Coking and Activity of Solid Acid Alkylation Catalysts in Supercritical Reaction MediaEPA Grant Number: R824729
Title: Coking and Activity of Solid Acid Alkylation Catalysts in Supercritical Reaction Media
Investigators: Subramaniam, Bala
Institution: University of Kansas
Current Institution: University of Kansas
EPA Project Officer: Klieforth, Barbara I
Project Period: October 1, 1995 through September 30, 1998 (Extended to September 30, 1999)
Project Amount: $220,000
RFA: Technology for a Sustainable Environment (1995) Recipients Lists
Research Category: Nanotechnology , Sustainability , Pollution Prevention/Sustainable Development
Description:This project addresses the following objectives: (a) whether supercritical reaction conditions can mitigate coke buildup and maintain the activity of solid-acid catalysts for producing alkylates; (b) whether the alkylates thus produced possess the desired product quality; and (c) if the supercritical process is reliable in maintaining catalyst activity even in the presence of trace impurities such as oxygenates and nitrogen compounds present in alkylate feeds. These objectives are addressed via systematic experimental investigations of 1-butene alkylation with isobutane over catalysts such as zeolites and sulfated metal oxides. The alkylation will be investigated in a temperature range of (145-170)o C and at pressures ranging from 45-60 bars that yield supercritical reaction mixtures. The liquid-like densities and gas-like transport properties of supercritical reaction media are exploited for the in situ extraction of coke precursors from the catalyst. This mitigates coke buildup, keeps the catalyst pores accessible to reactants, and thus enhances catalyst activity and longevity.
Industrial alkylation reactions have traditionally used either hydrofluoric acid or sulfuric acid as catalyst. Both these processes share inherent environmental and safety concerns associated with acid spillage and waste disposal. For nearly three decades, major oil companies have been active in developing solid acid catalysts as an alternative to the hazardous liquid acids. Although some zeolites (a class of solid acids) catalyze the alkylation reaction, they deactivate rapidly on stream. The deactivation is due to the formation of 'coke' deposits (low-volatile hydrocarbonaceous substance) that plug up the micropores and block the active sites. The problem of catalyst coking is also prevalent in other industrial processes such as olefin isomerization on acid catalysts. In the latter case, we have recently shown that what is needed to keep the catalyst pores clean and accessible is neither a liquid nor a gas (as employed in conventional practice) but a supercritical fluid that possesses an optimum combination of liquid-like densities and gas-like transport properties. This project is an application of the supercritical decoking concept to extend the life of solid alkylation catalysts. Successful completion of this project will eliminate a major technological barrier impeding the application of solid acid catalysts in alkylation practice.
A solid-acid-catalyzed alkylation technology with enhanced catalyst activity and longevity while retaining product quality and process reliability will clearly be an environmentally-superior alternative to conventional technology that employs liquid acids. Alkylates are valuable blending agents in the manufacture of gasolines. Because they contain only paraffins and virtually none of the components subject to EPA regulation, alkylates will play an increasingly important role in meeting the reduced emissions gasoline requirements established by the 1990 Clean Air Act. Development of an environmentally-friendlier alkylation technology is thus especially timely to industry.