Organic compounds -- part of the class 532-570 series – Organic compounds – Oxygen containing
Reexamination Certificate
1998-12-16
2001-08-21
Richter, Johann (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Oxygen containing
C568S579000, C568S697000, C585S800000, C585S833000, C585S867000
Reexamination Certificate
active
06278029
ABSTRACT:
This invention relates to a process that makes it possible to eliminate pollutants, particularly traces of polar compounds, which are contained in a fluid, by bringing it into contact with a vapor phase produced during the process or consecutively with a vapor phase and then possibly solid phase.
The expression “polar compounds” pertains in particular to nitrites and acetone.
Likewise, the term “nitriles” combines compounds that contain nitrogen, such as acetonitrile, propionitrile and any mixtures of them.
The invention is readily incorporated into etherification processes. Actually, in such processes, it is necessary to wash the hydrocarbon feedstock with water before sending it to the reaction zone. The washing water, which is loaded with pollutants, can be purified by using the process according to the invention.
In the description below, the word “washing” applies to devices and processes that make it possible to wash a second fluid with a first fluid, before sending said second washed fluid to a subsequent treatment process that is sensitive to said pollutants, which can be, for example, an etherification reaction by acid catalysis. The word “purification” is used to refer to operations for treating the first fluid that is loaded with pollutants.
The word “feedstock” represents the fluid which will be subjected to treatment. For the etherification process, the expression “hydrocarbon feedstock” will be used.
Etherification processes are commonly used to increase the octane number of gasolines. These units typically treat olefinic C
4
-C
5
fractions or light gasoline fractions that contain tertiary olefins such as isobutenes, isoamylenes, isohexenes, isoheptenes, which can react easily with alcohols, for example, methanol, to provide methyl or ethyl ethers.
The processes for etherification can also be used intermediately to extract pure isoolefins from hydrocarbon fractions that contain them. In this case, ether is produced by the etherification reaction, and then catalyzed decomposition of ether that is purified and thus pre-isolated is carried out. For example, pure isobutylene can be obtained for the production of polyisobutylene, tert-butyl-phenol and does so by decomposition of methyl-tert-butyl-ether (MTBE).
The process for the production of MTBE is the most widely used etherification process. The treated hydrocarbon feedstock, a C
4
fraction in this case, contains olefins in general and isobutene in particular. Like other processes for etherification which are of general importance and which have been incorporated into large-scale industrial applications, there is the production of tert-amyl-methyl ether (TAME) by reaction of isoolefins that contain 5 carbon atoms with methanol and the production of ethyl-tert-butyl ether (ETBE) that is obtained by reacting isobutene that is contained in a C
4
fraction with ethanol.
In general, all these reactions are carried out in the presence of acid catalysts, for example, and the most common industrial case is ion-exchange resins such as crosslinked sulfonic polystyrene resins in acid form.
When polar compounds, such as nitrites or ketones, are present in the hydrocarbon feedstock of these etherification processes, they react with the catalyst, which causes the catalyst to lose its properties and to be deactivated.
To increase the life of the catalysts, it is known in the prior art to wash the hydrocarbon feedstock before it passes to the catalyst, generally with demineralized water. For example, before being introduced into the reactor where the etherification reaction will be carried out, a standard operation involves circulating countercurrently in a washing column the hydrocarbon feedstock and washing water under established operating conditions so that the water for washing is loaded with pollutants. At the end of this operation, for the most part, the compounds that are likely to poison the catalyst and therefore limit its life are removed from the hydrocarbon feedstock. The washing water that is loaded with pollutants is sent to a general circuit for treating water from a refinery including an etherification unit.
This washing water, which contains the pollutants that are removed from the hydrocarbon feedstock in addition to small amounts of hydrocarbons, is then treated by physico-chemical and/or bacteriological processes to make it possible to dump all of it, if necessary, to a sewer system, whereby it is not possible to envisage any recycling to the washing unit that is located upstream from the etherification unit from which it comes. This approach requires the use of a large amount of water that is of high purity and is supplied from an outside source.
According to U.S. Pat. No. 5,569,790, the purification of the hydrocarbon feedstock washing water that contains the pollutants is accomplished by bringing it into liquid-liquid contact at least partially with a portion of the final effluent raffinate that comes from the etherification unit. The purified water is then recycled into the washing column of the feedstock. While such a process offers in particular the recycling of water as an advantage, it still suffers from the drawback of polluting the raffinate by loading it with pollutants or nitrites. This is not recommended; the raffinate may be intended for other treatment processes downstream, such as an alkylation process. Moreover, the degree of purification of the water is necessarily limited, on the one hand because the splitting of the pollutants is done in favor of the aqueous phase, as the washing of hydrocarbons shows, and, on the other hand, because the proportion of raffinate relative to the water that is loaded with pollutants is imposed by the process and cannot be increased. The result is that the recycled water is then impure, which reduces the effectiveness of the washing of the hydrocarbons. To increase the effectiveness of the washing, it is then necessary to inject water from the outside in relatively large amounts. Such an operation will, however, run counter to the need to conserve water or will have to operate in an almost closed loop when the available outside sources of water are not very numerous. In addition to a given effectiveness of washing, the overall flow rate of washing water to the washing column is larger than that which is used in processes that operate with lost water (outside source).
The technical teaching contained in the U.S. Pat. No. 5,684,212 relates to an improvement of a process of etherification which comprises a stage where the water that is loaded with pollutants while washing the hydrocarbon feedstock is brought into contact with a first vapor flow or a fuel gas flow under conditions which makes it possible to eliminate nitrites from water charged in pollutants.
The vapor flow or the fuel gas flow are supplied from outside source. Such a process presents in particular the disadvantage of having to have external sources which are not always available.
One of the objects of this invention is to use a vapor phase under given operating conditions to pick up such pollutants as polar compounds and more particularly nitrites (acetonitrile, propionitrile, . . . ) and acetone, which are contained in water for washing hydrocarbon feedstock that is intended for, for example, an etherification reaction.
The idea involves carrying out a process in 1 closed or quasi closed loop in which the phase vapor used for collecting of the pollutants is produced during the process.
The vapor phase can be produced by the fluid that is loaded with pollutants itself or else come from an outside source. For example, it is possible to use the water vapor that is generated by the reboiler of a stripping column to eliminate pollutants from the washing water.
Without exceeding the scope of the invention, the process according to the invention can be used to purify a first fluid which has been used to “wash” a second fluid, to eliminate pollutants that are contained in this second fluid, with the latter being intended for a subsequent treatment. As an example that is in no way limiting, it is poss
Debuisschert Quentin
Forestiere Alain
Marache Pierre
Mikitenko Paul
Institut Francais du Pe'trole
Millen White Zelano & Branigan P.C.
Richter Johann
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