Removal Of Sulfuric Acid From Sodium Lactate And Tetramethylguanidinium Lactate Aqueous Solutions For Flue Gas Desulfurization

Sulfur dioxide is the main component of air pollution,and most of it comes from coal combustion.Not only will it destroy the ecological environment and buildings,but it will also endanger human health.However,sulfur dioxide is also an important chemical raw material that can be used to produce sulfuric acid.Therefore,it is important to control the emission of sulfur dioxide and to recover sulfur dioxide from coal-fired flue gas.There are many reports on the reversible absorption of sulfur dioxide influe gas by new absorbents,which can efficiently reduce the sulfur dioxide content in the flue gas,and the absorbed sulfur dioxide can be recovered by desorption and further utilized as a chemical raw material.However,in the long-term absorption and desorption cycle experiment,it has be found that the partially absorbed sulfur dioxide is oxidized to sulfuric acid,which causes the sulfur dioxide cannot be desorbed and the absorption capacity of the absorbent is decreased.Therefore,the development of an effective method to remove sulfuric acid from the new absorbents for absorbing sulfur dioxide in flue gas can lay a solid foundation for the industrial application of the new absorbents in flue gas desulfurization.In this paper,the structural stability of three new absorbents,monoethanolaminium lactate,sodium lactate and tetramethylguanidinium lactate,under long-term absorption and desorption cycles using synthetic air was investigated.It was found that the degree of amidation of monoethanolaminium lactate in the process was gradually increased,while sodium lactate and tetramethylguanidinium lactate maintain good structural stability.Therefore,a method to remove sulfuric acid in sodium lactate aqueous solution and tetramethylguanidinium lactate aqueous solution therein has been further studied.The experimental results show that in the sodium lactate aqueous solution,the sulfuric acid formed by the oxidation of absorbed sulfur dioxide affects the absorption properties of the absorbent.And as the sulfuric acid content increases,the absorption capacity of sulfur dioxide by the absorbent gradually decreases.When the sulfuric acid content reaches 10 wt%,the saturated absorption of the aqueous sodium lactate solution decreases to 16%.Based on common-ion effect,when sodium hydroxide is added to sodium lactate aqueous solution and the water content is reduced to increase the sodium ion content,the sulfuric acid therein can be removed efficiently as Na2SO4.And as the water content decreases,the removal rate of sulfuric acid in the solution gradually increases.When the water content is reduced to 34 wt%,the sulfate content in the aqueous sodium lactate solution can be reduced to 0.46 wt%,and the removal rate of sulfuric acid reaches 95.6%.The absorbed sulfur dioxide has no significant effect on the removal rate.The absorption performance of sodium lactate after removal of sulfuric acid can be recovered to 97%,and the repeatability of the removal process is good.In the tetramethylguanidinium lactate aqueous solution,the presence of sulfuric acid affects its absorption capacity of sulfur dioxide.As the sulfuric acid content increases,the absorption capacity decreases gradually.When the molar ratio of sulfuric acid to tetramethylguanidinium lactate reaches 0.355,the absorption capacity even dropped to 32.3%of the original.Calcium carbonate is added to tetramethylguanidinium lactate aqueous solution,then the water content is reduced to remove the sulfuric acid.As the water content decreases,the removal rate of sulfuric acid gradually increases.When the water content is reduced to 30 wt%,the removal rate of sulfuric acid reaches 71.3%.According to the method proposed in this paper,the process flow of absorbing sulfur dioxide by new absorbents combined with the removal of sulfuric acid section has been designed.