Hydrotreating Diesel

Tables 5.29 and 5.30 show an example of the effects of hydrotreated diesel fuels on a diesel passenger car already having a low level of pollution owing to technical modifications such as sophisticated injection and optimized combustion. In the standard European driving cycle (ECE + EUDC), between...

Finally it is likely that attention will be focused on emissions of polynuclear aromatics (PNA) in diesel fuels. Currently the analytical techniques for these materials in exhaust systems are not very accurate and will need appreciable improvement. In conventional diesel fuels, emissions of PNA thought to be carcinogenic do not exceed however, a few micrograms per km, that is a car will have to be driven for several years and cover at least 100,000 km to emit one gram of benzopyrene for example These already very low levels can be divided by four if deeply hydrotreated diesel fuels are used. 

Due to the water requirement of biocatalytic systems, BDS is typically carried out as a two-phase aqueous-oil process. However, increased sulfur removal rates could be accomplished by using an aqueous-alkane solvent catalytic system [46,203,220,255], The BDS catalytic activity depends on both, the biocatalysts and the nature of the feedstock. It can vary from low activity for crude oil to as high as 60% removal for light gas-oil type feedstocks [27,203,256], or 70% for middle distillates, 90% for diesel, 70% for hydrotreated diesel, and 90% for cracked feedstocks [203,256], The viscosity of the crude oil poses mixing issues in the two-phase oil-water systems however, such issues are minimal for distillate feedstocks, such as diesel or gasoline [257]. 

The treatment of hydrotreated diesel oil (250 ppm sulfur) to achieve deep desulfurization by CYKS1 was also reported [192], Sulfur reduction to 61 ppm was reported within 20 hours using 18.6 g/L biocatalyst concentration and water/oil ratio of 10. A rate of 10.6 mmol/kg dcw/h was reported for first four hours however, the rate was significantly reduced thereafter. 

Lubricity additives are used to compensate for the poor lubricity of severely hydrotreated diesel fuels. They contain a polar group that is attracted to metal surfaces, causing the additive to form a thin surface film. The film acts as a boundary lubricant when two metal surfaces come in contact. Two additive chemicals, fatty acids and esters, are typically used for this purpose. 

Further evaluation of the substrate of ECRD-1, using a nonhydrotreated diesel cut and a hydrotreated diesel fraction (99), showed that all isomers of DBT up to those with at least four attached carbons were desulfurized. ECRD-1 also desulfurized substituted BTHs, with between two and seven pendant carbons. Some compounds containing sulfidic sulfur were also shown to be metabolized, although the identities of these compounds were not identified. X-ray absorption spectroscopy indicated that some of the sulfur was only partially oxidized and that the residual oil contained sulfones and sultines. 

Sulfur-specific desulfurization of DBTs and other organosulfur compounds is best characterized in the bacterial genus Rhodococcus and exemplified by R. erythropolis strain IGTS8 and involves a series of oxidations of the sulfur moiety followed by a hydrolytic release of sulfite. This and related pathways have been shown to desulfurize a wide range of DBTs, BTHs, and sulfides. Moreover, deep desulfurization to low ppm levels of sulfur has been demonstrated with a variety of hydrotreated diesel range oils. 

Li WL, Tang H, Zhang T, Li Q, Xing JM, Liu HZ (2010) Ultra-deep desulfurization adsorbents for hydrotreated diesel with magnetic mesoporous aluminosilicates. AIChE J 56 1391-1396... 

In a series of experiments, hydrotreated diesel fuels were extensively characterized using a state-of-the-art technique for N-compound analysis. This procedure has been reported elsewhere. Briefly, it consists of a novel pre-concentration step for the N-compounds on a silica SPE column followed by recovery of the N-compounds. The GC analysis was performed on a Hewlett-Packard 6890 equipped with an atomic emission detector (AED) model G2350A. In most cases, more than 60% of the N-containing molecules in the feed and products can be accounted for, and all the major peaks have been identified. The results of these studies showed that alkylcarbazoles were the least reactive N-compound class. Furthermore, it was established that the reactivity was the lowest for carbazoles with a high degree of substitution. These results led to the question of whether alkylcarbazoles were the major inhibitors in the HDS of the refractory S-compounds. 

The results are shown in Figure 6. It can clearly be seen that 3-methylindole and 1,4-dimethylcarbazole are not major inhibitors, whereas acridine is. The three component blend behaves essentially as an additive combination of the three different N-compounds. There are also indications to the effect that acridine strongly inhibits the conversion of 1,4-dimethylcarbazole. In the absence of acridine, a high degree of conversion was obtained even for this low reactivity alkylcarbazole. The results indicate that alkylcarbazoles are not the major species of concern in HDS inhibition, even though they are the major species detected in hydrotreated diesel fuels. This suggests that there may be some components of diesel fuels that inhibit both HDN of alkylcarbazoles and HDS of alkyldibenzothiophenes. To see whether or not this is the case, additional studies were conducted on the N-free diesel fuel. 

Influence of hydrotreating a diesel fuel on particulate emissions. 

In the future, European and worldwide refining should evolve toward the production of relatively high cetane number diesel fuels either by more or less deeper hydrotreating or by judicious choice of base stocks. However, it is not planned to achieve levels of 60 for the near future as sometimes required by the automotive manufacturers. 

Diesel Fuel. Eederal diesel specifications were changed to specify a maximum of 0.05% sulfur and a minimum cetane index of 40 or a maximum aromatics content of 35 vol % for on-road diesel. Eor off-road diesel, higher sulfur is allowed. CARB specifications require 0.05% sulfur on or off road and 10% aromatics maximum or passage of a qualification test. Process technologies chosen to meet these specifications include hydrotreating, hydrocracking, and aromatics saturation. 

Figure 3. The Synsat Process for Deep Hydrotreating of Diesel Fuels...

A follow up paper reported on the substrate preference of the strain ECRD-1 [86], Two different diesel oils were studied LCCO (light catalytic-cycle oil), which is heavily hydrotreated and OB oil, (not treated by HDS). Sulfur molecules ranging from Cl to C4 DBTs and C2-C7 BTs were identified in the oils and assessed before and after treatment (Fig. 15). 

The bauxite-treated distillate was not further refined, but it has been shown that this olefinic diesel could be hydrotreated to produce a diesel fuel with high cetane number (Table 18.7).15,26 Although the cetane number of Fe-HTFT distil-... 

A light diesel fuel was produced by distillate hydrotreating of the straight-run Fe-HTFT material, while the heavier fraction was hydrocracked over a dewaxing catalyst, which produced a heavy diesel (Table 18.10). Some diesel fuel was also produced by C3-C4 olefin oligomerization over solid phosphoric acid by recycling the naphtha thus produced. It has previously been pointed out that solid phosphoric acid is not well suited for distillate production,42 and the hydrogenated... 

Diesel production involved a straightforward design. The olefinic distillate from olefin oligomerization was combined with the straight-run HTFT distillate and hydrotreated. The hydrotreated Fischer-Tropsch-derived distillate was blended with the distillate fraction from the natural gas liquids to produce diesel fuel. In 2003 another hydrotreater (noble metal catalyst) was added to the refinery to convert part of the hydrotreated HTFT distillate into low aromatic distillate to serve a niche market.56... 

Akzo-Fina CFI A process for improving the quality of diesel fuel by dewaxing, hydrotreating, and hydrocracking. Developed by Akzo Nobel and Fina from 1988. 

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. 

Among the classes of feedstock processed in the hydrocracker the most highly aromatics feed are light cycle oils produced in the FCC unit Once formed by cyclization and the hydrogen transfer mechanism discussed above, they accumulate in the product due to the absence of a metal function in the FCC catalyst and adequate hydrogen in the process environment. They are typically sold as low-value fuel oil, or hydrotreated to reduce sulfur content and improve their quality as diesel blend stocks. Another approach to upgrade their value even further... 

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