Chemistry of hydrocarbon compounds – Product blend – e.g. – composition – etc. – or blending process...
Reexamination Certificate
2001-06-15
2002-05-21
Richter, Johann (Department: 1764)
Chemistry of hydrocarbon compounds
Product blend, e.g., composition, etc., or blending process...
C518S700000, C585S014000, C208S027000
Reexamination Certificate
active
06392108
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the use of antioxidants in Fischer Tropsch derived products. The present invention also relates to methods of inhibiting oxidation in Fischer Tropsch derived products.
BACKGROUND OF THE INVENTION
The majority of combustible fuel used in the world today is derived from crude oil. There are several limitations to using crude oil as a fuel source. Crude oil is in limited supply; it includes aromatic compounds that may be harmful and irritating, and it contains sulfur and nitrogen-containing compounds that can adversely affect the environment, for example, by producing acid rain.
Combustible liquid fuels can also be prepared from natural gas. This preparation involves converting the natural gas, which is mostly methane, to synthesis gas, or syngas, which is a mixture of carbon monoxide and hydrogen. An advantage of using products prepared from syngas is that they do not contain nitrogen and sulfur and generally do not contain aromatic compounds. Accordingly, they have minimal health and environmental impact.
Fischer-Tropsch chemistry is typically used to convert the syngas to a product stream that includes combustible fuel, among other products. These Fischer Tropsch products have very low levels of sulfur, nitrogen, aromatics and cycloparaffins. The Fischer Tropsch derived fuels are considered “green fuels” and are desirable as environmentally friendly.
Although environmentally friendly, these Fischer Tropsch products tend to oxidize relatively rapidly when exposed to air. The rapid oxidation may be due to a lack natural anti-oxidants, such as sulfur compounds. Further, some of the products produced by the Fischer Tropsch process may be waxy, and these products are frequently are shipped at elevated temperature. Shipping at elevated temperatures increases the tendency of Fischer Tropsch products to oxidize.
Various methods have been proposed to protect Fischer Tropsch products from oxidation during shipping and storage. For example, Berlowitz and Simon of Exxon Research and Engineering Company describe in World Patent Application Nos. WO 00/1116A1 and WO 00/11117A1 the blending of a Fischer Tropsch derived diesel fuel with high boiling sulfur containing streams, derived from gas field condensate or hydrotreated streams. Using the approach of Berlowitz and Simon to prevent oxidation adds high-boiling, sulfur-containing compounds to the Fischer Tropsch diesel fuel. Therefore, the products of Berlowitz and Simon contain sulfur, which prevents their use as low-sulfur, environmentally friendly fuels. Another undesirable feature of the products of Berlowitz and Simon is that a significant portion of the sulfur in those products is in the form of mercaptans (RSH). Mercaptans are well known to cause corrosion. Therefore, when shipping or storing products treated according to Berlowitz and Simon, corrosion of the large storage vessels can be a problem. Corrosion damage may lead to the need for eventual replacement of the large, expensive vessels used to ship and store hydrocarbonaceous products.
Various other well-known antioxidants may be used with Fischer Tropsch diesel fuels to prevent oxidation. These well-known antioxidants may include phenolic compounds and diphenylamine compounds. However, these antioxidants can be expensive when used on a large scale and must be transported to the remote site where the Fischer Tropsch diesel fuel is made.
There is a need for appropriate antioxidants for Fischer Tropsch derived products that do not impart polluting sulfur, corrosive mercaptans, or other undesirable components to the final product, and antioxidants that do not require shipping to the remote site where the Fischer Tropsch products are made. There is a need for efficient and economical methods of inhibiting oxidation of Fischer Tropsch derived products.
SUMMARY OF THE INVENTION
One aspect of the present invention is a blended hydrocarbonaceous product comprising: a) a Fischer Tropsch derived product; and b) an effective amount of a temporary antioxidant such that the blended hydrocarbonaceous product has a final peroxide number of less than 5 ppm, preferably less than 3 ppm and most preferably less than 1 ppm after 7 days. The temporary antioxidant may be derived from a petroleum product. The temporary antioxidant may be selected from the group consisting of sulfides, disulfides, polysulfides, and mixtures thereof.
An additional aspect of the present invention is a blended hydrocarbonaceous product comprising: a) a Fischer Tropsch derived product; and b) a sulfur-containing, temporary antioxidant, wherein the sulfur content of the blended hydrocarbonaceous product is ≧1 ppm.
A further aspect of the present invention is a method of inhibiting oxidation of a Fischer Tropsch product comprising the steps of:
a) synthesizing a Fischer Tropsch product by a Fischer Tropsch process;
b) adding an effective amount of a temporary antioxidant to provide a blended product having a final peroxide number of less than 5 ppm, preferably less than 3 ppm and most preferably less than 1 ppm after 7 days;
c) blending the Fischer Tropsch product and the antioxidant to provide a blended product; and
d) removing at least a portion of the antioxidant from the blended product after the period in which oxidation is to be prevented.
The temporary antioxidant may be derived from a petroleum product and this may be done at or near to the site where the Fischer Tropsch products are generated. The temporary antioxidant may be selected from the group consisting of sulfides, disulfides, polysulfides, and mixtures thereof. The temporary antioxidant may be removed by a variety of processes, including for example, simple distillation or stripping.
An additional aspect of the present invention is a method of inhibiting oxidation of a Fischer Tropsch product comprising the steps of:
a) synthesizing a Fischer Tropsch product by Fischer Tropsch process;
b) adding an effective amount of a sulfur-containing antioxidant to provide a product having a final peroxide number of less than 5 ppm, preferably less than 3 ppm and most preferably less than 1 ppm after 7 days;
c) blending the Fischer Tropsch product and the antioxidant to provide a blended product; and
d) processing the blended product to remove at least a portion of the sulfur after the period in which oxidation is to be prevented.
The antioxidant may be a temporary antioxidant or may be an antioxidant that has about the same boiling range as the Fischer Tropsch product. The antioxidant may be selected from the group consisting of sulfides, disulfides, polysulfides, mercaptans, and the like, and mixtures thereof. The antioxidant in the method of the present invention may be a mercaptan because the method of the present invention includes the step of processing the blended product to remove at least a portion of the sulfur after the period in which oxidation is expected. Although the antioxidant may be a mercaptan, it is preferred that the antioxidant be a compound other than a mercaptan.
The step of processing the blended product to remove sulfur may involve a variety of processes, including for example, hydrotreating, hydrocracking, hydroisomerization, extraction, adsorption, and the like. The preferred methods are those involving processing with hydrogen (i.e., hydrotreating, hydrocracking, and hydroisomerization), with hydrotreating being the most preferred.
A further aspect of the present invention is a method of inhibiting oxidation of a Fischer Tropsch product comprising the steps of:
a) synthesizing a Fischer Tropsch product by Fischer Tropsch process;
b) adding an effective amount of a temporary antioxidant to the Fischer Tropsch product to provide a product containing between 1 ppm and 1 wt % temporary antioxidant, preferably between 10 ppm and 1000 ppm temporary antioxidant.
c) blending the Fischer Tropsch product and the antioxidant to provide a blended product; and
d) removing at least a portion of the sulfur from the blended product after the period in which oxidation is to be prevented.
The tempora
Burns Doane Swecker & Mathis L.L.P.
Chevron U.S.A. Inc.
Parsa J.
Richter Johann
LandOfFree
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