Chemistry of hydrocarbon compounds – Plural parallel syntheses – With blending of products from two parallel reactions
Reexamination Certificate
2002-04-18
2004-03-09
Griffin, Walter D. (Department: 1764)
Chemistry of hydrocarbon compounds
Plural parallel syntheses
With blending of products from two parallel reactions
C585S302000, C585S304000, C585S329000, C585S330000, C208S950000
Reexamination Certificate
active
06703535
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a process for upgrading Fischer-Tropsch products by increasing the yield of lubricating base oil and diesel.
BACKGROUND OF THE INVENTION
The market for lubricating base oils of high paraffinicity is continuing to grow due to the high viscosity index, oxidation stability, and low volatility relative to viscosity of these molecules. The products produced from the Fischer-Tropsch process contain a high proportion of wax which make them ideal candidates for processing into lubricating base oil stocks. Accordingly, the hydrocarbon products recovered from the Fischer-Tropsch process have been proposed as feedstocks for preparing high quality lubricating base oils. See, for example, U.S. Pat. No. 6,080,301 which describes a premium lubricating base oil having a high non-cyclic isoparaffin content prepared from Fischer-Tropsch waxes by hydroisomerization dewaxing and solvent dewaxing.
The economics of a Fischer-Tropsch complex has in the past only been desirable in isolated areas, however, such a Fischer-Tropsch complex can benefit if the production of high-value products in the product slate, such as lubricating base oil and high quality diesel, can be increased. Lubricating base oils typically will have an initial boiling point above about 315° C. (600° F.). Using the process described herein the amount of lubricating base oils derived from the Fischer-Tropsch synthesis may be significantly increased. If desired, high quality diesel products also may be prepared from the syncrude recovered from the Fischer-Tropsch process. Fischer-Tropsch derived diesel typically has a very low sulfur and aromatics content and an excellent cetane number. In addition, the process of the present invention makes it possible to produce diesel having low pour and cloud points, which enhance the quality of the product. These qualities make Fischer-Tropsch derived diesel an excellent blending stock for upgrading lower quality petroleum-derived diesel. Accordingly, it is desirable to be able to maximize the yields of such higher value hydrocarbon products which boil within the range of lubricating base oils and diesel. At the same time, it is desirable to minimize the yields of lower value products such as naphtha and C
4
minus products. The present invention makes these goals possible.
Fischer-Tropsch wax refers to a high boiling fraction from the Fischer-Tropsch derived syncrude and is most often a solid at room temperature. For the purpose of this disclosure “Fischer-Tropsch wax” will be contained in the higher boiling portion of the Fischer-Tropsch syncrude. Fischer-Tropsch wax contains at least 10% by weight of C
20
and higher hydrocarbonaceous compounds, preferably at least 40% by weight of C
20
and higher hydrocarbonaceous compounds, and most preferably at least 70% by weight of C
20
and higher hydrocarbonaceous compounds.
All syncrude Fischer-Tropsch products as they are initially recovered from the Fischer-Tropsch reactor contain varying amounts of olefins depending upon the type of Fischer-Tropsch operation employed. In addition, the crude Fischer-Tropsch product also contains a certain amount of oxygenated hydrocarbons, especially alcohols, which may be readily converted to olefins by a dehydration step. These olefins may be oligomerized to yield hydrocarbons having a higher molecular weight than the original feed. Oligomerization also introduces desirable branching into the hydrocarbon molecule which lowers the pour point of the diesel and lubricating base oil products thereby improving the cold flow properties of the product. See for example U.S. Pat. No. 4,417,088. In the present invention most of the alcohols will be included in the condensate fraction recovered from the Fischer-Tropsch unit. As used in this disclosure, the term “Fischer-Tropsch condensate” refers generally to the C
5
plus fraction which has a lower boiling point than the Fischer-Tropsch wax fraction. That is to say, that fraction which is normally liquid at ambient temperature.
As used in this disclosure, the term “C
19
minus Fischer-Tropsch product” refers to a product recovered from a Fischer-Tropsch reaction zone which is predominantly comprised of hydrocarbons having 19 carbon atoms or less in the molecular backbone. One skilled in the art will recognize that such products may actually contain a significant amount of hydrocarbons containing greater than 19 carbon atoms. In general, what is referred to are those hydrocarbons having a boiling range of diesel and below. In general, for the purposes of this disclosure, diesel is considered as having a upper boiling point of about 700° F. (370° C.) and an initial boiling point of about 300° F. (about 150° C.). Diesel may also be referred to as C
10
to C
19
hydrocarbons. Likewise, Fischer-Tropsch wax preferably is comprised predominantly of “C
20
plus product” which refers to a product comprising primarily hydrocarbons having 20 or more carbon atoms in the backbone of the molecule and having an initial boiling point at the upper end of the boiling range for diesel, i.e., above about 600° F. (315° C.). It should be noted that the upper end of the boiling range for diesel and the lower end of the boiling range for Fischer-Tropsch wax have considerable overlap. The term “naphtha” when used in this disclosure refers to a liquid product having between about C
5
to about C
9
carbon atoms in the backbone and will have a boiling range generally below that of diesel but wherein the upper end of the boiling range will overlap that of the initial boiling point of diesel. The term C
10
plus hydrocarbons refers to those hydrocarbons generally boiling above the range of naphtha, i.e., the fractions boiling within the range of diesel and lubricating base oils or above about 150° C. Products recovered from the Fischer-Tropsch synthesis which are normally in the gaseous phase at ambient temperature are referred to as C
4
minus hydrocarbons in this disclosure. LPG which is primarily a mixture of propane and butane is an example of a C
4
minus product. The precise cut-point selected for each of the products in carrying out the distillation operation will be determined by the product specifications and yields desired.
EP patent application 0620264A2 discloses a process for making lubricating base oil from waste plastics by use of thermal cracking. U.S. Pat. No. 6,288,296 also teaches a process for converting polyethylene into high VI lubricating base oil using thermal cracking followed by dimerization and isomerization. However, neither process would be suitable for the processing of Fischer-Tropsch syncrude into lubricating base oils as contemplated herein. U.S. Pat. No. 4,579,986 describes a process in which linear paraffins are thermal cracked to yield olefins. The C
10
to C
19
olefins are treated with a peroxide to make an intermediate which may be converted into lubricating base oil. EP publication number 0584879A1 teaches the thermal cracking of a hydroprocessed Fischer-Tropsch syncrude to prepare lower olefins.
As used in this disclosure the words “comprises” or “comprising” is intended as an open-ended transition meaning the inclusion of the named elements, but not necessarily excluding other unnamed elements. The phrase “consists essentially of” or “consisting essentially of” is intended to mean the exclusion of other elements of any essential significance to the composition. The phrases “consisting of” or “consists of” are intended as a transition meaning the exclusion of all but the recited elements with the exception of only minor traces of impurities.
SUMMARY OF THE INVENTION
The present invention includes a process for upgrading a Fischer-Tropsch feedstock which comprises (a) recovering from a Fischer-Tropsch reactor a Fischer-Tropsch wax fraction containing paraffins and a Fischer-Tropsch condensate fraction, wherein the Fischer-Tropsch condensate fraction contains alcohols boiling below about 370° C.; (b) contacting the Fischer-Tropsch condensate fraction with a dehydration catalyst in a dehydration zone under dehydr
Cannella William J.
Driver Michael S.
Johnson David R.
Lee Stephen K.
Miller Stephen J.
Ambrosius James W.
Chevron U.S.A. Inc.
Griffin Walter D.
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