Resid desulfurization and demetalation

Abstract: This invention relates to improved processes for hydrotreating resid. Blending lower boiling petroleum fractions with the resid results in enhanced rates of demetalation and/or desulfurization, with enhanced reduction of sulfur and/or metals content in the hydroprocessed resid.

Description: This invention relates to improved demetalation and desulfurization of resids, e.g. vacuum resids. In accordance with the invention, demetalation and/or desulfurization are undertaken to substantially reduce or remove contaminants from the resid. The contaminants would interfere with catalysts, for example as poisons, in subsequent catalytic processing of the resid such as in the production of gasoline. German patent document DE-A- 1 034 302 discloses a process for treating an asphaltic hydrocarbon with a diluent comprising not less than 0.5 parts of gas oil-petroleum crude (as diluent) per part asphaltic hydrocarbon and treating the mixture with a desulphurization catalyst. The invention relates to contacting a resid with gas oil, a distillate, or FCC cycle stock diluent, under conditions including hydrogen pressures ranging from 4240 to 27,700 kPa (600 to 4000 psig); space velocities (WHSV) from 0.05 to 10, and temperatures ranging from 316 to 468°C (600° to 875°F) over a catalyst comprising silica, alumina or silica-alumina. One result is that the metal contaminant content of the treated resid is less than that of the resid treated under identical conditions in the absence of the gas oil, distillate, or FCC cycle stock. Another result is that the sulfur content of the resid treated in the presence of those lower boiling fractions (gas oil, distillate or FCC cycle stock) under the conditions is less than that of the resid treated under identical conditions in the absence of the gas oil, distillate, or FCC cycle stock. Figure 1 is a plot of the fraction of (nickel in the product)/(nickel in the feed) vs. WHSV and illustrates the effect of light cycle oil (LCO) on Nickel removal. Figure 2, wherein the fraction of (vanadium in the product)/(vanadium in the feed) is plotted against WHSV illustrates the effect of LCO on vanadium removal. Figure 3 illustrates the effect of LCO on resid desulfurization, wherein the change in sulfur in the resid is plotted against WHSV Figure 4 is a plot of nickel vs. WHSV and shows the effect of diluent on demetalation of 850+ bottom. Figure 5 is a plot of vanadium vs. WHSV and illustrates the effect of diluent on demetalation of 850+ bottom. Figure 6 is a plot of sulfur vs. WHSV and illustrates the effect of diluent on desulfurization of 850+ bottom. The objective of hydrotreating resids is to remove metals such as Ni and V, reduce product S, and reduce product CCR. Kinetic limitations and catalyst fouling by carbonaceous deposits and metal deposits are two common problems encountered in such processing. Atmospheric resids boil above 316 to 427°C (600° to 800°F), while vacuum resids boil above 482° up to 593°C (900° up to about 1100°F). Preferably, the resid which is subjected to demetalation and/or desulfurization, in accordance with the invention, is a vacuum resid. Resids are, by definition, the unevaporated liquid or solid bottoms from processes of distillation or cracking of petroleum crudes. Vacuum resids result from vacuum distillation which is undertaken, under 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 the process the first stage is providing a vacuum resid. Lower boiling diluents for the resid include atmospheric and vacuum gas oils, or cracked distillates such as LCO (light cycle oil) and HCO (heavy cycle oil). Gas oil is a petroleum distillate with a viscosity intermediate between kerosene and lubricating oil, boiling in the range of 204° to 427°C (about 400° to about 800°F). Distillate includes gasoline, kerosene and light lubrication oil. In a preferred embodiment, the diluent is an aromatic stream such as cracked FCC distillate. Cracked distillate, as an aromatic stream, includes LCO and HCO. Combination of the resid with the aromatic stream provided by cracked distillate, in the process of the invention, results in a beneficial impact on catalyst deactivation. The resid is blended with the lower boiling diluent. The resulting blend can contain up to 50 volume percent of the diluent. Practically, the blend will contain about 10 to 30 volume percent of the diluent. Optimum levels of dilution are determined for each combination of vacuum resid and diluent; optimum levels of dilution are amounts of diluents lower boiling than the resid effective to increase the dematalation and desulfurization of the resid under the hydroprocessing conditions reported below. In accordance with the invention, rate enhancement, of either or both demetalation and desulfurization, can be up to one hundred percent (100%). At one hundred percent rate enhancement with a specific diluent, rate enhancement will tend to be greater as the viscosity of the resid to be treated. The viscosity of the resid will vary with its source. The blend of resid and diluent can be subjected to the following hydroprocessing conditions in fixed-, ebullated-, or moving-bed reactors that are well known in the art for dematalation and desulfurization of petroleum resids. The hydroprocessing conditions include a catalyst. By definition, hydroprocessing requires a hydrogen stream. The hydrogen pressures, in the process of the invention, range from 4240 to 27,700 kPa (600 to about 4000 psig). Elevated temperatures in the process of the invention range from about 316° to 468°C (600°F to about 875°F). Space velocities (WHSV) range from 0.05 to 10. The catalyst for resid demetalation and/or desulfurization can be a conventional one. Those compositions useful as catalysts include silica, alumina or silica-alumina. Under the foregoing conditions, the rate constants for dematalation and/or desulfurization of resid hydroprocessed in the presence of said lower boiling diluent is enhanced. The extent of this enhancement allows a certain proportion of diluent to be hydrotreated in the same reactor with no negative consequence and even a positive effect on the treatment of the vacuum resid fraction. The product of this process can be optionally fractionated and set to other conversion units or used directly as a finished product. The invention has been illustrated above with respect to specific embodiments thereof. However, the invention will be defined by the claims appended hereto which are intended to embrace modifications within the skill of the art. EXAMPLES Example 1 An Arab Light (AL) vacuum resid was hydrotreated in the presence of 30% LCO at a variety of space velocities. Fig. 1 shows the effect of the LCO on the rate constant for Ni removal and Figure 2 shows the effect on V removal. The presence of 30% LCO enhances demetalation by more than a factor of two as measured by improvement of rate constants. For example, at 371°C (700°F) and 13,900 kPa (2000 psig) with 890 v/v (5000 SCF/BBL) hydrogen circulation, the calculated apparent rate constants for nickel removal is 0.022 when processsing the resid alone. The rate constant increases to 0.045 when 30% LCO is coprocessed. Similarly, the rate constant for vanadium removal is increased from 0.021 to 0.05 when 30% LCO is coprocessed. This improved demetalation rate translates to lower metals content in the product. Example 2 An AL vacuum resid was hydrotreated in the presence of 30% LCO. Sulfur in the resid fraction is calculated by backing out the residual sulfur in the LCO fraction after the treatment. In Figure 3, the observed desulfurization of vacuum resid in coprocessing is compared with the expected desulfurization when processing vacuum resid by itself. Again, at the same operating condition as in Example 1, the rate constant for desulfurization is increased from 0.2 to 0.36 by coprocessing. This translates to significantly lower sulfur content in the product stream. Example 3 To isolate the effects of LCO on catalyst deactivation, LCO was processed by itself for four days on an equilibrated catalyst at the same condition as in Example 1. Catalyst performance on resid hydrotreatment is compared before and after LCO runs. As shown below, metals removal from AL resid was increased from 43 to 46%, while sulfur removal was increased from 38 to 41%. The foregoing indicates that the presence of LCO actually restores catalytic activity. Therefore, coprocessing LCO is expected to slow catalyst deactivation. Example 4 An AL vacuum resid was coprocessed with 20% vacuum gas oil and 10% light distillate at 321° and 399°C (610° and 750°F), and 13,900 kPa (2000 psig) with 890 v/v (5000 SCF/BBL) hydrogen circulation. In order to follow sulfur removal from the vacuum resid, the product was cut to generate the 850+ (°F) (454 + °C) portion of which sulfur was measured. In Figure 4, the effect of diluent addition on nickel removal from vacuum resid is compared at various reactor temperatures. Similar improvement on vanadium and sulfur removal from the resid by coprocessing is shown respectively in Figures 5 and 6. As shown, coprocessing gives a substantial improvement of metals and sulfur removals.

Claims: A process for desulfurizing and demetallation of a resid comprising: blending the resid with a diluent having a boiling temperature ranging from 204°C up to less than the boiling temperature of the resid to form a blend containing up to 50 volume percent of the diluent; contacting the blend with a hydrotreating catalyst, under conditions including hydrogen pressures ranging from 4270 to 27700 kPa, elevated temperatures ranging from 316°C to 468°C and a space velocity ranging from 0.05 to 10; and recovering the processed blend. A process according to claim 1, wherein the diluent for the resid is selected from atmospheric gas oil, vacuum gas oils, and cracked distillate light cycle oil and heavy oil. A process according to claim 1 or 2, wherein the hydrotreating catalyst is one selected from silica, alumina, and silica-alumina. A process according to claim 1, 2 or 3, wherein the resid is a vacuum resid. A process according to any preceding claim, wherein the resid contains an amount of nickel or vanadium effective to act as a catalyst poison in subsequent downstream processing. A process according to any preceding claim, wherein the amount of nickel or vanadium in the recovered blend is less than the amount effective to act as a catalyst poison. A process according to any preceding claim, wherein the blend contains 10 to 30 volume percent of the diluent.

Inventors: CHOI BYUNG CHANG, VARGHESE PHILIP MOBIL OIL SING, CHOI, BYUNG CHANG, VARGHESE, PHILIP, MOBIL OIL SINGAPORE, PTE LTD.
Applicants: MOBIL OIL CORP, MOBIL OIL CORPORATION (A NEW YORK CORPORATION)
Application year: 1991
Main classification: C10G45
IPC codes: C10G45