Surface Acid Modifcation Of Zeolites And Its Influences On Adsorption Of Thiophenic S-containing Compounds

In recent years, the haze and other environmental issues are become increasingly serious, which has attracted public attention. In order to further ensure the clean utilization of energy and realize the sustainable development between economy and environment, the upgradtion of oil quality becomes increasingly important. The hydrodesulfurization(HDS) is used widely and very mature in the world’s oil refinery, but it is difficult to remove stable thiophene sulfide completely. By contrast, the adsorption desulfurization technology has the advantages of high desulfurization precision and low operating cost, simple operating conditions, which has attracted wide attention of the world’s scholars. Preparation of sorbent with high sulfur capacity and desulfurization precision is the key to adsorption desulfurization. The pore structure and surface acid sites of sorbent are important factors that influence on the desulfurization performance.Based on this, NaY, SBA-15 and MCM-41 zeolites with different pore structure and surface acidity has been selected as research object, and their surface acidity were modified. Adsorption of zeolites for cyclohexane, benzene, thiophene and tetrahydrothiohene was investigated by static adsorption experiments. With XRD, N2 adsorption-desorption, ICP, NH3-TPD, Py-FTIR and other characterization techniques, effects of pore structure and surface acid sites of sorbents on the adsorption performance were systematically investigated. The main conclusions are as follows:(1)The adsorption capacity of these four adsorbates over MCM-41 zeolite is higher than that over SBA-15 zeolite because the larger surface area and pore volume of MCM-41 zeolite. NaY zeolite has both Lewis and Br?nsted acid sites on its surface, and its pore size is closed to the dynamic diameter of cyclohexane, benzene, thiophene, and tetrahydrothiophene molecules, which result in the significantly larger adsorption capacity of Na Y than that of MCM-41 and SBA-15; Moreover, on NaY zeolite, the actions of π bond and Lewis acid sites contribute a lot on the adsorption performance, and the adsorption capacity follows the order: thiophene > tetrahydrothiophene > benzene > cyclohexane. Whereas, over MCM-41 and SBA-15 zeolites, the interaction of S atom with Br?nsted acid sites contributes more, and the adsorption capacity order is: tetrahydrothiophene > thiophene > benzene > cyclohexane.(2) A series of NNHY and NCHY zeolites with different surface acidity were prepared through modifition with different concentrations of ammonium nitrate and ammonium oxalate solution. The NNHY and NCHY zeolites maintained the basic skeleton structure of Y zeolite. The mium-strong Br?nsted acid sites produced during the modification process were the main reason why adsorption desulfurization performance greatly enhanced. A series of CCHY zeolites were through modification with different concentrations of oxalate solution. The modification process have not only produced mediate strong Br?nsted acid sites, also caused the sorbents dealumination and destroyed the structure of zeolites. The adsorption desulfurization performance is poor. The interaction between mediate strong Br?nsted acid sites and S atom contributes a lot on the adsorption performance, which makes that the NNHY and NCHY sorbents adsorption performance of thiophene and tetrahydrothiophene is greatly improved. The amount of Br?nsted acid is larger, the more adsorption. But the adsorption properties of cyclohexane and benzene have not greatly improved. The stability of the sorbent structure plays an important role in the adsorption process, which maked the adsorption properties of CCHY adsorbent for cyclohexane, benzene, tetrahydrothiophene are poor.(3) A series of Al-S-n and Al-M-n zeolites with different surface acidity were prepared through modified with different concentrations of aluminum. Compared with the blank sample S-B1 and M-B1, the adsorption properties Al-S-n and Al-M-n sorbent are greatly improved. With the feed silicon-aluminum ration decreased, adsorption capacity of sorbent increased first and then decreased. The largest adsorption capacity of thiophene is supported by Al-S-15 and Al-M-15, which is 2.46mmol/L and 3.35mmol/L, respectively. The dium-strong Br?nsted acid sites and Lewis acid sites produced during the modification process are the main reason why adsorption desulfurization performance is greatly enhanced;...