Mineral oils: processes and products – Refining – Sulfur removal
Reexamination Certificate
1999-04-13
2003-04-29
Griffin, Walter D. (Department: 1764)
Mineral oils: processes and products
Refining
Sulfur removal
C208S210000, C208S212000, C208S25100H, C208S25400R
Reexamination Certificate
active
06554994
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a reactor system and process for the hydrotreating of a heavy feedstock, particularly a residuum, in order to lower the amount of contaminants, especially metals, carbon residue, and sulfur. An upflow fixed bed reactor is described as containing a layered catalyst bed in which the catalyst in the different layers has different hydrogenation activities designed to selectively distribute the removal of the contaminants across the entire catalyst bed to prevent plugging and to increase the life of the catalyst.
DESCRIPTION OF THE RELATED ART
Hydrotreating is a well known method for removing contaminants and upgrading heavy feedstocks prior to further processing. The term “hydrotreating” will be used in this disclosure to denote a process for removing contaminants, especially metals, carbon residue, nitrogen, and sulfur from heavy feedstocks under supra-atmospheric pressure and at elevated temperatures in the presence of hydrogen and a catalyst. As used herein the term “heavy feedstock” refers to a hydrocarbon high in asphaltenes that is derived from a reduced crude oil, petroleum residuum, tar sands bitumen, shale oil, liquified coal, or reclaimed oil. Heavy feedstocks typically contain contaminants, such as carbon residue, sulfur, and metals, which are known to deactivate the catalysts used to upgrade the heavy feedstocks to more valuable products such as transportation fuels and lubricating oils. Hydrotreating operations also typically remove nitrogen from the heavy feedstocks along with the sulfur. Even the production of lower value products such as fuel oils usually requires that the heavy feedstock undergo some upgrading to remove contaminants, especially sulfur, prior to sale in order to reduce air pollution.
Various designs of hydrotreating reactors have been described in the literature for treating heavy feedstocks. Commercial designs may utilize a moving bed of catalyst, such as described in U.S. Pat. No. 5,076,908, or an ebullating catalyst bed, such as described in U.S. Pat. Nos. 4,571,326 and 4,744,887. Downflow fixed bed hydrotreating reactors are the most widely used commercially. They may be distinguished from moving bed reactors in that fresh catalyst cannot be added to the bed and spent catalyst in the bed cannot be removed during operation. In moving bed reactors the flow of feedstock and hydrogen is preferably upward. The catalyst moves downward and is removed from the bottom of the bed as spent catalyst while fresh catalyst is added at the top of the bed. In an ebullating bed the upward flow of feedstock and hydrogen is sufficient to suspend the catalyst and create random movement of the catalyst particles. During operation the volume of an ebullating bed will expand, usually by at least 20%, as compared to the volume of catalyst in the reactor when there is no flow of hydrogen and feedstock through the bed. By contrast, there is little or no expansion in an upflow fixed bed such as described in this disclosure during operation. In fact, the volume of the catalyst bed may actually decrease slightly during operation due to a settling of the catalyst particles. It should be understood that since the reactor walls are rigid the expansion of the catalyst bed will take place only along the vertical axis of the bed. Thus when referring to bed expansion in this disclosure, the increase in height of the bed or depth of the bed in the reactor is an appropriate measure of bed expansion and is directly related to volume.
Usually, the contaminants are removed by contacting the heavy feedstock with a catalyst in the presence of hydrogen at an elevated pressure and temperature. Typically, the catalyst will be an active catalyst, i.e., a catalyst with hydrogenation activity. Contaminating metals, such as nickel and vanadium, usually will be readily removed under hydrotreating conditions and will plate out on the surface and in the pores of the catalyst. The deposition of metals on the catalyst will result in a rapid loss of hydrogenation activity. However, hydrogenation activity is necessary for the removal of other contaminants, such as carbon residue, nitrogen, and sulfur, from the feedstock.
Catalysts used to carry out the removal of metals, carbon residue, and sulfur from heavy feedstocks, referred to generally as hydrotreating catalysts, typically consist of a porous refractory support, usually of alumina, silica, or silica/alumina, that may be impregnated with a metal or metals, such as for example, Group VIB metals (especially molybdenum and tungsten) and Group VIII metals (especially cobalt and nickel) from the Periodic Table, to enhance their activity. Of primary concern with the present invention are those hydrotreating catalysts having demetallation, desulfurization, denitrification, and carbon residue removal activity.
The pore structure of the hydrotreating catalyst is known to affect the desulfurization, denitrification, and carbon residue removal activity of the catalyst as well as how rapidly the catalyst is deactivated by metal contaminants. In general, catalysts having relatively large pores are preferred for removing metal contaminants. For example, catalysts having macropores, that is, pores having diameters of 1000 Angstrom Units or greater, are taught as useful in removing contaminating metals from heavy feedstocks by U.S. Pat. No. 5,215,955. However, for the removal of sulfur, nitrogen, and carbon residue a smaller pore size is usually advantageous, as for example, a catalyst such as described in U.S. Pat. No. 5,177,074 in which at least 70% of its pore volume consists of pores having a diameter of between 70 and 130 Angstrom Units. Unfortunately, catalysts having a smaller pore size are usually more quickly deactivated by the deposition of metals within the pore structure than are catalysts having a larger pore size. Thus in selecting a suitable catalyst to remove contaminants from a heavy feedstock, it is necessary to balance catalyst life against the need to retain sufficient activity to remove the contaminants, especially carbon residue and sulfur.
In order to gain the advantages of both the lower activity catalysts for removing metals and of the higher activity catalysts needed for desulfurization and carbon residue removal, dual or multiple catalyst systems have been proposed for use in fixed bed reactors. Layered catalyst beds are proposed in U.S. Pat. Nos. 4,990,243 and 5,071,805 in which discrete strata of catalyst are arranged in the catalyst bed to take maximum advantage of the different characteristics of each of the catalysts making up the bed. In a layered catalyst bed the demetallation catalyst will usually make up the upper layer of the fixed bed with the catalyst in the lower layer or layers increasing in hydrogenation and desulfurization activity. The heavy feedstock enters the top of the reactor and first contacts the demetallation catalyst where the metal contaminants are removed. The heavy feedstock with a significant portion of its metal contaminants removed passes down through the fixed bed to contact the hydrogenation and desulfurization catalysts where the sulfur and carbon residue contaminants are removed. Due to the lowered metal values in the feedstock the hydrogenation and desulfurization catalysts will have an increased useful life since there are fewer metals present in the feedstock to deactivate the catalysts. However, a disadvantage of the downflow layered catalyst system is the high pressure drop which is typical across the fixed bed. This problem is further aggravated over time as the metals plate out on the catalyst in the upper layer of the bed increasing the pressure drop and eventually plugging the reactor.
The physical admixture of catalysts with differing activity in a fixed reactor bed is proposed in U.S. Pat. No. 5,439,860. This may have the advantage of more evenly distributing the metal contaminants throughout the length of the bed to reduce plugging, but it does not entirely solve the problem of deactivation of the hydrogenation catalysts by the metal conta
Antezana Fernando J.
Bachtel Robert
Chabot Julie
Gibson Kirk R.
Lam Fred W.
Ambrosius James W.
Chevron U.S.A. Inc.
Griffin Walter D.
Prater Penny L.
LandOfFree
Upflow reactor system with layered catalyst bed for... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Upflow reactor system with layered catalyst bed for..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Upflow reactor system with layered catalyst bed for... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3001745