A Study On Hydrogen Transfer Reaction Over Catalytic Materials Used In FCC Process

The production of clean fuel has been an urgent target in worldwide refining industry as regulations for environmental protection become more and more stringent. Fluid Catalytic Cracking (FCC) is a refining process which primarily produce gasoline and diesel and other products such as LPG or C7, C4~ etc. In China, about 80% of gasoline pooi is contributed by FCC unit. Hence, the improvement of FCC gasoline has an important realistic significance to the production of clean fuel in China.Different types of reaction in FCC process must be properly adjusted in order to meet the needs of the limiting content of harmful components in gasoline pooi. According to the main index of clean gasoline, the occurrence or existence of the unwanted components in gasoline, such as olefm, aromatic, sulfur etc., are related to the hydrogen transfer reaction in FCC process. Conventional methods of improving the activity of hydrogen transfer reaction not only decrease gasoline octane number dramatically, but also increase the content of non-selective products, such as coke and dry gas. Therefore, it is becoming a new hot topic to improve hydrogen transfer reaction in FCC process, while coke and dry gas selectivities should be controlled to maintain or increase gasoline octane number.In this article, hydrogen transfer reaction in FCC process over various catalytic materials such as zeolites, matrices and catalysts have been systematically studied. Catalytic experiments at atmospheric pressure were carried out in a continuous fixed bed reactor. Based on the careful analysis of types of hydrogen transfer reaction in FCC process, a new concept of "selective hydrogen transfer reaction" has been defined, and it is differentiated from non-selective hydrogen transfer reaction'' and characterized by conventional method. Based on these results, this article investigated the factors that affect hydrogen transfer reaction in FCC process and the effect of modificationmethod on hydrogen transfer reaction over zeolites. Hydrogen transfer reaction over FCC catalyst matrix and its influence on FCC catalyst performance have been investigated for the first time. The activity of hydrogen transfer reaction and the crackability of large hydrocarbon moleculars on FCC catalysts were improved by using zeolites containing basic metal cation as additives. The role of basic metal cation exchanged zeolite in the FCC catalyst has also been investigated. The results can be summarized as follows:1. Hydrogen transfer reaction in FCC process includes two types of reactions, which are selective hydrogen transfer reaction and non-selective hydrogen transfer reaction. Selective hydrogen transfer reaction can be characterized by HTC (or HTA) and IBA selectivity. Non-selective hydrogen transfer reaction can be characterized by coke selectivity and H2+CH4 selectivity. Experimental results showed that selective hydrogen transfer reaction obeys mechanism of single site adsorption in double moleculars reaction - Rideal-Eley mechanism, while non-selective hydrogen transfer reaction obeys mechanism of double sites adsorption in double moleculars reaction - Langmuir-Hinshelwood mechanism. In order to meet the needs of clean fuel production, it is necessary to enhance selective hydrogen transfer reaction and to inhibit non-selective hydrogen transfer reaction.2. Reaction conditions such as reaction temperature, catalyst-to-oil ratio, reaction time can directly influence hydrogen transfer reaction over zeolites. Hydrogen transfer reaction performances over zeolite are determined by the structure types and silica-to-alumina ratio of zeolite framework . Hydrogen transfer reaction activity over large pore FAU zeolite is very high, but the yield of non-selective products, e.g. coke is very high too. BEA zeolite and new-developed medium-pore molecular sieves MCM-22 has high activity of hydrogen transfer reaction and good performance of catalytic crackingsimultaneously. High silica-to-alumina ratio of zeolite results in a decrease activity of hydro...