Mineral oils: processes and products – Refining – Sulfur removal
Reexamination Certificate
2001-07-31
2004-05-11
Griffin, Walter D. (Department: 1764)
Mineral oils: processes and products
Refining
Sulfur removal
C208S238000, C208S237000, C208S20800M
Reexamination Certificate
active
06733660
ABSTRACT:
TECHNICAL FIELD
The present invention relates to fuels for transportation which are liquid at ambient conditions and typically derived from natural petroleum. Broadly, it relates to integrated, multistage processes for producing products of reduced sulfur content from a feedstock wherein the feedstock is comprised of limited amounts of sulfur-containing organic compounds as unwanted impurities. More particularly, the invention relates to integrated, multistage processes which include treatment of a refinery stream with a solid adsorbent to remove basic nitrogen-containing compounds, chemical conversion of one or more of the sulfur-containing impurities to higher boiling products by alkylation using a first catalyst contacting stage at elevated temperatures and a subsequent catalyst contacting stage at lower elevated temperatures, and removing the higher boiling products by fractional distillation. Integrated processes of this invention advantageously include selective hydrogenation of the high-boiling fraction whereby the incorporation of hydrogen into hydrocarbon compounds, sulfur-containing organic compounds, and/or nitrogen-containing organic compounds assists by hydrogenation removal of sulfur and/or nitrogen. Products can be used directly as transportation fuels and/or blending components to provide fuels which are more friendly to the environment.
BACKGROUND OF THE INVENTION
It is well known that internal combustion engines have revolutionized transportation following their invention during the last decades of the 19th century. While others, including Benz and Gottleib Wilhelm Daimler, invented and developed engines using electric ignition of fuel such as gasoline, Rudolf C. K. Diesel invented and built the engine named for him which employs compression for auto-ignition of the fuel in order to utilize low-cost organic fuels. Equal, if not more important, development of improved spark-ignition engines for use in transportation has proceeded hand-in-hand with improvements in gasoline fuel compositions. Modern high performance gasoline engines demand ever more advanced specification of fuel compositions, but cost remains an important consideration.
At the present time most fuels for transportation are derived from natural petroleum. Indeed, petroleum as yet is the world's main source of hydrocarbons used as fuel and petrochemical feedstock. While compositions of natural petroleum or crude oils are significantly varied, all crudes contain sulfur compounds and most contain nitrogen compounds which may also contain oxygen, but oxygen content of most crudes is low. Generally, sulfur concentration in crude is less than about 8 percent, with most crudes having sulfur concentrations in the range from about 0.5 to about 1.5 percent. Nitrogen concentration is usually less than 0.2 percent, but it may be as high as 1.6 percent.
Crude oil seldom is used in the form produced at the well, but is converted in oil refineries into a wide range of fuels and petrochemical feedstocks. Typically fuels for transportation are produced by processing and blending of distilled fractions from the crude to meet the particular end use specifications. Because most of the crudes available today in large quantity are high in sulfur, the distilled fractions must be desulfurized to yield products which meet performance specifications and/or environmental standards. Sulfur containing organic compounds in fuels continue to be a major source of environmental pollution. During combustion they are converted to sulfur oxides which, in turn, give rise to sulfur oxyacids and, also, contribute to particulate emissions.
In the face of ever-tightening sulfur specifications in transportation fuels, sulfur removal from petroleum feedstocks and products will become increasingly important in years to come. While legislation on sulfur in diesel fuel in Europe, Japan and the U.S. has recently lowered the specification to 0.05 percent by weight (max.), indications are that future specifications may go far below the current 0.05 percent by weight level. Legislation on sulfur in gasoline in the U.S. now limits each refinery to an average of 30 parts per million. In and after 2006 the average specification will be replaced by a cap of 80 parts per million maxim.
The fluidized catalytic cracking process is one of the major refining processes which is currently employed in the conversion of petroleum to desirable fuels such as gasoline and diesel fuel. In this process, a high molecular weight hydrocarbon feedstock is converted to lower molecular weight products through contact with hot, finely-divided, solid catalyst particles in a fluidized or dispersed state. Suitable hydrocarbon feedstocks typically boil within the range of 205° C. to about 650° C., and they are usually contacted with the catalyst at temperatures in the range 450° C. to about 650° C. Suitable feedstocks include various mineral oil fractions such as light gas oils, heavy gas oils, wide-cut gas oils, vacuum gas oils, kerosenes, decanted oils, residual fractions, reduced crude oils and cycle oils which are derived from any of these as well as fractions derived from shale oils, tar sands processing, and coal liquefaction. Products from a fluidized catalytic cracking process are typically based on boiling point and include light naphtha (boiling between about 10° C. and about 221° C.), heavy naphtha (boiling between about 10° C. and about 249° C.), kerosene (boiling between about 180° C. and about 300° C.), light cycle oil (boiling between about 221° C. and about 345° C.), and heavy cycle oil (boiling at temperatures higher than about 345° C.).
Not only does the fluidized catalytic cracking process provide a significant part of the gasoline pool in the United States, it also provides a large proportion of the sulfur that appears in this pool. The sulfur in the liquid products from this process is in the form of organic sulfur compounds and is an undesirable impurity which is converted to sulfur oxides when these products are utilized as a fuel. These sulfur oxides are objectionable air pollutants. In addition, they can deactivate many of the catalysts that have been developed for the catalytic converters which are used on automobiles to catalyze the conversion of harmful engine exhaust emissions to gases which are less objectionable. Accordingly, it is desirable to reduce the sulfur content of catalytic cracking products to the lowest possible levels.
The sulfur-containing impurities of straight run gasolines, which are prepared by simple distillation of crude oil, are usually very different from those in cracked gasolines. The former contain mostly mercaptans and sulfides, whereas the latter are rich in thiophene, benzothiophene and derivatives of thiophene and benzothiophene.
Low sulfur products are conventionally obtained from the catalytic cracking process by hydrotreating either the feedstock to the process or the products from the process. Hydrotreating involves treatment of products of the cracking process with hydrogen in the presence of a catalyst and results in the conversion of the sulfur in the sulfur-containing impurities to hydrogen sulfide, which can be separated and converted to elemental sulfur. Unfortunately, this type of processing is typically quite expensive because it requires a source of hydrogen, high pressure process equipment, expensive hydrotreating catalysts, and a sulfur recovery plant for conversion of the resulting hydrogen sulfide to elemental sulfur. In addition, the hydrotreating process can result in an undesired destruction of olefins in the feedstock by converting them to saturated hydrocarbons through hydrogenation. This destruction of olefins by hydrogenation is usually undesirable because it results in the consumption of expensive hydrogen, and also because the olefins are valuable as high octane components of gasoline. As an example, naphtha of a gasoline boiling range from a catalytic cracking process has a relatively high octane number as a result of a large olefin content. Hydrotreating such a material causes a re
Burnett Ptoshia A.
Hodges Michael
McDaniel Stacey
Pradhan Vivek R.
Arnold Jr. James
BP Corporation North America Inc.
Griffin Walter D.
Kim Patrick L.
Schoettle Ekkehard
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