Catalysts motor fuel alkylation

Schechler, J.C. Schmidt, R.J. Motor fuel alkylation advances beyond liquid acid catalysts. Paper at Annual Meeting of National Petroleum Refiners Association, San Antonio, TX, Paper AM-97-47, Mar 16-18, 1997. 

Organic sulphur- and nitrogen-compounds in motor fuels are a source for acid rain and harmful to the environment. Moreover, they are poisonous to the auto exhaust catalysts. To meet new developments in EU regulations on the S-concentration, a commonly applied one-step hydrodesulfurization (HDS), using conventional catalysts, e.g. C0-M0/7-AI2O3, is insufficient. A second HDS step, viz. a deep HDS step, can be more economical to reduce the S-content to the currently allowed European level of 350 ppm. This level will be reduced further to 50 ppm in 2005 [1]. In the first HDS step, often the heavy organic sulfur-containing polyaromatics survived, such as dibenzothiophene (DBT) and (4-, and/or 6-) alkylated DBTs [2,3]. They are the most refractory. In crude oils, there are also aromatic N-compounds, which suppress the performance of the HDS catalysts. Hence, a model feed for representative HDS-activity measurements should contain characteristic S- and N- compounds for practical relevance. 

Svlfuric Add Alkylation. Despite some disadvantages, such as acid-reGOLYery expense and refrigeration to minimize oxidation, about four fifths of the alkylate produced for motor fuels is based on sulfuric acid as a catalyst. As with HF alkylation, isobutane is alkylated with olefins (other than ethylene), and a flow diagram for such a process is ven in Fig. 14-5. 

Certain organometallic compounds which find use as antiknock additives to motor fuels, catalysts, insecticides, and fungicides can be obtained by electrolysis of a solution of alkylating agent (ethyl bromide, diethyl sulfate, ethyl iodide, ethyl chloride, ethyl acetate, etc.) in an organic solvent (acetonitrile, dimethylformamide, methylene chloride, etc.) containing an electrolyte such as tetraethylammo-... 

Alkylation was first practiced for gasoline production about 60 yr ago. At that time, most of the alkylate was used as fuel for the airplanes used in World War II. Four quite distinct reactors were developed in which isobutane and olefins were introduced as liquids to the reactor. In the reactor, the hydrocarbon liquids are contacted with either liquid sulfuric acid or liquid hydrofluoric acid (HF), which acts as a catalyst. Dispersions of these two relatively immiscible liquids are formed. The alkylate product formed is a mixture of mainly C5-C16 isoparaffins. Alkylate products often have research octane numbers (RONs) varying from 93 to 98 (the motor octane numbers tend to be two to three units lower). 

Due to the Clean Air Act, increasing attention is paid to the production of alkylates, which is a very clean burning fuel and has a high MON (motor octane number) with a low octane sensitivity and moderate vapor pressure. Commercially operated alkylate production uses a liquid acid catalyst such as H2SO4 or HE, resulting in problems associated with cost, apparatus and the environment [47]. New synthetic methods utilizing solid acid catalysts have been developed but no commercial process has emerged due to fast catalyst deactivation [48]. 

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