Study On Co/ZSM-22 Catalyzed Hydroisomerization Of Stearic Acid To C₁₈ Iso-alkanes

The metal/molecular sieve dual-functional catalysts are used to realize the hydroisomerization of fatty acids to obtain long-chain iso-alkanes which have the characteristics of good low-temperature fluidity and high octane number.The long-chain iso-alkanes used in fuels,lubricants and other fields,can greatly improve the relative performance of fuels and lubricants.However,with the increase of carbon chain length,the selectivity of the long chain isomeric alkanes without carbon chain loss from the hydrogenation of fatty acid and the isomerization of the products is low.In this paper,ZSM-22 was selected as catalyst parent and Co as active metal.Hydroisomerization of stearic acid catalyzed by Co/ZSM-22 bifunctional catalyst was studied,and the influence of different conditions on the reaction were studied to obtain the higher selective of C₁₈ iso-alkanes.ZSM-22 has a special one-dimensional 10-member ring channel structure,and its adjustable acid center can effectively realize isomerization.As a non-noble metal,Co can reduce the synthesis cost of catalyst compared with precious metal,and has better metal activity.In the hydroisomerism of fatty acids,it can reduced carbon loss.To study the effect of the distribution of the active metal Co on the catalyst on the catalytic performance of the bifunctional catalyst.Co/ZSM-22 bifunctional catalysts were prepared by three different supporting methods（incipient wetness impregnation method,deposition-precipitation method and melt infiltration method）.The results showed that the bifunctional catalysts prepared by melt infiltration method,part of the active metal enters the pores and reacts to generate more C₁₈ alkanes without carbon chain loss.Melt infiltration method was used as the preparation method of the catalyst.In order to improve the yield of C₁₈ iso-alkanes,alleviate the problem of hole blockage caused by the load method.Na₂CO₃ solution was used to modify the molecular sieve and adjust the pore structure and acid center of the catalyst,and the metallic properties of the catalyst were adjusted by changing the metal loading.The results showed that the optimal concentration of Na₂CO₃ solution modification was 0.15 mol/L,and the theoretical loading of Co was8wt%.The reaction conditions were optimized,and the optimal reaction conditions were:reaction temperature 260°C,reaction pressure 2 MPa,and reaction time 4 h.Under the optimal conditions,the conversion rate of stearic acid could reach 100%,and the selectivity of C₁₈ iso-alkanes could reach 23.74%.The Co/ZSM-22 metal/molecular sieve bifunctional catalyst designed in this paper can effectively alleviate the pore blockage in the preparation process of the catalyst,and adjust the acidity and gold properties of the catalyst,compared with the current research,the complete conversion of stearic acid and higher selectivity of C₁₈ iso-alkanes can be achieved under milder reaction conditions.