CS231688B1 - Method of preprocessing of hydrocarbon for pyrolysis utilizing dissolvent extraction of aromatic hydrocarbon - Google Patents

Abstract

The invention relates to a pre-treatment process extraction hydrocarbon feedstock aromatic hydrocarbons a solvent in which the oil fraction is boiling in the range of 250 to 550 ° C extracted solvent mixtures of 50 to 99.9 wt. methanol, 0.05 to 50% wt. % isobutanol and 0.05 to 20 wt. water at 20 to 55 ° C, atmospheric pressure and weight ratio of solvent to the raw material 0.5 to 6, and raffinate is washed with water. This raw material can be directly hydrolyzed, without further modification hydrotreating or mixing with original raw material containing higher concentration open.

Description

The present invention relates to a process for pretreating a hydrocarbon feedstock for pyrolysis comprising extracting aromatics from a hydrocarbon fraction intended for pyrolysis.

It is known that by reducing the content of aromatic hydrocarbons, in particular multinuclear, the yields of the desired products obtained by pyrolysis of the hydrocarbon feedstock can be increased. Pyrolysis is understood to mean the process of thermal cracking of hydrocarbons in the presence of water vapor.

Reducing the aromatic content also has the effect of reducing the rate of pyrolysis carbon formation. The aromatic hydrocarbon content of the petroleum fraction can be reduced by hydrogenation or extraction. Both methods have already been verified for the need to treat the raw material for pyrolysis. In operation, hydrogenated atmospheric gas oil is pyrolyzed with an end of the distillation range below 370 ° C, yielding results comparable to the pyrolysis of gasoline. The extraction of aromatics from this fraction with dimethylformamide and water was verified in the laboratory. When the aromatics content of the feedstock was reduced to 5 to 10% by weight, the ethylene yield increased by 1 to 1.5% by weight.

As a result of rising world oil prices, it is increasingly being considered to be used more efficiently. One possibility is to pyrolyz the pre-treated vacuum gas oil with a distillation range of 300 to 550 ° C. The pretreatment consists primarily in the removal of aromatic hydrocarbons. A number of processes have been developed which allow selectively hydrogenating mainly multinuclear aromatics, while at the same time undesirable isomerization of the hydrocarbons occurs and the reaction product is separated by distillation and the fraction boiling above 340 ° C, which constitutes about 60% by weight. of the raw material is pyrolyzed. Hydrogen consumption for

However, the hydrogenation of aromatics is high and amounts to about 225 m < 2 > / m < 2 > Depending on the amount of vacuum gas oil processed, it is necessary to replenish the required amount of hydrogen by further producing it, eg by partial oxidation or steam reforming of methane from the olefin unit, eventually to remove hydrogen from other sources. Hydrogenation, which usually requires a higher hydrogen pressure than commonly available in the olefin unit and therefore requires compression from about 3.5 to 25 MPa, results in undesirable deep desulfurization. It is therefore necessary to mix the scrubbed feedstock with the sulfur fraction so that the sulfur content is above 500 ppm by weight. Therefore, attempting to replace the hydrogenation of aromatics by their extraction seems to be another way to utilize this fraction for pyrolysis. Generally, solvents suitable for reformate, atmospheric gas oil and the like cannot be used for extracting aromatics from these high-boiling fractions. For example, dimethylformamide has a comparable density to this fraction and therefore only very poor separation of the raffinate, i.e. depleted, and extract phases. Furfural and phenol are most commonly used for the extraction of vacuum gas oils. The aim of these processes is to improve the quality of the raw material - raffinate, eg viscosity index. The resulting aromatics can be mixed into petroleum fractions, hydrogenated or used to produce carbon black or needle coke. A disadvantage of the above extraction processes, e.g., as compared to dimethylformamide, is the need to operate at a higher extractor temperature of about 90 ° C and solvent-hydrocarbon separation. When using extraction to treat the feedstock for pyrolysis, it is also necessary that the solvent can be easily separated from the raffinate phase, for example by washing with water, and that any traces of solvent do not adversely affect the pyrolysis.

All of the above-mentioned disadvantages are overcome by the process of pre-treatment, the nature of which is that the hydrocarbon feedstock for the pyrolysis treatment is treated. solvent extraction of the aromatic hydrocarbons in which the petroleum fraction boiling in the range of 250 to 550 ° C is extracted with a solvent mixture of 50 to 99.9% by weight. % methanol, 0.05 to 50 wt. % isobutanol and 0.05 to 20 wt. water at 20-55 ° C, atmospheric pressure and mass

- 3 231 888 solvent to raw material ratio 0.5 to 6 and raffinate is washed with water ·

The solvent mixture preferably has a composition of 90 to 99% by weight of methanol, 0.05 to 0.95% by weight of isobutanol, 0.05 to 0.95% of water. After the solvent has been separated from the raffinate phase, the raw material thus treated can be pyrolyzed directly without it had to be further treated with hydrotreatment or blending with the original feedstock containing a higher sulfur concentration.

The experiments were carried out in a laboratory continuous column having 35 theoretical plates, at temperatures of 20 to 55 ° C, in a solvent to feed ratio of 0.5 to 6, and at atmospheric pressure. The raw materials were gas oils boiling in the range of 250 to 550 ° C. The solvent was a mixture of: methanol 50 to 100% by weight, preferably 90 to 99% by weight, isobutanol 0 to 50% by weight, preferably 1 to 10% by weight, water 0 to 20% by weight, preferably 0 to 1% by weight. The products of extraction, i.e. the raffinate phase after the scrubbing, were pyrolyzed in a quarter-through continuous unit allowing the injection of 0 to 0.5 kg of feedstock per hour. Water was added according to the ratios chosen. After preheating the raw materials, they were fed to a pyrolysis reactor, in which the temperature could be continuously adjusted and controlled. After cooling and partitioning, the reaction products were analyzed. Gaseous samples were chromatographed. Liquid samples were weighed and distilled into fractions boiling to and above 205 ° C, ie pyrolysis gasoline and pyrolysis oil.

The effect of the extraction of aromatic hydrocarbons from vacuum gas oil on its pyrolysis can be illustrated by example · Comparison shows results obtained from pyrolysis of hydrogenated vacuum gas oil · The results were obtained under the conditions given in Table 1 and are summarized in Table 2,

Table 1

231 688

Extraction Pomě r solvent / raw materials (kg / kg) Temperature Noc: 2 ° C Pyrolysis Composition (% by weight) Temperature Noc: 2 ° C Pressure Ratio MPa steam / hydrocarbons (kg / kg) 4 - 1 50 methanol 97 , 4 795 0.2 1: 1 i-butanol 2.5 water 0,1 Table 2 - Raw material After extraction After hydrogenation and stabilization distillation curve ° C 320-520 325-520 325-520 density at 20 Noc: 2 ° C 911 887 854 kg / m ³ sulfur content% wt. 1,8 0.7 0.030 aromatics content % wt. 43.4 10.2 9.5

Yield% wt.

gas C ₄ 58.6 74.8 76.1 ethylene 20.8 23.2 25.3 propylene 15.1 17.6 16.1 pyrobenzine 8.3 13.7 13.4 pyrolysis oil 33, i 11.5 10.5

From the results, it is clear that the extraction of aromatics positively affects the yields of the desired products and significantly reduces the formation of pyrolysis oil. The reduction in the formation of pyrolysis oils also suggests a probable reduction in the formation of pyrolysis carbon, which is one of the main reasons why it is not possible to pyrolize directly

Untreated vacuum gas oil. Traces of solvent, OH groups that may remain in the treated feedstock are likely to initiate the desired reactions rather than having an adverse effect on the operation of the pyrolysis furnace. The yields obtained from hydrogenated vacuum gas oil are even more favorable, in particular higher ethylene yield and lower pyrolysis oil formation. However, taking into account that hydrotreatment, ie reducing the sulfur content below the permissible level while maintaining the minimum content requirement, is likely to be avoided in the extraction of aromatics, and hydrogenation is not necessarily more favorable if compared to its own costs.

The minimum and maximum permissible sulfur content of the feedstock depends on the type of pyrolysis furnace, the way in which the reaction products are processed and the purity requirements of the products. It is therefore not possible to establish a generally applicable criterion for the sulfur content of liquid raw materials. However, it is generally recommended to operate in the range of 0.05 to 1% by weight. open.

It goes without saying that the proposed solvent can also be used in the extraction of low-boiling petroleum fractions, but according to the literature, it seems to be more advantageous to use, for example, dimethylformamide for these fractions. It will also be appreciated that the extraction of aromatics from the petroleum fraction of the process of the present invention does not always have to be grumbled for the purpose of treating the pyrolysis feedstock.

Claims (2)

SUBJECT OF THE INVENTION 231888 Process for the pre-treatment of a hydrocarbon feedstock for pyrolysis treatment by solvent extraction of aromatic hydrocarbons, characterized in that the fraction boiling in the range of 250 to 550 ° C is extracted with a solvent mixture of 50 to 99.9% by weight of methanol, 0.05 to 50 wt. % isobutanol and 0.05 to 20 wt. water at 20-55 ° C, atmospheric pressure and solvent to feed weight ratio of 0.5-6, and the raffinate is washed with water. 2. A process according to claim 1, wherein the solvent mixture has a composition of 90 to 99% by weight. methanol, 0.05 to 9.95% by weight, isobutanol, 0.05 to 0.95% water.