Modified Chitosan For Metal Removal From Spent FCC Catalyst

Catalytic cracking is an important process in refineries that converts heavy oil into products of higher market value such as gasoline and diesel.As the crude oil is heavier and inferior,more transition metals are deposited on the surface of the FCC catalyst,such as nickel and vanadium,causing irreversible poisoning of the FCC catalyst during recycling.Nowadays,the method of landfill has been banned.The traditional Demet method will cause secondary pollution to equipment and the environment.Finding an environmentally-friendly and efficient regeneration method has become a hot issue in the industry.Firstly,based on the characteristics of chitosan chelating alloy,such as strong metal ability,low cost,cleanliness,non-toxicity and easy modification,modified chitosan-dithiocarbamate(DTC-CTS)was synthesized by nucleophilic addition reaction from chitosan and CS2.The synthesis conditions were optimized with the aim of vanadium removal efficiency,and the structural differences before and after modification of chitosan were studied.Secondly,it was applied to the deactivation of FCC catalysts.The effects of feed ratio,acetic acid concentration,reaction temperature,reaction time and shear strength on the deactivation of vanadium were investigated,and the optimal process conditions for the deactivation and regeneration of vanadium were obtained.Finally,on the basis of vanadium removal,the structure of regenerated catalyst was characterized by H2 reduction and nickel removal,and the micro-reactivity of regenerated catalyst was tested,thus forming a complete regeneration process of balancing agent for vanadium removal and nickel removal.The following conclusions were drawn:(1)The optimal synthesis conditions for the modified chitosan DTC-CTS are as follows:synthesis temperature 50?,synthesis time 10 h,CS2(ml)/chitosan(g)feed ratio 10:2,hydrogen The sodium oxide concentration was 40%.(2)Modified chitosan DTC-CTS participates in vanadium complexation mainly by S in its molecule,which overcomes the disadvantage of poor demetallization ability of chitosan under acidic conditions.The demetallization ability of modified chitosan is twice that of chitosan.(3)The optimum conditions for vanadium removal and regeneration are as follows:feed ratio 1:1,acetic acid concentration 3.2%,reaction temperature 125 C,reaction time 4.5 h and rotational speed 500 r/min.Under these conditions,the removal rate of vanadium by modified chitosan reaches the maximum of 54.8%.The specific surface area,pore volume and microreactivity of regenerated FCC catalyst increased by 24.9%,4.4%and 5 units respectively.(4)On the basis of vanadium removal and regeneration,FCC catalyst was reduced by H2 at 700 C for 8 h and pickled with 0.65%dilute nitric acid for 30 min.The nickel removal rate was 65.8%under the optimum conditions.The specific surface area and pore volume of the regenerated catalyst increased by 7.1%and 2.8%respectively compared with those of the regenerated catalyst only after vanadium removal,and the microreactivity of the regenerated catalyst increased by 3 units.