Mineral oils: processes and products – Refining – Sulfur removal
Reexamination Certificate
1999-12-06
2001-05-15
Myers, Helane (Department: 1764)
Mineral oils: processes and products
Refining
Sulfur removal
C208S215000, C208S21600R
Reexamination Certificate
active
06231754
ABSTRACT:
BACKGROUND OF THE DISCLOSURE
1. Field of the Invention
The invention relates to selective naphtha desulfurization with reduced mercaptan formation and olefin saturation. More particularly, the invention relates to selectively removing sulfur compounds from a sulfur and olefin-containing naphtha feed, with reduced reversion mercaptan formation and olefin saturation, by reacting the feed with a hydrogen treat gas at a high temperature, in the presence of a low metal loaded, partially deactivated and at least partially regenerable hydrodesulfurization catalyst.
2. Background of the Invention
Future mogas sulfur specifications are being regulated through legislation to increasingly lower levels, due to environmental considerations. Sulfur specifications on the order of less than 150 wppm of total sulfur are likely near term, with values of no greater than 30 wppm of total sulfur possible in the not too distant future. Such sulfur specifications are without precedent and will require the production of low sulfur blend stock for the mogas pool. The primary sulfur sources in the mogas pool are the blend stocks derived from FCC naphthas, whose sulfur content can fall in the range of 1500-7000 wppm depending upon crude quality and FCC operation. Conventional fixed bed hydrodesulfurization can reduce the sulfur level of FCC naphthas to very low levels, but the severe conditions of temperature, pressure and hydrogen treat gas ratio results in significant octane loss, due to olefin loss from saturation. Selective hydrodesulfurization processes have been developed to reduce olefin saturation and concomitant octane loss. Such processes are disclosed, for example, in U.S. Pat. Nos. 4,149,965; 5,525,211; 5,243,975, and 5,906,730, some of which employ poisoned and permanently deactivated catalysts. The process disclosed in the '975 patent employs a deactivated resid catalyst loaded with at least 1% of nickel, iron and vanadium poisons. Besides introducing possible contaminants into the naphtha stream, this catalyst is not regenerable. On the other hand, the '211 patent teaches the use of a permanently deactivated catalyst composition containing alkali or alkaline metal. The process disclosed in the '965 patent teaches that the selectivity of a naphtha hydrodesulfurization catalyst for sulfur removal slightly increases over time. Catalyst deactivations of from 2 to 50% are disclosed. In these and in other processes, in the hydrodesulfurization reactor the H
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S formed as a consequence of the hydrodesulfurization reacts with the feed olefins, to form mercaptan sulfur compounds, which are known as reversion mercaptans. The amount of these mercaptans formed during the process typically exceeds future fuel specifications for mercaptan sulfur and, in some cases, total sulfur. Accordingly, it is desirable to have a deep and selective desulfurization process, with reduced mercaptan reversion and octane loss without introducing contaminants into the process and preferably with a catalyst that has not been permanently deactivated.
SUMMARY OF THE INVENTION
The invention relates to a high temperature process for removing sulfur compounds from an olefin-containing naphtha feed, with reduced reversion mercaptan formation, by reacting the feed with a hydrogen treat gas in the presence of a low metals loaded, partially spent hydrodesulflirization catalyst and preferably one that is at least partially regenerable. Thus, the process of the invention comprises reacting a naphtha feed containing organic sulfur compounds and olefins, with a hydrogen treat gas in the presence of a low metals loaded and partially deactivated or spent hydrodesulfurization catalyst, at a temperature of from 305 to about 455° C., a pressure of from 60-600 psig., a hydrogen treat gas ratio of from 2000-4000 scf/b, and a space velocity of from 1-10 v/v/hr, to remove most of the organic sulfur compounds, with reduced olefin saturation and mercaptan formation. By low metals loaded catalyst is meant catalytic metal loadings of no more and preferably less than 12 wt. %, based on the weight of the catalytic metal oxide. The temperature is preferably at least 315° C., more preferably at least 330° C., still more preferably at least 340° C. and most preferably at least 355° C. Lower pressures are preferred. Thus, preferred pressures will range from about 60-500 psig. and more preferably no more than about 350 psig. Preferred treat gas rates range from 2500-4000 scf/b, with from 3000-4000 scf/b being more preferred. While the level of desulfurization will be at least 75 wt. % and preferably at least 85 wt. %, from 90-100 wt. % sulfur removal may be achieved to form a desulfurized naphtha product having a total sulfur level of from 5-500 wppm, including from 5-200 wppm of mercaptan sulfur, with a feed olefin loss of from 5-60 wt. %. By hydrogen treat gas is meant a gas comprising hydrogen, which may or may not contain one or more diluent gases which don't adversely affect the desulfurization catalyst, process or product. It is preferred that the treat gas comprise from 60-100 vol. % hydrogen. By organic sulfur compound is meant any sulfur bearing organic compound.
Preferably the catalyst will comprise not more than 10 and more preferably not more than 8 wt. % catalytic metal components calculated as their oxides, based on the total catalyst weight. The catalyst will comprise at least one catalytically active metal component of a metal from Group VIII, and preferably a catalytically active metal component of a non-noble metal from Group VIII and a metal from Group VIB, supported on a suitable support. Particularly preferred is a catalyst comprising CoO and MoO
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on a support having a Co/Mo atomic ratio of from 0.1 to 1.0, which is explained in detail below. The catalyst is partially spent or deactivated (partially spent and partially deactivated are used herein synonymously), which means that it is neither a fresh catalyst having full desulfurization activity, nor is it a fully deactivated exhibiting essentially no desulfurization activity. The catalyst will have less than 50% and more than 1% of the hydrodesulfurization activity of a new or regenerated catalyst. The activity level will range from 2-40% and preferably from 5-25% of the activity of a new or regenerated catalyst. The catalyst may be presulfided or it may be sulfided in-situ, using conventional sulfiding procedures. It is also preferred that the catalyst be at least partially regenerable and neither permanently deactivated nor contain more than 500 wppm of non-regenerable poisons, such as compounds of nickel, iron and vanadium. The process of the invention is useful for deep and selective sulfur removal, with reduced olefin loss and mercaptan formation, particularly with a high sulfur content naphtha feed. By high feed sulfur content is meant from 0.1-0.7 wt. % (1000-7000 wppm) of sulfur in the form of organic sulfur bearing compounds.
DETAILED DESCRIPTION
It is anticipated that environmentally driven regulatory pressure on motor gasoline (mogas) sulfur levels, will result in the widespread production of 150 wppm total sulfur mogas by the year 2000 and 30 wppm perhaps shortly thereafter. Further, gas oil and other feeds for a fluid cat cracker used to produce cat cracked naphthas, are increasingly using ever more amounts of poorer quality, high sulfur content components, due to the dwindling supply of higher quality crude oil sources. This results in higher sulfur contents in the cat cracked naphthas, which are the major source of naphtha stocks for mogas pools. Thus, the deep desulfurization and reduction in mercaptan reversion achieved by the selective hydrodesulfurizing process of the invention, is important with respect to the desulfurized product meeting both low total sulfur and mercaptan sulfur specifications, while preserving the olefins valuable for octane. At deep levels of desulfurization, especially from 90-100 wt. % sulfur removal, and particularly with relatively high sulfur content naphtha feeds (e.g., >500 wppm and particularly feeds having 15
Brignac Garland B.
Clark Janet R.
Demmin Richard A.
Greeley John P.
Halbert Thomas R.
Exxon Research and Engineering Company
Hughes Gerard J.
Myers Helane
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