Recovery isobutane alkylation

Slightly over half of the papers deal with the alkylation of isobutane widi light olefins to produce high quality gasoline blending hydrocarbons. New information is presented for isobutane alkylation relative to die chemistry and mechanism, process improvements, recovery of acid catalyst, and status of commercial units. Papers are also presented for die alkylation of aromatics, heterocyclics, coal, and other hydrocarbons. Alkylations using transition metal catalysts, strong acids, free radicals, and bases are also reported. 

The second group of papers (chapters 13-20) discusses the more practical aspects of isobutane alkylation including mixing, reaction variables, computer modeling, recovery of catalyst, and an alternate fuel to alkylate. 

SARP [Sulphuric acid recovery process] A method for recovering sulfuric acid which has been used for alkylation, for re-use. The acid is reacted with propylene, yielding dipropyl sulfate, which is extracted from the acid tar with isobutane. It is not necessary to hydrolyze the sulfate to sulfuric acid because the sulfate itself is an active alkylation catalyst. 

In refineries or areas in which two or more alkylation units are operated, one SARP unit large enough to process the used alkylation acid from all of the alkylation units could be installed. The recovered acid in the form of isobutane-DIPS extract could be sent to the various alkylation units as needed or desired. Such a larger SARP unit would not only have a lower cost per unit of capacity, but would also have additional advantages if further processing of the SARP reject acid were carried out prior to conventional recovery. 

A process termed SARP has been developed for the recovery of the used or discarded catalyst from the alkylation of isobutane with olefins using strong sulfuric acid as the catalyst. The process was used commercially for several years by two companies, but currently is not in commercial operation. 

The feed ratios of isobutane to olefins with sulfuric acid tend to be lower, such as 6 1 to 8 1. When HF is used, the ratios are often 10 1 to 15 1 higher ratios then promote both mechanisms 1 and 4. Higher ratios, however, increase operating costs substantially with regard to the recovery and recycling of the unreacted isobutane. Isopentane, which is also readily alkylated, is sometimes deliberately added to supplement isobutane. Much lower-quality alkylates are produced, especially when propylene is a feed olefin, in which case, dimethylhexanes are produced in large amounts. 

Multiple supercritical isobutane regenerations of a partially deactivated USY solid acid catalyst also was tested utilizing a refinery alkylation feed blend Error Reference source not found,). The catalyst activity recovery was compared with the results of experiments that utilized a synthetic feed blend. 

Supercritical isobutane can provide complete activity recovery from partially deactivated USY catalysts. It can also be applied multiple times to maintain high levels of catalyst activity when the alkylation reaction is performed utilizing commercially available refinery blends. Pressure, temperature, and regeneration time played important roles in the SC isobutane regeneration process because of their effect on solute solubility, diffiisivity, surface desorption, hydride transfer rates, and coke aging. As a consequence, regeneration effectiveness may be maximized by manipulating those variables. 

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