Desulfurization present

Dautzenberg, F.M. van Klinken, J. Pronk, K.M.A. Sie, S.T. Wijffels, J.-B. Catalyst Deactivation through Pore Mouth Plugging during Residue Desulfurization presented at the 5th International Symposium on Chemical Reaction Engineering Houston, March 13-15,1978. 

Gupta, R. P., and Gasper-Galvin, L. D., 1991, Screening of Supported Metal Oxides for Hot-Gas Desulfurization, presented at the 1991 AIChE Annual Meeting, Los Angeles, CA, Nov. 17-21. 

Since the original cmde oils contain some sulfur compounds, the resulting products and gasolines also contain sulfur compounds, including hydrogen sulfide, mercaptans, sulfides, disulfides, and thiophenes. The processes used to sweeten, ie, desulfurize, the products depend on the type and amount of the sulfur compounds present and the specifications of the finished gasoline or other stocks. 

Absorption Processes. Most flue gas desulfurization (FGD) systems are based on absorption of the sulfur dioxide into a n on regen erabi e alkali-salt solvent. Sulfur absorbed using n on regen erabi e solvents is not recovered and the alkali sulfite—sulfate produced presents a disposal problem. 

Reaction With Sulfur. An important use of calcium carbide has developed in the iron (qv) and steel (qv) industries where the carbide has been found to be an effective desulfurizing agent for blast-furnace iron. Calcium carbide and sulfur present in the molten metal react... 

Effect of HjS, Carbon Oxides, Etc. Hydrogen sulfide in the treat gas has an inhibiting effect on the kinetics of hydrotreating. Being a product of the desulfurization reactions, HjS must diffuse from the catalyst surface into the bulk gas stream. Any HjS present beyond that formed, further slows down the rate of diffusion with a consequent decrease in the amount of desulfurization for a given amount of catalyst. Therefore, additional catalyst would be required. 

Although desulfurization is a process, which has been in use in the oil industry for many years, renewed research has recently been started, aimed at improving the efficiency of the process. Envii onmental pressure and legislation to further reduce Sulfur levels in the various fuels has forced process development to place an increased emphasis on hydrodesulfurization (HDS). For a clear comprehension of the process kinetics involved in HDS, a detailed analyses of all the organosulfur compounds clarifying the desulfurization chemistry is a prerequisite. The reactivities of the Sulfur-containing structures present in middle distillates decrease sharply in the sequence thiols sulfides thiophenes benzothiophenes dibenzothio-phenes (32). However, in addition, within the various families the reactivities of the Substituted species are different. 

Feeds to hydrotreatment units vary widely they could he any petroleum fraction, from naphtha to crude residues. The process is relatively simple choosing the desulfurization process depends largely on the feed type, the level of impurities present, and the extent of treatment needed to suit the market requirement. Table 3-12 shows the feed and product properties from a hydro treatment unit. ... 

The more generally known mercuric oxide-mercuric chloride hydrolysis 2 may also be used, and in the present case it gives a yield of about 90%. The reductive desulfurization of Part E is also based on the work of Mukaiyama.12 It is clearly superior to Raney nickel desulfurization, which gives only 36-45% of 3-benzylindole. 

Catalytic desulfurization is at present carried out industrially by at least three of the major types of gas-liquid-particle operations referred to in Section I trickle reactors, bubble-column slurry reactors, and gas-liquid fluidized reactors. 

Sulfur in cmde oil is mainly present in organic compounds such as mercaptans (R-SH), sulfides (R-S-R ) and disulfides (R-S-S-R ), which are all relatively easy to desulfurize, and thiophene and its derivatives (Fig. 9.2). The latter require more severe conditions for desulfurization, particularly the substituted dibenzothiophenes, such as that shown in Fig. 9.2. Sulfur cannot be tolerated because it produces sulfuric add upon combustion, and it also poisons reforming catalysts in the refinery and automotive exhaust converters (particularly those for diesel-fueled cars). Moreover, sulfur compounds in fuels cause corrosion and have an unpleasant smell. 

Effects of Sulfur Coverage. The kinetic results reported in the previous section are from reactions performed on surfaces that are initially clean. The surfaces after reaction were examined by AES and shown to be covered with carbon and sulfur at coverages close to a monolayer. It is interesting to note that although this is the case even after reaction times on the order of minutes the reaction rate is constant for a period of approximately one hour. Either the reaction is occurring on top of this oarbon/sulfur layer or these species are present as sulfur containing hydrocarbon fragments that are intermediates in the desulfurization process. 

Data presentations should include the parent compound and all toxic transformation products. This is particularly important for oxidation of sulfide linkages to sulfoxides or sulfones. These products are often equally toxic to the parent with increased availability. Attention should also be given to oxidative desulfuration of phosphorothionate esters. 

As one more common example of liquid fuels present reference may be drawn to liquified petroleum gas (LPG) or bottled gas or refinery gas. This fuel is obtained as a by-product during the cracking of heavy oils or from natural gas. It is dehydrated, desulfurized and traces of odours organic sulfides (mercaptans) are added in order to identify whether a gas leak has occurred. Supply of LPG is carried out under pressure in containers under different trade names. It consists of hydrocarbons of great volatility such that they can occur in the gaseous state under atmospheric pressure, but are readily liquifiable under high pressures. The principal constituents of LPG are n-butane, iso-butane, butylene and propane,... 

In the fourth and final step, the intermediate 2-(2,-hydroxyphenyl)ethen-l-sulfmate (HPESi ) is desulfinated to 2-(2 -hydroxyphenyl)ethan 1-al (HPEal). As seen from Fig. 4, this step cannot be catalyzed by the arylsulfinate desulfinase like DszB. Instead, the enzyme has to be an alkenylsulfmate desulfinase. The alkenyl C-S bond as present in the intermediate, can only be desulfurized by hydroxylase-type enzyme, giving an enol, which can then tautomerize to HPEal and sulfite. However, the identity of the sulfur-containing product has not been confirmed [34],... 

Pseudomonas has been disclosed [233], The method consists of mutating the genes by UV irradiation or other methods and separating the desired protein. A specific amino acid sequence, present in that protein, shows the function for regulating the expression of benzothiophene oxidase gene. The fact that the protein is thought to be useful for both, desulfurization and for purification of sulfur contaminated soil or waste waters indicates a probable destructive pathway. 

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