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Isobutane/2-butene alkylation was carried out in a semibatch slurry reactor using the hydrogen and lanthanum exchanged form of hexagonal faujasite (EMT, Si Al bulk ratio of 3.5) as catalysts. 51% La exchange in the EMT sample (La-EMT-51) gave a very slight enhanced alkylate activity and yield compared to the parent H-EMT catalyst. The improved activity correlated with a higher relative concentration of strong acid sites as measured by IR. The alkylation experiments were performed with a rather high dilution of butene to be able to investigate the product selectivity for a longer period at high butene conversion. Important changes in the distribution of the trimethylpentanes (TMP) could be observed with time of reaction and were separated into four regions based on catalyst activity. These were the regions of initial activity, high activity, rapid deactivation and complete deactivation. In the high activity period, the fraction of the more spacious and thermodynamically favoured 2,2,4-and 2,2,3-TMP actually increased unlike experiments with fast decay, mainly attributed to kinetic effects such as diffusional limitation in the zeolite pores. The La-EMT-51 was regenerated by burning off coke in air and reused in alkylation under similar conditions as the fresh sample. The catalyst proved to be regenerable with only a slight loss in alkylation activity. Thorough investigations showed that the alkylate selectivity, in particular towards the 2,2,4-TMP among the isooctanes, was improved. |
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