A new process for the treatment of waste sulfuric acid - research on coupled extraction method

Sulfuric acid is widely used in processes such as alkylation, sulfonation, nitration, and esterification. Most sulfuric acid does not form products in production, but is converted into waste sulfuric acid containing impurities. Dacheng waste sulfuric acid is difficult to handle, and has become a sustainable industry. major issues of development and environmental protection.

The current methods for treating waste sulfuric acid include pyrolysis, adsorption, oxidation, extraction and neutralization. Pyrolysis has been applied in industry to a certain extent, but it has disadvantages such as high cracking temperature and serious corrosion of equipment. The adsorption method uses activated carbon and resin to separate organic matter in waste acid, but there are generally disadvantages such as high energy consumption for adsorbent regeneration and high requirements for equipment materials. The oxidation method uses ozone, hydrogen peroxide and other oxidation brakes to treat the organic matter in the waste acid, which generally has the disadvantages of high treatment cost and low oxidation efficiency. The extraction method uses an extractant to separate the organic matter in the waste sulfuric acid, which has the disadvantages of low extraction rate and large consumption of extractant. The neutralization method uses alkaline substances such as lime and ammonia to react with waste sulfuric acid, which can effectively eliminate the interaction force between organic matter and sulfuric acid molecules, so that organic matter can be effectively released, and sulfuric acid can be converted into valuable downstream products at the same time. Some scholars use ammonia to neutralize alkylation waste acid to produce ammonium sulfate. There are also scholars who use air-lift flotation equipment to separate. Above-mentioned two kinds of methods can obtain valuable ammonium sulfate product. However, the introduction of solvent and water will increase the energy consumption of subsequent evaporation, and the price of ammonia water is high, which affects the economy of this method.

Therefore, there should be an economical and effective waste acid treatment process. However, a new method of coupling solvent extraction with urea and sulfuric acid is used to treat waste sulfuric acid in acetylene process. This method can obtain urea sulfuric acid product and extract and separate organic matter in waste acid at the same time.

So, which coupling extraction agent should be selected for the new process? In order to effectively separate the extraction agent and the mother liquor after the reaction, the extraction agent should not be miscible with the waste sulfuric acid. A comparative study was carried out on 11 common organic solvents, and the results are shown in Table 1. Cyclohexane, heptane, carbon tetrachloride, toluene, dichloromethane and chloroform form two immiscible phases with spent sulfuric acid, and the color of the extract phase of carbon tetrachloride, dichloromethane and chloroform is obviously darkened , indicating that it has a certain extraction effect, while the color of the extraction phase of cyclohexane, heptane, and toluene has no obvious change, indicating that it has basically no extraction effect. However, when urea was added to react, the above six extractants all showed a certain extraction ability, indicating that the reaction-coupled extraction process can more effectively separate and remove organic impurities than the simple solvent extraction process. Among them, cyclohexane, heptane, and toluene have weaker extraction effects, while carbon tetrachloride, dichloromethane, and trichloromethane have better extraction effects. Considering factors such as the toxicity and stability of the extractant, dichloromethane was selected as the extractant.

Experimental results show that:

(1) Organic impurities in waste sulfuric acid include ketones, esters, unsaturated hydrocarbons, sulfate esters, sulfonates and other substances. These organic substances can form strong intermolecular interactions with sulfuric acid molecules, making it difficult for waste sulfuric acid to separate its organic impurities through extraction and cannot be used directly.
(2) Urea reaction coupling extraction separation is an effective and economical waste sulfuric acid treatment method. While effectively removing organic impurities in waste sulfuric acid, urea sulfate products can be obtained. The optimal process conditions are: dichloromethane/waste sulfuric acid volume ratio 3:1; reaction time 1.5h, urea/HSO. molar ratio 1.5:1, H, SO. concentration 64.56%. At this time, the organic carbon removal rate reached 95.21%. The method has the advantages of simple process, high removal rate of organic carbon, and less impurity content of the obtained urea sulfate, and not only realizes the low energy consumption treatment of waste sulfuric acid, but also can be used for the production of compound fertilizer, and has a good market prospect.