Hydrogen consuming processes

Hydrotreating is a hydrogen-consuming process primarily used to reduce or remove impurities such as sulfur, nitrogen, and some trace metals from the feeds. It also stabilizes the feed hy saturating olefrnic compounds. 

Figure 16.1 Pathways toward hydrogen-consuming processes involving water-gas shift including a possible ultralow temperature shift.

So what is needed to set up a hydrogen balance Firstly, flow rates, compositions and pressures must be determined at certain key points in the hydrogen system. Flow diagrams of the hydrogen-consuming processes are also needed so that reactor and separator configurations as well as recycle locations can be determined. 

Operating at high pressure (150 to 200 bar) in the presence of hydrogen, the process is a large consumer of catalyst because of the high amount of metals in the feedstock which deposit on the catalyst. 

Most refinery/petrochemical processes produce ethylene that contains trace amounts of acetylene, which is difficult to remove even with cryogenic distillation. Frequently it is necessary to lower the acetylene concentration from several hundreds ppm to < 10 ppm in order to avoid poisoning catalysts used in subsequent ethylene consuming processes, such as polymeri2ation to polyethylene. This can be accompHshed with catalytic hydrogenation according to the equation. 

Fig. 15.3 C02 emissions associated with the three central hydrogen production cases of Fig. 15.2. In each case the impact of C02 capture at the central manufacturing complex is indicated. Note that C02 capture is an energy consuming process, causing an increase in the C02 produced in the CCS cases. The lines between bars serve as guides to the eye, illustrating reduction in total C02 emitted upon application of CCS.

Compression of hydrogen consumes energy depending on the thermodynamic process. The ideal isothermal compression requires the least amount of energy (just compression work) and the adiabatic process requires the maximum amount of energy. The compression energy W depends on the initial pressure p and the final pressure pf, the initial volume V and the adiabatic coefficient y ... 

Generally, hydrodesulfurization of naphtha feedstocks to produce catalytic reforming feedstocks is carried to the point where the desulfurized feedstock contains less than 20 ppm sulfur. The net hydrogen produced by the reforming operation may actually be sufficient to provide the hydrogen consumed in the desulfurization process. 

As severity is decreased, aromatics and nitrogen in the product rise and the kerosene and naphtha must be further hydrotreated to make jet fuel and reformer feed. This type of operation constitutes Case 2A, with initial severity corresponding to about 2000 SCF of hydrogen consumed per barrel (Figure 5). The case was included to see if the reduction in the initial hydrotreating cost was larger than the increased cost due to the need for additional lower severity downstream processing. 

The objective of the present work is to evaluate the effect of a wide range of process or reaction variables— reaction temperature, hydrogen partial pressure, catalyst loading, and reaction time—on hydrodesulfurization and hydrogenation of filtered liquid product (coal-derived liquid) obtained from the coal dissolution stage in the presence of a commercial presulfided Co-Mo-Al catalyst. The selectivity for desulfurization over hydrogenation (Se) is used to rate the effectiveness of the above mentioned process variables. Se is defined as the fraction of sulfur removal per unit (g) of hydrogen consumed, that is,... 

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