JPS6015376B2 - Exhaust gas desulfurization method - Google Patents

Description

[Detailed description of the invention] The present invention relates to a method for desulfurizing exhaust gas.

Desulfurization of exhaust gas is generally carried out by reacting hydrogen sulfide with sulfur dioxide gas in the exhaust gas at a temperature of 115 to 15 psi in a polyalkylene glycol derivative solvent in the presence of a catalyst, and recovering the generated sulfur.

As catalysts, alkali and alkali metal salts of carboxylic acids are used.

This catalyst is a salt consisting of an acid and a base, but acids have no catalytic effect and instead inhibit the separation of sulfur, so it is necessary to maintain a basic state at all times, and it acts as an acid. It is necessary to avoid contamination with compounds. Therefore, the solvent used here cannot be a compound that reacts with sulfur dioxide gas or hydrogen sulfide to produce an acid. For this purpose, chemically relatively stable and inexpensive polyalkylene glycol derivatives are used. During the desulfurization reaction, the polyalkylene glycol derivative that is the solvent comes into contact with sulfur dioxide gas, hydrogen sulfide, nitrogen gas that is the carrier of hydrogen sulfide, etc., but it is extremely difficult to prevent air from being mixed in at all during the reaction. At present, it is unavoidable that air is mixed in at a rate of about 1.5%. Therefore, the desulfurization reaction gas contains about 0.2% oxygen, and the polyalkylene glycol derivative is gradually oxidized and decomposed by the existing oxygen to produce a low-molecular carbonyl compound. The final product of this oxidative decomposition is a low-molecular-weight carboxylic acid such as acetic acid, which shifts the acid-alkali balance to the acid side and impairs the separation of sulfur. This oxidative decomposition continues as long as oxygen is present, and becomes a major problem especially at the start of operation when air is likely to be mixed in. Adding an antioxidant may be considered to increase the oxidation stability of polyalkylene glycol derivatives, but since the exhaust gas desulfurization operation is a chemical reaction using a catalyst, it may inhibit the activity of the catalyst or sulfur The selection of antioxidants is not easy, as it is not possible to use antioxidants that cause chemical reactions with the solvent or impair the separation of the solvent and sulfur. As a result of intensive studies on this problem, the present inventors have discovered that only a certain antioxidant can solve all of the above problems and is particularly effective, leading to the present invention. The present invention is a method for desulfurizing exhaust gas, which is characterized in that a polyalkylene IJ coal derivative to which a phenolic antioxidant is added is used as a solvent when desulfurizing exhaust gas.

The phenolic antioxidants referred to in the present invention include butylated hydroxyanisole, dibutylated hydroxytoluene, tocopherol, 2,2-methylenebis(61-Prt-butyl-4-methylphenol), 4,4'-butylidenebis(61te-butyl) -3-methylphenol), 4
- 4'-thiopis (6 batches of rt-butyl-3-methylphenol), hydroquinone, tecol, alkylcatechol, coumarin derivatives, propyl gallate, etc.

The amount of antioxidant added is preferably in the range of 50 to 2000 antioxidants based on the weight of the polyalkylene glycol derivative. Although the antioxidant used in the present invention is sufficiently effective when used alone, it is also possible to obtain a synergistic effect by blending several types of antioxidants or using them in combination with an oxyacid.

However, when using a compound having a carboxyl group or an ester bond, it is preferable that the amount of these compounds added is 20 or less. Examples of polyalkylene glycol derivatives used in the present invention include polyethylene glycol, polypropylene glycol, and polyoxyethylene-polyoxypropylene copolymers, and those having an average molecular weight of 200 to 60°F can be used.

Catalysts include potassium adipate (sodium), potassium benzoate (sodium), and potassium salicylate (sodium).
sodium) etc. can be used. In carrying out the present invention, for example, there is a method in which exhaust gas containing sulfur dioxide gas and hydrogen sulfide gas are blown into a solvent containing a catalyst and an antioxidant. An excellent effect of the present invention is that by adding a phenolic antioxidant to a polyalkylene glycol derivative solvent, separation and recovery of the solvent and sulfur can be reliably performed from the beginning of operation, and furthermore, the separation and recovery of the solvent and sulfur can be carried out from the beginning of operation. This means that the solvent can be recycled and used many times, extending its lifespan.

The desulfurization method of the present invention is particularly suitable for treating large amounts of exhaust gas from coke ovens, oil refineries, power plant boilers, and the like. The present invention will be explained below with reference to Examples. Example 1 Samples of 100 polyalkylene glycol derivatives shown in Table 1 were dissolved by adding 0.7 g of potassium adipate as a catalyst and 50 g of an antioxidant at a temperature of 120°C.
Then, air was blown in at a flow rate of 2 som/min for 24 hours to oxidize it, and the degree of oxidation was expressed in terms of alcohol value.

To each of the oxidized polyalkylene glycol derivatives, 12 hours of sulfur, 2.5 hours of water, and 0.5 hours of sodium sulfate were added, stirred at 120°C for 15 minutes in a homomixer, and then heated to 120 qo for 3 times. The specimens were placed in a heating tank to observe the state of sulfur separation, and their superiority or inferiority was determined according to the following criteria. ○・
・・・・・・The polyalkylene glycol derivative layer is transparent.

×・・・・・・Sulfur is suspended in the polyalkylene glycol derivative layer and it is opaque.

The above test results are shown in Table 1.

In the table, PEG is polyethylene glycol, PPG is polypropylene glycol, the numerical value is the average molecular weight, and the mark ◎ is the phenolic antioxidant (product of the present invention).

Table 1 *Polyoxyethylene '41 Polyoxypropylene ■Block polymer.

As is clear from Table 1, all the products using the antioxidant of the present invention have good separation of solvent and sulfur, but the products using Q-phenylnaphthylamine and dilauryl thiodipropionate, which are not phenolic, Poor separation.

Example 2 In an autoclave equipped with two blowing tubes, 500% polyethylene glycol (average molecular weight 400) was probed.
After 4 hours of potassium benzoate and 0.3 hours of dibutylhydroxytoluene were added and dissolved by heating to 130° C., 64 hours of sulfur dioxide gas and 68 hours of hydrogen sulfide were blown into the mixture through a blowing tube.

When the temperature was kept at 130°C for 3 hours, the pressure inside the container became almost zero.

After blowing in nitrogen gas to remove unreacted gas, the reactor was allowed to stand still at the same temperature for 1 hour, and sulfur was separated into the lower layer. When only the transparent upper layer was collected by decantation, 480
It was evening. Perform the same operation as above using this toplight solution.
q batches were repeated, but still 4009 supernatants were obtained. When this toplight solution was cooled, sulfur of 12 sulfur was precipitated as crystals. After the precipitated sulfur was filtered and compared with polyethylene glycol before use, only a slight yellow coloration was observed, and no difference was observed in viscosity, pH, etc. Table 2 shows the analytical values before and after use. Table 2 When the same operation was carried out using polyethylene glycol without adding dibutylhydroxytoluene, the first yield was 400 kg, but the recovery rate decreased with each repetition, and it was impossible to recover the 6th L round. Met.

Claims (1)

[Claims] 1. Sulfur dioxide gas in exhaust gas is reacted with hydrogen sulfide in a polyalkylene glycol derivative solvent in the presence of an alkali metal salt or alkaline earth metal salt of a carboxylic acid as a catalyst, and the generated sulfur is recovered. A non-gas desulfurization method characterized in that the method uses a polyalkylene glycol derivative to which a phenolic antioxidant is added as a solvent. 2. The method for desulfurizing exhaust gas according to claim 1, wherein the phenolic antioxidant is dibutylhydroxytoluene.