Document oMRjGkKbwLj00yEzg7drKaJGr

B> F. Goodrich Chomicai Company a mvtaioN or thb a. r. oooonich comtamy DEVELOPMENT CENTER PREVENTION OF RESIN BUILD-UP ON THE SURFACE OF THE REACTORS IN PVC POLYMERIZATION By C. E. Parks December 15, 1967 Distribution E. K. Bean A. Behrens C. B. Cooper - J. Piers L. G. Crunkleton - 8. 8. Michels A. A. Etter J. E. Jansen P. H. Lawrence T. R. Linak H. H. Marty J. L. Nelson J. H. Powell R. N. Rylands - R. W. McKay R. D. Scott W. L. Semon A. R. Webber - D. W. Robb J. M. Whitney R. J. WoU C. L. Woods Operations Council Technical Council C. T. F. File i N5 01 w o o B. F. GOODRICH CHEMICAL COMPANY DEVELOPMENT CENTER PREVENTION OF RESIN BUILD-UP ON THE SURFACE OF THE REACTORS IN PVC POLYMERIZATION By C. E. Parks In a long and continuing search to find some way to reduce or eliminate resin build-up on the walls of the PVC polymerizers, magnesium oxide and/or magnesium hydroxide, at very low levels, has been found to be effective. It appears now that the hydroxide is probably the active ingredient. About a dozen charges have been run in the IS gal. and 175 gallonpolymerizers under various conditions and levels of MgO and Mg(OH)2 ranging from 2S00 to 156ppm. All results with 62S ppm or more have been consistently good. In the most recent charge, with 1800 ppm of magnesium hydroxide, the reactor was almost completely clean. When it was rinsed with water all resin flushed into the blow down tank except 34 grams (out of 360 lbs). The reaction time was six hours (10 is normal) for 73% conversion. The resin appears to be slightly course. Conclusions Milk of magnesia is recommended as an effective, yet gentle, ingredient for eliminating build-up in a reactor; causing no harmful side-affects, when used according to directions. 2S. Originally, the addition of magnesium oxide to a polymerizer to prevent build-up was based on the theory that it would neutralize all of the HC1 which is normally split out, maintain a high pH and thereby eliminate the adhesion to the polymerizer walls. It proved to be a terrific buffer and it does eliminate build-up on the walls of the polyamrlzer but, apparently, not because of the high pH. Charges with 2500, 1250, 625, 312 and 156 ppm MgO (based on the monomer) have been run. The pH was almost identical la every case. They were about 10. 5 pH before polymerization and 10.0 pH after polymerization. The one with 156 ppm MgO had as much build-up as the control yet the pH was 10.0 The 312 ppm was low, but more than the other changes. The ones with 625 ppm and higher had very little and it was not 'ightly bound. At present, it appears that 625-1250 ppm will be the optimum amount for the elimination of build-up in the polymerizers. * Magnesium oxide was chosen because it is inexpensive, non-toxic, and previous work had shown that it would Improve stability without causing haze in transparent films. BFG39307 ZOQIZZSZ Magnesium. hydroxide has similar proparties and is apparently more effective in preventing build-up. It will be completely evaluated as soon as possible. SURFACE EFFECT Since the high pH does not explain the prevention of build-up, it is now believed that the MgO/Mg(OH) slurry forms a molecular coating on the surface of the stainless stee? walls. Furthermore, it is theorized that the part In solution Is not effective and that a quantity sufficient to coat the walls must be added over and above the amount which goes Into solution. When 156 ppm MgO was added, it all went into solution In the water and was ineffective. After running five charges with MgO. one was run with none and the build-up was one-fifth the control Indicating possible surface effect. A stainless steel strip was Immersed In a MgO slurry for 16 hours and then mounted in a production potymeriaer. It had very little build-up for two charges. After six charges it had normal build-up. This test will be repeated and the strip removed after one charge. BUILD-UP QM PttIjVMEttIZEB WAT T* MqQ Added Grams Build-up 175 gallon poly, control m* N N w m n H ft NN N MM m n ft as N M i B| m w m 0 ppm 2500 " 1250 " 625 " 312 " 156 " 0" 1250 1800 Mg (OH)j 1600 128 245 135 480 1400 315] 1500 34 This charge was run in the same polymeriser after the preceding four charges which contain magnesium oxide. Perhaps this is the mason for the low build-up. *%his charge was ran with "Maglite D", a cheap inactive rubber grade MgO. which obviously did not work. /--w / ) O OLYMERIZATIOH CYCLE I VjO V In the above mentioned series, the times to blow-down have ranged from 15-20 hours which is 50% to 100% longer than the control. A charge with double the IP? catalyst came down In six hours and appears to be normal. (It had 1/t pt. magnesium hydroxide. It is being repeated with magnesium oxide.) It la very encouraging that the polymerisation rate responded to lagrsaesd catalyst. It should be easy now to adjust to desired cycle time, but some increase in catalyst level will be necessary. -3- PARTICLE SIZE All of the charges in the above mentioned series produced coarse resin. The coarseness seemed to be Independent of the amount of MgO added. It was suspected that the MgO was reacting with the "tween" in the "Elvanol-tween" emulsifier system. A charge was run with all Elvanol and particle sice appears to be about normal, but an increase In the emulsifier level Is necessary. In a well buffered system, Elvanol alone may be satisfactory. CONVERSION The percent conversion with magnesium oxide in the polymerlzer has been about normal even when the cycles were longer. The last charge with double IPP went to 73% in six hours. MOLECULAR WEK3HT The inherent viscosity apparently is' unaffected by the presence of magnesium oxide in the polymerlser. 103EP - Specification - 96 103EP - 17S gallon control - 96 103EP - 17S gal. 1250 ppm MgO - 95 ELECTRICAL INSULATION RESISTANCE This property was determined by George Small's Electrical Group by compounding the resins from the 175 gallon polymerlzer into a plasticized 2042 electrical recipe. It was extruded onto wire. Immersed in water overnight and run by their standard test procedure. Meg-ohms/ MrtMfrd loooft* 103EP Production - control 0 103EP 176 gallon poly. - oontrol 0 m mm m w n m ss m ts m m mm m m m m N 1250 ppm (on mill) 625 1250 * fin poly) 625 " 312 156 " " 2920 3780 3780 4330 4760 2660 4650 5320 These data indicate that MgO add improve insulation rsslstanoe. A for this leer value in the polymerlzer may actually it BFG39309 7T nvEW HEAT STABILITY Q 450 F. Earlier work had shown that vary small amounts of magnesium oxlda addad to a batch on tha mill significantly improves tha stability of tin stabilised compounds. It is more affective and more efficient when added in the polymerlzer. Vynaloy 350 recipe - with 4 parts tin tbilizer Parts MoO Time in minutes to black 103EP - Production control 103EP - 175 gal. control 0 0 156 (in poly) 312 - 625 " 1250 " 1250 (on mill) Vynaloy 350 recipe - with 2 parts tin stabilizer Rw Ma<? Time in minutes -- tables*; 103EP - Production control 103EP - 175 gal. control 0 0 156 ppm (in poly) 312 625 " " 1250 " 2500 -. * 1250 " (on mill) 1 3 5 6 9 11 9 8 It appears that 1250 ppm addad in tha poly gives tha maximum increase in stability in this system. It is interesting to note that the 2500 ppm hurt the stability. TMnjTy .............................. ' -4- stability above). im by John Whitney's Groutmii^r* Whlc^nS(T tin stabiliser (same as the one used for oven MgO added 1ft Pofr- Use 103EP - 175 gal. poly control 103EP - 175 gal. " mum 16 min. 53 25 min. 20 25 min. SO 21 min. 30 27 min. 45 (hv) BFG39310 It li interesting that only 156 ppm MgO added In the polymerlzer increased the D.T.S. about 34%. 1250 ppm Increased the time 4 7% over the control. RESIN CHARACTERIZATION Samples of the resins polymerized with various levels of MgO have been given to Ed Collins. No report as yet. ANALYTICAL EXAMINATION Samples of the resins polymerized In the presence of magnesium oxide have been examined by Lin Crider's Group. They report the magnesium Is not chemically bound, but it is very Intimately dispersed. It was impossible to throw it out of solution with a normal centrifuge. However, they w*re able to separate it with an ultra high centrifuge. In solution, the control sample seemed to have more gelled particles. ASH The amount of magnesium oxide remaining in the resin varies widely according to the ash results obtained by the Analytical Group. The percentage of the amount charged ranged from 16 to 50%. Additional data will be gathered on future charges. FISHEYE8 No information yet. However, it has previously been established that the well cleaned polymerlzers reduce the number of gelled resinous particles. BULK DENSITY Only one sample run. It will be &urther Investigated as soon as the process Is under control. Bulk Density oms/cc 103EP Y74 Specification # 175 gsllae poly, control IS * all Elvanol - 1250 ppm MgO . 55 - . 60 . 55 . 30 It is not known whether the all Elvanol or magnesium oxide caused the low bulk density. (Probably the Etvanol)* Do not know yet whether .his will be a serious pros'en.. * Elvanol tween with no magnesium oxide. PQRpSlH Only om sample run. It will be further Investigated aa toon a* procesa la under control. It la not known yat whether the high poroalty la good or bad. BRABENDER FUSION TIME No data aa yat. ANGLE OF REPOSE No data aa yet. STATISTICAL STUDIES We have now run enough chargea to fine out what factors Influence the polymerisation in the presence of magnesium oxide and hydroxide. A statistically designed series has been set up, with the help of Bob Bowles and Claude Brunet, to optimise polymerisation conditions. ECONOMICS High quality magnesium oxide la about 75$ per pound whereas the same quality magnesium hydroxide is about 25$ per pound. Obviously, we would like to use the hydroxide. Also, the hydroxide is a more reliable, uniform quality product. We have only run one charge with the hydroxide and it looked good. In any case, at 1250 ppm the cost la insignificant. POTENTIAL COST SAVINGS It la difficult to arrive at an actual figure, but If we can succeed In eliminating polymerlser cleaning completely, it could save several million dollars per year in labor and lost production time. OTHER APPMOATIOSM To date, all of tfiawock has been done with 103EP pearl resin. It is expected to m equelly well with the aoetate, vinylidene, and propylene copol0Hes. It may also be usefcl in bulk and/or continuous imlysljflHsellijiis. The use of magnesium oxide and/or hydroxide should be Investigated in latex and rubber polymerizations if build-up on the polymerlser wells la a problem. PRODUCTIQN uniformity The unusual capacity of magnlslum oxida and/or hydroxide to maintain a constant pH of 10.0 throughout the reaction may tend to level out operational variables such as loss of 'acuum, changes in the water, seasons of the year; resulting In more uniform quality. f-EfrAf STATUS A patent record, covering the use of magnesium oxide and hydroxide to improve heat stability and to eliminate build-up in polymerlzers has been written. It has been discussed twice with J. Hughes Powell and additional, specific data Is being gathered so patent application can be made as soon as possible. SCALE-UP Since charges with magnesium compounds added in the polymerlxer require more catalyst and more emulsifier than standard recipes, additional data will be needed before going to larger equipment. The surface volume ratio is much lose in production polymerixers and this probably will change the amount of magnesium compound needed. Also* e thorough evaluation of all resin properties must be made to make sure no unforeseen difficulties develop. -7- Note: All polymerization studies have been supervised by A. A. Etter. His contribution is gratefully acknowledged. C. E. Partes a 800 BFG39313