DE69101670T2 - Desulphurization and demetallization of residues. - Google Patents

Description

This invention relates to the improved demetallization and desulfurization of residues, e.g. vacuum residues. In this invention, the demetallization and/or desulfurization is carried out in order to substantially reduce or remove impurities in the residue. These impurities would interfere with the catalyst in the subsequent catalytic processing of the residue, e.g. in the production of gasoline, for example as poisons.

The German patent specification DE-A-1 034 302 describes a process for treating an asphaltenic hydrocarbon with a diluent comprising not less than 0.5 parts of gas oil crude oil (as diluent) per part asphaltenic hydrocarbon and for treating this mixture with a desulfurization catalyst.

This invention relates to contacting a residue with gas oil, a distillate or an FCC recycle oil diluent under conditions comprising hydrogen pressures in the range of 4240 to 27700 kPa (600 to 4000 psig); WHSVs of 0.05 to 10 and temperatures in the range of 316 to 468°C (600 to 875°F) over a catalyst comprising silica, alumina or silica-alumina. One result is that the metal impurity content of the treated residue is less than that of the residue treated under identical conditions in the absence of gas oil, distillate or FCC recycle oil. Another result is that the sulphur content of the residue treated in the presence of these lower boiling fractions (gas oil, distillate or FCC recycle oil) under these conditions is lower than that of the residue treated under identical conditions in the absence of gas oil, distillate or FCC recycle oil.

Fig. 1 is a graphical representation of the book of (nickel in product)/(nickel in feed) versus WHSV and shows the effect of low boiling point return oil (LCO) on the removal of nickel.

Fig. 2, which plots the fraction of (vanadium in product)/(vanadium in feed) versus WHSV, shows the effect of the LCO on vanadium removal.

Fig. 3 shows the effect of LCO on the desulfurization of the residue, with the change in sulfur in the residue compared to the WHSV being graphically shown.

Fig. 4 is a plot of nickel versus WHSV showing the effect of diluent on demetallization of the 850+ residue.

Fig. 5 is a plot of vanadium versus WHSV showing the effect of diluent in demetallizing the 850+ residue.

Fig. 6 is a graph of sulfur versus WHSV showing the effect of diluent in desulfurizing the 850+ residue.

The task of hydrotreating the residues is to remove the metals, e.g. Ni and V, to reduce S in the product and to reduce CCR in the product. Kinetic Limitations and fouling of the catalyst by carbonaceous deposits and metal deposits are two common problems associated with this processing. Atmospheric distillation residues boil above 316 to 427°C (600 to 800°F) while vacuum residues boil above 482 to 593°C (900 to about 1100°F). The residue subjected to the demetallization and/or desulfurization of this invention is preferably a vacuum residue or vacuum distillation residue (hereinafter referred to as vacuum residue). These residues are, by definition, non-vaporized liquid or solid residues from crude petroleum distillation or cracking processes. Vacuum residues result from vacuum distillation which is carried out at reduced pressure to reduce the distillation temperature and the boiling temperature of the distilled material to prevent decomposition and cracking of the material being distilled. Accordingly, in preferred embodiments of this process, the first step is to provide the vacuum residue.

Lighter boiling diluents for the residue include atmospheric and vacuum gas oils or cracked distillates, e.g. LCO (low boiling cycle oil) and HCO (high boiling cycle oil). Gas oil is a petroleum distillate having a viscosity between kerosene and lubricating oil, boiling in the range 204 to 427°C (about 400 to about 800°F). Distillate includes gasoline, kerosene and light lubricating oil. In a preferred embodiment, the diluent is an aromatic stream, e.g. cracked FCC distillate. The cracked distillate aromatic stream includes LCO and HCO. The combination of this residue with the aromatic stream formed from the cracked distillate leads to a beneficial effect on the deactivation of the catalyst in this process according to the invention.

The residue is mixed with a lower boiling point diluent. The resulting mixture may contain up to 50% by volume of the diluent. The mixture conveniently contains about 10 to 30% by volume of the diluent. For each combination of vacuum residue and diluent, the optimum dilution values are determined; the optimum dilution values are effective amounts of diluents boiling below the residue to enhance demetallization and desulfurization of the residue at the hydrotreating conditions listed below. In this invention, the rate increase in either or both demetallization and desulfurization can be up to one hundred percent (100%). For a one hundred percent rate increase in a specific diluent, the rate increase tends to be greater than the viscosity of the residue being treated. The viscosity of the residue varies with its source.

The residue and diluent mixture may be subjected to the following hydrotreating conditions in fixed bed, boiling bed or moving bed reactors, which are well known in the art for demetallization and desulfurization of petroleum residues. The hydrotreating conditions include a catalyst.

By definition, hydrotreating requires a hydrogen flow. Hydrogen pressure in the process of the invention ranges from 4240 to 27,700 kPa (600 to about 400 psig). Elevated temperatures in this process of the invention range from about 316 to 468°C (600°F to about 875°F). WHSVs range from 0.05 to 10.

The catalyst for demetallization and/or desulphurization of the residue can be a conventional one. Compositions useful as catalysts include silica, alumina or silica-alumina.

Under the above conditions, the rate constants for demetallization and/or desulfurization of the residue hydrotreated in the presence of the lower boiling diluent are improved. The extent of this improvement allows a certain ratio of diluent to be hydrotreated in the same reactor without deleterious consequences and even allows a positive influence on the treatment of the vacuum residue fraction.

The product of this process may be fractionated and sent to other conversion plants or used directly as a final product.

The invention has been described above with reference to specific embodiments. However, the invention is defined by the following claims, which are intended to include modifications known to those skilled in the art.

EXAMPLES example 1

An Arab Light (AL) vacuum residue was hydrotreated in the presence of 30% LCO at varying space velocities. Fig. 1 shows the effect of LCO on the rate constant for Ni removal and Fig. 2 shows the effect on V removal. The presence of 30% LCO improves demetallization by a factor of more than 2, as measured by the improvement in rate constants. For example, at 371ºC (700ºF) and 13980 kPa (2000 psig) with a hydrogen circulation of 890 V/V (5000 scf/bbl), the calculated apparent rate constants for the removal of Nickel 0.022 when the residue alone is treated. The rate constant increases to 0.045 when 30% LCO is treated simultaneously. The rate constant for vanadium removal is similarly increased from 0.021 to 0.05 when 30% LCO is treated simultaneously. This improved rate of demetallization results in a lower metal content in the product.

Example 2

An AL vacuum residue was hydrotreated in the presence of 30% LCO. The sulfur in the residue fraction is calculated by burning off the remaining sulfur in the LCO fraction after treatment. In Fig. 3, the observed desulfurization of the vacuum residue with this simultaneous treatment is compared with the expected desulfurization if the vacuum residue is treated alone. Under the same process conditions as in Example 1, the rate constant for desulfurization is again increased from 0.2 to 0.36 by this simultaneous treatment. This translates into a significantly lower sulfur content in the product stream.

Example 3

To separate the effects of LCO on catalyst deactivation, LCO alone was treated on an equilibrium catalyst for four days at the same condition as in Example 1. The catalyst performance in hydrotreating the residue is compared before and after the LCO experiments. As shown below, the removal of metals from the AL residue increased from 43 to 46%, while the removal of sulfur increased from 38 to 41%. Comparison of hydrotreatment of the residue Feed Before After Process conditions Product properties Demetallization, % Desulfurization, %

The above table shows that the presence of LCO actually restores the catalytic activity. Consequently, it is assumed that the co-treatment with LCO slows down the deactivation of the catalyst.

Example 4

An Al vacuum residue was treated together with 20% vacuum gas oil and 10% light distillate at 321ºC and 399ºC (610 and 750ºF) and 13,900 kPa (2000 psig) with a hydrogen circulation of 890 V/V (5000 scf/bbl). To monitor sulfur removal from the vacuum residue, the product was fractionated to produce the 850+ (ºF) (454+ ºC) portion from which sulfur was measured. Figure 4 compares the effect of diluent addition on nickel removal from the vacuum residue at various reactor temperatures. A similar improvement in vanadium and sulfur removal from the residue by simultaneous treatment is shown in Figures 5 and 6, respectively. As shown, this simultaneous treatment results in a significant improvement in the removal of metals and sulfur.

Claims (7)

1. Process for desulfurization and demetallization of a residue, which comprises: mixing the residue with a diluent having a boiling temperature in the range of 204ºC to less than the boiling temperature of the residue to form a mixture containing up to 50% by volume of the diluent; contacting the mixture with a hydrotreating catalyst under conditions including a hydrogen pressure in the range of 4270 to 27700 kPa, elevated temperatures in the range of 316 to 468ºC and a space velocity in the range of 0.05 to 10; and Obtaining the treated mixture. 2. The process of claim 1 wherein the diluent for the residue consists of atmospheric gas oil, vacuum gas oil and cracked distillate, light cycle oil and heavy oil. 3. A process according to claim 1 or 2, wherein the catalyst for the hydrotreating is a catalyst selected from silica, alumina and silica-alumina. 4. The process of claim 1, 2 or 3, wherein the residue is a vacuum residue. 5. A process according to any preceding claim, wherein the residue contains an effective amount of nickel or vanadium to act as a catalyst poison in the subsequent downstream treatment. 6. A process according to any preceding claim, wherein the amount of nickel or vanadium in the recovered mixture is less than the effective amount acting as a catalyst poison. 7. A process according to any preceding claim, wherein the mixture contains 10 to 30% by volume of the diluent.