Process for extracting and concentrating dilute aqueous formaldehyde solution by using composite solvent

Abstract

The invention relates to a process for extracting and concentrating a dilute aqueous formaldehyde solution by using a composite solvent. A process device comprises a recovery extraction tower, a concentration extraction tower, a desolventizing rectifying tower and a plurality of heat exchangers, wherein tower equipment in the process is a plate type tower in which a plurality of sieve plates are arranged, a solvent is selected as a continuous phase during operation, and the aqueous formaldehyde solution is a dispersed phase. The process comprises the following specific steps: completely extracting formaldehyde in a dilute formaldehyde solution into a composite solvent phase in a recovery extraction tower, allowing the composite solvent phase to flow out from the top of the tower, removing most of a cosolvent through heating and evaporating, enabling the composite solvent phase to enter the bottom of a concentration extraction tower, and allowing the content of formaldehyde in the solvent phase to be continuously increased under the action of adding concentrated formaldehyde into the tower top until a concentration requirement is met. The composite solvent adopted by the process can obviously improve the partition coefficient of formaldehyde under the condition of a low concentration, and a concentrated product is obtained by further concentration through fractional extraction, so efficient purification and phase separation are realized, and an energy-saving and effective production method is provided for concentration of the low-concentration aqueous formaldehyde solution.

Description

technical field [0001] The invention relates to the technical field of chemical production, in particular to a process method for extracting and concentrating dilute formaldehyde aqueous solution with a composite solvent. Background technique [0002] Formaldehyde has a wide range of industrial uses. It can be used as the basic raw material for the production of resins such as urea-formaldehyde, phenolic formaldehyde and melamine. It is also used to produce chemical products such as vinylon, pentaerythritol and isoprene. However, low-concentration formaldehyde waste liquid is often produced during use. , which brings great difficulties to purification treatment and environmental protection. [0003] The recovery of formaldehyde can be concentrated by rectification. For example, the concentration of formaldehyde can be increased to about 20% under conventional rectification, but the energy consumption is very large, and the effect of further concentration is limited. There i...

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Problems solved by technology

There is also a method of reactive distillation to convert formaldehyde into methylal and then concentrate it, but the process equipment is complex and there are side reactions

In principle, formaldehyde can be concentrated by solvent extraction, but since formaldehyde and water mainly exist in the state of hemiacetal and have a strong binding force, it is difficult to find an effective extraction solvent

[0004] By analyzing the characteristics of formaldehyde aqueous solution, it is found that formaldehyde can be separated from water to a certain extent by solvent extraction when the concentration is moderate, but when the concentration of formaldehyde is low, the extraction effect of the solvent is greatly reduced, making it very difficult to rely on solvent extraction. Difficult to separate formaldehyde completely

In fact, solvent extraction mainly utilizes the condensation of formaldehyde and multi-carbon alcohol solvent to form an aldol hemiacetal structure, but when the concentration of formaldehyde is low, the weak polarity of multi-carbon alcohol is difficult to compete with water for formaldehyde to undergo a chemical reaction

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