What are the main operational factors affecting reformation pre-hydrogenation?

(1) Reaction pressure: Increasing the reaction pressure can accelerate the hydrogenation reaction, facilitate the removal of impurities (especially nitrogen removal), enhance the degree of hydrogenation, and at the same time reduce carbon deposition on the catalyst, thereby extending its lifespan. (2) Reaction temperature: Increasing the reaction temperature can accelerate the reaction rate; therefore, raising the temperature promotes the hydrogenation reaction and reduces the impurity content in the refined oil. However, excessively high temperatures facilitate cracking reactions, resulting in a decrease in the yield of liquid products, and they also speed up carbon deposition on the catalyst, shortening its lifespan. (3) Space velocity: Reducing the space velocity increases the contact time between the feed oil and the catalyst, which allows for greater hydrogenation and a lower level of impurities in the refined oil. However, too low a space velocity not only reduces the processing capacity of the unit but also leads to a decrease in the liquid yield due to increased cracking reactions, as well as increased carbon deposition, thereby shortening the catalyst’s lifespan. The selection of the general air velocity mainly depends on the catalyst's activity. (4) Hydrogen-to-oil ratio: The ratio of the hydrogen flow rate entering the reactor to the feed oil flow rate is called the hydrogen-to-oil ratio. If both the hydrogen flow rate and the feed oil flow rate are expressed in volume units, it is called the hydrogen-to-oil volume ratio ； When calculated in terms of molar flow rate, it is called the hydrogen-to-oil molar ratio. When calculating the hydrogen-to-oil volume ratio, the hydrogen flow rate is usually the volume flow rate of the hydrogen-rich gas (which contains a small amount of small-molecule hydrocarbons) at 0°C and normal pressure, while the feed oil refers to its liquid volume flow rate at 20°C. When calculating the molar hydrogen-to-oil ratio, the hydrogen flow rate is often taken as the flow rate of pure hydrogen. Volume ratios are commonly used in industrial production, while molar ratios are commonly used in scientific research. Increasing the hydrogen-to-oil ratio means raising the hydrogen partial pressure, which helps to suppress carbon deposition on the catalyst in hydrogenation reactions and facilitates the removal of reaction heat. However, with a constant processing volume, increasing the hydrogen-to-oil ratio means reducing the reaction time, which is unfavorable for the reaction; therefore, even if the hydrogen-to-oil ratio is too high, the degree of hydrogenation does not necessarily increase, nor does the product quality necessarily improve. (5) Properties of the feed oil: The composition of the feed is a key factor in determining the reaction temperature; when the impurity content in the feed is high, in order to ensure that the resulting oil meets quality standards, it is necessary to increase the reaction temperature or reduce the space velocity appropriately. When the metal content in the feedstock is too high, metals will accumulate in large quantities on the surface of the catalyst, causing permanent poisoning of the catalyst and a significant decline in its activity; therefore, it is essential to strictly control the level of metal impurities in the feed oil.

Reforming pre-hydrogenation is primarily used to produce qualified reforming feedstock by removing impurities such as S, N, O, and metal elements from the feedstock; these impurities can poison the reforming catalyst, in some cases causing permanent poisoning. If the impurity content in the feed increases, the temperature of the pre-hydrogenation reactor can be appropriately increased. The boiling range of the raw material can be adjusted using a distillation tower; for example, to produce high-octane gasoline, the initial boiling point can be kept low, while to produce aromatic feedstocks, the initial boiling point can be kept high. For the production of aromatic feedstocks, the higher the aromatic potential of the raw material, the better – that is, the higher the proportion of naphthenes and aromatics in the raw material. The higher the final boiling point, the heavier the feed components and the greater the density of the feed, which can lead to severe coking of the catalyst and impose a burden and risks on the regeneration unit. Therefore, strict control is exercised over various parameters of pre-hydrogenation and the feedstock.

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The reaction pressure is generally not adjusted; it is determined based on economic optimization of the plant design, as too high a pressure can affect the equipment’s lifespan. The reaction temperature is set according to the properties of the feedstock, while product quality serves as a means for making adjustments. The amount of recycled hydrogen is regulated based on the space velocity in order to control the hydrogen-to-oil ratio. If secondary processed oil is used in the mixture, attention must also be paid to the temperature rise in the bed layer, and cold hydrogen should be adjusted accordingly (as too high a level can lead to thiol reactions, thereby affecting the desulfurization process)

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In practical operation, pay attention to the reactor heat exchanger, as high temperatures and pressures can cause the flanges to leak. During the pre-hydrogenation reaction, hydrogen sulfide is likely to be generated, so safety protocols must be strictly implemented.