Preparation Of Solid Carbon With High Carbon And Low Ash Content By Thermo-Alkaline Hydrolysis And Hydrothermal Carbonization Of Municipal Sludge

With the development of urbanization process of China,the production of municipal sludge is increasing year by year,and the environmental pollution caused by sludge has become an important constraint factor for the sustainable development of society.The development and utilization of sludge carbon material is an important way to solve the sludge problem based on resource utilization.Aiming at the problems of high ash content and low carbon content of carbon materials prepared by direct hydrothermal carbonization of sludge,the technology of high carbon and low ash content of solid carbon prepared by hydrothermal carbonization and thermo-alkali hydrolysis was proposed in this study.The experimental results show as follows:The dissolution rate of organic matter and inorganic matter reached the highest value of 39.09%and 12.89%at 180°C during direct thermal hydrolysis of sludge.When the hydrolysis p H was adjusted to 13,the dissolution rate of organic matter reached 42.37%at the hydrolysis temperature of 150°C,and the dissolution rate of inorganic matter decreased by 63.37%.Increasing the water content of sludge during hydrolysis can increase the dissolution of organic and inorganic matter.The ash content of the solid carbon is 44.46%when the hydrolyzate of sludge is directly hydrolyzed at 150°C and carbonized at 220°C for 720 min.When the p H of hydrolysis is adjusted to 13,the ash content of the solid carbon is reduced to 14.08%.When the hydrolysis temperature is reduced to 30°C,the rate of dissolved organic matter fixed into solid carbon is up to 50.97%,but the ash content is also up to45.58%.When the p H of hydrolyzate was adjusted to 1 and carbonized at 180°C for720 min,the rate of dissolved organic matter fixed into solid carbon and ash content of solid carbon at 30°C are decreased to 40.10%and 9.14%respectively,while for thermo-alkali hydrolyzate at 150°C the rate of dissolved organic matter fixed into solid carbon was only 26.20%.However,the rate of inorganic matter fixed into solid carbon and ash content of solid carbon decreased significantly to 1.53%and 2.33%.After carbonization,the content of ketone compounds in the aqueous phase increased significantly.When the thermo-alkali hydrolyzate at 150°C was carbonized at 260°C for 720 min,the TOC conversion rate reached the maximum value of 47.40%,and the carbon content of the solid carbon reached the maximum value of 70.06%.The apparent morphology of the solid carbon is microspheroid with lower I_D/I_G,H/C,O/C and(O+N)/C values,lower aliphatic compound structure and higher amorphous carbon structure,as well as abundant C-C/C-H/C=C,graphite-N,C=O and sulfide-S functional groups on the surface.In this paper,a solid carbon with high carbon and low ash content was prepared by thermo-alkaline hydrolysis and hydrothermal carbonization of sludge,which provides an experimental basis for resource utilization of sludge carbon materials and enriches the way of resource utilization of sludge and preparation of high-quality carbon materials.