Study On Hydroisomerization Performance Of Supported Phosphate Catalysts

In recent years,with the increasing pressure of environmental protection and the rapid development of the automobile manufacturing industry,the quality requirements of vehicle fuels are becoming more and more strict in the world.The general trend of fuel cleanliness in the world is to turn gasoline into low sulfur,low olefins and low aromatics.The development of low benzene,low steam pressure and high octane number,among which alkane isomerization oil is one of the important components of clean gasoline with high octane number.At present,the most commonly used alkane isomerization catalyst in the industry is a bifunctional catalyst supporting precious metal Pt.However,the kind of catalyst has some problems such as strict feedstock requirements,environmental pollution caused by chloride and high price and so on.In this paper,the catalytic performance of nickel phosphide catalyst for hydroisomerization of n-hexane was studied by using self-made MCM-41/MOR composite molecular sieves as support and nickel phosphide supported by non-precious metals as active component,and the reaction mechanism was preliminarily explored.The alkali-treated mordenite?MOR?is a partial silicon-aluminum source,and the MOR/MCM-41 micro-mesoporous composite molecular sieve is synthesized by hydrothermal synthesis while adding an external silicon-aluminum source.The self-made carrier was characterized by N₂ physical adsorption-desorption and transmission electron microscopy.The results show that the surface area,pore volume and pore size are higher than ordinary molecular sieves.The specific surface area of MCM-41/MOR composite molecular sieve is up to 566 m²·g^-1,the pore volume is 0.46 cm³·g^-1,and the average pore diameter is 3.26 nm.The MCM-41/MOR composite molecular sieve was used as the carrier,and Ni_xP_y was used as the active component of the metal.The precursor of the supported phosphide catalyst was prepared on the synthesized micro-mesoporous composite molecular sieve by the equal volume impregnation method,and in a hydrogen atmosphere.The supported nickel phosphide catalyst was prepared by temperature programmed reduction method.The conversion and selectivity of hydrogen isomerization reaction of n-hexane were used as indicators in the fixed bed hydrogenation reactor.The loading,nickel to phosphorus ratio,and The influence of preparation conditions such as reduction temperature on the performance of the catalyst for isomerization of alkane.The results showed that the optimal preparation conditions of the catalyst were:loading of 4%and nickel-phosphorus ratio of0.5;when the reduction temperature was 650?,the catalyst showed good catalytic performance for the isomerization of the alkane,and the conversion of n-hexane.The rate was 41%and the selectivity was 89%.The effects of reaction conditions,such as reaction temperature,reaction pressure and volume space velocity,on the catalytic performance of4%Ni₂P-MCM-41/MOR catalyst for n-hexane isomerization were also investigated.The optimum reaction conditions were as follows:reaction temperature 250?,reaction pressure 3 MPa,volume space velocity 2 h^-1.Under this reaction condition,Ni₂P-MCM-41/MOR catalyst showed good catalytic activity for isomerization of n-hexane.The conversion of n-hexane is 73%,while the selectivity of isoparaffin is 84%.Finally,the isomerization mechanism of n-hexane was discussed,and the isomerization of n-hexane followed the mechanism of positive carbon ion.