Document e5EQXZBEZe9yO6y29j220XLY4

ABD00248931 To: R. B. Quy, R&D, Ponca City Interoffice Communication From: Date: Subject: R. J. Lahiere and W. C. Turk, Polymers Research September 30, 1987 VKIASILO RECIRCULATION LOOP DOES NOT ENHANCE RVCM REMOVAL OBJECTIVE Previous work with the bench-scale silo has shown that RVCM removal is greater at higher resin temperatures. The temperature of the resin is increased by hot air aeration and by adequate air distribution. An alternative scheme for aerating the resin is to recirculate resin from the bottom of the silo to the top in an external loop. The effectiveness of the recirculation loop in increasing vinyl chloride removal from silo resin was evaluated in this work. CONCLUSIONS The recirculation loop on the bench-scale silo did not increase RVCM removal from 5265 resin. This is shown in Figure 1 for 77F air and in Figure 2 for 150F air. In the recirculation loop experiment using air at 77F, less RVCM was removed than in the study with the normal silo configuration. This was probably due to sampling error. The silo recirculation loop does not affect vinyl chloride monomer removal because the rate-limiting step of the silo mass transfer process is VCM diffusion from resin particles, not VCM convection in air*. VCM diffusion is not influenced by resin recirculation. If sufficient aeration and air distribution are provided in the silo to remove VCM from the resin particles' surface as it diffuses out of the pores, recirculation of resin will not affect VCM transfer rates. EXPERIMENTAL The normal silo configuration was modified slightly to accomodate the external recirculation loop. An eductor tube, using air as a driving force, transferred resin from the bottom of the silo to the top. A cyclone separator at the silo top separated the air from the recirculated resin. It should be noted that there were two types of resin-air contact in the recirculation experiments: (1) air at either 77F or 150F that aerated the silo resin (exactly like the normal configuration) and (2) air at 1TF that circulated resin in the external loop. The turnover rate of silo resin using the external loop was once every 1.75 hours. 1. IOC R.J. Lahiere to L.Z. Kardos, "Summary of Bench-Scale Silo Experiments", August 10, 1987. ABD00248932 R. B. Quy Page 2 September 30, 1987 Static build-up presented a major problem with the operation of the external loop on the silo. It was eliminated by dispersing the resin with an anti-static agent, glycerol, as the resin was dried in a fluid bed dryer. RECOMMENDATIONS Plant silos should not be equipped with external loops for recirculating resin to enhance RVCM removal from resin. Recirculation loops would be useful for redistributing resin more uniformly in the silos, however. Research Engineer William C. Turk Assistant Chemist RJL/ck attachments cc/attachments: Ponca City: SEM CJMc AWW MEO RRH Aberdeen: VEM FGJ . Houston: LZK