| Coal chemical industry is an important way for clean and efficient utilization of coal resources.In recent years,with the increasing number of coal chemical enterprises in China,the industry of coal gasification has been expanding,which leads to the continuous growth of coal gasification slag generation.However,a large amount of coal gasification slag has not been effectively treated,the resource utilization rate of coal-based solid waste is too low,and no large-scale recycling system has been formed,which seriously restricts the sustainable development of coal chemical industry and brings serious environmental problems.It is also resulting human health problem.Therefore,coal and environmental science are increasingly concerned about the solid waste generated by coal gasification.In order to reduce the problems caused by the slag of coal gasification,large amount of land waste,air pollution and heavy metal pollution,it is urgent to explore the comprehensive utilization methods of coal gasification slag.Coal gasification fine residue has the natural characteristics of rich silica-alumina source,certain amount of residual carbon and unique pore structure,which is suitable for the preparation of high value-added molecular sieve materials.At present,most of the molecular sieve materials are prepared by pure chemical reagents or solid waste from other aspects as the basic silica-alumina source,and this preparation method has the problem of high cost of pure chemical reagents,low utilization rate after alkali excitation,large amount of acid-base wastewater generation,and water resources are not recycled.To solve the above problems,this paper proposes to prepare P-type/carbon composites with low silica-aluminum ratio and high value-added ZSM-5 molecular sieves with high silica-aluminum ratio by simple acid leaching-alkali solubilization process with the direct raw material of coal gasification fine slag,meanwhile,to conduct recycling experiments on desiliconization liqiud so that its silicon source,sodium source and water can be efficiently utilized.And for the difficult problem of synthesizing nanoscale molecular sieves by traditional hydrothermal method,it is proposed the hydrothermal synthesis of nano ZSM-5 molecular sieves by nano seed emulsion addition method,which is beneficial to the industrialization.The main research contents and conclusions are as follows:(1)The coal gasification fine slag is activated by simple acid leaching and desilicification by alkali solution to prepare low silica-aluminum ratio P-type/carbon composites,while the supernatant(desilicification solution)after alkali solution provides silica-aluminum source,water source and alkaline environment to prepare high value-added high silica-aluminum ratio ZSM-5 molecular sieve by grading,and the desilicification liqiud is circulated for experiment,which fully utilizes the silica-aluminum source,alkali source and large amount of water to realize the coal gasification,which achieves efficient utilization of fine slag.The mechanism of acid leaching activation is described that the metal oxides on the surface of coal gasification slag starts to dissolve and remove when attacked by H+,which leads to the breakage of the amorphous wrapped particles,the pore structure on the surface of the particles is opened,and a large number of reactive sites are exposed,in which the non-crystalline structures such as Si-O-Al,Si-O-Fe and Si-O-Ca are destroyed and transformed into Si-O-H bonds to improve the reaction activity.The effects of different alkalinity and alkali dissolution time on the P-type/carbon composites are explored,and the optimal alkalinity of 2.5 mol/L and alkali dissolution time of 9 h are obtained,which results in a uniform distribution of C,Si and Al elements in the P-type/carbon composites and an overall flower shape.The cell parameters of ZSM-5 molecular sieve are obtained by Rietveld structural refinement,with side lengths a=19.92 ?,b=20.12 ?,c=13.41 ?,angles α=90°,β=89.95°,γ=90°,and cell volume of 5373.85 ?3,which is slightly larger than the standard ZSM-5 molecular sieve cell volume(5343.32 ?3)and belongs to orthorhombic crystal structure.The total specific surface area of ZSM-5 molecular sieve is 437.72 m2/g,the specific surface area of mesopores is 141.41 m2/g,the specific surface area of micropores is 296.31 m2/g,the pore volume is 0.21 cm2/g,and the pore diameter is 1.94 nm.This technology not only saves cost,but also achieves "zero" emission of coal gasification slag,which is important to realize the development of coal chemical recycling and green chemical industry.(2)The nanoscale ZSM-5 molecular is synthesized by seed emulsion addition method.Which is using tetraethyl orthosilicate as the silica source and adding TPAOH templating agent,the nanoscale seed emulsion is synthesized rapidly(6h)by hydrothermal method at low temperature(150℃).The filtrate obtained from coal gasification slag under alkaline conditions is used as a silicon source,and the nano-seed emulsion is added to rapidly synthesize nano-ZSM-5 molecular sieves.Meanwhile,the effects of crystallization time and seed emulsion addition on the synthesis of nano-ZSM-5 molecular sieve are investigated,and it is found that the reaction temperature is low and the reaction time is short.The optimal raw material content:15 mL of desilicon solution,20 ml of H2O,0.75 mL of nano-seed emulsion,and hydrothermal method at temperature of 160℃ and time of 15 h can synthesize nano-ZSM-5 molecular sieves.NH3-TPD characterization shows that the acidity of strong acid sites in nano-H-ZSM-5 molecular sieves after ion exchange is enhanced and the acid amount is increased.For the nano-molecular sieves,the increase in acid amount after ion exchange is greater than that of the micron molecular sieves.Because of the higher number of active sites on the exterior,so the higher adsorption capacity of the nano-molecular sieve.The preparation of nano-molecular sieves by adding seed emulsion is not only a simple synthesis method with mild conditions,but also significantly shortens the synthesis time compared with the general crystal seed method,and most importantly,solves the problem that it is difficult to synthesize nano-molecular sieves by the traditional hydrothermal method,and is easy to realize industrial production. |
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