Study On Extraction Technology Of Sodium Carbonate And Sodium Sulfate From Waste Alkali Of Cyclohexanone

In recent years,the production of cyclohexanone grows rapidly in China,in 2015 the yield of cyclohexanone reached 2.841 million tons.Every year,Hubei San-ning Company creates about 20 thousand tons of by-product solid cyclohexanone waste alkali,which contain Na₂CO₃ 70% to 75%,Na₂SO₄ 22 % to 25% and other impurities 2% to 3%.However,the current price of cyclohexanone waste alkali is low and the market is very poor,therefore,it is urgent to carry out the research on extracting sodium carbonate and sodium sulfate from the waste alkali.For the problem that the recrystallization method and chemical precipitation were unable to separate the sodium carbonate and sodium sulfate effectively,dissolving the cyclohexanone waste alkali and react with the byproduct CO₂ of the synthetic ammonia process in the factory innovatively,in this way,the Na₂CO₃ in the waste alkali lye were converted to the lower solubility Na HCO3 and crystallized out sodium bicarbonate crystals.Separating and calcining the sodium bicarbonate crystals,the sodium carbonate was obtained.Then using the filtrate to dissolve the cyclohexanone waste alkali again and react with CO₂ and crystallize out sodium bicarbonate crystal,the sodium carbonate were obtained after calcining the sodium bicarbonate crystals.The filtrate after multiple cycles were acidized with sulfuric acid and then extracting sodium sulfate by evaporation crystallization.In this paper,the technology of extracting sodium carbonate and sodium sulfate from cyclohexanone waste alkali was studied and the main conclusions are as follows:?1?During the carbonation reaction process of dissolving cyclohexanone waste alkali with pure water,when the initial concentration of alkali was 125?140 g/L,the concentration of sodium carbonate decreased linearly with time,the reaction rate was the fastest,and the reaction rate was independent of the initial concentration of alkali.In the carbonation reaction process of dissolving cyclohexanone waste alkali with the filtrate,the reaction rate was slower than the process that dissolving cyclohexanone waste alkali with pure water.However,because of the higher concentration of Na HCO3 in the filtrate,the time required to reach saturation and crystallize out Na HCO3 crystals was shorter in this process.?2?The most suitable conditions of dissolving waste alkali with pure water and filtrate respectively to extraction Na₂CO₃ are basically the same: the initial alkali concentration was 125 ? 140g/L,the reaction time was 60 min,the reaction temperature was 45?,the CO₂ flow rate was 0.35L/min,the crystallization time was 8h,the crystallization temperature was 10? and the washing amount of saturated sodium bicarbonate solution was 10 m L.?3?Dissolving waste alkali with crystallization filtrate to extract sodium carbonate,the recoveries of Na₂CO₃ were up to 85%.Filtrate was used cyclically to dissolve alkali to extract Na₂CO₃,the recovery rate can be stable more than 80%,and the purity could meet the requirements of industrial grade of Class ?.When the content of Na₂SO₄ were accumulated to 13%,the purity of Na₂CO₃ product will not reach the industrial standard.?4?The cycling filtrate was acidified with sulfuric acid to convert Na HCO3 and Na₂CO₃ to Na₂SO₄.Sodium dodecylbenzenesulfonate was added to improve the quality of Na₂SO₄ crystal and the suitable addition was 10 ? 20 ppm.When the evaporation rate was 70?90m L/?dm2 · h?,the average grain size can reach 0.5mm and the purity of Na₂SO₄ product meet the industrial standard.