vulcanizing agent
Chemical substance
China? |? This entry is reviewed by the writing and application project of "Popular Science China".
Review expert? Pu Fuyong
There are two kinds: inorganic and organic. The former category includes sulfur, sulfur monochloride, selenium and tellurium. The latter category includes sulfur-containing accelerators (such as TMTD), organic peroxides (such as benzoyl peroxide), quinoxime compounds, polysulfide polymers, polyurethanes, maleimide derivatives, etc.
Rubber vulcanizing agents include elemental sulfur, selenium, tellurium, sulfur-containing compounds, peroxides, quinones, amines, resins, metal oxides and isocyanates. The most commonly used are elemental sulfur and sulfur-containing compounds.
Chinese name
vulcanizing agent
Foreign name
vulcanizing agent
The vulcanization principle, synthetic route and TA theory of rubber vulcanizing agent are briefly described.
biographical notes
There are two kinds: inorganic and organic. The former category includes sulfur, sulfur monochloride, selenium and tellurium. The latter category includes sulfur-containing accelerators (such as TMTD), organic peroxides (such as benzoyl peroxide), quinoxime compounds, polysulfide polymers, polyurethanes, maleimide derivatives, etc.
Rubber vulcanizing agents include elemental sulfur, selenium, tellurium, sulfur-containing compounds, peroxides, quinones, amines, resins, metal oxides and isocyanates. The most commonly used are elemental sulfur and sulfur-containing compounds. The most commonly used are elemental sulfur and sulfur-containing compounds. [ 1]
Vulcanization principle
Dry vulcanization in the catalyst is carried out in a high-pressure circulating loop consisting of heating, reaction, heat exchange, cooling, high-pressure separation, circulating hydrogen compressor and hydrocracking logistics pipeline. The procedure includes: heating the catalyst with circulating hydrogen heated by the heating furnace at the maximum circulating hydrogen flow rate and the required heating rate, injecting vulcanizing agent (DMDS) into the inlet of the reaction heating furnace at a strictly controlled flow rate, and decomposing the generated H2S sulfurized catalyst with the vulcanizing agent in the presence of hydrogen. When the catalyst is presulfurized, the following two main reactions will occur in the reactor:
(1) The vulcanizing agent (DMDS) first reacts with hydrogen to produce hydrogen sulfide and methane, which is an exothermic reaction. This reaction usually takes place at the entrance of the refining reactor R 10 1, and the reaction speed is relatively fast.
(2) Active catalyst components (nickel oxide, molybdenum oxide, etc.) in oxidation state. ) reacts with hydrogen sulfide to become an active catalyst component in sulfide state, which is an exothermic reaction and occurs on each catalyst bed in the reactor. The temperature rise during presulfurization is caused by this reaction.
(3) According to the above chemical reaction equation and the content of active metal components in the catalyst, the theoretical quantity of vulcanizing agent and the theoretical water production required for the complete vulcanization of the unit catalyst can be calculated.
Adverse side reactions may also occur during vulcanization: the active components of the oxidized catalyst (nickel oxide, molybdenum oxide, tungsten oxide) are reduced by hydrogen to produce elemental metal and water, which will greatly destroy the activity of the catalyst. This reaction is extremely harmful and should be avoided as much as possible. In the presence of hydrogen without hydrogen sulfide, this side reaction is more likely to occur at a higher temperature (greater than 230℃).
The vulcanization process mainly goes through two constant temperature stages: 230℃ and 370℃. The degree of vulcanization completion is generally based on the fact that the amount of vulcanizing agent added in the whole process reaches 120% (calculated by metal) of the theoretical sulfur content of the catalyst. The constant temperature time can be determined by measuring the concentration of hydrogen sulfide at the outlet of the reactor. Before the constant temperature of 230℃, hydrogen sulfide must completely penetrate the catalyst bed (marked by the beginning of a large amount of hydrogen sulfide in circulating hydrogen). The final vulcanization temperature is generally 360℃-370℃. In fact, every temperature has an equilibrium limit. Even if the vulcanization time is prolonged, the sulfur content will not increase again. When the temperature is higher than 300℃, the vulcanization reaction speed is very fast and the vulcanization can be completed. [2]
Synthetic route
Using mercaptan as raw material
Thiol is one of the main raw materials for synthesizing vulcanizing agent. Thiol can react with oxygen under the action of hydroxides of alkali metals and alkaline earth metals to obtain vulcanizing agent. It can also be mixed with elemental sulfur as raw material to synthesize organic vulcanizing agent under the action of alkaline catalyst. The earliest catalysts used in this synthetic route are amines, alkanolamines, thiolates, alkoxides and inorganic bases, but there are some shortcomings in the use of these catalysts, such as low yield, low product purity and bad smell. Therefore, the research on new catalysts is the focus of this synthetic route. The alkylene oxide group in the composition is replaced by alkylene oxide, so that the yield of polysulfide is further improved, the chromaticity becomes low and the chromaticity is less than or equal to, and the product has no unpleasant smell or turbidity. Some scholars began to use resin as catalyst. It is suggested to use organic anion exchange resin containing quaternary ammonium hydroxide group or tertiary amine group as catalyst. This kind of resin exists as beads or dentate in the reaction system, which has low solubility and is easy to recover, but the yield of organic vulcanizing agent is not high. In order to solve this problem, the first study was carried out, and one or one form of resin was proposed as a catalyst. The resin has a highly crosslinked macroporous structure, and compared with gel resin, it has greater catalytic activity in the reaction process, which can effectively improve the yield of organic vulcanizing agent. Aretz proposed that using polystyrene-divinylbenzene-1 resin containing muscle group and narrow group as catalyst, low-grade organic disulfide and polysulfide can react with elemental sulfur to obtain high-grade polysulfide. In addition, the resin can also make high-grade organic vulcanizing agent react with mercaptan to obtain low-grade polysulfide. Resin exists in the reaction solution in the form of particles or beads, which is easy to separate after the reaction. Freimut developed a polystyrene-based resin, divinylbenzene, which was functionalized with ethylenediamine or polyethylene polyamine. This catalyst can effectively improve the conversion rate of reactants. The application of these new catalysts not only effectively improves the sulfur content of vulcanizing agent, but also broadens the range of raw materials. More importantly, it overcomes the shortcomings of traditional catalysts, such as low yield, low product purity and unpleasant smell. However, the synthesis of new catalysts is complicated, the cost of raw materials is too high, and some raw materials are not easy to obtain, which is not convenient for industrial application. [ 1]
Contains olefins and sulfur.
The reaction mechanism of sulfur and olefin to synthesize organic vulcanizing agent is that in the presence of catalyst, at a certain temperature, ring-opening forms linear molecules, which exist in the system in the form of free radicals and react with olefins to generate organic vulcanizing agent. The method of synthesizing organic vulcanizing agent with sulfur and olefin as raw materials is the most widely used and has been highly valued by scholars. This patent discloses the synthesis of organic vulcanizing agent from sulfur and isobutylene. The organic vulcanizing agent synthesized by this method has little odor, few by-products and no pollution. However, this method has strict requirements on reaction conditions and high cost, and is not suitable for industrial application. This patent discloses the direct reaction of elemental sulfur and olefin to synthesize vulcanizing agent. The process of synthesizing organic vulcanizing agent by this method is simple, but there are many by-products, which have unpleasant smell, and some by-products are corrosive, causing serious damage to equipment. In order to solve the above problems, Sun Laiyin proposed to synthesize organic vulcanizing agent from isobutylene under high pressure. This method has few by-products, little odor, almost no pollution to the environment and high sulfur content, but isobutylene is not easy to obtain and the price is high. Jiyong iron and steel co., ltd. proposed to use butene, a by-product with low utilization rate in the process of butene separation, as the raw material for synthesizing vulcanizing agent. The method has simple synthesis process, cheap and easily available raw materials, and greatly reduces the production cost. Although several compounds with different sulfur contents can be obtained by synthesizing organic vulcanizing agents from a single olefin, there is still the problem of excessive heat release during the catalyst presulfurization. In order to solve this problem, many scholars put forward to presulfide the catalyst with mixed vulcanizing agent, but the proportion of each component of mixed vulcanizing agent is not easy to determine, the cost is high, and many by-products are produced during presulfurization. Yu Shouzhi synthesized organic vulcanizing agent from distillate oil produced by wax cracking. This method solves the problem of concentrated heat release of single polysulfide during presulfurization, but the product anvil is large and the fluidity is poor, so it needs to be diluted before presulfurization. Wang Deqiu proposed to synthesize organic vulcanizing agent from distillate oil. The organic vulcanizing agent synthesized by this method has high sulfur content, low toxicity, small porosity and good fluidity. Synthesis route with sulfur, hydrogen sulfide and olefin as raw materials Organic vulcanizing agent is prepared with elemental sulfur, olefin and hydrogen sulfide as raw materials. [ 1]
Olefin, sulfur halide
Synthesis of vulcanizing agent from olefin and sulfur halide is a common method in China's industry. Sulfur halide and olefin generate halogen-containing organic vulcanizing agent in the presence of catalyst, and then the organic vulcanizing agent is obtained through dehalogenation process. At the beginning of the 20th century, China scholar Huang Jinxia proposed to synthesize organic vulcanizing agent from sulfur chloride and isobutylene. The organic vulcanizing agent synthesized by this method has high sulfur content, good stability and low corrosiveness. However, in the production process of synthesizing organic vulcanizing agent, this method will produce a lot of waste gas, waste water and waste liquid to pollute the environment. In recent years, many literatures reported the improvement of this synthetic route. For example, Yang Jingpei proposed to synthesize an organic vulcanizing agent containing impurities in a closed pipeline in two steps, and then obtain a pure organic vulcanizing agent through separation, dehydration, refining and other steps. The process is carried out in a closed pipeline, which avoids the pollution of waste gas and waste liquid to the environment. However, this method has complex synthesis process and high requirements for equipment, which is not suitable for industrial application. Zhou Bo put forward the method of adding sulfur and dechlorinating twice to treat sulfurized isobutylene containing chlorine atoms. This method simplifies the process steps and saves the cost, but the production cycle is long. Qi Xiangyang proposed to recycle the sulfur-containing waste liquid generated in the second step of vulcanization and dechlorination reaction for the next step of vulcanization and dechlorination reaction, which not only reduced the discharge of waste liquid, but also saved the production cost. The new synthesis process solves the problem of "three wastes" and reduces the production cost, but it is difficult to realize industrial application because of large equipment investment, long production cycle and complicated operation process. [ 1]
Rubber vulcanizing agent
Substances that can vulcanize rubber under certain conditions are collectively called vulcanizing agents. Vulcanization means that the linear molecular structure of rubber is transformed into a three-dimensional network mechanism through the "bridge" of vulcanizing agent, so that the mechanical and physical properties of rubber are obviously improved.
1, sulfur: yellow solid substance, widely used in natural rubber and some synthetic rubber. Commonly used sulfur is sulfur powder, sublimated sulfur (also known as sulfur flower) and precipitated sulfur. Sulfur is insoluble in water, slightly soluble in ethanol and ether, and soluble in carbon disulfide and carbon tetrachloride. It is characterized by low heat resistance, high strength, corrosive effect on copper wire, and is suitable for natural rubber and partially synthetic rubber. In the rubber formula of wire and cable, the amount of sulfur is about 0.2 ~ 5 phr, but due to the addition of accelerator, the amount of sulfur can be reduced accordingly.
2. Metal oxides: Metal oxides are mainly used as vulcanizing agents for chloroprene rubber and chlorosulfonated polyethylene. Commonly used are zinc oxide, magnesium oxide, lead oxide and lead tetroxide.
Zinc oxide with a specific gravity of 5.6 is a white powder, which is nontoxic and tasteless. Zinc oxide is widely used in rubber, and it is often used as the main vulcanizing agent together with magnesium oxide in general chloroprene rubber. It can be used as an activator of accelerators in natural rubber and other olefin rubbers. In addition, it also has a strengthening effect. It plays a role in shielding ultraviolet rays in rubber resistant to sunlight aging. The dosage of zinc oxide in natural rubber and butyl rubber is 5 ~ 10, and the general dosage of zinc oxide combined with magnesium oxide in chloroprene rubber is 5.
Magnesium oxide is used as a secondary vulcanizing agent in chloroprene rubber, which can prevent chloroprene rubber from vulcanizing in advance during mixing. This product can improve the tensile strength, modulus and hardness of chloroprene rubber. It can neutralize a small amount of hydrogen sulfide produced by halogenated rubber during vulcanization or other oxidation conditions. P-chlorosulfonated polyethylene rubber can give it good physical and mechanical properties, especially the permanent deformation is relatively small. But the water resistance is poor. The general dosage is 3 ~ 7 parts. Magnesium oxide is a white loose powder with a specific gravity of 3.2. In the air, water and carbon dioxide can be gradually absorbed into alkali or magnesium carbonate, which reduces its activity and should be strictly sealed and preserved.
3. Resin vulcanizing agent: resin vulcanizing agents are mainly thermosetting alkyl phenolic resin and epoxy resin. Vulcanizing unsaturated carbon chain rubber and butyl rubber with alkyl phenolic resin can significantly improve the heat resistance of vulcanized rubber. The main varieties commonly used are phenolic resins, such as tert-butyl phenolic resin and tert-octyl phenolic resin. Epoxy resin has good curing effect on carboxyl rubber and chloroprene rubber, and its vulcanized rubber has good buckling resistance.
4. Qiu Lan: The full name is tetramethylthiuram disulfide and the trade name is TMTD. It is a curing agent widely used in wire and cable rubber and can also be used as a curing accelerator. The pure product has a melting point of 147℃ ~ 148℃ and a specific gravity of 1.29, and is a gray powder. It is an overspeed accelerator of natural rubber, which decomposes at 100℃ to produce free radicals, so rubber crosslinking can be carried out. Using Qiu Lan as vulcanizing agent can improve the heat resistance and aging resistance of rubber. The vulcanization curve is flat and not easy to burn. Suitable for natural rubber, styrene-butadiene rubber, nitrile rubber and all unsaturated rubbers containing double bonds. In general heat-resistant rubber, the amount of Qiu Lan is 2-3 parts, while in the formula of continuously vulcanized rubber, it is 2-5 parts, and when used as an accelerator, it is 0.3-0.5 parts.