JPS6316031A - Sulfur dioxide gas adsorbent - Google Patents

Abstract

PURPOSE:To absorb sulfur dioxide from gas containing sulfur dioxide, by contacting the gas containing sulfur dioxide with diglycolic acid and/or an aqueous diglycolate solution. CONSTITUTION:Gas containing sulfur dioxide is contacted with diglycolic acid and/or an aqueous diglycolate solution to absorb sulfur dioxide. Diglycolic acid and/or the aqueous diglycolate solution shows action as a buffer agent at the time of the absorption of sulfur dioxide. The absorbent containing sulfur dioxide is sent to a regeneration process and contacted with hydrogen sulfide gas to be regenerated. At this time, sulfur dioxide being adsorbed is reacted with hydrogen sulfide to generate element sulfur rapidly and irreversibly.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a novel sulfur dioxide gas absorbent that absorbs and removes sulfur dioxide from gas. Specifically, in order to separate and recover elemental sulfur by the liquid-phase Claus method by contacting a gas containing sulfur dioxide with an aqueous solution of diglycolic acid and/or a diglycolic acid salt to absorb sulfur dioxide from the gas containing sulfur dioxide. sulfur dioxide gas absorbent.

(Prior art) Desulfurization methods for sulfur dioxide-containing gas that have been proposed to date include a wet method in which sulfur dioxide is absorbed by a solution absorbent;
It is broadly divided into dry methods that remove sulfur dioxide using powdered or granular absorbents, adsorbents, and catalysts. Since the dry method has a lower sulfur oxide removal rate than the wet method and requires a large-scale equipment, almost all desulfurization methods currently in practical use are classified as wet methods. Furthermore, most of the methods classified as wet methods produce gypsum as a by-product. However, as the commercial value of gypsum has decreased considerably in recent years, it is becoming increasingly economically disadvantageous to use processes that produce such gypsum. Therefore, from the viewpoint of by-product sulfur compounds, a process that produces by-product elemental sulfur, which has higher industrial utility value, is considered to be more desirable as a desulfurization method in the future.

A well-known method for recovering sulfur components in gas as elemental sulfur is the citric acid method developed by the US Bureau of Mines.

This method uses an aqueous solution of citric acid with a buffering capacity in the appropriate p)-1 range as an absorbent for sulfur dioxide, and the absorbent that has absorbed sulfur dioxide is blown with hydrogen sulfide to absorb It is regenerated by precipitating the sulfur component in the agent as elemental sulfur.

In order to reduce sulfur dioxide with hydrogen sulfide to produce elemental sulfur, it is necessary to carry out the reaction in the regeneration step at a pH of 7 or lower, preferably at a pH of 5 or lower, due to the redox potential of both.

Therefore, it is desirable that the absorbent used in this type of process be cycled through the absorption and regeneration steps at a pH of 5 or less.

For this purpose, it is necessary to add a third substance having pH buffering ability in a desired pH range. Until now, in addition to citric acid,
Methods using organic acids such as tartaric acid and malic acid as absorbents have been devised, but the chemicals used in either method are expensive and are not practical. A method using phosphate has also been proposed, but this has the disadvantage that the absorption rate of sulfur dioxide is low and the equipment becomes large.

Examples of patents related to such technology include the following patent documents.

U.S. Pat. No. 2,729,543 describes the use of aqueous solutions containing organic acids such as citric acid, lactic acid, maleic acid, tartaric acid, oxalic acid, glutaric acid, etc. as sulfur dioxide absorbents. There is.

JP-A No. 48-101359 describes meta-alkali salts of inorganic acids such as tm acid, phosphoric acid, carbonic acid, silicic acid, and vanadic acid, and organic carboxylic acids such as acetic acid, citric acid, benzoic acid, and salicylic acid. The use of an aqueous solution containing at least one mixture of an alkali salt of and the acid as a desulfurization agent is described.

In the specification of JP-A-50-392869, alkalis of non-volatile acids such as lactic acid, glycolic acid, citric acid, orthophosphoric acid, maleic acid, succinic acid, selenic acid, tartaric acid, glutaric acid, and diglyochic acid are described. Aqueous sulfur dioxide absorbents composed of metal salts are described.

JP-A No. 51-146370 specifies that oxalic acid,
It is described that an aqueous solution of at least one organic polybasic acid selected from malonic acid, glutaric acid, adipic acid, maleic acid, fumaric acid, citraconic acid, and phthalic acid is used as a desulfurizing agent.

In the specification of JP-A-53-106382, oxalic acid,
Malic acid, tartaric acid, maleic acid, succinic acid, citric acid,
A desulfurizing agent consisting of an aqueous solution of salts such as lactic acid, glycolic acid, selenic acid, and glutaric acid is described.

JP-A-59-207808 describes the use of organic acid aqueous absorbents containing sulfur dioxide in removing hydrogen sulfide from gas streams.

(Problem to be solved by the invention) Although the process of recovering sulfur dioxide from gas as elemental sulfur is itself attractive, this type of process has so far not reached the level of practical application. Almost nothing exists. There are several reasons for this, but the biggest one is operating costs.

When recovering the precipitated elemental sulfur, heating the absorption liquid containing elemental sulfur causes thermal decomposition of the organic acid, which requires replenishment, but the cost of the acid is high; Overall, operating costs are very high, offsetting other benefits.

The present invention is effective and economical by using diglycolic acid and/or diglycolate, which has the same level of sulfur dioxide absorption capacity as citric acid but is significantly cheaper than citric acid, as an absorbent. The present invention aims to provide a method for absorbing sulfur dioxide.

(Means for solving the problem) The present invention relates to a sulfur dioxide gas absorbent for absorbing sulfur dioxide, which is characterized by containing diglycolic acid and/or a diglycolate salt.

The sulfur dioxide gas absorbent of the present invention is implemented as follows.

In the gas absorption tower, sulfur dioxide can be separated and recovered by contacting the gas containing sulfur dioxide with an aqueous solution of diglycolic acid and/or diglycol M salt to absorb sulfur dioxide from the gas containing sulfur dioxide. .

The diglycolic acid and/or diglycolate aqueous solution of the present invention has a diglycolic acid and/or diglycolate concentration of 0.1 to 3.0 mol/11, preferably 0.2
~1.5 mol/j! It is prepared within the range of.

The diglycolic acid and/or diglycolic acid salt aqueous solution of the present invention has a gas absorption temperature in the range of 10 to 160°C, preferably 20 to 100°C.

The diglycolic acid and/or diglycolic acid salt aqueous solution of the present invention has a pH of 6.5 to 2.5, preferably a pH of 5 to 2.5.
The range is 3.

For the adjustment of p)-1, alkali metal hydroxides such as sodium hydroxide and potassium hydroxide and IAM can be used.

The present inventors have repeatedly investigated additives that are inexpensive and have performance equivalent to or better than citric acid as an absorbent for sulfur dioxide, and have developed diglycolic acid and/or diglycol Mf! We have found realistic performance and price that are profitable.

(For writing) The liquid phase Claus reaction to which the present invention relates is well known.

In the absorption step, the sulfur dioxide-containing gas is brought into contact with a liquid absorbent, and the sulfur dioxide is absorbed by the absorbent.

At this time, when sulfur dioxide dissolves in the absorbent, sulfurous acid is generated as shown in formula (1), and a part of it is ionized and the formula (
As shown in 2), bisulfite ions and hydrogen ions are generated.

As a result, the pH of the absorbent decreases, so there is a natural limit to the degree of absorption of sulfur dioxide into the absorbent. However, significantly higher sulfur dioxide absorption can be obtained by incorporating WvBl into the absorbent to prevent the pH from decreasing due to sulfur dioxide absorption. diglycolic acid and/or
Alternatively, diglycolate acts as a buffer during absorption of sulfur dioxide. The absorbent containing sulfur dioxide is sent to a regeneration step and is regenerated by being brought into contact with hydrogen sulfide gas. The sulfur dioxide absorbed at this time reacts with hydrogen sulfide as shown in equation (3) to quickly and irreversibly produce elemental sulfur.

2H2S + SO2 → 3S + 2H20 (3) The reaction that is thought to actually occur is much more complicated than the formula (3), but in this reaction, under the most favorable conditions, diglycolic acid and/or diglycolate are , is rarely consumed.

Patents describing such processes include: For example, National Patent No. 3,911.093, US Patent No. 3.98
3,225, British Patent No. 1,450.845, US Patent No. 2,729.453, etc. According to them, it is disclosed that the reaction between sulfur dioxide and hydrogen sulfide is carried out under approximately the following conditions.

Temperature 20°C to 160°C, preferably 20°C to 95°C pH 2.5 to 6.5, preferably 2.5 to 5! lVB
Agent Concentration [2,5 Morph 1 or Less (Example) The present invention will be explained in more detail with reference to Examples and Comparative Examples below.

Example 1 0.3 mol/j! An aqueous solution of diglycolic acid was adjusted to pH 4.5 with sodium hydroxide, and the absorption rate of sulfur dioxide was measured when this was used as an absorbent.

Diameter 10c! R. Using an absorption tower with a length of 2.5 m, a gas containing 0.3% by volume sulfur dioxide diluted with nitrogen was added to it.
Table 1 shows the results of a test in which absorption and regeneration were performed continuously at a pH of 4 to 4.5 with contact at 45° C. at a rate of 0.5 drops per minute.

Example 2 A 0.3 mol/1 aqueous solution of diglycolic acid was adjusted to pH 4.5 with sodium hydroxide, and the absorption rate of sulfur dioxide was measured when this was used as an absorbent.

Using an absorption tower with a diameter of 10cm and a length of 2.5m, a gas containing 0.5% by volume sulfur dioxide diluted with nitrogen was added to it.
Contact at 45°C, 0.5 Tlt/min, pH 4-4
．． Table 1 shows the results of a test in which absorption and regeneration were performed continuously in 5.
Shown below.

Example 3 A 0.3 mol/i aqueous solution of sodium diglycolate was adjusted to pH 4.5 with VA acid, and the absorption rate of sulfur dioxide when used as an absorbent was measured.

An absorption tower with a diameter of 10 ctx and a length of 2.5 m was used, and a gas containing 0.3% by volume sulfur dioxide diluted with nitrogen was brought into contact with the tower at 45°C and 0.5 Td per minute until the pH was 4 to 4.
Table 1 shows the results of a test in which absorption and regeneration were performed continuously in 5.

Example 4 A 0.3 mol/1 aqueous solution of sodium diglycolate was adjusted to pH 4.5 with sulfuric acid, and the absorption rate of sulfur dioxide when used as an absorbent was measured.

Using an absorption tower with a diameter of 10 cIR and a length of 2.5 m, a gas containing 0.5% by volume sulfur dioxide diluted with nitrogen was added to it.
Contact at 45°C, 0.571 t/min, pH 4-4.5
Table 1 shows the results of a test in which absorption and regeneration were performed continuously.

Comparison Example 1 When an aqueous solution of 0.3 mol/l diglycolic acid and 0.20 mol/1 citric acid with the same carboxyl group concentration was adjusted to pH 4.5 with sodium hydroxide and used as an absorbent. The absorption rate of sulfur dioxide was measured.

Using an absorption tower with a diameter of 10 cI and a length of 2.5 m, a gas containing 0.5% by volume sulfur dioxide diluted with nitrogen was added to it.
Table 1 shows the results of a test in which absorption and regeneration were performed continuously at a pH of 4 to 4.5 with contact at 45° C. at a rate of 0.5 degrees per minute.

Comparison Example 2 0.3 mol/1 diglycolic acid and 0.6 mol/j with the same carboxyl group concentration! An aqueous solution of glycolic acid was adjusted to pH 4.5 with sodium hydroxide, and the absorption rate of sulfur dioxide was measured when the solution was used as an absorbent.

An absorption tower with a diameter of +0 cm and a length of 2.5 m was used, and a gas containing 0.5% by volume sulfur dioxide diluted with nitrogen was brought into contact with the tower at 45°C at a rate of 0.5 m/min to reach a pH of 4 to 4. 5
Table 1 shows the results of tests in which absorption and regeneration were performed continuously.

(Effect) By using the sulfur dioxide gas absorbent containing diglycolic acid and/or diglycolate of the present invention,
It is possible to increase the amount of 5A yellow gas absorbed from the gas containing sulfur dioxide by bringing the gas containing sulfur dioxide into contact with an aqueous solution of diglycolic acid and/or diglycolate.

Claims (1)

[Claims] (1) A sulfur dioxide gas absorbent for absorbing sulfur dioxide, characterized by containing diglycolic acid and/or diglycolic acid salt.