Effect Of Zeolite On Catalytic Cracking Characteristics Of Medium And Low Temperature Coal Tar In Northern Shaanxi

The low temperature coal tar production in northern Shaanxi is abundant.The development of medium and low temperature coal tar conversion technology is an important way to realize the efficient utilization of low rank coal.The main components of medium and low temperature coal tar are aliphatic hydrocarbons,aromatic hydrocarbons and oxygen-containing compounds,and the content of phenols is relatively high.Although low temperature coal tar is rich in organic compounds,it is low in single chemicals due to the extremely complex composition of coal tar.Therefore,it is of great significance to optimize the distribution of tar products through catalytic cracking of modified molecular sieves and explore the influence of molecular sieves on catalytic cracking characteristics of coal tar at medium and low temperature for the enrichment of high-value chemicals in coal tar at medium and low temperature.In this paper,"the influence of modified molecular sieves on the catalytic cracking characteristics of coal tar in northern Shaanxi" is adopted.The solution extraction method is adopted,and the rotary evaporator is used to obtain light coal tar fractions and heavy coal tar at a reduced pressure of 90°.Distillate,at the final reaction temperature of 800 ℃,using Py-GC/MS(Py-GC/MS)reaction device to study the pore structure distribution and coupling of ZSM-5 catalyst with metal active center,flake ZSM-5 Catalyst,characterize the physicochemical properties and evaluate the catalytic performance of the modified ZSM-5 molecular sieve,explore the product distribution of the modified molecular sieve catalyst for the catalytic upgrading of coal tar,and clarify the internal correlation and influence between the catalyst structure parameters and the pyrolysis product distribution.First,ZSM-5(referred to as Z50)with a silicon-to-aluminum ratio of 50 was synthesized by the seed induction method.On this basis,using different mixed alkali treatments to assist desiliconization,a series of meso-microporous composite porous grade ZSM-5 molecular sieves were prepared,and the catalyst morphology and pore structure were characterized.The porous molecular sieve exposes more of the outer surface.Desiliconization causes a decrease in the ratio of silicon to aluminum in the molecular sieve.Excessive desiliconization leads to serious loss of micropores and partial skeleton collapse,which leads to a decrease in the catalytic performance of the molecular sieve.Studies have shown that the Na OH+PI-ZSM-5 molecular sieve assisted desiliconization can maximize the retention of the microporous structure while forming the mesoporous structure,which is conducive to the diffusion of the carbon deposit precursor and the substantial reduction of oxygen-containing compounds during the reaction process.Other alkali-treated molecular sieve catalysts show better aromatic selectivity and carbon deposition resistance.Secondly,construct a metal/hierarchical pore active center catalytic system.Using the metal/hierarchical pore synergistic catalysis,the acidity and pore structure of the ZSM-5 molecular sieve can be reasonably controlled.Under the catalyzed condition of Na OH+PI-Z50 molecular sieve supported by monometallic Mo,the yield of total aromatics in coal tar(CT/LCTF/HCTF)is the highest,33%,34%,48%,respectively.Compared with Z50,the bimetallic Ga and Mo modified porous molecular sieves promote the formation of aromatic hydrocarbons in the pyrolysis products of HCTF and the reduction of phenols.Finally,the thin ZSM-5 molecular sieve is prepared by adding urea,and the thin ZSM-5(referred to as S/ZSM-5)molecular sieve with a shorter b axis is synthesized,and the metal modification is carried out to prepare the bimetal/flaky molecular sieve.The metal-modified S/ZSM-5 is a dual-functional catalyst,which effectively promotes the conversion of benzene series and naphthalene series in the HCTF fraction.Among them,benzene series are mainly increased by benzene,p-xylene and methyl naphthalene.In this catalyst,the olefin oligomerization reaction and aromatization reaction performance is promoted,which is beneficial to the enrichment of aromatic hydrocarbon substances in the product distribution.