The Preparation Of Modified Alumina Supports And Their Catalytic Performance In The Ultra-Deep Hydrodesulfurization Of Diesel

With the further strengthening of people’s environmental awareness,the requirement of sulfur content in oil products at home and abroad is becoming more and more stringent.This requires the refiner to accelerate the development of oil desulfurization technology,especially the research and development of ultra deep desulfurization technology,and promote the acceleration and upgrading of oil quality.Targeted at the removal of the large molecules containing sulfur compounds in diesel oil,in this work,we selected4,6-dimethyldi benzothiophene(4,6-DMDBT)as model molecule,which has strong steric hindrance and is recognized as one of the most difficult sulfur compounds to be removed.By modifying the alumina support,we have increased the amount of Br?nsted(B)acid on the surface of the alumina support to explore the possible removal of 4,6-DMDBT via the isomerization path.In this paper,the surface acidity of the alumina support was modified by using ammonium fluoroborate,ammonium borate and boric acid as modification agents.The modified alumina was used as the support for preparation of the bimetallic Ni-Mo catalyst,which was evaluated in the ultra-deep desulfurization of diesel.Combined with the surface acidity and pore structure of the support,as well as analysis of the reaction products,the relationship between the B/L ratio and the pore structure of the support,4,6-DMDBT conversion of the catalyst,and the desulfurization pathways were constructed.Characterization and catalytic evaluation results indicated that the alumina support modified by using ammonium fluoroborate has a specific surface area of about 271.9m~2/g together with a large pore diameter of 15 nm and riched B acidsites.Moreover,the L acid content of the sample was significantly reduced,resulting in a B/L value of above 1.0.Using this material as the support,the catalyst exhibited a 4,6-DMDBT conversion of up to 90.9%,which was 18.9 percentage points higher than that of the catalyst prepared with unmodified alumina.Especially,the isomerization ratio in the desulfurization paths was up to 2.42%.With ammonium borate as the modifier,the specific surface area of modified alumina can reach up to 435.9m~2/g with a B/L value of 1.44,and the conversion of 4,6-DMDBT is up to 82%,which is10 percentage points higher than that using unmodified alumina.With boric acid as the modifier,the amount of L acid was greatly reduced,although the concentration B acid was not high,and B/L ratio was close to B/L=2.50.The 4,6-DMDBT conversion of the resulting catalyst was up to 78%,6 percentage points higher than that of unmodified samples.In this study,it was found that that ammonium fluoborate is very conducive to the production of B acid,and the effect of boric acid on the reduction of L acid is obvious.In the future,the modification using combined ammonium fluoroborate and ammonium borate can be considered to optimize the ratio of B/L acid on the surface of the alumina support to improve the catalyst’s performance in ultra deep desulfurization of diesel.