Diesel fuel production

HTFT syncrude is easier to refine to on-specification transportation fuels than LTFT syncrude. This is partly due to its olefinic nature, giving it considerable synthetic ability, and partly due to the large proportion of material already in the fuels boiling range (C5-360°C). Historically fuels refining from HTFT syncrude focused mainly on motor gasoline production and only to a lesser extent on diesel fuel production. Jet fuel production became possible only recently (2008) with the international qualification of fully synthetic jet fuel. 

A spedal feature of zeolites which makes them such superb catalysts in some cases is their shape selectivity. The shape selectivity may arise in three ways reactant selectivity, product selectivity and, of lesser importance, transition state selectivity. Reactant selectivity arises from the ability of only certain molecules to be absorbed into the zeolite cavities and thus reach the active acid sites. An important commercial process that exploits this type of reactant selectivity is catalytic dewaxing. Compared to the branched isomers, the straight chain alkanes have low octane numbers and contribute to wax formation in diesel fuel. Product selectivity is derived from the fact that only certain products are of the correct dimension to escape from the zeolite once they have been formed. Transition state selectivity relies upon the fact that certain intermediates, which are formed during a chemical reaction at the active site, will not fit in... 

Hirano, T. (2001) Advances in Diesel fuel Production in Japan, Idemitsu Kosan Co. Ltd, Tokyo. 

Figure 3 shows the GC-FPD chromatograms that illustrate reactivities of various sulfur compounds in gas oil HDS for diesel fuel production. In deep HDS, the conversion of these key substituted dibenzothiophenes largely determines the required conditions. In gas oils, the reactivities of (alkyl-substituted) 4-methyldibenzothiophene and 4,6-dimethyldibenzothiophene are much lower than those of other sulfur-containing compounds " . Gates and Topsoe pointed out in 1997 that 4-methyldibenzothiophene and 4,6-dimethyldibenzothiophene are the most appropriate compounds for investigations of candidate catalysts and reaction mechanisms. 

Japan, Germany, and the United States recently the Shenhua Group Gorp. in Ghina took the initiative to start the construction of a commercial 5000 t/day plant for mainly diesel fuel production in the Inner Mongolia. 

First of all, a technical clarification is necessary in the wider sense, motor fuels are chemical compounds, liquid or gas, which are burned in the presence of air to enable thermal engines to run gasoline, diesel fuel, jet fuels. The term heating fuel is reserved for the production of heat energy in boilers, furnaces, power plants, etc. 

For a long time the official specifications for diesel fuel set only a mciximum viscosity of 9.5 mm /s at 20°C. Henceforth, a range of 2.5 mm /s minimum to 4.5 mm /s maximum has been set no longer for 20°C but at 40°C which seems to be more representative of injection pump operation. Except for special cases such as very low temperature very fluid diesel fuel and very heavy products, meeting the viscosity standards is not a major problem in refining. 

In Europe, the classification of diesel fuels according to cold behavior is shown in Tables 5.13 and 5.14. The products are divided into ten classes, six for temperate climates, four for arctic zones. 

Figure 5.9 shows an example of the efficiency of these products. The reductions of CFPP and pour point can easily attain 6 to 12°C for concentrations between 200 and 600 ppm by weight. The treatment cost is relatively low, on the order of a few hundredths of a Franc per liter of diesel fuel. In practice, a diesel fuel containing a flow improver is recognized by the large difference (more than 10°C) between the cloud point and the CFPP. 

The European specifications require a minimum cetane number of 49 for the temperate climatic zones and the French automotive manufacturers require at least 50 in their own specifications. The products distributed in France and Europe are usually in the 48-55 range. Nevertheless, in most Scandinavian countries, the cetane number is lower and can attain 45-46. This situation is taken into account in the specifications for the arctic zone (Table 5.14). In the United States and Canada, the cetane numbers for diesel fuels are most often less than 50. 

Table 5.15 gives some physical-chemical characteristics of selected main refinery streams capable of being added to the diesel fuel pool. Also shown is the weight per cent yield corresponding to each stock, that is, the quantity of product obtained from the feedstock. 

As their name implies, these products are used essentially for jet aircraft they can also be used in stationary turbines, which are themselves adaptable to a large variety of fuels such as natural gas, LPG, diesel fuel, and heating oil. 

It is mainly in cold behavior that the specifications differ between bome-heating oil and diesel fuel. In winter diesel fuel must have cloud points of -5 to -8°C, CFPPs from -15 to -18°C and pour points from -18 to 21°C according to whether the type of product is conventional or for severe cold. For home-heating oil the specifications are the same for all seasons. The required values are -l-2°C, -4°C and -9°C, which do not present particular problems in refining. 

The flroduction of No. 1 fuel oil is thus quite marginal whereas the BTS and TBTS products will be undergoing important development in the coming years. In applications as diesel fuel, ordinary No. 2 fuel, and No. 2 BTS fuel are the most commonly used. 

The tendency of the color to become darker with time is often indicative of chemical degradation. The test is conducted with the aid of a colorimeter (NF T 60-104 and ASTM D 1500) and by comparison with colored glass standards. The scale varies from 0.5 to 8. The French specifications stipulate that diesel fuel color should be less than 5, which corresponds to an orange-brown tint. Generally, commercial products are light yellow with indices from 1 to 2. 

The flash point of a petroleum liquid is the temperature to which it must be brought so that the vapor evolved burns spontaneously in the presence of a flame. For diesel fuel, the test is conducted according to a closed cup technique (NF T 60-103). The French specifications stipulate that the flash point should be between 55°C and 120°C. That constitutes a safety criterion during storage and distribution operations. Moreover, from an official viewpoint, petroleum products are classified in several groups according to their flash points which should never be exceeded. 

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. 

All modern refineries have conversion units, designed to transform black effluent streams into lighter products gas, gasoline, diesel fuel. Among these conversion units, coking processes take place by pyrolysis and push the cracking reaction so far that the residue from the operation is very heavy it is called coke . 

The reaction mechanism for these products is not clearly understood, but the introduction of organo-metallic compounds (barium or iron salts in colloidal suspension) has been shown to have a beneficiai action on the combustion of diesel fuel in engines and reduce smoke. However, these products cause deposits to form because they are used in relatively large proportions (on the order 0.6 to 0.8 weight %) to be effective. 

The elimination of lead, the reduction of aromatics in gasoline, and the desulfurization of diesel fuels are oing to require significant reformulations of these products that will irripiy development of specific additives that allow the refiner to optimize costs while meeting the required specifications. 

However, this conventional method presents a certain number of limitations. In the first place, the traditional end-use property itself can be difficult to determine. Consider the cetane number for example is it a good characterization of diesel fuel with respect to its behavior in commercial diesel engines In the second place, concern for protecting the environment imposes new specifications which are often specifications linked to the composition of products very low content of certain contaminants, reduced levels of certain families of compounds, or even a specific compound as already discussed. 

Petroleum Industry Gas chromatography is ideally suited for the analysis of petroleum products, including gasoline, diesel fuel, and oil. A typical chromatogram for the analysis of unleaded gasoline is shown in Figure 12.25d. 

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