Discussion on Methanol and Its Post-processing Technology

Since the middle and late 1990s, formaldehyde has entered a period of rapid growth. By 2004 it had accounted for 22% of the world's total formaldehyde production. At present, our formaldehyde has two processes of “silver method” with mature “iron-molybdenum method”, among which silver is the main method of formaldehyde production. The “iron-molybdenum method” has a large investment in production technology, but the unit consumption of methanol is low. About 425kg/t; The current "silver" production process methanol consumption has dropped to about 450kg / t, some advanced equipment has reached 440kg / t.

First, further reduce costs

At present, the improvement of the traditional silver process is mainly in the following aspects:

(1) Improve catalyst production methods to improve catalyst performance

(2) Rapidly passing the reaction gas and generated gas through the high temperature zone to reduce side reactions

(3) Reduce system resistance to reduce fan power consumption

(4) Improve the oxidizer waste pan structure to extend the life of the pan

(5) Form high concentrations of formaldehyde with inert gas such as equipment off-gas or flue gas in place of batching steam

(6) Recovery of produced water and unreacted methanol, reducing methanol consumption and increasing methanol concentration

A company uses the formaldehyde recycling process to produce new formaldehyde to reduce the unit consumption of methanol, electricity consumption, and cooling water consumption. It is basically the same as the traditional silver process. The differences are mainly two points: one is that the absorption tower is equipped with a dealcoholization section or a single dehydration tower, and the heat source is the reaction generated gas leaving the oxidizer waste heat boiler; the second is an evaporator. Internally evaporated is a mixture of methanol and dilute methanol and formaldehyde from the absorption tower.

Methanol is pumped by a methanol metering tank through a methanol pump with a variable frequency motor, and the filter is filtered into the evaporator tray. The evaporator level is controlled by the number of rotations of the methanol pump motor; the air is filtered through the air filter and the Roots blower boosts the pressure. Into the evaporator, the air volume is controlled by the number of rotations of the fan motor; the batching steam is sent from the steam purifier to the evaporator, the amount of steam is controlled by the regulating valve, and the recovered methanol-containing aqueous solution is metered into the evaporator by the rotameter. The evaporator is equipped with a residual liquid concentrator that separates and discharges impurities, formaldehyde, and water. The evaporator is a compound evaporator, and the methanol is circulated externally and exchanged with the formaldehyde solution. The entire process of generation, purification, overheating and filtration of the mixture gas is completed in the evaporator.

A mixture of methanol, air, water vapor, and a small amount of formaldehyde vapor enters the oxidizer. A dehydrogenation reaction occurs on the silver catalyst, and the reaction temperature is lower than other silver methods. The top cover of the oxidizer is equipped with a flame arrester to prevent the mixture from tempering. At the bottom of the catalyst layer, the central influent water is used to reduce the temperature of the generated gas and recover the reaction heat to generate water vapor.

The higher temperature reaction gas enters the dehydration dehydration section of the absorption column, and then enters each absorption section. The absorption water is added from the top of the absorption column. The hot methanol circulating liquid exchanges heat with methanol first and then heat exchange with the cooling water. Formaldehyde products are produced from the bottom of the dehydration dehydration section.

The exhaust gas enters the tail gas furnace for combustion and produces steam.

This method can obtain a formaldehyde solution with a low content of methanol in the product. We can add a de-alcoholization section. Production Process