Study On A New Process For Preparing Magnesium Sulfate From Alkylation Spent Sulfuric Acid

Alkylation process units with concentrated sulfuric acid as catalyst in alkylated oil production technology in our country account for more than 85%,about 2?3 million tons of alkylation spent sulfuric acid is produced each year.Alkylation spent sulfuric acid contains more than 200 kinds of organics which are difficult to remove,it is difficult to deal with and is a typical hazardous waste.If alkylation spent sulfuric acid can't be treated properly,it will not only pollute the environment,but also cause the waste of sulfur resources.In this paper,based on the research accumulation on spent sulfuric acid treatment of our research team,a new concept of quasi-solid reaction were presented,and on this basis,a new technology of resource utilization of alkylation spet sulfuric acid were developed.In this article,the study on the quasi-solid reaction of alkylation spent sulfuric acid with light burned magnesium oxide,the study on the process and kinetic of removal of organics by calcination,the preparation of magnesium sulfate heptahydrate by extraction and crystallization,and the economic evaluation of the whole process were carried out systematically,the integrated technology of wet-leaching,fire-calcination,inorganic chemical preparation and cascade utilization of energy was formed,and the technology provided a new way for the resource utilization of spent alkylation sulfuric acid.The main research contents and conclusions of this paper are as follows:(1)The appropriate process parameters of the quasi-solid reaction between alkylation spent sulfuric acid and light burned magnesium oxide were obtained as follows:the acid ore mass ratio is(2.45?2.47):1,the acid addition time is 20?25 mins,the aging time is 7.5?12.5 mins,under these conditions,the utilization of spent sulfuric acid is more than 90%.Spectral analysis results show that MgSO4·H2O was the main form of the quasi-solid reaction product,and the particle morphology had a variety of structural characteristics,mainly layered or lamellar structure.Preliminary investigation of the mechanism of quasi-solid reaction shows that some organics will undergo polymerization and carbonization with sulfuric acid to form non-polar carbon,while some organics will undergo REDOX reaction with sulfuric acid to form SO2 and CO2.(2)The study on the calcination characteristics of the quasi-solid reaction material shows that,under air atmosphere calcination,organics mainly react with oxygen to form H2O and CO2,the maximum reaction rate peaks occur at 450?460?,and the total weight loss is about 19%,and magnesium sulfate is almost never lost;under nitrogen atmosphere calcination,REDOX reaction between organics and magnesium sulfate is happened to produce MgO,SO2 and CO2,the maximum reaction rate peaks occur at about 750?,the total weight loss is about 35%,and the loss of magnesium sulfate is bigger.The kinetic study of the calcination process shows that the fitting reaction mechanism function f(?)is closest to the mechanism function of Avrami-Erofeev equation,and the reaction order n=3,the average activation energy of the calcination process is 127.1 kJ/mol,and the frequency factor is 3.39×1010.The optimum calcination process parameters were obtained as follows:the calcination temperature is 550?600?,the calcination time is 60 mins,and the calcination method is dynamic calcination.Under these conditions,The anhydrous MgSO4 accounts for 90.33%of the calcination products,the organics were removed completely,and the yield of magnesium sulfate can reach more than 94%.(3)The optimum process parameters of extraction were obtained:the extraction temperature is 80?90?,the extraction time is 10 mins,the liquid-solid ratio is 2.6:1,the extraction solution has the characteristic of self-impurity removal and can produce pure magnesium sulfate crystallization solution.The optimum crystallization parameters were obtained:the crystallization solution pH is 5-7,the crystallization temperature is 10?15?,the crystallization time is 6?8h,under these conditions,the crystal has the best morphology,the highest crystallization rate and the most economical.The various indicators of the magnesium sulfate heptahydrate products produced in this paper meet all the requirements of the industry standard HG/T2680-2017(industrial magnesium sulfate),and the quality is excellent.(4)The material balance,the heat cascade utilization analysis and the economic benefit analysis of the process flow of alkylation spent sulfuric acid to prepare heptahydrate magnesium sulfate were carried out and the researches show that,the technology has strong competitive advantages,significant environmental benefits and certain economic benefits,and it has a broad prospect for industrial application.