Distillate middle

European countries, including the UK, and covers about 5% of the total European diesel market. It contains less than 5 vol%. of mono-ring aromatics and less than 0.1 vol%. of di- and higher-ring aromatics. Eurthermore it is low in sulfur. Both EC and SEC methods have been developed for the rapid analysis of aromatics in diesel fuel. 

1 AN EC-SEC SYSTEM EOR THE ANALYSIS OE TOTAL AROMATICS IN DIESEL LULL 

Different approaches utilizing multidimensional EC or SEC systems have been reported for the analysis of middle distillates in diesel fuel. A method, based on the EC separation of paraffins and naphthenes by means of a micro-particulate, organic gel column has been described (23, 24). The complete system contained up to four different EC columns, a number of column-switching valves and a dielectric constant detector. However, the EC column for the separation of paraffins and naphthenes, which is an essential part of the system, is no longer commercially available. 

A more sophisticated method, giving a much more detailed characterization, involves the on-line coupling of EC and GC (LC-GC). Analysis schemes for middle distillates (kerosine, diesel and jet fuels) combining EC and GC have been reported by various authors (25-31). However, only Davies et al. (25) andMunari et al. (27) have reported on the required automatic transfer of all of the individual separated fractions from the EC unit the GC system. Davies used the loop-type interface and Munari the on-column interface. Only Beens and Tijssen report a full quantitative characterzation by means of LC-GC (31). 

Since the majority of middle distillates are used as a fuel, combustion of these products will contribute to SO2/SO3 air pollution and acid rain. However, in catalytic processes of petroleum fractions Sulfur levels are also important. Lor instance, quantities 

1 AN LC-SFC SYSTEM FOR THE ANALYSIS OF TOTAL AROMATICS IN DIESEL FUEL 

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Finally, note that hydrocracking is ideal for obtaining middle distillate cuts that can be used in jet fuel formulation. 

FOD is very similar to diesel fuel. Both are designated in economic studies by the generic term, middle distillates . 

In two stages with recycle to the second stage, the conversion per pass is approximately 50 wt. % and the selectivity to middle distillates is maximal 75 to 80 wt. %. However, the investment is clearly higher and is justified only when feedstocks are difficult to convert and that their content in nitrogen is high. Figure 10.11 represents two variants of the hydrocracking process. 

Maier, C.E., P.-H. Bigeard, A. Billon and P. Dufresne (1988), Boost middle distillate yield and quality with a new generation of hydrocracking catalyst . NPRA paper No. AM-88-76, Annual meeting, San Antonio, TX. 

Simple conventional refining is based essentially on atmospheric distillation. The residue from the distillation constitutes heavy fuel, the quantity and qualities of which are mainly determined by the crude feedstock available without many ways to improve it. Manufacture of products like asphalt and lubricant bases requires supplementary operations, in particular separation operations and is possible only with a relatively narrow selection of crudes (crudes for lube oils, crudes for asphalts). The distillates are not normally directly usable processing must be done to improve them, either mild treatment such as hydrodesulfurization of middle distillates at low pressure, or deep treatment usually with partial conversion such as catalytic reforming. The conventional refinery thereby has rather limited flexibility and makes products the quality of which is closely linked to the nature of the crude oil used. 

Thermal Cracking. In addition to the gases obtained by distillation of cmde petroleum, further highly volatile products result from the subsequent processing of naphtha and middle distillate to produce gasoline, as well as from hydrodesulfurization processes involving treatment of naphthas, distillates, and residual fuels (5,61), and from the coking or similar thermal treatment of vacuum gas oils and residual fuel oils (5). 

Fig. 3. The Shell middle distillate synthesis (SMDS) process. HPS = heavy paraffin synthesis. HPC = heavy paraffin conversion.

Fig. 4. Product compositions as a function of carbon number for the Shell middle distillate synthesis process (a) the Fischer-Tropsch product following...

Table 3. Compounds Found in Petroleum Middle-Distillates ...

SASOL South African operation of synthetic fuels plants SMDS Shell Middle Distillate Synthesis Process... 

Shell Gas B.V. has constructed a 1987 mVd (12,500 bbhd) Fischer-Tropsch plant in Malaysia, start-up occurring in 1994. The Shell Middle Distillate Synthesis (SMDS) process, as it is called, uses natural gas as the feedstock to fixed-bed reactors containing cobalt-based cat- yst. The heavy hydrocarbons from the Fischer-Tropsch reactors are converted to distillate fuels by hydrocracking and hydroisomerization. The quality of the products is very high, the diesel fuel having a cetane number in excess of 75. 

Middle Distillates Lower volatility distillates including diesel fuel, kerosene, jet fuels, and lighter fuel oils. 

Calcium chloride is the most common nonregenerative reagent used to dry low molecular weight refinery streams to moderately low dew points. Anhydrous potassium or sodium hydroxide have also been used at times to dry liquefied petroleum gas. Sodium chloride is used most commonly to remove entrained and some soluble water from middle distillate streams. 

J. Beens and R. Tijssen, An on-line coupled HPLC-HRGC system for the quantitative chai acterization of oil fractions in the middle distillate range , J. Microcolumn Sep. 7 345-354(1995). 

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. 

It is for this reason that not only the various Sulfur-containing groups present, but also the mono- and dimethyl-substituted species of benzothiophenes and dibenzoth-iophenes have to be separated and quantified individually. As the number of sulfur compounds present in (heavy) middle distillate fractions may easily exceed 10 000 species, a single high resolution GC capillary column is unable to perform such a separation. 

Figure 14.18 Typical GC cliromatogram of the separated mono-aromatics fraction of a middle distillate sample the numbers indicate the retention time of the various -alkanes.

Figure 14.19 Typical GC chromatogram of the separated di-aromatics fraction of a middle distillate sample Peak identification is as follows 1, naphthalene 2, 2-methylnaphthalene 3, 1-methylnaphthalene 4, biphenyl 5, C2-naphthalenes 6, C3-naphthalenes 7, C4-naph-thalenes 8, C5+-naphthalenes 9, benzothiophene 10, methylbenzothiophenes 11, C2-ben-zotliiopIrenes. Note the clean baseline between naphthalene and the methylnaphthalenes, which means that no overlap with the previous (mono-aromatics) fraction has occuned.

J. Beens and R. Tijssen, The characterization and quantitation of sulfur-containing compounds in (heavy) middle distillates by FC-GC-FID-SCD , J. High Resolut. Chromatogr. 20 131-137 (1997). 

Liquid fuels for use in internal-combustion engines are extracted and refined from crude oil, with diesel fuels being part of the middle distillate or kerosene fraction. Kerosene was initially derived from coal pyrolysis. The initial main use of this type of distillate was for the kerosene lamp, which had replaced lamps based on whale oil. 

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