The Reaction Mechanism Of Hydrocracking Of Diesel

Light cycle oil has disadvantages such as low cetane number,high density,and high polycyclic aromatic hydrocarbon content,among which bicyclic aromatic hydrocarbons are dominant.The hydrocracking of light cycle oil to prepare high-octane gasoline and BTX（benzene,toluene and xylene）can not only solve the problem of diesel fuel overcapacity,but also provide considerable production of high-octane gasoline and BTX,which has a very important industrial and economic value.The core of the hydrocracking reaction is how to improve the selectivity and yield of the target products.To address this critical issue,this paper adopts NO.1 and NO.2 cracking agents and hydrotreating refiner provided by a company as hydrocracking catalysts,and uses tetralin and decalin as model compound feedstocks,and adopts a six-level,four-factor（reaction temperature,pressure,hydrogen-oil volume ratio and air velocity）approach from two perspectives of reaction conditions and cracking agent structure（acid quantity,acid strength and distribution）.The catalytic hydrocracking reaction laws were discussed by using a six-level orthogonal experimental design method to study the variation of the product yields and the selectivity of hydrogenation,isomerization and dehydrogenation reactions in the hydrocracking reaction,and the detailed characterization of the catalysts by X-ray diffraction（XRD）,nitrogen low-temperature adsorption-desorption,transmission electron microscopy（TEM）and ammonia-programmed temperature desorption（NH₃-TPD）.Firstly,through a series of characterization means,it is concluded that NO.1cracking agent has many hydrogenation active phases,high acid amount and low side compression strength,i.e.low crush resistance strength during the reaction.NO.1cracking agent has high hydrogenation and cracking properties and is an advantageous cracking agent for obtaining gasoline.Compared with NO.1 cracking agent,NO.2cracking agent has uniform distribution of active sites and low hydrogenation performance,which is advantageous for the production of BTX.The conclusions drawn from the experimental results are:NO.1 cracking agent has good performance of high temperature and high pressure resistance,which is favorable for hydrogenation reaction and inhibits dehydrogenation reaction under high pressure（9 MPa）.hydrogenation reaction occurred by NO.2 cracking agent is affected by pressure,but cracking reaction occurred by pressure is less affected,and it is easy to occur isomerization and dehydrogenation reaction.NO.1 cracking agent and NO.2 cracking agent the reaction paths occur differently,but both cracking agents correspond to higher conversions at 2h^-1 and 3 h^-1 WHSV.After that,the hydrocracking reactions were carried out with tetralin and decalin as reactants,and the following conclusions were drawn:the best experimental combination for gasoline production was to use decalin as feedstock,NO.1 cracking agent and hydrogenation refining agent as catalyst,reaction temperature 375℃,reaction pressure10 MPa,hydrogen-oil volume ratio 600,and WHSV 2 h^-1;the experimental combination for BTX production was to use decalin as feedstock and NO.2 cracking agent as catalyst the experimental combination of decalin as feedstock,NO.2 cracking agent and hydrogenation refiner as catalyst,reaction temperature 375℃,reaction pressure 8 MPa,hydrogen to oil volume ratio 700,and WHSV 1.5 h^-1,was used to produce gasoline.Finally,the effects of cracking agent and reaction conditions on the reaction were discussed.The best reaction conditions for the hydrogenation reaction of tetralin were405℃,7 MPa,400 hydrogen-oil volume ratio and 2 h^-1 WHSV;the best reaction conditions for the isomerization reaction were 405℃,9 MPa,400 hydrogen-oil volume ratio and 2 h^-1 WHSV;the best reaction conditions for the dehydrogenation reaction were the optimal reaction conditions for the dehydrogenation reaction are 330℃,5MPa reaction pressure,800 hydrogen to oil volume ratio,and 2.5 h^-1 WHSV;the optimal reaction conditions for the decalin hydrogenation reaction are 360℃,9 MPa reaction pressure,400 hydrogen to oil volume ratio,and 3.5 h^-1 WHSV;the optimal reaction conditions for the primary dehydrogenation reaction are 330℃,5 MPa reaction pressure,and 2.5 h^-1 WHSV;and the optimal reaction conditions for the isomerization reaction are 405℃,9 MPa reaction pressure,400 hydrogen to oil volume ratio,and 2 h^-1 WHSV.The optimal reaction conditions for the primary dehydrogenation reaction were 330℃,5 MPa reaction pressure,700 hydrogen oil volume ratio,and 1.5 h^-1 WHSV;the optimal reaction conditions for the isomerization reaction were 330℃,5 MPa reaction pressure,700 hydrogen oil volume ratio,and 1.5h^-1 WHSV;the optimal reaction conditions for the dehydrogenation reaction were345℃,7 MPa reaction pressure,600 hydrogen oil volume ratio,and 2.5 h^-1 WHSV.