Silver-method formaldehyde production process

Abstract

The invention discloses a silver-method formaldehyde production process, and belongs to the technical field of formaldehyde production, raw material feeding and temperature in the process are strictly controlled, superheated water vapor is supplemented at the stage of an oxidizer, and under the condition that the reaction process is not affected, the temperature of generated aldehyde-containing mixed gas is reduced, and local peroxidation is avoided. And part of formaldehyde is absorbed in the cooling process of the water vapor and returns to the absorption tower as a circulating liquid for further absorption, so that the aldehyde-containing mixed gas can be circularly absorbed step by step. According to the method, superheated water vapor is supplemented, the methanol conversion rate is increased, the yield of formaldehyde is increased, the consumption of methanol is reduced, the process is simple, and cost reduction of silver-method formaldehyde production can be achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of formaldehyde production, and specifically relates to a silver-based formaldehyde production process. Background Art

[0002] Formaldehyde is one of the most important derivatives of methanol and an important basic organic chemical raw material. At present, the main production process in my country's formaldehyde production industry is the "silver method" process. The development of this process has mainly experienced the changes from pumice silver catalyst to electrolytic silver catalyst, the tail gas boiler from scratch, and the evaporator from steam heating to hot water or hot formaldehyde heating, forming the classic silver method formaldehyde equipment and process. The production raw material of the "silver method" formaldehyde process is methanol, which reacts with oxygen under certain temperature, pressure and catalyst to generate formaldehyde. The generated formaldehyde gas is absorbed by water to make a 37% formaldehyde solution. During the reaction, the output of formaldehyde production depends on the conversion rate of the reaction and the completeness of the absorption.

[0003] The methanol consumption is relatively high in the production process, and the main reasons for the high methanol consumption are: the methanol conversion rate is relatively low, and there are a lot of alcohols in the product; the methanol side reaction is difficult to control, and there are a lot of carbon monoxide and carbon dioxide in the tail gas; when absorbing the tail gas at the top of the tower, the efficiency of formaldehyde absorption is very low, and a large amount of formaldehyde will escape; when screening methanol raw materials, there are unqualified phenomena; formaldehyde decomposition. The current main research direction is to improve the methanol conversion rate by improving the arrangement of the catalyst in the oxidizer and avoiding catalyst deactivation, thereby reducing the methanol consumption, but the reduction of methanol consumption needs to be considered comprehensively, and the optimization of the production process is the key factor. Summary of the invention

[0004] The object of the present invention is to provide a silver-method formaldehyde production process, which reduces the production cost by reducing the methanol consumption.

[0005] The purpose of the present invention can be achieved through the following technical solutions:

[0006] The present invention provides a silver-based formaldehyde production process, comprising the following steps:

[0007] S1, methanol is filtered and then sent to the preheater, and then sent to the bottom of the evaporator. The filtered air is sent to the bottom of the evaporator to form a binary mixed gas with the evaporated methanol;

[0008] S2, water vapor enters the upper part of the evaporator after filtering, and is mixed with the binary mixed gas and transported to the superheater for heating and mixing to form a ternary mixed gas;

[0009] S3, the ternary mixed gas is transported to the upper part of the oxidizer through the flame arrester, and the formaldehyde-containing mixed gas is obtained by reaction. Superheated water steam is added to the middle part of the oxidizer to enter the formaldehyde-containing mixed gas, and then it is quenched and output through the primary heat exchanger and the secondary heat exchanger at the bottom of the oxidizer in sequence. The primary heat exchanger realizes primary cooling, and the secondary heat exchanger realizes secondary cooling;

[0010] S4, the condensed liquid after rapid cooling enters the B absorption tower as a circulating liquid, the formaldehyde-containing mixed gas after rapid cooling is transported to the A absorption tower, the formaldehyde solution at the bottom after absorption is cooled by the A cooler to obtain a finished formaldehyde solution, the unabsorbed gas at the top of the A absorption tower enters the B absorption tower for absorption, and the formaldehyde solution at the bottom of the B absorption tower is circulated back to the A absorption tower;

[0011] The unabsorbed gas at the top of S5 and B absorption towers is transported to the tail gas boiler and preheater as tail gas.

[0012] Furthermore, the filtration adopts two-stage filtration of activated carbon and ultrafiltration membrane. Impurities in methanol will affect the activity of the catalyst. Providing two-stage filtration of activated carbon and ultrafiltration membrane can remove metal ions and other ions in methanol that may cause catalyst poisoning.

[0013] Furthermore, the heat source of the preheater is the tail gas output from the absorption tower, and the temperature of the preheated methanol is 40-50° C. Methanol preheating can reduce the energy consumption of the evaporator.

[0014] Furthermore, the heat source of the evaporator is the water vapor output from the secondary heat exchanger at the bottom of the oxidizer, the oxygen-to-alcohol ratio in the binary mixed gas is 0.35-0.4, and the evaporation temperature of the evaporator is 65-70°C.

[0015] Furthermore, the water vapor in S2 is water vapor heated by tail gas in a tail gas boiler, and the water-to-alcohol ratio in the ternary mixed gas is 1.0-1.2.

[0016] Furthermore, the heating temperature of the superheater is 110-120°C, and the heat source of the superheater is the water vapor output by the primary heat exchanger at the bottom of the oxidizer.

[0017] Further, the reaction temperature of the oxidizer is 640-660°C;

[0018] The temperature of the supplementary superheated water steam in S3 is 110-120° C., and the flow ratio of the supplementary superheated water steam to the ternary mixture is 1:15-20.

[0019] Furthermore, the catalyst in the oxidizer is an electrolytic silver catalyst, and the silver content of the electrolytic silver catalyst is above 99.99%.

[0020] Furthermore, the temperature of the formaldehyde-containing mixed gas after rapid cooling is 90-100°C.

[0021] Furthermore, the mass concentration of the finished formaldehyde solution is 37%.

[0022] Beneficial effects of the present invention:

[0023] (1) The present invention supplements superheated steam in the middle of the oxidizer, and the formaldehyde gas and unreacted methanol gas obtained by the reaction below the catalyst are taken away by the flow of water vapor, thereby promoting the reaction. The temperature of the formaldehyde-containing mixed gas after the catalytic reaction can be reduced while reducing the presence of excess oxygen, thereby preventing unreacted methanol or obtained formaldehyde from reacting with oxygen to generate carbon monoxide and carbon dioxide, reducing side reactions, and improving the methanol conversion rate, thereby reducing methanol consumption.

[0024] (2) The superheated water vapor and the aldehyde-containing mixed gas added in the present invention are mixed and cooled through a heat exchanger at the bottom of the oxidizer, and the water vapor condenses to form a low-concentration formaldehyde solution that absorbs a small amount of formaldehyde. The solution is used as the circulating liquid of the absorption tower B, and a three-stage cycle of water vapor absorption, absorption in the absorption tower B, and absorption in the absorption tower A can be achieved, thereby improving the yield of formaldehyde. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The present invention will be further described below in conjunction with the accompanying drawings.

[0026] Figure 1 The present invention is a silver-method formaldehyde production process flow chart. DETAILED DESCRIPTION

[0027] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0028] Example 1

[0029] S1, methanol is filtered through activated carbon and ultrafiltration membrane in turn, and then enters the preheater. The heat source of the preheater is the tail gas output from the absorption tower, and the temperature of the preheated methanol is 40-50°C. Then it is transported to the bottom of the evaporator, and the filtered air is transported to the bottom of the evaporator to form a binary mixed gas with the evaporated methanol. The oxygen-to-alcohol ratio in the binary mixed gas is 0.35. The heat source of the evaporator is the water vapor output from the secondary heat exchanger at the bottom of the oxidizer, and the evaporation temperature of the evaporator is 65-70°C;

[0030] S2. The water vapor heated by the tail gas in the tail gas boiler is filtered and enters the upper part of the evaporator, mixed with the binary mixed gas and transported to the superheater for heating and mixing to form a ternary mixed gas. The heating temperature of the superheater is 110-120°C, and the heat source of the superheater is the water vapor output from the first-level heat exchanger at the bottom of the oxidizer;

[0031] S3, the ternary mixed gas is transported to the upper part of the oxidizer through the flame arrester. The catalyst in the oxidizer is an electrolytic silver catalyst with a silver content of more than 99.99%. The reaction obtains a mixed gas containing formaldehyde. The reaction temperature of the oxidizer is 640-660°C. Superheated water steam with a temperature of 110-120°C is added to the middle of the oxidizer to enter the mixed gas containing formaldehyde. The flow ratio of the supplementary superheated water steam and the ternary mixed gas is 1:15, and then it is quenched and output through the primary heat exchanger and the secondary heat exchanger at the bottom of the oxidizer in turn;

[0032] S4, the condensed liquid after rapid cooling enters the B absorption tower as a circulating liquid, the formaldehyde-containing mixed gas at 90-100°C after rapid cooling is transported to the A absorption tower, the formaldehyde solution at the bottom after absorption is cooled by the A cooler to obtain a finished formaldehyde solution with a concentration of 37%, the unabsorbed gas at the top of the A absorption tower enters the B absorption tower for absorption, and the formaldehyde solution at the bottom of the B absorption tower is circulated back to the A absorption tower;

[0033] The unabsorbed gas at the top of S5 and B absorption towers is transported to the tail gas boiler and preheater as tail gas.

[0034] Example 2

[0035] The difference from Example 1 is that the flow ratio of the supplementary superheated water steam and the ternary mixed gas is adjusted to 1:18, and the other steps are the same as Example 1.

[0036] Example 3

[0037] The difference from Example 1 is that the flow ratio of the supplementary superheated water steam and the ternary mixed gas is adjusted to 1:20, and the other steps are the same as Example 1.

[0038] Example 4

[0039] The difference from Example 1 is that the oxygen-alcohol ratio in the binary mixed gas is adjusted to 0.38, and the other steps are the same as Example 1.

[0040] Example 5

[0041] The difference from Example 1 is that the oxygen-alcohol ratio in the binary mixed gas is adjusted to 0.4, and the other steps are the same as Example 1.

[0042] Comparative Example 1

[0043] The difference from Example 1 is that superheated water steam is not added in the middle of the oxidizer, and the other steps are the same as Example 1.

[0044] The components of the materials in the formaldehyde production process of Examples 1 to 5 and Comparative Example 1 were detected, and the methanol consumption, formaldehyde yield and methanol conversion rate in the production process were calculated. The results are shown in Table 1.

[0045] Table 1

[0046] Example Methanol consumption kg / t Formaldehyde yield% Methanol conversion rate % Example 1 435 91 92 Example 2 421 94 95 Example 3 426 93 94 Example 4 428 92 93 Example 5 432 91 92 Comparative Example 1 465 85 86

[0047] As can be seen from Table 1, when adding superheated water vapor in the oxidizer, it is necessary to control the flow ratio of superheated water vapor and ternary mixture. When too much water vapor is added, it will affect the reaction temperature of the catalyst, resulting in a lower conversion rate and increased consumption. When too little water vapor is added, it cannot significantly reduce the temperature of the aldehyde-containing mixer and has a poor dilution effect on the oxygen concentration, and cannot effectively inhibit side reactions, and the conversion rate of methanol will also decrease. In addition, increasing the oxygen-to-alcohol ratio can promote the reaction to generate formaldehyde, but excessive oxygen will promote side reactions and affect the formaldehyde yield.

[0048] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device.

[0049] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A silver-based formaldehyde production process, characterized in that: The following steps are involved: S1, methanol is filtered and then sent to the preheater, and then sent to the bottom of the evaporator. The filtered air is sent to the bottom of the evaporator to form a binary mixed gas with the evaporated methanol; S2, water vapor enters the upper part of the evaporator after filtering, and is mixed with the binary mixed gas and transported to the superheater for heating and mixing to form a ternary mixed gas; S3, the ternary mixed gas is transported to the upper part of the oxidizer through the flame arrester, and the formaldehyde-containing mixed gas is obtained by reaction. Superheated water steam is added to the middle part of the oxidizer to enter the formaldehyde-containing mixed gas, and then it is rapidly cooled and output through the primary heat exchanger and the secondary heat exchanger at the bottom of the oxidizer in sequence; S4, the condensed liquid after rapid cooling enters the B absorption tower as a circulating liquid, the formaldehyde-containing mixed gas after rapid cooling is transported to the A absorption tower, the formaldehyde solution at the bottom after absorption is cooled by the A cooler to obtain a finished formaldehyde solution, the unabsorbed gas at the top of the A absorption tower enters the B absorption tower for absorption, and the formaldehyde solution at the bottom of the B absorption tower is circulated back to the A absorption tower; The unabsorbed gas at the top of S5 and B absorption towers is transported to the tail gas boiler and preheater as tail gas.

2. A silver-based formaldehyde production process according to claim 1, characterized in that: The methanol filtration adopts two-stage filtration of activated carbon and ultrafiltration membrane.

3. A silver-based formaldehyde production process according to claim 1, characterized in that: The heat source of the preheater is the tail gas output from the absorption tower, and the temperature of the preheated methanol is 40-50°C.

4. A silver-based formaldehyde production process according to claim 1, characterized in that: The heat source of the evaporator is the water vapor output from the secondary heat exchanger at the bottom of the oxidizer, the oxygen-to-alcohol ratio in the binary mixed gas is 0.35-0.4, and the evaporation temperature of the evaporator is 65-70°C.

5. A silver-based formaldehyde production process according to claim 1, characterized in that: The water vapor in S2 is the water vapor heated by the tail gas in the tail gas boiler, and the water-to-alcohol ratio in the ternary mixed gas is 1.0-1.

2.

6. A silver-based formaldehyde production process according to claim 1, characterized in that: The heating temperature of the superheater is 110-120°C, and the heat source of the superheater is the water vapor output by the primary heat exchanger at the bottom of the oxidizer.

7. A silver-based formaldehyde production process according to claim 1, characterized in that: The reaction temperature of the oxidizer is 640-660°C; The temperature of the supplementary superheated water steam in S3 is 110-120° C., and the flow ratio of the supplementary superheated water steam to the ternary mixed gas is 1:15-20.

8. A silver-based formaldehyde production process according to claim 1, characterized in that: The catalyst in the oxidizer is an electrolytic silver catalyst, and the silver content of the electrolytic silver catalyst is above 99.99%.

9. A silver-based formaldehyde production process according to claim 1, characterized in that: The temperature of the formaldehyde-containing mixed gas after rapid cooling is 90-100°C.

10. A silver-based formaldehyde production process according to claim 1, characterized in that: The mass concentration of the finished formaldehyde solution is 37%.

Images