A method for reducing acid value of tdi product by heavy solvent method

Abstract

The invention belongs to the technical filed of chemical production and relates to a method for reducing the acid value of a toluene diisocaynate (TDI) product prepared through a heavy solvent method. Photochemical reaction materials of the TDI prepared through the heavy solvent method are sent to a product tower after undergoing preheating of a feeding preheater, a gas phase inside the product tower enters a product tower condenser from the top of the product tower to perform condensation, the gas phase of a noncondensable gas material is extracted to be vacuum, part of the condensed materials serve as backflow, and the other part of the condensed materials serve as TDP product liquid phase to be extracted. DEIP extracted from the product tower is sent to a blowing tower after undergoing pressure boosting of a kettle liquid pump, is sprayed to the blowing tower after the distribution of a distribution device, flows under the effect of gravity and is fully in contact with inert gas blowing into the blowing tower. Acid components in the DEIP gather at the top of the blowing tower along with the inert gas and enter a blowing tower condenser in a gas phase mode to be condensed, the gas phase of the noncondensable gas material is extracted to be vacuum, the condensed acid components pass through the bottom of the blowing tower condenser to be extracted in a liquid phased mode, and recycling solvent of a small acid value is obtained from the bottom of the blowing tower. The method is novel in design, scientific in principle and simple in technology.

Description

Technical field: [0001] The invention belongs to the technical field of chemical production, and relates to a method for reducing the acid value of TDI products produced by a heavy solvent method, which can reduce the generation of by-products when the circulating solvent returns to the previous process to participate in the photochemical reaction, thereby improving the efficiency of the photochemical reaction and the stability of the system sex. Background technique: [0002] Toluene diisocyanate (hereinafter referred to as TDI) is an important isocyanate product. Common production and preparation methods in the industry include phosgenation, nitro compound carbonylation and dimethyl carbonate. Among them, phosgenation is generally The following two processes are used: one is to use diethyl isophthalate (hereinafter referred to as DEIP) as a solvent, and carry out photochemical reaction under high pressure conditions, which is called "heavy solvent method"; Chlorobenzene (...

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Problems solved by technology

[0004] The acidic components produced in the process of producing TDI by the heavy solvent method mainly include hydrogen chloride, benzylic chlorotoluene diisocyanate (hereinafter referred to as Cl-TDI), m-ethyl benzoyl chloride (hereinafter referred to as CBC), etc., wherein Cl- The boiling points of TDI and CBC are between the product TDI and the solvent DEIP. In the product refining process, the product and the solvent are separated in the final product tower. On the one hand, if the acidic component is extracted from the tower with the heavy solvent , because the solvent has to be returned to the system for recycling, the presence of acidic components will cause more photochemical side reactions to generate by-products such as residues, which will affect the reaction yield and the stable operation of the system; if the acidic components enter the product If it is extracted from the top of the tower, it is a heavy component compared to TDI. At this time, if the method of rectification or purging is used, a large amount of products will be brought into the gas phase, which requires high equipment size and energy consumption. and cannot reasonably and effectively separate the acidic components

Therefore, the rectification method and gas purging method, which are more suitable for the light solvent method, are not suitable for the removal of acidic components in TDI products produced by the heavy solvent method.

[0005] In addition, in the prior art, there is also a method of reducing the acid value and acidic component content of TDI products by adding additional substances, such as US Pat. Above 180°C, the heating time is preferably above 240min, which can significantly reduce the content of acidic components in isocyanate; although the above method of adding substances can better remove the acidic components in the product, but at the same time introduces a new impurity group After that, it needs to be separated from the product by nitrogen purging, rectification or extraction, which virtually increases the workload

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