Study On Desulfurization Technology Of Gasoline

With the consciousness of protecting environment enhancing all over the world,the limit for the sulfur content in gasoline are getting more and more strict. Usingclean fuel are pushed forward in the big and middle city of our country now. In 2004,Refinery No. 4 document of SINOPEC requested that the sulfur content in gasoline inall the enterprises in subjection to China Petroleum have to reach the standard of theEurope â…¢ until July 1,2008, namely, the sulfur content in gasoline is less than 150ppm. The raw material of Nanyang Wax Fine Chemical Plant is Nanyang oil in lowsulfur and paraffin group, but the sulfur content in FCC gasoline is 230 ppm and themercaptan-sulfur content often is ineligible even after sweetening besides assuring itup to standard in Doctor-test. (The criterion for gasoline product requests that eitherthe sulfur of mercaptan content must be less than 10 ppm or up to standard inDoctor-test.) So this enterprise is still facing the pressure of improving the gasolineproduct's quality.Combining with the domestic and foreign development of desulfurization anddemercaptan technologies in gasoline, this thesis researched the methods of reducingthe sulfur content in gasoline in the process of FCC, alkali washing and sweeteningand analysed the influencing factors that arouse the sulfur and mercaptan content ingasoline of Nanyang Wax Fine Chemical Plant high according to the distributing ruleof sulfur and mercaptan content in FCC gasoline. At last, some conclusions wereobtained as follows.1, The sulfur content in FCC stable gasoline will be reduced by 25 percent(m)through controlling the operation conditions and adding additives fordesulfurization in the stock .2,The sulfur content will be reduced by 20 percent(m) through controllingalkali washing of stable gasoline .3,The present â… type and â…¡type alkali-free sweetening technology doesn'tremove the general sulfur but changing the poisonous mercaptan into neutralbisulfide .4,If the sulfur content is to reach the standard of the Europe â…¢, the followingmethod must be taken into consideration. First, the gasoline desulfurized is cut offinto light part and heavy part. Then the heavy part of gasoline containing higher sulfurcontent must apply the adsorption desulfurization process of Luoyang petroleum andchemical engineering corporation to be desulfurized further. At last, the light part andthe heavy part processed are mixed together again. This technology is a suitable andeconomic process for our low sulfur content in gasoline to reach the standard owing tolow investment, low operating cost and good effect of desulfurization.With regard to the problem of the mercaptan-sulfur content ineligible, this thesispointed out that the prime factors are the mercaptan content and structure in rawgasoline, the solubility of activator in gasoline, the relation between air pressure andthe pressure drop across reaction bed and activity of reaction bed in demercaptanprocess. It can be settled through optimizing the operation conditions of FCC todecrease the big molecule mercaptan and iso-mercaptan content, adjusting the ratio offeed gasoline and activator, reducing the bed pressure, increasing air pressure andchanging the old bed into a new one of advanced â…¡type alkali-free sweetening.This thesis also discussed the feasibility and economic benefits of transformingthe presentâ… type orâ…¡type alkali-free sweetening process into the gasolinesweetening process using fiber membrane invented by MECHI corporation. The resultshows that although this process can increase the efficiency of sweetening,decreaseoperation cost and alkali residue,the revamping is not taken into consideration nowbecause it will take 10 years to draw back the investment.