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The Journal of the Royal Institute of Thailand Vol. 27 No. 3 Jul.-Sept. 2002 Commercialization of the Worldûs First Oleflex Unit ˆˆ¯ entering reactor internals were added by installing an electric heater at the surge pot in 1992. In addition, a system for trickle mode operation of the catalyst circula- tion was provided to limit the cata- lyst circulation rate during the start-up after a quick shut-down, such as a compressor trip. This is to prevent a hoop stress problem. 4. Polythionic acid attack Stainless steel is susceptible to polythionic attack. The standard procedure is to neutralize the equipment to remove the acidic sulfide prior to opening to the at- mosphere. In the case of equip- ment heavily fouled by coke de- posit as was the case of Oleflex re- actor, the standard procedure was not effective since the neutraliza- tion solution could not get under the deposit. An additional step had to be added, i.e. hydrogen stripping of the reactor system prior to the neutralization. 5. Impact of Heavies on heat exchangers Although the amount of Heavies formed in the C 3 - Oleflex was much less than the C 4 - ones, it was enough to cause prob- lems in the downstream heat ex- changers and coolers. For the hot combined feed heat exchangers, coke penetrated the small opening between the tubes and the tubesheet, eventually causing tube leaks. They had to be replaced by new ones with tubes welded to the tube sheet on both sides of the sheet. As for the Reactor Effluent Coolers, fouling by Heavies limited the effective heat exchanger duty. More cooler surface had to be added. Catalyst Performance and De- velopment 1. Catalyst deactivation by carbon monoxide (CO) The phenomenon of catalyst deactiva- tion was discovered only a few months after a steady operation of the unit, i.e. December 1990. The catalyst did not readily respond to the process; variable changes and catalyst poisoning was suspected. A rush research program in the UOP lab finally established that the presence of CO in the hydro- gen recycle stream used for reduc- ing the metal oxides at the catalyst reduction step was responsible for poisoning the metal function of the catalyst. The presence of CO at the level found in hydrogen re- cycle gas will not cause any prob- lem in other parts of the reactor system. Arrangement to supply PSA hydrogen to the reduction zone was made during the first quarter of 1991 and the CO-dam- aged catalyst was subsequently re- placed by a new DEH-6 batch in April 1991. 2. DEH-8 Development The new DEH-6 batch, however, did not live up to expectation. The catalyst performance was inad- equate and catalyst activity decline was noted in successive months of operation. UOP accelerated their catalyst development program and a reformulated catalyst, DEH-6B, became available early 1992. The catalyst was renamed DEH-8 which was to become the standard cata- lyst for all Oleflex units. NPC loaded DEH-8 catalyst into its unit in April 1992. DEH-8 was proven to be a stable catalyst. The catalyst activity decline with time was much slower that had been the case with the other catalysts. 3. DEH-10 development UOP research, in the meantime, gained more understanding of the platinum/attenuator interaction and the deactivation mechanism. New formulations of catalyst were developed, aiming at the reduc- tion of platinum content as well as those of modifier and attenuator. The low platinum content not only makes the catalyst cheaper, but also reduces the Heavies forma- tion. The first in the series of the new catalysts was DEH-10. At the time of the announcement of the DEH-10 catalyst, the performance of DEH-8 in NPC unit was still satisfactory. NPC, however, stud- ied and followed the progress of DEH-10 used in other units. At the end of 1994 the performance of DEH-8 dropped off rather sharply and DEH-10 was loaded on the fly replacing DEH-8 in January 1995. Normally the operating conditions of the unit at the beginning of run and the end of run are practically the same. The selectivity decline determines the acceptable limit of the catalyst life. 4. DEH-12 development Further improvement in catalyst formulation resulted in the avail- ability of DEH-12 catalyst with fur- ther reduction in platinum and at-