Diesel hydrotreating process

The case study is a diesel hydrotreating process and the flowsheet is shown in Figure 9.14. The combined feed is preheated by reaction effluent via E-lOO and furnace and then goes to the reactor. After transferring heat to the combined feed, the reaction effluent is cooled in the air cooler and then goes to the high-pressure... 

FIGURE 9.16. Composite curves for example diesel hydrotreating process. 

The process can be operated at moderate pressures, 50 - 70 bar at reactor outlet. Temperatures have to be low (below 320 °C) to achieve deep hydrogenation. Space velocities are low (below 0,5 hr ) if low product aromatic contents of e.g. 5 vol% are required. The first step of the process is not different from a typical diesel hydrotreating unit. Five different catalyst types in staged loading can be used to obtain the required desulfurization and hydrogenation level. Catalysts are only available under license. At the spring NPRA meeting of 1995 it was announced that 13 companies have taken a license. This impressive success is for an important... 

Trickle-bed reactors are widely used in hydrotreating processes, i.e., hydrodesulfurization of gasoline and diesel fuel, in petroleum refining, chemical, petrochemical, and biochemical processes. The knowledge of hydrodynamic parameters is vital in the design of a TBR because the conversion of reactants, reaction yield, and selectivity depend not only on reaction kinetics, operating pressure, and temperature, but also on the hydrodynamics of the reactor. Special care is also required to prevent flow maldistribution, which can cause incomplete catalyst wetting in some parts... 

TABLE 9.3. Process Stream Data for the Diesel Hydrotreating Unit... 

The diesel hydrotreating (DHT) process design is shown in Figure 9.14. The existing design is not energy efficient and thus requires relatively high fuel consumption in... 

The hydrotreating process for desulfurization of petroleum products was developed in the 1960s mainly to reduce the sulfur concentration in gasoline and diesel oil to reduce sulfur dioxide emissions. In Europe, North America, and Japan this has led to a strong decrease in sulfur emissions caused by transportation fuels for road traffic. A similar trend can be forecast for countries in Asia like China and India, where until recently the sulfur limit has been much higher. 

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...

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]. 

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. 

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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