000020453 FIG. 6. EFFECTS OF PRESSURE AND STEAM PURGE ON VCM REMOVAL IN LABORATORY STRIPPING OF TYPE B RESIN (VCM 45,000 PPM) STRIPPING TIME 15 MIN. vvc 000020454 FIG. 7. EFFECTS OF NITROGEN SPARGING ON VCM REMOVAL IN LABORATORY TYPE B RESIN (VCM 45,000 PPM) STRIPPING TIME 15 MIN. 1 Wc 0oOO^O455 FIG. 8. EFFECT OF POROSITY ON VCM REMOVAL IN PLANT STRIPPING 000020^56 VVC ^/ti '/iux/u& amt C/ietmea& TABLE V TEMPERATURES OF SLURRY AND VAPOR FOR RESIN TYPES A AND B IN PLANT STRIPPING* Samp!ing Point* Time (Minutes) 10 2 15 3 30 4 45 5 60 6 75 7 100 Slurry Temperature F Resin A Resin B Vapor Temperature F Resin A Resin B 133 136 136 136 167 170 170 170 167 168 172 172 170 168 174 172 170 170 170 -- 170 ... 175 172 175 -- 175 ... *See Figure 8 WC 000020457 FIG. 9. LABORATORY STRIPPING OF RESIN TYPES A, B AND C AT ATMOSPHERIC PRESSURE (VCM 43,900, 47,000, 23,400 PPM, RESPECTIVELY) STRIPPING TIME 15 MIN. 00020458 VVC 0 A -jr/ii '7~*ux/uc& utu/ tVeenuca/2 TABLE VI EFFECT OF PARTICLE POROSITY ON RESIDUAL LEVEL OF VCM IN RESINS STRIPPED IN LABORATORY AT 100C, ATMOSPHERIC PRESSURE, 15 MINUTES Resin Type __ Porosity - IPTU* PPM Of VCM In Resin Initially After Stripping % Original VCM Remaining A BC 20 26 30 43,900 47,000 23,400 450 60 15 1.05 0.13 0.06 *Irreversib1e Plasticizer Take-Up Procedure Reference 1. VVC 000020459 FIG. 10. EFFECT OF RESIN POROSITY ON RESIDUAL VCM VVC 00002CK60 'T^ioc/uc.fi u, :</ TABLE VFI INFLUENCE OF STRIPPING TEMPERATURE AND PRESSURE ON PARTICLE POROSITY IN LABORATORY STRIPPING STUDIES TYPE B RESIN Resin1* Stripping Conditions 15 Minutes o In* Temp. C Vacuum Resin VCM-Content After Strlppinq IPTU* Control 45,000***** 26 a 50 A'em. 10,900 24 b 60 Atm. 14,000 27 c 75 Atm. 4,700 29 d 100 Atm. 40 28 e 53 14 7,400 29 f 62 14 4,100 30 g 68 14 1 ,000 30 h 77 14 100 31 *Resin in all experiments filtered by suction and dried at 40C (105F} in a vacuum oven. **0rigina1 VCM content of master batch slurry. ***Irrevers1ble plasticizer take up according to reference (1). VVC 000020461 PVCM " P ' PW VAPOR rLUJi L LXZ1 Z. C7 Z'TJ'T FLUX VCM (CONDUCTANCE) (DRIVING FORCE) fsl ^ (as*sl) fc< 7sl PLV ^ (alklv VCM ' H LV FIG. 11. MODEL FOR SLURRY STRIPPING r* s, v l, p r vcm are concentrations or partial pressure of VCM; K LV KSL are mass Trans fer coefficients; HLV HSL are Hsnry Law constants; As AL are areas at S/L and L/V interfaces. VVC 00020462 ) FIG. 12. STRIPPING OF VCM FROM DRY PVC RESINS v vc 00002.0463 % INITIAL VCM FIG. 13. STRIPPING VCM FROM SOLID RESIN TYPE E-1 RESIN (VCM 305 PPM) VVC 000020464 J77& 'fiioductl am/ C/te*fUCO& TABLE VIII INFLUENCE OF TEMPERATURE IN PLANT DRYING OF TYPE A RESIN Inlet Air Temperature (F) 280 260 220 VCM Residual In Resin Drier Inlet** Drier Exit** 850 200 850 350 1050 500 % VCM Remaining 24 41 48 Rotary drier with capacity of 5,500 lbs./hr; Residence time 15 minutes; Air exit temperature approximately 150F Average of several samples vvc 0000Z0A65