Chemistry: fischer-tropsch processes; or purification or recover – Liquid phase fischer-tropsch reaction
Reexamination Certificate
2000-02-10
2001-10-30
Killos, Paul J. (Department: 1621)
Chemistry: fischer-tropsch processes; or purification or recover
Liquid phase fischer-tropsch reaction
C518S702000, C518S703000, C518S704000, C208S046000, C208S133000, C208S308000, C585S352000, C585S734000
Reexamination Certificate
active
06310108
ABSTRACT:
This invention relates to the synthesis of an atmospheric distillate from a hydrocarbon feedstock and often from a feedstock that contains hydrocarbon compounds and in particular from naphtha, natural gas or methane. Within the context of this description, the term atmospheric distillate refers to one or more fractions that basically contain liquid hydrocarbons under normal pressure at a temperature of about 20° C., i.e., compounds that have at least five carbon atoms in their molecule.
The process for synthesis of an atmospheric distillate according to this invention comprises the use of the Fischer-Tropsch technology that is incorporated in a comprehensive system that comprises the preparation of the synthesis gas from a liquid or gas hydrocarbon feedstock, and most often gas hydrocarbon feedstock. There are only very few industrial units that have been built and integrated into a comprehensive scheme for the production of atmospheric distillate. For example, the magazine Oil and Gas Journal describes in 1949 Vol. 47, pp. 248-250 the production done in Texas within the framework of the Carthage Hydrocol project.
As this is emphasized in particular in the description of Patent US-A-5 621 155, a very large number of problems is linked to the implementation of a comprehensive production system of atmospheric distillate that comprises the use of the Fischer-Tropsch technology. Thus, for example, the hydrocarbon feedstock that is used is converted into a gas mixture that is called synthesis gas that contains a mixture of carbon monoxide and hydrogen before this mixture is introduced into the Fischer-Tropsch reactor. Economic conditions for operating a Fischer-Tropsch reactor of a given size require obtaining for the gas mixture that is introduced into the reactor a hydrogen to carbon monoxide ratio in a well-established range. The implementation of the Hydrocol project uses partial oxidation of natural gas to form a gas mixture that contains a hydrogen to carbon monoxide ratio of about 2. Another approach for the formation of the gas mixture that contains hydrogen and carbon monoxide is the use of the technique for steam reforming of natural gas or other light hydrocarbons. In the case of steam reforming, it is generally necessary to treat the gas that is produced so as to eliminate the carbon dioxide that it contains, which complicates the operation. Furthermore, an adjustment of the hydrogen to carbon monoxide ratio is essential since the amount of hydrogen in the gas mixture that is formed is considerably larger than the ratio that is usually used in the Fischer-Tropsch reactor. This set of problems leads the inventors of this patent to consider the specific advantages of the use of partial oxidation which makes it possible to avoid the use of a system for separating the carbon dioxide and which makes it possible to obtain a gas mixture whose hydrogen to carbon monoxide ratio is closer to the desired ratio. Partial oxidation, however, is not the ideal solution.
This is why the inventors are considering using one or the other method for the production of synthesis gas with, in the case where steam reforming is used, the introduction of a predetermined amount of carbon dioxide in the reforming reactor and the use of a system for absorption and recovery of the carbon dioxide at the outlet of the reforming reactor. Furthermore, the process that is described in this patent requires the recycling of an amount of carbon dioxide in the formation stage of the synthesis gas whether in the partial oxidation stage or in the steam reforming stage that would make possible, according to the authors of this invention, a better conversion of total carbon, introduced in the scheme, into hydrocarbon products that contain in particular waxes that cannot be upgraded directly as an atmospheric distillate fraction and in particular as an engine fuel. The teaching of this patent therefore does not relate directly to a process that allows the optimization of the production of atmospheric distillate in a comprehensive system that comprises the use of Fischer-Tropsch technology.
The process according to this invention has as its object the optimization of the formation of atmospheric distillate, and mainly of engine fuels, from a hydrocarbon feedstock in an integrated process that limits as much as possible the drawbacks that are cited in the prior art and that comprise the production of a synthesis gas, whereby the transformation of this synthesis gas with Fischer-Tropsch technology into hydrocarbon compounds and an isomerizing hydrocracking transforms the heaviest compounds into lighter compounds that have, for those that are of the diesel variety and in particular of the diesel engine, a zero aromatic compound level, a very high cetane number, and lead to a very small soot formation, whereby those that are of the naphtha variety form an excellent steam-cracking feedstock, and those of the kerosene variety have a very good smoke point and a zero aromatic compound level.
In its broadest embodiment, this invention is defined as a process for the production of atmospheric distillate from a hydrocarbon feedstock that comprises the following stages:
a) a formation stage of a gas mixture that contains hydrogen and carbon monoxide in a ratio of about 1.7:1 to about 2.5:1, preferably about 2.0:1 to about 2.5:1, and more preferably about 2.1:1 to about 2.3:1 from said hydrocarbon feedstock,(both here and below the H
2
:CO ratio is in terms of a molar ratio),
b) an at least partial conversion stage of the gas mixture that is obtained in stage a) at high temperature and pressure in the presence of a catalyst to obtain a liquid effluent that contains hydrocarbons that have at least 5 carbon atoms in their molecule and a gas effluent that contains the unconverted fraction of the gas mixture of stage a) and that contains carbon dioxide,
c) a stage for treating the gas fraction that is obtained in stage b) under conditions that make it possible to eliminate the carbon dioxide at least partly and to obtain a gas fraction that is low in carbon dioxide and that is preferably recycled in stage a) for the formation of the gas mixture that contains hydrogen and carbon monoxide,
d) a first fractionation stage of the liquid fraction that is obtained from stage b) in which a heavy fraction FL
1
that contains basically hydrocarbons that have at least seven carbon atoms in their molecule and often at least 9 carbon atoms in their molecule, and a light fraction FL
2
that contains basically hydrocarbons that have at most six carbon atoms in their molecule are separated,
e) an isomerizing hydrocracking stage in which in the presence of a catalyst, at high temperature and pressure, and in the presence of hydrogen, heavy fraction FL
1
that is obtained from stage d) is transformed into a fraction F
2
that contains a larger amount of branched compounds than fraction FL
1
,
f) a second fractionation stage, in which light fraction FL
2
that is obtained from stage d) and fraction F
2
that is obtained from stage e) are sent, and from which are separated a fraction that contains basically hydrocarbons that have at most 4 carbon atoms in their molecule from final boiling point to atmospheric pressure that is lower than about 37° C., often lower than 25° C. and most often lower than 5° C., a fraction that has a final boiling point at an atmospheric pressure that is greater than about 300° C., often greater than about 350° C. and most often greater than about 370° C., and at least one intermediate atmospheric distillate fraction that has a boiling point of between about 5° C. and about 370° C., often between about 25° C. and about 350° C.
According to a first embodiment, the formation of the gas mixture that contains carbon monoxide and hydrogen in the ratios that are indicated above will comprise a first stage a1) for catalytic steam reforming of a portion of the hydrocarbon feedstock at high temperature and pressure under conditions of formation of a basically gaseous effluent that contains hydrogen and carbon monoxide in a ratio th
Bonneau Reynald
Clerici Mario-Gabriele
Viltard Jean-Charles
Institut Francais du Pe'trole
Killos Paul J.
Millen White Zelano & Branigan P.C.
Parsa J.
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