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This post was last edited by LQ198619 on 2017-5-29 19:01. Chapter 4: The Impact of Feedstock on Catalytic Reforming. The factors that influence catalytic reforming due to the feedstock include its distillation range, hydrocarbon composition, and impurity content. 1 Selection of the fraction range: When the goal is to produce C6–C8 aromatics, fractions in the range of 60–145°C are used as raw materials. This is determined based on the boiling points of C6–C8 hydrocarbons. The fractions with a boiling point below 60°C contain C5 hydrocarbons, which cannot be converted into aromatics, whereas those with a boiling point above 145°C are C9 hydrocarbons. Blended Octane Number BON: If the goal is to produce high-octane gasoline, fractions with a temperature range of 80–180°C are used as raw materials. Hexane or cyclohexane alkanes with a boiling point below 80°C produce large amounts of benzene, while automotive gasoline has limits on its benzene content ； Therefore, this lighter fraction does not go into reforming. As for the reason why the final boiling point of the reformation feedstock is set at 180°C, on the one hand, it is because heavier fractions with a boiling point >180°C tend to form carbon deposits on the reformation catalyst, thereby shortening the production cycle ； On the other hand, it is to ensure that the final boiling point of the reformed product meets the specifications for gasoline (the final boiling point of the reformed product is generally about 15°C higher than that of the feedstock). 2. The influence of hydrocarbon composition: The octane number of catalytic reforming products and the content of aromatics in them are directly related to the hydrocarbon composition of the feedstock. The more naphthenes are present in the feedstock, especially hexacyclic naphthenes, the higher the aromatic content in the reforming products and the higher their octane number. It can be seen that the light fractions of naphthenic and intermediate-base crude oils are ideal feedstocks for reforming. Catalytic reforming of the light fractions of paraffin-based crude oil requires more stringent conditions to enhance the alkanes dehydrogenation and cyclization reactions; as a result, the aromatic yield is low, and so is the liquid yield. Aromatic potential content: refers to the sum of the inherent C6–C8 aromatic content in the feedstock and the C6–C8 aromatic content that can be generated from the complete conversion of the corresponding naphthenes. The method for calculating the potential aromatic content (m%) is as follows: In the formula, 78, 84, 92, 98, 106, and 112 represent the molecular weights of benzene, C6 naphthenes, toluene, C7 naphthenes, C8 aromatics, and C8 naphthenes respectively. The aromatic yield index (N+2A), where N denotes the content of naphthenes and A denotes the content of aromatics, is used to characterize the chemical composition of the reforming feedstock; generally, the higher the value of (N+2A), the higher the yield of aromatics obtained from reforming. Reformation conversion rate (aromatics conversion rate): refers to the percentage of aromatic hydrocarbons produced relative to the potential amount of aromatic hydrocarbons present. This way of expressing the reformation conversion rate eliminates the influence of differences in the chemical composition of the feedstock, thereby allowing for an accurate indication of the catalyst’s activity level and the degree of reaction during reformation. As can be seen from the definition of the above aromatic content, aromatics generated by the dehydrogenation and cyclization of alkanes are not included in it. In fact, when platinum-rhodium or platinum-tin catalysts are used, the dehydrocyclization of alkanes also accounts for a significant proportion; as a result, the conversion rate of aromatics can exceed 100%, and sometimes even reach 150%. 3. The impact of impurity content: Platinum-based catalysts used in catalytic reforming are expensive and delicate, and they are highly sensitive to impurities in the feedstock. Therefore, all impurities in the raw materials that can permanently or temporarily poison the catalyst must be strictly controlled. Since platinum-rhodium and platinum-tin catalysts are more sensitive to impurities, the requirements for raw materials are stricter. To meet such stringent requirements, the feedstock for catalytic reforming generally needs to be pre-treated. For ordinary raw materials, pre-hydrogenation can be used to convert sulfur and nitrogen into H2S and NH3, and to decompose metal-organic compounds; the metals then deposit on the surface of the hydrogenation catalyst, thereby reducing the impurity content in the raw materials to acceptable levels. However, for the light fractions of Daqing and Xinjiang crude oils with extremely high arsenic content, conventional pre-hydrogenation is not sufficient to meet the requirements; therefore, additional pre-arsenic removal equipment is needed. There are three methods for pre-arsenic removal, with hydrogenation being the most commonly used method at present; in addition, there are oxidation and adsorption methods. For water, a dedicated dehydration tower is required to distill out the small amount of water present in the raw material in the form of an azeotrope.