Synthesis Of SAPO Molecular Sieves Using MTO Catalyst-Relevant Industrial Waste Liquids And Solids

Methanol-to-olefins(MTO)technology has opened up a non-oil way to produce ethene and propene,which can diversify the raw materials of olefins production,alleviate the dependence on foreign crude oil and guarantee the energy safety.With the commissioning and operation of many MTO industrial plants,large amount of liquid/solid waste relevant to MTO process are also produced.The production of these industrial wastes will not only increase the operation cost of relevant processes,but also increase the risk of environment pollution.Therefore,the research on the utilization of liquid/solid waste related to MTO catalyst has important practical value.This thesis is devoted to the utilization of mother liquid from SAPO-34 synthesis and industrial MTO spent catalyst,by using them as part of raw material for SAPO molecular sieve synthesis,investigating the effect of the addition of waste,the Si contents in the gel and the types of template on the synthesis of SAPO molecular sieves.The catalytic performances of the synthesized samples are also investigated.The mother liquid from SAPO-34 crystallization was first explored as raw material for the synthesis of SAPO-34 and SAPO-18.SAPO-34 was synthesized using triethylamine(TEA)and diethylamine(DEA)as composite templates.It was found that the textural properties,morphology and atom coordination environments of the samples were similar with those synthesized from conventional sources,but the acid density and surface Si enrichment were reduced to a certain extent.The samples showed improved ethylene plus propylene selectivity in the MTO reaction.Moreover,SAPO-18 was synthesized by using N,N-diisopropyl ethylamine(DIEA)as template.Due to the possible existence of small amount of SAPO-34 microcrystals or primary/secondary structural units in the mother liquid,there are small amounts of SAPO-18/34 intergrowth in the product.The morphology,atom coordination environment and acidity of the samples changed with the increase of the amount of mother liquid.Prolonged lifetime and slightly improved ethylene plus propylene selectivity in MTO reaction can be observed for SAPO-18 samples.Using industrial MTO spent catalyst as part of raw materials,we further explore the synthesis of SAPO-34 molecular sieve templated by DEA and tetraethyl ammonium hydroxide(TEAOH).The characterization revealed that the physical and chemical properties of SAPO-34 with different Si contents were similar to those synthesized from conventional raw materials.Low-silica SAPO-34 shows better catalytic performance in the MTO reaction.In addition,SAPO-34-DEA sample showed excellent catalytic performance in methanol ammoniation reaction.Although the methanol conversion decreased by 26%after 800℃ high-temperature hydrothermal treatment,the selectivity of monomethylamine and dimethylamine in the three methylamine products was as high as 94%,indicating to be a potential catalyst for methanol gas-phase ammoniation reaction.