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The Properties and Production Methods of MDI

Views: 295     Author: Vickey     Publish Time: 2023-04-23      Origin: Site


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The Properties and Production Methods of MDI

MDI is a polyurethane material synthesized by isocyanate, polyol, and their combined additives. With its excellent properties, various varieties, and broad uses, it is unique among many synthetic materials and has become one of the fastest-developing materials today.

Diphenylmethane-4,4-diisocyanate is a light yellow solid. It is not soluble in water. It may be toxic through ingestion, inhalation, or skin absorption.

With aniline as a raw material, reaction with formaldehyde, condensation in acid solution, neutralization with alkali, and then distillation can produce diamino dibenzane, which can then be made by reacting with carbonyl chloride and then distilling and refining.

The primary products of this product are widely used in polyurethane coating, in addition to waterproof materials, sealing materials, pottery materials, etc.; polyurethane foam made of this product for warm (cold), building materials, vehicles, and ships; refined products can be made into automobile gear, buffer, synthetic leather, non-plastic polyurethane, polyurethane elastic fiber, no plastic elastic fiber, film, adhesive, etc.

At present, the production methods of MDI mainly include photogasification methods and non-photogasification methods.

Photogasification method

The condensation reaction with aniline and formaldehyde in acidic conditions is a fully mature technical route for MDI production abroad. The reactants are neutralized by alkali and distilled to obtain diphenylmethandiamine (MDA). After MDA is dissolved in solvent, a photogasification reaction is performed to make polyphenyl polyisocyanate (4,4-MDI), 2,2-MDI, or mixed PMDI, and then distilled to obtain pure MDI.

The photogasification method is a commonly used industrial production method at home and abroad, but the disadvantage is that highly toxic phosgas is needed, hydrogen chloride is generated in the reaction process, which is seriously corrosive to the equipment, and the yield and quality of pure MDI are also low.

A few multinational chemical giants, including Bayer, Huntsman, and BASF, own the core technology for the product.

Non-photogasification method

The non-photogasification method has little pollution and a high yield, most of which is in the research stage and cannot fully realize industrial production.

At present, the production methods of MDI mainly include photogasification methods and non-photogasification methods.

Monsanto has issued its patent. TDI and MDI were produced by non-photamic methods such as amine, carbon dioxide, and dehydrating agents. Reaction under near normal pressure and low pressure to form carbamate, and then use phosphorus pentoxide and triethyamine as dehydrators to produce isocyanate. From the perspective of the whole reaction, the dominant direction in the future is the pyrolysis of MDI after the synthesis of carbamate by the catalytic group. It is reported that BASF has industrial production facilities in Belgium and the United States. Data reported by Asahi showed that the non-phosgas method costs 20% less than the phosgas method.

This product contains an isocyanate group (-N=C=O) in the synthetic resin or coating process, with the coating or resin in the hydroxyl group reaction and curing.

MDI is a general term for 4,4′-methylene methane diisocyanate (pure MDI), a mixture of pure MDI and polyphenyl polyisocyanate (polymerization MDI), and a modification of pure MDI and polymer MDI. It is the most important raw material for the production of polyurethane, and a small amount of MDI is used in other aspects other than polyurethane. Polyurethane has the elasticity of rubber, plastic strength, and excellent processing performance, especially in heat insulation, sound insulation, wear resistance, oil resistance, elasticity, and other advantages of other synthetic materials. It is after polyethylene, polyvinyl chloride, polypropylene, polystyrene, and ABS. Six major plastics (which have now surpassed ABS to become the fifth largest plastics) have been widely used in national defense, aerospace, light industry, chemical industry, petroleum, textiles, transportation, automobiles, medical treatment, and other fields and have become indispensable emerging materials for economic development and people's lives.

MDI and TDI are substitutes for each other and are both raw materials for polyurethane production. The price of MDI is slightly lower, and the toxicity is lower than TDI, but the density of foam is larger than TDI system, and the molding of polyurethane products formed by MDI is relatively good.

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