BDS process is an oxidation reaction between aerobic bacteria and organic sulfide produced in nature. Selective oxidation destroys the C-S bond, oxidizes sulfur atoms into sulfate or sulfite and transfers it to the water phase, while the skeleton structure of DBT oxidizes into hydroxybiphenyl and remains in the oil phase, thus achieving the purpose of removing sulfide. BDS technology has been developed for decades since its appearance, and it is still in the stage of development and research. Because BDS technology has many advantages, it can be organically combined with existing HDS devices, which can not only greatly reduce the production cost, but also have stronger economic competitiveness than HDS because of the high added value of organic sulfur products. At the same time, BDS can also be combined with catalytic adsorption desulfurization, which is an effective method to realize deep desulfurization of fuel oil. Therefore, BDS technology has a broad application prospect, and it is predicted that industrial devices will appear around 20 10.
4 new desulfurization technology
4. 1 oxidation desulfurization technology
Oxidative desulfurization technology is to oxidize thiophene sulfide into sulfoxide and sulfone with oxidant, and then remove sulfoxide and sulfone from oil by solvent extraction. The oxidant is recycled after regeneration. At present, low sulfur diesel oil is produced by hydrogenation technology. Because the structure of dimethyl dibenzothiophene in diesel oil is stable and hydrodesulfurization is difficult, in order to reduce the sulfur content in oil to 10 μg/g, higher reaction pressure and lower space velocity are needed, which undoubtedly increases the investment cost and production cost of hydrogenation technology. Oxidation desulfurization technology can not only meet the requirements of diesel fraction 10 μg/g, but also set a simple and feasible desulfurization device at the redistribution outlet, which is a better way to meet the final oil quality.
(1) ASR-2 oxidation desulfurization technology
ASR-2 [12] oxidation desulfurization technology is a new desulfurization technology developed by Unipure Company. This technology has the advantages of low investment and operating cost, mild operating conditions, no need for hydrogen source, low energy consumption, no pollution emission, production of ultra-low sulfur diesel oil, flexible device construction and so on, which provides an economical and reliable method for refineries and sales outlets to meet the sulfur content requirements of oil products.
In the experimental process, the technology can finally reduce the sulfur content in diesel oil from 7000 μg/g to 5μ g/g/g. In addition, the technology can also be used to produce ultra-low sulfur diesel oil as a blending component of oil products to meet the needs of oil processing and sales markets. At present, ASR-2 technology is undergoing pilot test and industrial experiment design. The process flow is as follows: sulfur-containing diesel oil is mixed with the aqueous phase of oxidant and catalyst in a reactor, and thiophene sulfur-containing compounds are oxidized to sulfone compounds at near normal pressure and mild temperature; Then, the water phase containing waste catalyst and sulfone is separated from the oil phase and sent to the regeneration part to remove sulfone and regenerate the catalyst; Sending the oil phase containing sulfone into an extraction system to realize the separation of sulfone and oil phase; The sulfone obtained from the water phase and the oil phase is sent to the treatment system together to produce chemical products with high added value.
Although ASR-2 desulfurization technology has been studied for many years, it has not been applied in industry, mainly because some technical problems such as catalyst regeneration cycle and oxide removal have not been solved. ASR-2 technology can make the sulfur content of diesel products reach 5 μ g/g/g. Compared with the sulfur content of diesel products with hydrotreating technology of 30 μg/g and 15 μg/g respectively, the sulfur content and total treatment cost are much less. Therefore, if some technical problems can be solved well, ASR-2 oxidation desulfurization technology will have a very broad market prospect.
(2) Ultrasonic oxidation desulfurization technology
SUPHCO [13] technology is a new type of desulfurization technology jointly developed by the University of Southern California and Suphco. The chemical principle of this technology is basically the same as ASR-2 technology, but the difference is that SulphCo technology adopts ultrasonic reactor, which strengthens the reaction process and has better desulfurization effect. The process is as follows: raw materials are mixed with water phase containing oxidant and catalyst in a reactor, and under the action of ultrasonic waves, small bubbles are rapidly generated and burst, so that the oil phase and the water phase are violently mixed, and ultrasonic waves can rapidly increase the local temperature and pressure in the mixed material in a short time, and hydrogen peroxide is generated in the mixed material to participate in the sulfide reaction; Sulfone and sulfate are removed by solvent extraction and recycled after solvent regeneration. Sulfone and sulfate can be used to produce other chemical products.
SulphCo carried out pilot scale-up experiments after completing the laboratory work, and achieved satisfactory results, that is, the sulfur content of diesel oil with different sulfur content can be reduced to below 10 μg/g after being treated by oxidation desulfurization technology. At present, Bechtel Company is carrying out the industrial test of sulfur molding technology.
4.2 Photoplasma Desulfurization Technology [14]
The National Institute of Pollution and Resources of Japan and the University of Tubingen in Germany have studied the desulfurization by ultraviolet irradiation and plasma technology. The mechanism is as follows: disulfide forms free radicals by breaking S-S bonds, and thioether and mercaptan form free radicals by breaking C-S and S-H bonds respectively. The reaction is as follows:
Oxidant-free reaction:
CH3S- + -CH3 CH4+CH2 ==== S
CH3S-+ch 3c H2 r CH3SH+CH2 = = = = SCH2R
CH3S-+CH3S-ch 3s CH3
CH3S-+CH2 = = = = S ch 3s ch2s--CH3 ch 3s CH2 sch 3
Reactions in the presence of oxidants:
CH3S- + O2 CH3SOO- RH CH3SOOH + R-
SO3+ -CH3
CH3SOOH Rr CH3SO- + -OH
CH3SO- + RH CH3SOH + R-
3CH3SOOH CH3SOOSCH3 + CH3SO3H
According to the different molecular structures, the products of this technology are alkanes, alkenes, aromatics, sulfides or elemental sulfur, and the desulfurization rate can reach 20% ~ 80%. If air is introduced at the same time of irradiation, the desulfurization rate can be increased to 60% ~ 100%, and sulfur can be converted into SO3, SO2 or sulfur, which can be removed by washing with water.