Mineral oils: processes and products – Refining – Sulfur removal
Reexamination Certificate
2000-01-21
2003-07-29
Norton, Nadine G. (Department: 1764)
Mineral oils: processes and products
Refining
Sulfur removal
C208S062000, C208S066000, C208S097000, C208S213000, C208S218000, C208S088000
Reexamination Certificate
active
06599417
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a process for removing sulfur-containing impurities from olefin-containing hydrocarbon mixtures. More particularly, the process involves converting the feedstock to an intermediate product of reduced bromine number, separating the intermediate product into fractions of different boiling point, and subjecting the low boiling fraction to hydrodesulfurization.
BACKGROUND OF THE INVENTION
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 from about 205° C. to about 650° C., and they are usually contacted with the catalyst at temperatures in the range from about 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.).
Naphtha from a catalytic cracking process comprises a complex blend of hydrocarbons which includes paraffins (also known as alkanes), cycloparaffins (also known as cycloalkanes or naphthenes), olefins (as used herein, the term olefin includes all acyclic and cyclic hydrocarbons which contain at least one double bond and are not aromatic), and aromatic compounds. Such a material typically contains a relatively high olefin content and includes significant amounts of sulfur-containing aromatic compounds, such as thiophenic and benzothiophenic compounds, as impurities. For example, a light naphtha from the fluidized catalytic cracking of a petroleum derived gas oil can contain up to about 60 wt. % of olefins and up to about 0.7 wt. % of sulfur wherein most of the sulfur will be in the form of thiophenic and benzothiophenic compounds. However, a typical naphtha from the catalytic cracking process will usually contain from about 5 wt. % to about 40 wt. % olefins and from about 0.07 wt. % to about 0.5 wt. % sulfur.
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. The 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.
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. The hydrotreating process involves treatment of the feedstock 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. The hydrotreating process can result in the destruction of olefins in the feedstock by converting them to saturated hydrocarbons through hydrogenation. This destruction of olefins by hydrogenation is usually undesirable because: (1) it results in the consumption of expensive hydrogen, and (2) the olefins are usually valuable as high octane components of gasoline. As an example, a typical naphtha of 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 reduction in the olefin content in addition to the desired desulfurization, and the octane number of the hydrotreated product decreases as the degree or severity of the desulfurization increases.
U.S. Pa. No. 5,865,988 (Collins et al.) is directed to a two step process for the production of low sulfur gasoline from an olefinic, cracked, sulfur-containing naphtha. The process involves: (a) passing the naphtha over a shape selective acidic catalyst, such as ZSM-5 zeolite, to selectively crack low octane paraffins and to convert some of the olefins and naphthenes to aromatics and aromatic side chains; and (2) hydrodesulfurizing the resulting product over a hydrotreating catalyst in the presence of hydrogen. It is disclosed that the initial treatment with the shape selective acidic catalyst removes the olefins which would otherwise be saturated in the hydrodesulfurization step.
International Patent Application No. WO 98/30655 (Huff et al.), published under the Patent Cooperation Treaty, discloses a process for the production of a product of reduced sulfur content from a feedstock wherein the feedstock is comprised of a mixture of hydrocarbons and contains organic sulfur compounds as unwanted impurities. This process involves converting at least a portion of the sulfur-containing impurities to sulfur-containing products of a higher boiling point by treatment with an alkylating agent in the presence of an acid catalyst and removing at least a portion of these higher boiling products by fractionation on the basis of boiling point.
U.S. Pat. Nos. 5,298,150 (Fletcher et al.); 5,346,609 (Fletcher et al.); 5,391,288 (Collins et al.); and 5,409,596 (Fletcher et al.) are all directed to a two step process for the preparation of a low sulfur gasoline wherein a naphtha feedstock is subjected to hydrodesulfurization followed by treatment with a shape selective catalyst to restore the octane which is lost during the hydrodesulfurization step.
U.S. Pat. No. 5,171,916 (Le et al.) is directed to a process for upgrading a light cycle oil by: (1) alkylating the heteroatom containing aromatics of the cycle oil with an aliphatic hydrocarbon having at least one olefinic double bond through the use of a crystalline metallosilicate catalyst; and (2) separating the high boiling alkylation product by fractional distillation. It is disclosed that the unconverted light cycle oil has a reduced sulfur and nitrogen content, and the high boiling alkylation product is useful as a synthetic alkylated aromatic functional fluid base stock.
U.S. Pat. No. 5,599,441 (Collins et al.) discloses a process for removing thiophenic sulfur compounds from a cracked naphtha by: (1) contacting the naphtha with an acid catalyst in an alkylation zone to alkylate the thiophenic compounds using the olefins present in the naphtha as an alkylating agent; (2) removing an effluent stream from the alkylation zone; and (3) separating the alkylated thiophenic compounds from the alkylation zone effluent stream by fractional distillation. It is also disclosed that the sulfur-rich high boiling fraction from the fractional distillation may be desulfurized using conventional hydrotreating or other desulfurization processes.
U.S. Pat. No. 5,863,419 (Huff, Jr. et al.) discloses a catalytic distillation process for the production of a product of reduced sulfur content from a feedstock wherein the feedstock is comprised of a mixture of hydrocarbons which c
Burnett Ptoshia A.
Huff George A.
Pradhan Vivek R.
BP Corporation North America Inc.
Ekkehard Schoettle
Kim Patrick J.
Norton Nadine G.
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