Research For N-heptane Isomerization On AlMCM-41 Catalysts

Hydroisomerization is an important reaction in crude oil processing, n-alkane isomerization turn into its corresponding isomers has wide application in producing high-octane gasoline. Along with people attach importance to environmental protection in the worldwide, new regulations of gasoline required reducing aromatic and alkene content, and using aether additive were forbidden. Reducing amount of high-octane component promoted demand of high-octane composition. Researching of alkane isomerization improve gasoline octane has drawn much attention throughout the world.We synthesized AlMCM-41 mesoporous sieves using water-heat synthesis, prepared Ni loaded on AlMCM-41 bifunctional catalysts, investigated isomerization of n-heptane on Ni/AlMCM-41 catalysts, discussed the property of C7 isomerization on different preparation conditions of catalysts and changing of reaction conditions, and researched characterization on catalysts. The main conclusion were as follows: (1) Reviewed reduction conditions on AlMCM-41 catalysts we knew: H2 reduction temperature and flow rate of H2 were nearly correlative with its catalytic property. When reduction temperature was 410℃, the activity of catalysts were high, conversion of C7 achieved 70%, isomerization selectivity achieved 44.5%, continued to increase temperature, Bronsted acid turn to Lewis acid on catalysts, in too high temperature Ni will be sintered, isomerization activity declined. Changing of flow rate of H2 in 15⁵0ml/min, along with flow rate of H2 increased, catalysts activity increased, and then declined, when flow rate of H2 was 20-30 ml/min, the property of catalysts were well.(2) Changing of reaction conditions had important effect on reaction, reaction temperature form 250℃to 320℃, conversion of C7 increased and then declined, isomerization selectivity declined, reaction temperature 300℃, H2/C7=12, isomers yield achieved 30%. we selected 300℃as optimal reaction temperature. Reviewed time on stream on catalysts, when reaction achieved 6h, along with reaction time increase conversion declined 20%, selectivity increased slowly.(3) Along with content of Ni increased from 1% to 6%, Ni loading on 3-4%, conversion of C7 achieved 70%, selectivity reached stabilization. so in our experiment the optimal Ni loading was 3-4%. Si/Al changed in the range of 15-50, when Si/Al was 20, the conversion of C7 were most. We considered that 3-4%Ni and AlMCM-41(Si/Al=20) achieved metal-acid site well matching.(4) XRD result indicates that the sample we synthesized were mesostructure AlMCM-41because diffraction angle 2θ=2°appears (100) crystal surface characteristic peak. BET indicates that the sample had high surface area(925.41m2/g) and regular pore size(average pore size 40.32?), after loading on Ni, surface area and pore size were all declined, and A1MCM-41(Si/Al=20)had bigger pore volume(0.79cc/g). Form Py-IR characterization of catalysts we received that AlMCM-41 had Bronsted(1620cm^-1)acid site and Lewis acidsit(e1454cm^-1). Exterior acidity of AlMCM-41 was main weak and mid-strong acid, after loading on nickel, the total acidity of catalysts increased.