In-depth article | Advances in acid gas treatment technologies for refineries!

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Abstract: This paper reviews the research and development progress of bio-based butadiene by major companies at home and abroad, as well as its industrialization status, and points out the future development trends of bio-based butadiene. Based on a preliminary investigation into the technologies for treating acidic gases in China’s oil refineries, this paper describes the current status of acidic gas treatment, and puts forward some suggestions regarding emission standards and existing problems. (Author: Li Tao, Nanjing Research Institute, Sinopec Yangzi Petrochemical Co., Ltd.) Keywords: Bio-based ； butadiene ； In terms of research and development, as refineries increase their capacity for processing crude oil and handle a greater proportion of imported sulfur-containing crude oil, along with increasingly stringent environmental regulations, the facilities designed to handle acidic gases in refineries have become more sophisticated, and their scale has also grown larger. The Claus sulfur recovery process is commonly used to produce sulfur from the acidic gases generated in the dry gas and liquid hydrocarbon desulfurization units of petroleum refining secondary processing facilities, as well as from the acidic gases produced by the stripping units for sulfur-containing wastewater in hydrogenation refining (desulfurization) processes. In recent years, significant progress has been made at home and abroad in acid gas treatment technologies. The following is a summary from aspects such as sulfur recovery catalysts, exhaust gas treatment, and acid gas separation. 1. Advances in Acid Gas Treatment Technologies for Refineries 1.1 Catalysts The catalysts used for Claus sulfur recovery were initially natural bauxite, but they were later replaced by synthetic activated alumina with higher activity. However, pure activated alumina catalysts have limited activity; to improve their efficiency, it is necessary to make various improvements to these catalysts. A representative example is the CR series of activated alumina catalysts developed by the French company Rhone–Progil, which features high catalytic activity, low pressure drop across the bed, pressure resistance, low wear, and a high sulfur recovery rate. Similar catalysts include Alcoa’s S-series catalysts, which feature high activity and good resistance to sulfation. They can be used in various reactors for different processes, as well as in sulfur recovery reactors that operate at temperatures below the dew point. Acidic gases containing sulfides contain a certain amount of organic sulfides that are difficult to remove, which severely affects the overall sulfur recovery rate of sulfur recovery units and the compliance of exhaust gas emissions with standards. The CSR-2 alumina catalyst from Nippon Catalyst Kasei Co., Ltd. exhibits high activity in the hydrolysis of organic sulfur. Furthermore, titanium-based catalysts have been developed in recent years; representative examples include TiO2-based catalysts, TiO2-Al2O3-based catalysts, and TiO2-Al2O3-additive-based catalysts. Two new types of catalysts developed by Zhejiang Deqing Sanlong Catalyst Co., Ltd. – the titanium-based Claus sulfur recovery catalysts created by Sanlong Catalyst Company – are characterized by their high reaction activity, achieving almost thermodynamic equilibrium conversion rates ； Secondly, it has a strong ability to hydrolyze organic sulfur, with a hydrolysis rate that is almost twice that of aluminum oxide catalysts. This catalyst also exhibits strong resistance to poisoning; once it becomes \"poisoned\" due to abnormal operating conditions, it can quickly return to its original level of activity once the normal operating conditions are restored. In addition, the company has developed exhaust gas hydrogenation catalysts with high activity at low temperatures; their performance is significantly superior to that of imported similar products, with an organic sulfur hydrolysis activity of over 98%, making them catalysts with excellent hydrogenation properties. Both the CRS-31 catalyst developed by Rhône-Poulenc in France and the TiO2-type catalyst LS-901 from the R&D institute of Sinopec Qilu Branch are excellent catalysts for the hydrolysis of organic sulfur. Representative hydrogenation catalysts include KF-756 from AKZO and LS-951 from the R&D institute of Sinopec Qilu Branch. CPII, a subsidiary of NTV Technologies Inc. in the United States, has recently received a patent grant from the U.S. Patent and Trademark Office for a method for desulfurization that simplifies the oil and gas processing process by removing bottlenecks in midstream and downstream sulfur recovery units (SRUs). It can also be used as an independent economic method to recover sulfur in smaller mini-refineries. This new chemical solution is currently being developed for internal use and for end-users. This patent uses a highly active nano-iron catalyst to absorb hydrogen sulfide. This patent relates to the preparation of stable iron(II) oxides and/or hydroxides. These oxides and/or hydroxides exist as nanoparticles in the range of 5-10 nanometers. Compared to existing processes, by using a specialized iron source, these nanoparticles can be prepared from various ferrites such as sulfates and chlorides at lower costs and with fewer impurities. These novel nanoparticles are particularly suitable for removing sulfur compounds, such as hydrogen sulfide, from liquid and/or gas streams that include, but are not limited to, hydrocarbon streams. 1.2 In terms of exhaust gas treatment, International Shell Research Ltd. has disclosed a method for recovering sulfur from acidic gas streams (publication number CN100532250). This method involves a Claus sulfur recovery step combined with direct reduction steps and biological sulfur recovery steps, in order to produce a desulfurized gas stream containing very low concentrations of hydrogen sulfide and sulfur dioxide. The method involves reacting an acidic gas stream with oxygen under oxidizing conditions to obtain combustion gases containing hydrogen sulfide and sulfur dioxide. The combustion gases are reacted under Claus reaction conditions to obtain a reaction gas containing sulfur. Sulfur is recovered from the reaction gas to obtain Claus off-gas containing hydrogen sulfide and sulfur dioxide. The Claus off-gas is reacted under direct reduction conditions to obtain a sulfur-containing directly reduced gas. Sulfur is recovered from the direct reduction reaction gas to obtain exhaust gas containing a certain concentration of hydrogen sulfide. This directly reduced exhaust gas is brought into contact with a lean absorbent, thereby removing part of the hydrogen sulfide contained in the exhaust gas to yield a desulfurized gas and a rich solvent containing dissolved hydrogen sulfide. The hydrogen sulfide dissolved in the rich solvent is biooxidized to elemental sulfur by bringing the rich solvent into contact with sulfur bacteria under appropriate biooxidation conditions. Pan Wei and others from Wuhan Guolitong Energy and Environmental Protection Co., Ltd. have disclosed a system, method, and desulfurization agent for reducing the sulfur dioxide emission concentration in sulfur recovery units (application number: CN201510147363.2). The desulfurization agent consists of amino-polycarboxylic acid-chelated iron, amino-polycarboxylic acid chelators, acrylamide, PEG-9, and water. The system includes a complex iron desulfurization unit, a sulfur recovery unit, and a gas stripping unit for liquid sulfur tanks. It purifies the gas from the liquid sulfur tanks as well as the exhaust gases from the sulfur recovery unit, thereby eliminating at the source all factors that cause sulfur dioxide emissions from the sulfur recovery unit ； Ensure that the sulfur dioxide concentration in the flue gas after combustion is below 50 mg/Nm3 ； Without altering the thermal reaction and conversion sections of the existing sulfur recovery units, it requires low investment and operating costs. The degassing of the liquid sulfur tank utilizes air, which serves as the regeneration air for the ferrous sulfate-based desulfurization system, thereby reducing the operating costs associated with the degassing and purification of liquid sulfur ； It provides a comprehensive and thorough solution to reduce the sulfur dioxide emission concentration in sulfur recovery units. Wang Zhenyu and others from Shandong Sanwei Petrochemical Engineering Co., Ltd. have disclosed an SWSR-6 sulfur recovery process and apparatus (application number: CN201510633242.9), which specifically relates to an SWSR-6 sulfur recovery process ； Acidic gas containing hydrogen sulfide is subjected to the Claus reaction to produce sulfur and sulfur production off-gases; the sulfur is recovered while the sulfur production off-gases are burned, with all sulfur-containing substances being converted into SO2, thus forming SO2-containing flue gas. This SO2-containing flue gas comes into contact with an absorbent in a flue gas purification tower, where the SO2 in the flue gas is absorbed by the absorbent. The salt solution formed in the flue gas purification tower reacts with an alkaline solution, and after crystallization and centrifugation, sodium sulfite is obtained. The flue gas that has had its SO2 removed is then released. The desulfurization process of this invention produces an anhydrous sodium sulfite product that meets the standards of GB-1894; the sulfur recovery rate of the system is close to 100%, and the desulfurization efficiency is also close to 100%, ensuring that the SO2 concentration in the gases emitted by the sulfur recovery unit remains low