Distillate desulfurization

Table V presents the tabulated experimental results of hydro-treating the middle distillates. Desulfurization results reveal at least 96% sulfur removal at 700 F for all three middle distillate materials. Nitrogen...

These factors have akeady led to a substantial investment in fuel oil-desulfurization facilities in several parts of the world, notably Japan, the Middle East, and the Caribbean. With few exceptions these facilities have been based on indirect desulfurization, i,e., vacuum distillation, desulfurization of the vacuum gas oil, and reblending. This technique has limits in a market for fuels below the 1% sulfur level because none of the heavy, high sulfur vacuum residue is processed. To some extent this can be mitigated by preferentially blending this material to bunkers and by using naturally occurring low sulfur residues as blending stocks. 

The catalytic distillation desulfurization process developed by CDTech is significantly different from conventional hydrotreating.76 77 The most important portion of the CDTech desulfurization process is a set of two distillation columns loaded with desulfurization catalyst in a packed structure. In this process, the LCN, middle cut naphtha (MCN), and HCN are treated separately, under optimal conditions for each. The first column, called CDHydro, treats the lighter compounds of FCC gasoline and separates the heavier portion of the FCC gasoline for treatment in the second column. The second column, called CDHDS (catalytic distillation hydrodesulfurization), removes the sulfur from the heavier compounds of FCC gasoline. Figure 5.6... 

Biodesulfurization ( 93) Energy BioSystems Light and heavy distillate Desulfurization 23 No... 

Hydrofining usually involves only minor molecular changes of the feed with hydrogen consumption in the range of about 100 to 1,000 cu.ft./bbl. Typical applications include desulfurization of a wide range of feeds (naphtha, light and heavy distillates, and certain residua) and occasional pretreatment of cat cracker feeds. 

All refining operations may be classed as either conversion processes or separation processes. In the former, the feed undergoes a chemical reaction such as cracking, polymerization, or desulfurization. Separation processes take advantage of differences in physical properties to split the feed into two or more different products. Distillation, the most common of all refinery separation processes, uses differences in boiling points to separate hydrocarbon mixtures. 

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. 

Products from coking processes vary considerably with feed type and process conditions. These products are hydrocarbon gases, cracked naphtha, middle distillates, and coke. The gas and liquid products are characterized by a high percentage of unsaturation. Hydrotreatment is usually required to saturate olefinic compounds and to desulfurize products from coking units. 

Desulfurization of other diesel feedstocks from Total Raffinage was also reported by EBC. In these studies, different engineered biocatalysts were used. Two different middle distillate fractions, one containing 1850 ppm sulfur and other containing 650 ppm sulfur, were tested. R. erythropolis sp. RA-18 was used in one experiment and was reported to desulfurize the diesel from 1850 to < 1200ppm sulfur within 24 hours. On the other hand, it removed sulfur from a middle distillate with 650ppm sulfur to below 200 ppm sulfur [222], Various Pseudomonas strains were also tested in this study and reported to remove less amounts of sulfur. A favorable characteristic of the Pseudomonas strains is their inability to form stable emulsions, which can be useful trait for product recovery. 

Folsom, B. R. Schieche, D. R. DiGrazia, P. M., et al., Microbial Desulfurization of Alkylated Dibenzothiophenes From a Hydrodesulfurized Middle Distillate by Rhodococcus Erythropo-lis 1-19. Applied and Environmental Microbiology, 1999. 65(11) pp. 4967-4972. 

Lee, M. K. Prince, R. C. Pickering, I. J., et al., Microbial Desulfurization of Crude Oil Distillate Fractions Analysis of the Extent of Sulfur Removal and the Effect on Remaining Sulfur. Abstracts of Papers of the American Chemical Society, 1997. 213 p. 11-FUEL. 

The overall rate of desulfurization for enabling commercialization has to be greater than 1.2mmol/g dcw/h [1,12,13], The rates of desulfurization of model compounds such as DBT is usually higher than that achievable for real feedstocks such as diesel and other middle distillates. Thus, it is estimated that a more than 100-fold improvement in rates for removal of total sulfur (not just DBT) over wild-type organisms is necessary to achieve rates suitable for commercialization. 

DODD A process for the deep desulfurization of middle petroleum distillates. Introduced by Exxon in 1989. 

Assuming that demand for petroleum continues to increase at a rate of 1.2% per annum to 2010,37 and that all gasoline and diesel produced by U.S. refineries will have a sulfur content of less than 30 ppm, desulfurization of gasoline and diesel to these low levels will require extensive hydrotreating of both catalytic cracker feed and product of distillate. 

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