A catalyst refers to a substance that can change the reaction speed in a chemical reaction, but its composition and quality remain unchanged after the reaction.
The catalyst that accelerates the reaction is called a positive catalyst, and the one that slows down is called a negative catalyst or retarder.
Generally speaking, the catalyst refers to the positive catalyst. Such catalysts are used more in industry, especially in the organic chemical industry, and are of great significance, such as the production of sulfuric acid by contact method, synthesis of ammonia, the hydrolysis of esters and polysaccharides, and the hydrogenation of fats and oils. The commonly used catalysts mainly include metals, metal oxides and inorganic acids. If the catalyst is a solid, the reactant is a gas, forming a heterogeneous catalytic reaction. This catalyst is sometimes called a catalyst or contact agent. The catalyst is generally selective, it can only accelerate a certain reaction or a certain type of reaction. However, for some reactions, multiple catalysts can be used. For example, platinum, palladium, and nickel are often used for hydrogenation reactions, which should be carefully selected.
In catalytic reactions, substances other than catalysts, called promoters, are often added to enhance the catalytic effect of the catalyst. For example, iron is a catalyst for the synthesis of ammonia industry, adding a small amount of potassium oxide and alumina can enhance the catalytic effect of iron. The composition and weight of the catalyst and the co-catalyst remain unchanged before and after the reaction. The above are all inorganic catalysts. Enzymes are proteins and are very important organic catalysts.
Catalysts And Auxiliaries
Types of Catalyst
There are many types of catalysts.
Which are classified according to the phase state of the catalyst and the reaction system. There are two types of catalysts, homogeneous and heterogeneous. Heterogeneous catalysts are the most widely used, with three states: gas, liquid, and solid.
The variety and application of solid catalysts are the most. Solid catalysts are fine particles made of metals (nickel, platinum, palladium, chromium, cobalt, titanium, vanadium, etc.) or metal oxides (copper oxide, vanadium pentoxide, lead oxide, etc.), or are dispersed and deposited on a carrier , In order to obtain a good dispersion effect and increase the specific surface area. The catalyst requires reliable activity, stability, selectivity, long working life, not easy to be poisoned and overburned, and easy to regenerate.
In order to improve the catalytic efficiency, pure metal catalysts are made into alloy catalysts (such as nickel-aluminum alloy) and composite catalysts (ZieglerNatta catalyst). The composite catalyst is composed of a main catalyst and a co-catalyst. Other components must be added to the new high-efficiency catalyst. The production and development of high-efficiency catalysts has promoted the development of polymer materials and produced many new-generation high-performance and high-value-added polymer functional and structural materials.
Use of Catalyst
With the wide application of catalysts and the emergence of some new types of catalysts, many new chemical reactions can be industrialized to provide an increasing number of chemical products; some original chemical reaction conditions can also be improved to improve production efficiency and Product quality, make full use of resources. Continuous selection and development of a new generation of more and better catalysts has always been an important topic in the field of modern chemistry and chemical research. However, the role of catalysts is not all beneficial to human beings. For example, the combustion products of supersonic jet fuel as a catalyst can cause the decomposition of ozone in the stratosphere (10-50 kilometers above the sky), and weaken the absorption of solar ultraviolet rays in the atmosphere, causing certain Skin cancer patients increased in some areas. New supersonic jet fuels are being developed, and their combustion products are required not to become catalysts that cause the decomposition of ozone in the stratosphere.
Application range of Auxiliaries
Auxiliaries have a wide range of applications, and are usually named after the target, such as polymerization aids, water treatment agents, metal surface treatment agents, etc. The choice of additives has some common considerations
The appearance, smell, pollution, durability, electrical properties, and weather resistance of additives directly affect the usage of the product.
The loss of additives is mainly through 3 ways of volatilization, extraction and migration. The appropriate variety must be selected according to the use environment and processing conditions of the product.
including their miscibility and their mutual influence in terms of stability.
Food and drug packaging materials, drinking water pipes, medical equipment and other high-molecular materials products, their sanitation mainly depends on the additives used.
if properly matched, they will increase each other’s effectiveness and reduce the total amount of additives.
Auxiliary agent refers to in industrial and agricultural production, especially chemical production, in order to improve the production process, increase product quality and yield, or endow the product with a specific application performance, it is usually necessary to add some auxiliary chemicals. It is a large class of important auxiliary raw materials in chemical production, which can give products with special properties and improve the use of finished products; it can accelerate the speed of chemical reactions and increase the yield of products; it can save raw materials and improve processing efficiency. It is widely used in the chemical industry, especially in organic synthesis, post-processing of synthetic materials and petroleum refining, pesticides, medicine, dyes, coatings and other industrial sectors.
According to the purpose, it can be divided into synthetic additives and processing additives. Various auxiliary agents used in the synthesis and polymerization of monomers such as resins, fibers, and rubbers are called synthetic additives, including catalysts, initiators, solvents, dispersants, emulsifiers, polymerization inhibitors, regulators, terminators, etc. . Auxiliary chemicals used in the process of manufacturing rubber and plastic products from raw rubber, as well as chemical fiber spinning and spinning, are called processing additives, including plasticizers, heat stabilizers, antioxidants, and light stabilizers , Flame retardants, foaming agents, lubricants, mold release agents, vulcanizing agents, accelerators, softeners, anti-scorching agents, surfactants, oils, fillers, etc. Among these auxiliaries, many are chemical hazardous substances, such as synthetic initiators such as dibenzoyl peroxide, azobisisobutyronitrile, hydrogen peroxide-ferrous blue, aluminum alkyl, titanium chloride, etc. The catalysts are all flammable and explosive materials, and should be stored, transported, operated and used in accordance with the relevant provisions of the “Regulations on the Safety Management of Chemical Hazardous Materials”.
Classification of Auxiliaries
Adhesive AuxiliariesThere are many types of adhesive additives with different functions. According to their functions and functions, they can be divided into five categories: synthesis additives, crosslinking additives, functional additives, stability additives, and process additives.
Synthetic additives include phenolic resin, polyurethane, urea-formaldehyde resin, melamine-formaldehyde resin, furfural resin, unsaturated polyester resin, neoprene, nitrile rubber, grafted neoprene, SBS, SIS, SEBS, a-cyano Acrylate, anaerobic adhesive, modified acrylate fast curing adhesive, acrylate pressure-sensitive adhesive, polyvinyl acetate emulsion, acrylate emulsion, modified starch and other adhesives used in the synthesis and preparation process of catalysts, initiators, Emulsifier, dispersant, polymerization inhibitor, terminator, oxidant, molecular weight regulator, chain extender, neutralizer, dehydrating agent, solvent, etc.
Cross-linking additives refer to compounds with reactive groups that can react with the matrix polymer in the adhesive to enter the structure to form a network or cross-linked structure. Such additives include addition molding and latent curing agents, crosslinking agents, photoinitiators, reactive diluents, reactive flame retardants, etc.
Functional additives, also known as modified additives, can improve the original properties of the adhesive and give new functions. Functional additives play a very important role in adhesives, accounting for the largest proportion of additives. Specifically include tougheners, tackifiers, reinforcing agents, plasticizers, flame retardants, coupling agents, fillers, accelerators, softeners, conductive agents, foaming agents, coloring agents, decolorizers, and antistatic agents Agent, chelating agent, deodorant, etc. The improvement and perfection of functional additives can make the quality of the adhesive icing on the cake, and will play an extremely important role in the improvement of the performance of the adhesive.
The additives that can prevent the aging and deterioration of the adhesive during the process of synthesis, preparation, storage, transportation and use, prolong the service life, and improve the storage stability are all classified as stability additives. Traditionally, stabilizers are called antioxidants, including antioxidants, heat stabilizers, light stabilizers, and so on. In order to stabilize the performance of the adhesive during storage, it is necessary to add anti-mold bactericides, preservatives, metal ion deactivators, antifreeze, etc.
In order to facilitate the preparation and use of the adhesive, and to ensure the expected performance, the additives used are called process additives, such as diluents, thickeners, defoamers, thixotropic agents, anti-scorching agents, and anti-sticking agents,etc.
Plastic profile Auxiliaries
If the impact modifier is not added in the production of plastic profiles, the plastic profiles will be very brittle and hard, and will be easily broken with a little impact. The commonly used impact modifiers in the production of plastic profiles mainly include the following three categories: chlorinated polyethylene, polyacrylates, and ethylene-vinyl acetate copolymer (EVA).
The plastic profile is a heat-sensitive plastic, so in the production and processing of the plastic profile, a heat stabilizer is indispensable. The metal salt in the heat stabilizer can absorb the HCL from the decomposition of PVC, so it can delay the decomposition rate of the plastic and prolong the decomposition time. The most commonly used in the production of plastic profiles is the composite lead salt, which has high thermal stability efficiency and low price.
Processing aids are a class of improving aids developed mainly to improve the processing performance of plastics. The processing temperature of the plastic profile is relatively close to the decomposition temperature, and the fluidity is poor, and it is easy to stick to the equipment and coke. Therefore, a certain amount of processing aids need to be added in the production of plastic profiles to overcome the defects of the plastic profile itself.
Filler is a solid additive that is different from plastic in composition and structure, also known as filler. It has obvious effect and economic value for improving certain physical and mechanical properties of plastics and reducing the cost of plastics. Adding fillers to the plastic profile production formula can reduce the dimensional change rate of the plastic profile after heating, increase the impact strength and rigidity, and also reduce the production cost.
Light stabilizer can inhibit the photo-oxidative degradation reaction of polymers by shielding and absorbing ultraviolet rays, quenching excitation energy and capturing free radicals, so as to give products a good light stabilization effect and extend their service life.
The main function of the lubricant is to reduce the mutual friction between the polymer and the processing equipment and the molecules inside the polymer, prevent the resin degradation caused by excessive frictional heat, and improve the efficiency of the heat stabilizer.
The special ingredients contained in the anti-biting agent can make the oral mucosa and taste nerves of cats, dogs, mice, etc. are strongly stimulated and abandon the destruction of plastics by chewing and cutting, thereby playing a protective effect.