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«“√ “√ √“™∫— ≥±‘µ¬ ∂“π ªï ∑’Ë Ú˜ ©∫— ∫∑’Ë Û °.§.-°.¬. ÚıÙı Pramote Chaiyavech ˆˆ˘ tenuator contents. The develop- ment was primarily aimed at the reduction of Heavies formation as well as the increase of on-stream time. The new catalyst was dis- cussed at the 1997 Oleflex confer- ence. Again the performance of the DEH-10 catalyst in the unit was still satisfactory. The switch-over to DEH-12 at NPC was carried out in April 1998 with satisfactory re- sults. Figures 3, 4, 5 show the performance of DEH-8, DEH-10, and DEH-12 catalyst on the NPC unit. The slower selectivity decline of the newer catalyst version con- tributed significantly to the longer catalyst life and the improved eco- nomics of the operation. The cycle length is not limited by the cata- lyst activity but by the maximum allowable reactor pressure drop. The current DEH-12 batch has been in service for some three years and it is still in good condi- tion. It is expected that this batch can last 1-2 years longer than had previously been the case. 5. DEH-14 catalyst DEH-14 is the latest version of the newly improved catalyst. UOP revealed this new catalyst at the 2001 Oleflex conference. With the lower attenuator level, the perfor- mance targets for DEH-14 are : - Equivalent initial activity - Equivalent selectivity - Higher coking stability - Higher long-term stabil- ity NPC will have to study the benefit of the new catalyst for the next catalyst replacement opera- tion. Table 2 summarizes the cata- lyst composition comparison. UOP will continue to come up with newer catalyst versions. The Economic Performance of the Unit In justifying the construction of the Propane Dehydrogenation Unit, the offtaker, which is a polypropylene producer, agreed to pay for the propylene on a cost- plus basis. The total production cost was passed on to the offtaker plus 15 per cent return on invest- ment. This was acceptable in the beginning since the market price of propylene was high and the gov- ernment put 20 per cent duty on Fig. 3 C 3 propylene yield comparison (%wt.)