Diesel hydrocracking

Hydrocracking makes very good quality diesel fuels concerning the cetane number, cold behavior, stability, and sulfur content. However this type of stock is only available in limited quantities since the process is still not widely used owing essentially to its high cost. 

Hydrocracking is the preeminent process for making high quality kerosene and diesel oil (Figure 10.10). 

Hydrocracking is a major process for the production of diesel motor fuel catalytic cracking is its counterpart for the gasoline production. 

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. 

Additional gasoline and diesel fuel can be produced through further refining, such as hydrocracking or catalytic cracking of the wax product. 

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. 

A major use of gas oil is as a fuel for diesel engines. Another important use is as a feedstock to cracking and hydrocracking units. Gases produced from these units are suitable sources for light olefins and LPG. Liquefied petroleum gas LPG may be used as a fuel, as a feedstock to... 

Figure 8.17. Hydrocarbon distribution of the products formed by Fischer-Tropsch synthesis over cobalt-based catalysts and by additional hydrocracking, illustrating how a two-stage concept enables optimization of diesel fuel yield. [Adapted from S.T. Sie,...

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... 

Superficially the Oryx GTL refinery design has much in common with the SMDS process, but there are important differences. There is no separate hydrotreater, which limits production of chemicals, such as waxes. The hydrocracker employs the Chevron Isocracking technology, which is based on a sulfided supported base-metal catalyst that was designed for crude oil conversion. The operating conditions of the hydrocracker are also more severe (>350°C, 7 MPa) than those required by the SMDS process (300-350°C, 3-5 MPa). Only intermediate products are produced (Table 18.13),5 with the naphtha slated as cracker feed and the distillate as blending component for diesel fuel. 

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. 

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