The Hydrotreating Process

The Hydrofining process is acmally one of many processes that exist, but all are very similar in nature.The main difference in the various processes is in know how . Each process differs by catalysts, equipment and/or methods, but these are rather narrow since the general field of hydrogenation is an old and well established art. 

While not shown here. Hydrofining also removes nitrogen from various nitrogen compounds. Nitrogen is one of the causes of instability. Removal of nitrogen is much more difficult than sulfur removal. 

Group II — Ramovol of Oxygen (Stability A Combustion Improvement] 

Saturation of olefins other than reactive olefins usually is not desired. The added hydrogen is often expensive or useful elsewhere, and it does not provide any real improvement in product quality. Acmally, product quality may be reduced in the case of gasolines. Research octane number losses may be correlated with increasing olefin saturation. So in many cases, hydrodesulfurization conditions are selected with an eye toward minimizing olefin saturation over and above that needed for product quality improvement. There is one exception saturation of certain olefins shows substantial improvements in Motor octane number. This is true for iso- and n-pentenes and to a lesser extent for higher boiling isoolefins. The higher n-olefins show octane losses upon saturation. 

The discussion that follows will show the effects of several operating variables on product inspections. The effects of the variables are illustrated best by deep desulfurization of heavier gas oils. 

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In regard to kerosene, the hydrotreating processes are used to reduce aromatics in order to improve the smoke point. 

Hydrotreating reduces the sulfur content of all the products. With hydrotreated feeds, more of the feed sulfur goes to coke and heavy liquid products. The same sulfur atoms that were converted to H S in the FCC process are also being removed first in the hydrotreating process. The remaining sulfur compounds are harder to remove. The heavier and more aromatic the feedstock, the greater the level of sulfur in the coke (Table 2-7). 

As processing conditions increase, that is pressure and temperature, the hydrotreating process emerges more as a hydrocracking/ hydrodesulfurization/hydrodearomatizing event. Deeper desulfurization of processing/ product streams is inevitable. 

CATALYSTS USED IN THE HYDROTREATING PROCESS AND ITS RECENT DEVELOPMENT... 

In the last years, rhodium-based catalysts have shown a relatively high activity and selectivity for NO reduction to N2. The highest selectivity distinguishes the Rh catalyst from other Pt- and Pd-based ones in the ability to promote N-pairing in adsorbed NO molecules before the N-0 bond is broken. This property is related to the highly dispersed supported Rh catalysts used in practice [10]. Hence, clean combustion (CO elimination and NOx reduction) can be another promising use of the catalysts based on RhMoe, in addition to the hydrotreating processes. 

E.g. in the so-called "pseudo-equilibrium model, developed by Sylvester [53-56], the same design procedure is used as in a single phase catalytic gas phase reaction, where the mass transfer resistance is replaced by a suitable overall term. Bulk flow and dispersion of the liquid phase are neglected and the whole transport mechanisms are lumped into the equilibrium of the reactant concentrations between gas-, liquid- and particle phase. It is an application of the same principle used successfully in fluid/fluid reactions [57], But the necessary precondition is that the rate of reaction is slow compared to the transfer rate across the phase boundaries, so that equilibrium can really by assured. This might be justified in some of the hydrotreating processes, but certainly not in case of an aqueous liquid phase, existing in waste water treating. Earlier models used in petroleum industry have taken in-... 

The hydrotreating process needs a large amount of hydrogen to treat crude oils. Pressure varies from 10-20 atm for naphtha to 25—40 atm for gas oil. Temperature conditions are generally 320-340°C. However, for some hydrocracking residues, pressure and temperature conditions can reach 100-150 atm and 400-440 C. 

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. 

Table 1. Main chemical reactions involved in the hydrotreating process.

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