Process for preparing trioxymethylene by taking methanol as raw material

Abstract

The invention discloses a process for preparing trioxymethylene by taking methanol as a raw material. The process comprises the following steps of: preparing concentrated formaldehyde with the concentration of over 50 percent by taking methanol, and methanol and methylal produced by catalytic conversion in a recovery section as raw materials; synthesizing the concentrated formaldehyde into trioxymethylene under the catalytic action of a solid acid, subjecting a formaldehyde aqueous solution containing trioxymethylene to rectification and membrane coupling process for purifying, and separatingimpurities out to obtain pure trioxymethylene. According to the process disclosed by the invention, the generation amount of dilute aldehyde is reduced, the separation energy consumption is reduced, the impurity content of trioxymethylene is reduced, the utilization rate of raw materials is increased through catalytic conversion and circulation of dilute aldehyde and byproducts, and long-period stable operation of trioxymethylene production can be realized.

Description

technical field [0001] The invention provides a process for preparing paraformaldehyde by using methanol as a raw material, which belongs to the field of chemical production process. Background technique [0002] Polyoxymethylene (POM), also known as acetal resin and polyoxymethylene, is a thermoplastic engineering plastic with excellent comprehensive properties. It is one of the five major engineering plastics. "Super Steel" or "Sai Steel". The main key monomer for the production of polyoxymethylene is trioxane (TOX), a stable form of anhydrous formaldehyde polymer. Preparation of fine chemicals. [0003] The traditional synthesis method of paraformaldehyde is to use 50-65% concentrated formaldehyde as raw material to synthesize paraformaldehyde under the action of sulfuric acid catalyst. This reaction is a fast reversible reaction, but the reaction equilibrium constant is small, the conversion rate of formaldehyde is low, and only the paraformaldehyde whose equilibrium ...

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Problems solved by technology

[0004] The traditional paraformaldehyde synthesis process mainly has the following problems: the sulfuric acid catalyst severely corrodes the equipment, the product is difficult to separate from the catalyst, and the product separation is complicated; the continuous production stability of the formaldehyde synthesis and formaldehyde concentration unit is poor, it is difficult to run at full load, and the energy consumption is high; The conversion rate of the paraformaldehyde monomer reaction system is low, the load of the recovery system is large, the extraction effect is poor, the steam consumption is large, and the impurity content exceeds the standard

The current process generally adopts the method of crystallization or extraction to carry out preliminary separation of the synthetic product, plus the refining of rectification, but it is still unable to obtain paraformaldehyde with ultra-purity or close to 100% purity. At the same time, the extraction process introduces new solvents, resulting in The separation system is more complicated, resulting in energy consumption and dilute aldehyde recovery difficulties, and often requires a separate dilute aldehyde recovery unit for recovery

[0016] Second, in the existing and above-mentioned paraformaldehyde preparation process, there are difficulties of large amount of dilute aldehyde and high recovery energy consumption. For example, every ton of paraformaldehyde produced will produce about 4 tons of 15% dilute formaldehyde , producing 1 ton of paraformaldehyde consumes 7-8 tons of steam, and the steam used for dilute aldehyde recovery accounts for more than 70%

[0026] Therefore, in the synthesis process of paraformaldehyde, there are by-products such as methanol, formic acid and methyl formate, especially methanol and formaldehyde are very easy to form hemiacetal, and the separation is difficult. However, if methanol is not separated, it will cause methanol to accumulate in the system. Reduced production rate of paraformaldehyde

[0027] Fourth, when using the rectification method to recover dilute aldehyde, the continuous heating of the formaldehyde solution causes the disproportionation reaction (Cannizzaro) of formaldehyde to generate methanol and formic acid, and formic acid is extremely corrosive, causing corrosion of equipment, making The rectification tower for recovering dilute aldehyde cannot be used for a long time

[0028] In summary, the above-mentioned patented technologies are only optimized and improved from the aspects of catalyst, separation process and preparation process, and still cannot solve the long-term constraints on the production of dilute aldehyde, which have a large amount of dilute aldehyde recovery, many by-products, difficult recycling, high energy consumption, and equipment Key issues such as high material requirements

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