| With the development of the economy, the diesel fuel as a major driving fuel is of increasing demand. And the sufur compands in diesel which constitute a leading cause of fuel fossils contamination increased a lot. Besides being converted to sulfur oxides during combustion, thereby contributing to air pollution and acid rain, they have been shown to poison catalytic convers. Nowadays, deep desulfurization of diesel fuels is receiving increasing attention in the research community worldwide in order to satisfy the upcoming environmental regulations and fuel specifications. Therefore, extensive reseach is carried out to propose technologies to obtain low-sulfur fuels. Among them, the selective adsorptive of sulfur-containing compands seems particularly interesting. This approach is an attractive field of research owing to such advantages as being a low-energy demanding process and having the availability of regeneration of the spent adsorbent and broad availability of adsorbents. Lignite semi-coke is regarded as a desired raw material in China to prepare higher efficiency adsorbent because it is abundant and inside the internal pore of suface of semi-coke contains a lot of atoms of Hydrogen and Oxygen which provided the condition for modification of semi-coke. So an atempert was made to modify the semi-coke to obtain excellent adsorbet.In this paper, lignite semi-coke from Zhalainuoer of Inner Mongolia is selected to prepare adsorption desulfurizer. To increase the desulfurizing activity of semi-coke, the following modification methods are selected and researched. That is :high-pressure hydrothermal chemical activation,HNO3 or H3PO4 modification, calcinations and loading with activated ingredient.The influences of fix-bed temperature and space velocity on activity of desulfurization are studied. By means of the measurements of physical and chemical properties and structures, the effect factors of activated semi-coke desulfurization are investigated. Finally, several regeneration methods of activated semi-coke are elementary analyzed.Results of measurements of specific surface area, pore volume and the surface property of alkaline and acid indicated that 1) The volatile content of lignite semi-coke is much higher than that of normal active carbon. After HNO3 or H3PO4 modification, the volatile content of lignite semi-coke increased greatly. This provided the condition for the further modification of semi-coke. 2) The treatment by both H2O vapor and O2 under high temperature is favorable to form/widen pore in the surface of semi-coke, which changes chemical and physical properties of semi-coke. And combined modification, especially calcinations with the treatment by both H2O vapor and O2 under high temperature, can make semi-coke with the largest specific surface area and the biggest pore volume. 3) The content of surface acidic and basic functional groups is little, while the content of basic functional groups is higher than that of acidic functional groups. The acidic functional groups of modified semi-ckes increase greatly after HNO3 and H3PO4 modification while the content of basic functional groups enhance to a large degree after calcination and high-pressure hydrothermal chemical activation. The semi-coke after H3PO4 modification has the largest number of acidic functional groups.The semi-coke prepared from lignite semi-coke by pre-activating in an autoclave, oxidizing with HNO3 for 3h and then calcining at 700oC in N2(water, 5%oxygen)showed good performances for sulfur removal efficiency. And the sulfur removal efficiency enhanced remarkably after loaded with activated ingredient the semi-coke, the best loading amount is 1%. Both Co and Mo are favorable catalyst of HDS, but not worked exactly after be loaded on semi-coke in adsorption desulfurization. Among the desulfurizers of H3PO4 modification series the semi-coke loaded with CuO which is prepared by several steps gets the highest sulfur removal efficiency. To prepare the desulfurizer, first of all, according to 1.5:1dipping ratio dipped the semi-coke 20 hours in 40% H3PO4, and then calcination at 700℃for 1.5 hours, finally, loaded with CuO. The optimal operational conditions of sulfur removal by semi-coke are space velocity of 2h-1and desulfurization temperature of 240℃. According to the influence of fix-bed temperature for desulfurization, it is concluded that the main action in desulfurization of the semi-coke loaded with activated ingredient is chemistry adsorption while that of the semi-coke without loading is physical adsorption. Compared the spectra of diesel oil to that of treated oil, along with the sulfur removal result of model compounds, it is showed that the removed sulfur compounds are mainly Benzothiophene and dibenzothiophene derivatives which are difficult to remove by HDS.Combining the performance of sulfur removal with physical and chemical properties, it is found that 1) The activated semi-coke with high content of acid functional groups shows pretty well performance for sulfur removal, but the desulfurizing capacity has no linear relationship to the content of acid groups. 2) The activated semi-coke with large specific surface area shows desirable performance for sulfur removal, and the desulfurizing capacity has linear relationship to the specific surface area.Elementary regeneration of spent semi-coke by different methods is researched and it is showed that solvent regeneration especially dimethylbenzene regeneration has the best regenerative result. |
PDF Full Text Request