Technology for hydrogenating crude benzene to produce refined benzene

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Crude benzene is a complex mixture composed of various aromatic hydrocarbons and other compounds, and cannot be used directly. Benzene, toluene, and xylene account for over 90% of the content in crude benzene, and they are the main products obtained through the refining of crude benzene. The main methods for refining crude benzene are acid washing refinement and hydrogenation refinement. The acid washing method was initially used to produce benzene from crude benzene recovered from coke oven gas. This method features a simple process flow, flexible operation, low equipment investment, readily available materials, and operation at normal temperature and pressure. However, it can only remove sulfur-containing compounds (mainly thiophene) to a partial extent; significant losses of aromatics occur during the processing (about 8%–10%). There are no effective ways to deal with the by-product wastes, namely acid tar and slag, which cause environmental pollution. Moreover, the quality of the aromatics produced by this method is poor, and such products can no longer meet market demands. Currently, the more advanced methods for refining crude benzene at home and abroad are mainly hydrogenation refining. The hydrogenation refining of crude benzene can be divided into two methods based on reaction temperature: the high-temperature method (600–630°C) and the low-temperature method (320–380°C). The reaction temperature (600–630°C) and reaction pressure (6.0 MPa) in the high-temperature method are both high, which also results in higher requirements for the materials used in equipment, pipelines, instruments, etc ； At the same time, this method converts the more expensive toluene and xylene into benzene, which is also not economically reasonable. Our company has developed a low-temperature hydrogenation refining technology for crude benzene. This technology is mature and reliable, features a simple process flow, requires low investment, produces high-quality products that meet petroleum standards, has low energy consumption, and results in low production costs. This technology consists of three units: a pressure swing adsorption unit for producing pure hydrogen (with a purity of ≥99.99%), a catalytic hydrogenation unit (for pre-hydrogenation and main hydrogenation), and a product purification unit (using extractive distillation). The low-temperature method can produce high-quality benzene, toluene, and xylene products. This method features mild reaction conditions: the reaction temperature ranges from 320 to 380°C, and the reaction pressure is between 3.0 and 3.5 MPa. The materials for the equipment and pipelines are easy to find; CrMo steel can be used, and high yields of benzene, toluene, and xylene are achieved. Therefore, the low-temperature hydrogenation refining technology for crude benzene features high yield, low investment costs, mild operating conditions, and high product quality, making it a relatively ideal method for the hydrogenation refining of crude benzene at present. I. Technical characteristics of crude benzene hydrogenation refining: Crude benzene contains many impurities; pre-distillation is used to separate out the heavy benzene residues, thereby reducing system clogging and effectively extending the lifespan of the catalyst as well as the operating cycle of this facility. By adopting the low-temperature crude benzene hydrogenation process, the plant exhibits high operational safety. The low-temperature crude benzene hydrogenation process is employed for thorough desulfurization, denitration, deoxygenation, and hydrogenation, resulting in high product purity and a high recovery rate. Formylmorpholine was selected as the non-aromatic extractant for extractive distillation, thereby altering the vapor pressures of the components present in the hydrogenated oil and enabling the effective separation of non-aromatic impurities, thus achieving an optimal combination of high selectivity for the extractant and high efficiency of the solvent. The formylmorpholine extractant exhibits high thermal stability and good thermal conductivity, provides excellent separation results, does not cause corrosion to equipment, and has relatively low costs for solvent consumption and regeneration. Properly handle the ‘three wastes’ to ensure that emissions meet regulatory standards. II. Process Principle and Flowchart: The principle of the crude benzene hydrogenation refining process is to subject coking crude benzene to low-temperature hydrogenation treatment in order to remove various impurities present in it, primarily thiophenes, through desulfurization, denitration, deoxygenation, and hydrogenation. Subsequently, extraction and distillation processes are used to further remove these impurities, resulting in a high-purity product. The process flow diagram is as follows: III. Product specifications ⑴ Pure benzene: The pure benzene product meets the standards of GB3405—89 (petrochemical grade). ⑵ Toluene: The toluene product meets the standards of GB3406—90 (petrochemical grade). ⑶ Xylenes: The xylenes product meets the standards of GB3407—90 (petrochemical grade). IV. Main raw materials and utility consumption (calculations based on processing 1 ton of crude benzene as raw material): Sequence Number, Name and specification of raw material, Unit, Consumption quota, Remarks: 1. Crude benzene, t, 1; 2. Hydrogen, Nm3, 50; 3. Fuel coal, t, 0.15; 4. Low-pressure steam consumption, 1.0 Mpa, 0.63; 5. Circulating water, Nm3, 120; 6. Soft water, t, 0.6; 7. Fresh water, t, 2.5; 8. Electricity, 380V/220V, kwh, 50; 9. Composite catalyst, kg, 0.04; 10. Instrument air, 0.6 Mpa, Nm3, 20; 11. Nitrogen, 0.6 Mpa, Nm3, 5. V. Product recovery rate: The recovery rate of the three xylene types is ≥98%. VI. Plant investment: The investment for a 50 kt/a crude benzene hydrogenation plant is approximately 45 million yuan ； The investment for a 100kt/a crude benzene hydrogenation unit is approximately 75 million yuan. Civil engineering and general layout are not included.