Method and device for reducing methanol content in formaldehyde process by silver method

Abstract

The invention relates to a method and a device for reducing methanol content in a formaldehyde process by a silver method, and belongs to the technical field of chemical production. The technical scheme is that the method comprises the following steps of: after thermally recovering and cooling a formaldehyde liquid at the bottom of an absorption tower in the formaldehyde process by the silver method, extracting and feeding part of the formaldehyde liquid to a vacuum groove; conveying gas analyzed at the top of the vacuum groove to an inlet of an air fan; arranging a concentration evaporator between the outlet of an oxidation reactor and the inlet of the absorption tower; evaporating and condensing residual liquid of the evaporator by reaction waste heat at 90-110 DEG C; evaporating methanol in the residual liquid with water; recovering mixed gas of vapor and methanol steam to material gas; and recovering methanol which is less than 0.5% in percentage by weight in the condensed residual liquid to the absorption tower. According to the invention, the inlet temperature of the absorption tower is reduced, while the heat recovery efficiency of the system is improved. The load of a water cooler of the absorption tower is reduced, and the consumption of cooling water is reduced, so that the residual liquid is recovered in grades by 100%, and methanol recovered is free from backmixing, therefore, the energy-saving, consumption reducing and environmental protecting purposes are realized.

Description

technical field [0001] The invention relates to a method and a device for reducing methanol content in a silver-based formaldehyde process, belonging to the technical field of chemical production. Background technique [0002] At present, there are mainly two processes for formaldehyde production: silver method and iron-molybdenum method. Compared with iron-molybdenum method, the silver method formaldehyde method has the advantages of less investment and low power consumption, and is widely used. However, the silver method formaldehyde process has the disadvantages of high methanol unit consumption, high methanol content in formaldehyde products, and low formaldehyde concentration; people have adopted a variety of methods to improve the silver method formaldehyde process, such as tail gas circulation and flue gas circulation. , dilute methanol liquid circulation method, dealcoholization tower etc. are set, but all do not fundamentally above-mentioned solve. The above-mentio...

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Problems solved by technology

①Using the tail gas or flue gas circulation process, the formaldehyde concentration increases, but the power consumption increases significantly, and the raw material methanol consumption does not decrease significantly; ②A dealcoholization tower is installed, and the temperature of the dealcoholization tower needs to be controlled at 80- 85°C, the heat recovery rate of the system decreases due to the high temperature, and at the same time, the high temperature leads to a large amount of formaldehyde desorption, and the recovered methanol gas contains more formaldehyde. Although the dealcoholization temperature is high, it does not reach the level of formaldehyde. The boiling point temperature of the solution, the dealcoholization effect is poor, because the evaporation temperature of the evaporator is low, most of this part of formaldehyde enters the residual liquid of the evaporator, and the residual liquid of the evaporator contains more formaldehyde and methanol, which is not effective for the residual liquid. The recovery of waste caused waste and polluted the environment at the same time. The consumption of raw material methanol has not been significantly reduced, and the removal effect of methanol has been limited; The lower section is used as a dealcoholization tower, and the dilute methanol recovered in the upper section enters the evaporator. The existing problems are similar to those of a separate dealcoholization tower. The temperature is higher but also does not reach the boiling point of the formaldehyde solution, and the dealcoholization effect is poor. At the same time, the formaldehyde content in dilute methanol is relatively high. Because the evaporation temperature of the evaporator is low, the raffinate of the evaporator also contains more methanol and Formaldehyde is recovered to the bottom of the dealcoholization tower, and the methanol in the raffinate returns to the formaldehyde solution. There is a problem of methanol back-mixing. The methanol content in the formaldehyde product has not decreased significantly, and the consumption of methanol as a raw material has not decreased significantly.

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