Yield of benzene hydrogenation product

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Methods for Improving the Yield and Quality of Benzene and Toluene Abstract: Crude benzene was refined using hydrogenation and extractive distillation methods. In the extractive distillation stage, by controlling process parameters such as the temperatures at the top and bottom of the tower, the effect of the benzene content in the non-aromatic compounds on the yield and quality of benzene and toluene was studied, in order to determine the optimal values. Keywords: coking crude benzene, hydrorefining, extractive distillation, pure benzene, toluene. 1. Hydrorefining process technology for Weijiao crude benzene: In collaboration with Sichuan Tianyi Technology Co., Ltd., our company uses a low-temperature hydrogenation process to produce pure benzene, toluene, and xylene. The process flow is as follows: The crude benzene from coking is subjected to impurity removal in two benzene distillation columns, after which it enters the hydrogenation system. There, sulfur-containing impurities such as thiophenol are removed through hydrogenation under low temperature and pressure conditions. The hydrogen used for hydrogenation is supplied by a pressure swing adsorption hydrogen production unit using coke oven gas. The hydrogenated oil coming out of the hydrogenation system enters the light-end removal system, where low-boiling-point substances are removed before it proceeds to the distillation process. In the distillation process, a pre-distillation tower is first used to separate the light oil into two fractions: a BT fraction mainly composed of benzene and toluene, and a heavier fraction containing xylene. The BT component enters the extractive distillation system to remove non-aromatics, and is then separated into pure benzene product and toluene in a distillation column. The Reorganization fraction is separated by batch distillation to yield xylene product. The process flow diagram for crude benzene refining is shown in Figure 1 below. Figure 1: Process flow diagram for crude benzene refining. 2. Methods for improving the quality and yield of benzene and toluene in extraction distillation. The contents of benzene, toluene, and xylene in crude benzene are approximately 75%, 12%, and 2.5%, respectively. Due to the low content of xylene, and the difficulty in producing high-quality xylene products using current hydrogenation methods, it is not meaningful to study the yield of xylene products. Benzene and toluene are produced in large quantities and serve as important chemical raw materials; the quality of these products directly affects the development potential of the downstream high-end chemical products market. Therefore, it is crucial to improve the yield and quality of these two products. Below are the effects of extractive distillation on the quality and yield of benzene and toluene. Extractive distillation has a significant impact on the quality and yield of benzene and toluene. The BT liquid enters the extractive distillation column, where the non-aromatic compounds and some light components present in the BT mixture are separated from the pure aromatics. It is necessary to ensure that the product at the bottom of the column meets the required standards, while also keeping the levels of benzene and toluene in the non-aromatic compounds at the top of the column as low as possible, so as to achieve high yields for these two products. 2.1 Effect of benzene content in non-aromatics on the quality and yield of pure benzene: During the production process, by adjusting the temperature at the top of the extractive distillation column, we determined the impact of varying benzene contents in non-aromatics on the quality and yield of pure benzene; the experimental data are shown in Table 3-1 below. Table 3-1 shows a summary of the mass and yield of pure benzene obtained under different benzene contents in non-aromatic compounds. As can be seen from the table, the higher the benzene content in the non-aromatic compounds, the higher the purity of the pure benzene obtained, but the lower the yield. Overall, its impact on the quality of pure benzene is minimal; a purity level of 99.95% is sufficient to meet the requirements for first-grade petroleum-grade benzene. The key factor here is the impact on the yield of benzene. As can be seen from the table, keeping the benzene content in the non-aromatic compounds between 10% and 20% allows for the production of first-grade petroleum-grade pure benzene while also maximizing the yield of pure benzene. 2.2. Effect of benzene content in non-aromatic compounds on the quality and yield of toluene: The impact of toluene content in non-aromatic compounds on the quality and yield of toluene under different conditions is shown in Table 3-2 below. Table 3-2 shows a summary of the toluene mass and yield obtained under different toluene contents in non-aromatic hydrocarbons. As can be seen from the table, the effect of the toluene content in non-aromatic hydrocarbons on the quality and yield of toluene is roughly similar to that on pure benzene; however, its impact on the quality of toluene is more pronounced. Given that the current market requirement for the purity of toluene is over 99.5%, it is ideal to keep the content of toluene in the non-aromatic components at 1%–2% in order to achieve the highest yield while still meeting this quality standard. 3. Conclusions Based on the experimental data, the following conclusions can be drawn: By adjusting the temperature at the top of the extractive distillation column, the contents of benzene and toluene in the non-aromatic compounds can be controlled within the ranges of 10%–20% for benzene and 1%–2% for toluene. This approach enables the production of pure benzene with a purity of 99.95% and toluene with a purity of over 99.5%, while also achieving the highest yields for these two products in the extractive distillation column, at 99.5% and 99.7% respectively.