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More than a hundred types of sulfides have been identified in crude oil, which can be mainly divided into three categories: the first category consists of acidic sulfur-containing compounds, primarily hydrogen sulfide and thiolates； The second category consists of neutral sulfur compounds, mainly thioethers and disulfides ； The third category consists of sulfides with good thermal stability, mainly thiophene and its derivatives, as well as thiophenol, etc. Sulfides usually have a foul odor, are highly toxic, and highly corrosive, having an adverse effect on the transportation and processing of crude oil as well as the quality of refined oil. Sulfides dissolved in crude oil can cause severe corrosion of pipelines and equipment, posing a threat to human safety. During the crude oil refining process, sulfides lead to equipment corrosion, catalyst deactivation, and unsatisfactory sulfur content in the refined products, among other problems. The development of desulfurization agents and various desulfurization technologies have become important means to address the aforementioned problems. Currently, desulfurization methods can be classified according to the characteristics of their removal processes into absorption methods, adsorption methods, oxidation methods, biological methods, pulse corona methods, etc ； Based on the process, it can be divided into desulfurization by regenerated solvent absorption, fixed-bed adsorption desulfurization, membrane separation desulfurization, biological desulfurization, and physical-field desulfurization, etc ； Based on the state of the material, it can be divided into two main categories: wet and dry methods. This paper mainly introduces the current research status of chemical desulfurizers used in wet flue gas desulfurization. 1 Current Research Status of Desulfurizing Agents in Crude Oil Chemistry 1.1 Amine Desulfurizing Agents Ethanolamines and their derivatives possess strong H2S absorption capabilities, which has drawn considerable attention; many research institutions and companies have conducted extensive studies in this area. The desulfurization agent developed by Yangzi Petrochemical Co., Ltd. consists of 10%–20% hydroxylamine, 30%–50% homoxime, and 30%–60% organic acid. The desulfurization is carried out at a temperature of 100–150°C for a reaction time of 0.5–1.5 hours, with the mass concentration of the desulfurization agent ranging from 10–1000 mg/L. 2%–10% distilled water is added to the crude oil, the electric field in the electrodesalination tank is maintained at 300–900 kV/cm, and the high temperature is retained for 1–3 hours to allow the desulfurization agent to react with the sulfur-containing compounds in the crude oil. After the reaction, the mixture is left to stand for about 1 hour to enable separation of water from oil. This method reduces the sulfur content of crude oil by 15% to 20%. Xi’an University of Architecture and Technology has developed two types of desulfurizers, one oil-soluble and the other water-soluble. The components of the oil-soluble desulfurizer are: 50%–70% (by volume, same below) pure benzene, 10%–30% ethanol, and 10%–30% diethanolamine. First, react ethanol with pure benzene, then add diethanolamine drop by drop, heat until it dissolves, and let it stand to obtain the desulfurizer. This oil-soluble desulfurizer can dissolve effectively in crude oil and can be used to reduce hydrogen sulfide gas in crude oil. The components of the water-soluble desulfurizer are: 16%–27% (by mass, same below) methyl diethanolamine (MDEA), 2.8%–4.2% diethanolamine (DEA), 3.3%–4.8% sulfolane, 60%–68% sodium nitrite, with water as the solvent. This agent possesses excellent immediate desulfurization capabilities; it can also reduce the number of sulfate-reducing bacteria in crude oil, thereby decreasing the hydrogen sulfide gas produced by their metabolism, and thus improving the durability of the desulfurizing agent. Calculations show that this desulfurizer has a sulfur capacity of 80 mg/L; with an addition amount of 40 mL, it can reduce the sulfur content from 0.12% to 0.001% within 30 minutes. Southwest Petroleum University has developed a water-soluble desulfurizing agent with the following composition: 10%～25% hydroxyethylhexahydrimethazine, 5%～20% alcohol amine, 5%～20% small-molecule alcohols, and the remainder being water. This agent can effectively reduce hydrogen sulfide in crude oil or natural gas; meanwhile, the desulfurization agent and the products formed by the reaction with hydrogen sulfide dissolve in water, so as not to clog the wellbore and disrupt the normal operation of oil and gas wells. Magsumovic et al. formulated a desulfurizing agent using methanol ethanamine, dimethanol diethanamine, and methanol diethanamine as raw materials; this agent is capable of removing hydrogen sulfide from crude oil, with an operating temperature range of 20–80°C. Khan et al. heated crude oil to 149°C, introduced an inert gas into it, and added polyalkyl amines such as diethylenetriamine, tetraethylenepentamine, and aminoethyl**, to remove hydrogen sulfide; the amount of polyalkyl amines used was 0.2%. Zaid et al. used a desulfurizing agent composed of 40% alkylphenol polyoxyethylene ether, 10% amine, and 50% alkali metal nitrate to remove sulfur and sulfur compounds from crude oil and fuel oils. Amine desulfurization is primarily used to remove hydrogen sulfide from crude oil, with only a few amine desulfurizers showing some effectiveness against other sulfides. Although amine-based desulfurization has received so much attention, there is still one issue that needs to be addressed: the salts formed from hydrogen sulfide absorbed by this method release hydrogen sulfide when heated, requiring further treatment and thus increasing the technical complexity and economic costs. 1.2 Hydroxide desulfurizers: NaOH, KOH, and ammonia are also commonly used agents for removing hydrogen sulfide from crude oil. Lyushin et al. added chelants and demulsifiers to remove iron and H2S from crude oil. The chelant consisted of 28%–32% aminotrimethylenephosphonic acid, 7%–9% vinyl alcohol, 15%–18% urea, 10%–13% ammonia water, and 0.5%–1% corrosion inhibitor, with ammonia water being the main component used for removing hydrogen sulfide. Hassan et al. used ammonium hydroxide and sulfuric acid in a mass ratio of 1:1 as desulfurizing agents, and employed a new type of desulfurization device to desulfurize crude oil. NaOH and KOH can effectively remove hydrogen sulfide from crude oil, but they form alkaline stable emulsions, increasing the difficulty of downstream dehydration processes. The ammonium salts formed by the reaction of ammonia water with hydrogen sulfide are easier to remove in downstream processes than sodium salts. However, ammonia water tends to cause flashing at higher temperatures, is somewhat corrosive to equipment, and can also lead to environmental pollution. For these reasons, hydroxide desulfurizers are now rarely used. 1.3 Aldehyde-containing desulfurizing agents: Qingdao Haiyitian Instrument Co., Ltd. has developed a reagent for removing hydrogen sulfide, whose components are 40%~50% formaldehyde, 5%~10% acetaldehyde, 4%~8% propanal, with the remainder being pure water. Allen et al. found that adding formaldehyde to crude oil transmission pipelines can effectively remove hydrogen sulfide from the crude oil within ten days, but over time, the reaction between formaldehyde and hydrogen sulfide reverses, resulting in the reformation of hydrogen sulfide. Karas et al. used glyoxal and cocoalkyl dimethylbenzyl ammonium chloride as hydrogen sulfide removal agents, achieving a desulfurization rate of over 70%. Formaldehyde has a strong absorption capacity for hydrogen sulfide, but this effect can be reversed easily, leading to the reformation of hydrogen sulfide and increasing the difficulty of subsequent treatment ； Furthermore, formaldehyde is highly harmful to humans; it can affect the olfactory organs, immune function, and the central nervous system, and it can cause damage to the genetic material within cells. It is considered a suspected carcinogen. Therefore, the use of formaldehyde as a desulfurization agent has been discontinued. 1.4 Strongly oxidizing desulfurizers: H2O2 and KMnO4 are commonly used strongly oxidizing desulfurizers, and they pose certain risks. H2O2 is easily decomposed by metals to produce oxygen, water, and a large amount of heat, causing combustion or explosion ； KMnO4 solution cannot be used in acidic conditions, and the resulting MnO2 may also cause combustion. Therefore, special attention must be paid to the operating conditions during use, which limits its scope of application. Shen Ying used the method of electrolyzing sodium chloride solution, and determined the optimal operating conditions through orthogonal experiments; the static desulfurization efficiency reached 96.5%, while the dynamic desulfurization efficiency reached 72.4%. This method primarily uses the highly oxidizing sodium hypochlorite generated to remove hydrogen sulfide from crude oil, but it has not yet been widely adopted. Strongly oxidizing desulfurizers can not only remove hydrogen sulfide from crude oil, but also be combined with ionic liquids to eliminate organic sulfur in oils, thereby enhancing their effectiveness in removing organic sulfur; however, their dosage must be strictly controlled. 1.5 Other types of desulfurizers: Tianjin Disaifu Technology Co., Ltd. has developed an environmentally friendly desulfurizer that can effectively remove hydrogen sulfide, elemental sulfur, thiols, and carbonyl sulfide (COS) from petroleum products, without producing any sulfur-containing waste residues. The components of this agent are 30%~70% hydroxyurea, 0~15% cyclobutane sulfone, 0~10% pyridine compounds, and 20%~70% deionized water. This agent is suitable for the desulfurization of various crude oils, refined oils, and semi-finished oils. Its removal efficiency of hydrogen sulfide in gasoline reaches 100%, and its removal efficiency of thiols is above 85%; no effects on crude oil and other petroleum products are mentioned. Wu Jianming, Chao Hongzhou, and others introduced an efficient desulfurizer for crude oil hydrogen sulfide, whose composition consists of 3% or 6% macromolecular desulfurization components, 25% micromolecular desulfurization components, 1% penetrant, and 5% cosolvent. Mine tests showed that when the hydrogen sulfide concentration was between 480 and 650 mg/L, adding a desulfurization agent at a concentration of 50 mg/L resulted in an average desulfurization rate of 78%. The desulfurizer GX-201D produced by Lanzhou Yoshino Environmental Additives Factory is a multi-functional, water-soluble desulfurizer that appears as a light yellow-brown liquid. This agent was applied on-site at CNPC Qingyang Petrochemical Company, with good results. GX-201D cannot be regenerated; when crude oil is added, it undergoes physical and chemical reactions with the organic sulfur in the crude oil, extracting the organic sulfur into the aqueous phase. The desulfurizer containing organic sulfur is then discharged along with the desalinated wastewater. The addition amount is 30–70 μg/g, with an average removal rate of 40%–50%. Xi’an Jiahong Petrochemical Company’s crude oil desulfurizer JH6011 is a oil-soluble/water-dispersible composite organic compound, appearing as a pale yellow transparent liquid. After adding crude oil, the sulfides and some organic sulfur compounds in it are converted into water-soluble compounds, which are ultimately removed through the desalination and dewatering processes of the crude oil. This process is irreversible, with no environmental hazards occurring. When 1 mg/L of the desulfurizing agent JH6011 is added to crude oil products, it can remove 1 to 3 times the amount of sulfur present in them. The desulfurization takes place at a temperature of 40–80°C over a reaction time of 3–5 hours; the desulfurization efficiency for H2S is over 80%, while that for organic sulfur is over 20%. 2 Conclusion (1) Common wet chemical desulfurization agents include amine desulfurizers, hydroxide desulfurizers, aldehyde-containing desulfurizers, strong oxide desulfurizers, and other new types of desulfurizers. Among them, amine desulfurizers are the most widely used and extensively studied; however, the salts formed from hydrogen sulfide absorbed using this method release hydrogen sulfide again when heated, requiring further treatment, which increases the technical complexity and economic costs ； Hydroxide desulfurizers tend to form stable emulsions, making post-treatment difficult or causing ammonia flash issues ； Aldehyde-containing desulfurizers are prone to reversal ； The strong oxide desulfurization method can easily cause combustion and explosions ； The effectiveness of the new desulfurizing agent still needs further verification. (2) Looking at the existing chemical desulfurizers on the market, most of them act on acidic sulfides such as hydrogen sulfide and thiols in crude oil. There are few desulfurizers that can remove both acidic sulfides such as hydrogen sulfide and thiol, as well as neutral sulfides such as thioethers and disulfides, as well as stable sulfides such as thiophene and benzothiophene; moreover, most of these desulfurizers do not achieve high efficiency. New, efficient desulfurizers that can effectively remove various sulfides hold broad prospects for development. The two desulfurizers, GX-201D and JH6011, exhibit a certain degree of removal efficiency for both inorganic and organic sulfur, representing the future development trend of desulfurizers.