Carbon disulfide (CS 2 ) is a toxic organic sulfur compound, which is not only widely found in coke oven gas, water gas, natural gas, coal gas, refinery gas, Clause exhaust gas, but also in the production workshop of the chemical fiber industry. A small amount of carbon disulfide contaminants is present. Carbon disulfide is continuously emitted in the sublayers of the atmosphere through photochemical reactions to generate sulfur dioxide, which causes acid rain. The slow hydrolysis of carbon disulfide generates hydrogen sulfide, which corrodes production equipment and causes economic losses. At the same time poison the catalysts of downstream industries, such as catalysts for methanol synthesis, alkylation and ammonia synthesis. Therefore, the removal of carbon disulfide is important for environmental protection and reducing economic losses in industrial production.
1 Nature and hazards of carbon disulfide
1.1 Properties of carbon disulfide
Pure carbon disulfide is a clear, colorless liquid with aromatic sweetness. Industrial products are slightly yellow and have a rotten odor. The molecular weight is 76.14, the density is 1.2632 g / cm 3 (20 ° C), the freezing point is -111.6 ° C, and the boiling point is 46.3 ° C. This product is easy to volatilize at room temperature. Its vapor is 2.62 times heavier than air. It can form explosive mixture with air. The upper and lower explosion limits are 50% and 1%. CS 2 liquid is a flammable and explosive chemical. It can generate static electricity and cause an explosion. When it is exposed to high temperatures and oxidants, it will burn. This product is easily soluble in alcohol, benzene and ether, slightly soluble in water.
1.2 Harm of carbon disulfide
Carbon disulfide is harmful to the environment. Carbon disulfide has low chemical reactivity, but is easily oxidized to sulfur dioxide in the stratosphere, which is the main component of acid mist or acid rain. Therefore, the harm caused by carbon disulfide to the atmospheric environment cannot be ignored.
Carbon disulfide is also very harmful to industrial production. Due to the slow hydrolysis of carbon disulfide to generate hydrogen sulfide, which corrodes production equipment, it also poisons catalysts in downstream industries, such as catalysts for methanol synthesis, alkylation processes, and ammonia synthesis. This has brought great economic losses to industrial production.
The inhalation of carbon disulfide is very harmful to human health. Carbon disulfide can enter the human body through breathing and skin, and affects various organs of the human body, endangering people's health. It has been reported that carbon disulfide can cause embryonic developmental disorders and offspring birth defects, and that this teratogenic effect can be inherited from generation to generation. Carbon disulfide can be inhaled through the respiratory tract. It can also be ingested by the digestive tract or absorbed through the skin. Carbon disulfide is absorbed in the body by red blood cells and plasma, and is sent to the whole body through the blood circulation. It is quickly dissolved in fats and lipids and combines with amino acids and proteins. Therefore, carbon disulfide in the body is mostly present in tissues and organs, and there is less blood. If the body is strong. The toxicity of carbon disulfide varies depending on the absorption route, exposure concentration and duration of exposure. Generally manifested as neurasthenia symptoms, multiple peripheral neuritis, autonomic dysfunction and other such as hyposexuality, irregular menstruation in women, premature delivery, abortion and eye diseases. The symptoms of acute poisoning are usually nerve palsy, even coma, and even respiratory failure. The carcinogenic and mutagenic effects of carbon disulfide have not yet been reported. However, some experiments have shown that rats have a weak qi-induced effect when combined with low concentrations of hydrogen sulfide and carbon disulfide.
2 carbon disulfide removal method
The methods for removing carbon disulfide are divided into dry desulfurization and wet desulfurization. Wet desulfurization can be divided into physical desulfurization and chemical desulfurization. The two methods have similar processes. Both adopt absorption regeneration mode. The absorbent absorbs or reacts with sulfur-containing components in natural gas. The rich liquid is recycled to the regeneration tower after the absorbent is regenerated. However, the desulfurizing agent needs to be replenished continuously, the equipment is heavy, the energy consumption is large, and the process is complicated. The desulfurizing agent waste liquid generated in the production process needs to be processed. materials. In general, the sulfur content of the feed is above 60 mg / m 3 , and the sulfur content of the natural gas after desulfurization is still generally above 10 mg / m 3 . At present, the wet removal of carbon disulfide is an older method of ethanolamine desulfurization. CS 2 is easy to generate degradation products with ethanolamine. This product cannot be decomposed at the regeneration temperature of ethanolamine, which will cause the amount of ethanolamine to decrease continuously. Removal of 2 is not effective. More widely used is dry carbon disulfide. In dry carbon desulfurization, the commonly used methods include adsorption, chemical conversion absorption, catalytic hydrogenation, and catalytic hydrolysis. The following mainly introduces the dry carbon dioxide removal method.
2.1 Adsorption method
Activated carbon, activated carbon fiber (ACF), and resin are commonly used in the removal of carbon disulfide by adsorption methods. The static and dynamic adsorption behavior of carbon disulfide vapor on different ACFs is mainly diffusion outside the gas phase boundary film. The adsorption behaviors are physical adsorption, that is, low temperature is favorable for adsorption, and the adsorption amount is related to the specific surface and micropore volume of the adsorbent. However, as a means of adsorption, the carbon disulfide is only transferred to the adsorbent, and the carbon disulfide is not truly eliminated. During the post-treatment, carbon disulfide is eluted and the process of condensation and separation can easily cause secondary pollution.
Wang Yaning and others used the XDA-1 resin adsorption fixed bed process to separately treat CS 2 saturated aqueous solution and CS 2 containing air, and explored a simple and efficient resource recycling of CS 2 saturated aqueous solution and CS 2 air. Dealing with new processes. At room temperature and a gas flow rate of 600 BV / h, the adsorption efficiency of XDA-1 resin for CS 2 in the air is 63.9% -90.0%, and the adsorption amount of CS 2 can reach 28.0-36.8 mg / mL. XDA-1 resin has a very strong adsorption capacity for trace CS 2 in water. Even at high flow rates, the resin adsorption efficiency can still reach 86.4% -98.8%.
2.2 Chemical conversion absorption method
The chemical conversion absorption method uses a chemical reaction to convert and absorb carbon disulfide so as to reach the removal method. For example, the MZX high-temperature organic sulfur conversion absorption type fine desulfurizer developed by the Hubei Chemical Research Institute is made of a variety of metal oxides. After adding a certain proportion of binder to extrude the strip, the active component is impregnated. Dry roasted. MZX fine desulfurizer can effectively reduce the conversion and removal of carbon disulfide, and the use temperature is 350 ～ 450 ℃. At the same time, the EZ-2 wide temperature zinc oxide fine desulfurizer developed by Hubei Chemical Research Institute has passed:
2ZnO ＋ CS 2 = 2ZnS ＋ CO 2
The reaction converts carbon disulfide into absorption, and can be used in a wide temperature range from normal temperature to 400 ° C. EZ-2 Wide Temperature Zinc Oxide Fine Desulfurizer has fast reaction speed, high desulfurization accuracy, can remove organic sulfur (carbon disulfide), simple operation and convenient use, effectively protect downstream sulfur-sensitive catalysts, solve equipment sulfur corrosion and The problem of high-efficiency catalyst poisoning has significant economic benefits. KDS-I absorbent is a conversion absorption desulfurizer that can remove carbon disulfide under normal temperature and pressure. This desulfurizer is prepared by loading amine on calcium silicate carrier. Under the condition of temperature of 45 ℃, KDS-I absorbent The removal rate of carbon disulfide by the absorbent can reach more than 70%.
2.3 Catalytic hydrogenation
Catalytic hydrogenation is based on catalytic hydrogenation at a certain pressure and temperature. The catalytic hydrodesulfurizing agent is a substance having a hydrogenation function, and is impregnated on an Al 2 O 3 or Al 2 O 3 / SiO 2 carrier as an active component to form a hydrogenation catalyst. The active components are mainly WNi, MoNi, MoCo, MoCoNi, WmoNi, WmoNiCo, etc., and sometimes a small amount of P, B, F and other additives are added. Catalytic hydrogenation is mainly used to remove organic sulfur compounds, including mercaptans, thioethers, disulfides, thiophenes, benzothiophene (BT), dibenzothiophene (DBT) and its derivatives.
Removal of carbon disulfide is carried out at 300-400 ° C using a CO-MO / Al 2 O 3 catalyst through hydrogenation to generate H 2 S. The reaction occurs:
CS 2 ＋ 4H 2 = CH 4 ＋ 2H 2 S
The fixed bed reactor was connected in series to remove hydrogen sulfide.
2.4 Catalytic hydrolysis
Catalytic hydrolysis of carbon disulfide is carried out at a reaction temperature of 200 to 300 ° C, with relatively low energy consumption and few side reactions. Carbon disulfide is hydrolyzed and converted to hydrogen sulfide on the catalyst, and then the hydrogen sulfide is adsorbed and removed by iron oxide or activated carbon desulfurizing agent. The hydrolysis catalyst usually uses activated alumina. Basicity is favorable for the hydrolysis of carbon disulfide, and the basic center plays a very important role in catalysis.
Wang Li et al. Studied the feasibility of removing carbon disulfide by a one-step catalytic hydrolysis-oxidation coupling at low temperature. To reduce the hydrolysis temperature of carbon disulfide and to remove the generated hydrogen sulfide. The reaction formula of carbon disulfide catalytic hydrolysis-catalysis coupling reaction is as follows:
CS 2 + H 2 O = COS + H 2 S
COS ＋ H 2 O = CO 2 ＋ H 2 S
H 2 S + 1 / 2O 2 = H 2 O + S
H 2 S ＋ 2O 2 = H 2 SO 4
The macro course of the entire reaction can be expressed as:
Wang Li et al. Concluded that this method is feasible at low temperatures (100-130 ℃).
3 Prospects and prospects for removal of carbon disulfide
The existing methods for removing carbon disulfide have some disadvantages. Removal of carbon disulfide by catalytic hydrogenation and catalytic hydrolysis requires two steps, and under high temperature conditions, this is not only a complicated process and a large investment. The adsorption method requires post-treatment and will cause secondary pollution. More importantly, the load of various desulfurizing agents is relatively low. To sum up the various problems mentioned above, it is necessary to develop a desulfurizing agent for one-step removal of carbon disulfide at low temperature. Wang Li et al. Discussed in this field, but the problem of low load still exists. Therefore, it is very promising to develop a desulfurizer with simple operation, low energy consumption and high load in this field.
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