Study On Synthetic Technology Of Pseudo Boehmite By Impinging Flow Technology

Currently,the domestic crude oil is easy to block the catalyst pore channel because of its serious deterioration,increasing proportion of heavy oil with long carbon molecular chain and residual oil.This will lead to catalyst deactivation during the catalytic cracking process.One of the activated alumina series products,pseudoboehmite,is widely used as catalyst and catalyst carrier in the field of petrochemical industry because of its characteristics of high specific surface area,adjustable pore size and high thermal stability.Generally,the specific surface area and average pore diameter of traditional pseudo-boehmite production produced by tower and kettle reaction equipments cannot satisfy the demand of catalytic cracking of inferior oil because of the poor heat dissipation and mixing uniformity of traditional process.In order to solve above problems,the impinging stream technology was introduced to prepare pseudo-boehmite,and the impinging stream experimental device was developed to investigate the effects of double-aluminum method and carbonization method on the product performance.The samples were characterized by X-ray diffraction(XRD),scanning electron microscopy(SEM),specific surface area and porosity analyzer(BET).The main contents of this paper are as follows:(1)Pseudo-boehmite was prepared by double-aluminum method using aluminum sulfate and sodium metaaluminate as raw materials under different conditions using impinging stream equipment,and the prepared samples were characterized.The results show that the pH value of gel has an important effect on the crystal form of the product.With the increase of pH value from 7 to 10,the crystal form of the product changes from amorphous alumina to pseudo-boehmite;With the increase of gelling temperature,aging temperature and feed flow rate,the specific surface area and BJH(Barrett-Joyner-Halenda)maximum average pore size of the product increased first and then decreased,and reached the maximum at gelling temperature and aging temperature of 70℃and feed flow rate of 150 L/h.The results show that the specific surface area of the pseudo-boehmite prepared by the impinging stream method under the optimal process conditions is as high as 438 m~2/g,and the maximum average pore diameter of the pseudo-boehmite prepared by the BJH method is 12 nm.Although the crystallinity of the product prepared under the optimal process conditions is4.8%lower than that of the traditional double-aluminum method,the specific surface area of the product is increased by 21.7%.The maximum average pore diameter of BJH method increases by 44.5%,and the effective pore distribution is more concentrated.(2)Sodium metaaluminate and high-pressure carbon dioxide gas are adopted as raw materials to prepare pseudo-boehmite with an carbonation method under different conditions using impinging stream equipment,and the prepared samples are characterized.The results show that the pH value of the gel has an important effect on the crystal form,specific surface area and the maximum average pore size of the product.The product represents the best properties in the crystal form,specific surface area and the maximum average pore size when the pH value of the gel is 10.The increasement of gelling temperature,raw material concentration and gas-liquid ratio will promote or inhibite the neutralization reaction and hydrolysis reaction of sodium metaaluminate to a certain extent,which determines the crystal form,specific surface area and maximum average pore size of the product in BJH method.The maximum property of the product is achieved when the gelling temperature is 30℃,the raw material concentration is 40 g/L and the gas-liquid ratio is 2:1.The results show that the specific surface area of the pseudo-boehmite prepared by the impinging stream method under the optimum conditions is as high as 380 m~2/g,and the maximum average pore size of the pseudo-boehmite prepared by the BJH method is 9 nm.Compared with the traditional process,the crystallinity,specific surface area and maximum average pore size of the product prepared by the impinging stream method are increased by 8.2%,18.6%and 69.7%,respectively.(3)According to the laboratory data and industrial production operation parameters,the related process flow design,material and heat balance,equipment selection,workshop layout,benefit balance and other work are carried out.According to the calculation results,the process package for producing pseudo-boehmite with an annual output of 500 tons through carbonation method is designed.The economic benefit of the whole process production is calculated.The calculation shows that the production process of impinging stream technology is obviously superior to the traditional production process in terms of equipment consumables and water purification consumption.Through the quantitative calculation of transmission,mass transfer and heat transfer of each unit operation,it is shown that no additional heat exchange equipment is needed in the impinging stream reactor with the introduction of impinging stream technology.The neutralization heat produced by the reaction is converted into latent heat of vaporization and carried out of the reactor with the waste gas as the carrier,which provides a new solution for the gas-liquid reaction type heat exchange process.At the same time,it provides a theoretical data basis for industrial applications.