Organic compounds -- part of the class 532-570 series – Organic compounds – Carbonate esters
Reexamination Certificate
2001-06-26
2003-09-16
McKane, Joseph K. (Department: 1626)
Organic compounds -- part of the class 532-570 series
Organic compounds
Carbonate esters
Reexamination Certificate
active
06620958
ABSTRACT:
The present invention relates to the separation of organic liquids. More specifically it relates to a process for separating organic liquids based upon their polarity utilizing a low polarity or non-polar membrane.
BACKGROUND OF THE INVENTION
It is well known to separate mixtures of liquids by various techniques including adsorption or distillation. These conventional processes, however, generally have high capital costs. For example, separating liquids by distillation requires expensive distillation towers, heaters, heat exchangers, as well as a substantial amount of auxiliary equipment, such as, pumps, collection vessels, vacuum generating equipment, etc. Distillation operations also generally have high operating costs associated with heating, cooling and material transfer.
Additionally, the specific properties of the materials being separated may warrant equipment or processing beyond that required for simple distillation to complete the separation. For example, when the mixture to be separated forms an azeotrope, the separation may require a series of steps (e.g., use of two or more towers) or by the addition of other materials to the separation system.
Adsorption systems also encounter comparable problems to those associated with distillation.
Thus, it would be advantageous to be able to separate mixtures of materials which are difficult or expensive to separate by distillation or adsorption systems.
The use of membrane technology to separate mixtures which are difficult to separate by distillation or adsorption are known in the art and include the use of porous and non-porous membranes. Non-porous membranes are used to separate mixtures of miscible liquids by exploiting the differences in the rate of transport through the membrane by means of a solution and diffusion mechanism. Methods have been proposed which utilize membranes to separate mixtures of organic substances or water/organic substance mixtures through pervaporation, vapor permeation or perstraction. Although each of these techniques rely upon a solution and diffusion mechanism for transport through the membrane, the operating parameters are quite different.
In the case of pervaporation, the liquid to be subjected to separation is fed on one side of a membrane, while the pressure is decreased or a carrier gas is passed on the other side of the membrane to permeate the material to be separated in the form of a gas through the membrane. Vapor permeation differs in that a vapor of a mixture is fed on the one side of the membrane and the material permeated through the membrane is recovered by cooling and condensing the permeated vapor. Perstraction differs from pervaporation in that the material to be separated is permeated through the membrane as a liquid and the carrier stream is also a liquid.
Examples of methods employing such membrane separations include separation of organic substance/water mixtures using a polymeric membrane having active anionic groups, separation of ethanol/water mixtures using a cellulose acetate membrane or a polyvinyl alcohol membrane, separation of organic substance/water mixtures or organic substance mixtures using a poly acrylonitrile copolymer membrane and separation of organic substance mixtures using a cross-linked polyvinyl alcohol membrane.
U.S. Pat. No. 4,798,674 to Pasternak et al. describes a method for concentrating a charge solution containing a C
1
-C
3
alcohol and an organic oxygenate selected from organic ethers, aldehydes, ketones and esters through pervaporation using a membrane of cross-linked polyvinyl alcohol and a high molecular weight ion exchange resin in membrane form. The alcohol permeates the membrane at a higher rate than the oxygenate, thus concentrating the oxygenate.
The present inventors have unexpectedly discovered that a liquid of reduced polarity relative to a mixture of liquids having varying polarity can be selectively separated from the mixture using a low polarity or non-polar, non-porous membrane.
SUMMARY OF THE INVENTION
The present invention is a method for separating at least one lower polarity fluid from a mixture of fluids having varying polarity.
A method for separating at least one lower polarity fluid from a mixture of fluids having varying polarity, comprising contacting at least one low polarity or non-polar polymeric membrane with the mixture comprising fluids of varying polarity under conditions such that at least one lower polarity fluid selectively permeates through the membrane, wherein the membrane is one which has a ratio of heteroatoms chemically bonded to the carbon atoms in the membrane to the number of carbon atoms of less than about 0.2, preferably less than about 0.05. Preferably, the method includes the step of eluting the at least one lower polarity fluid which has permeated through the membrane. The eluting step includes passing a solvent fluid over the side of the membrane opposite to the side which is contacted with the mixture under conditions such that the lower polarity fluid is carried away from the membrane. The mixture typically comprises fluids of varying polarity, e.g., dimethyl carbonate, ethylene glycol, and methanol, and wherein the lower polarity fluid comprises dimethyl carbonate. It is also desirable to use the method of the present invention when hydrogen is the lower polarity fluid.
The present invention also includes the use of such a membrane integral to a chemical reactor, wherein the mixture comprising the fluid of varying polarity is formed via the reaction of ethylene carbonate and methanol.
Optionally, two or more low polarity or non-polar polymeric membranes are contacted by the mixture in series, wherein the permeated liquid from one membrane contacts the next adjacent membrane and so forth. The membranes preferably have different flux rates and different selectivities relative to the selectively permeable fluid or fluids which contact each respective membrane. The membrane may further comprise a porous support layer and typically is a composite membrane comprising a plurality of polymeric layers.
The present invention also includes a process for producing a dialkyl carbonate which comprises the following steps: (a) reacting an alkanol with an alkylene carbonate, thereby forming a product mixture comprising the dialkyl carbonate, the alkanol, the alkylene carbonate and, optionally, an alkylene glycol; and (b) separating at least a portion of the dialkyl carbonate from the product mixture by contacting at least one low polarity or non-polar polymeric membrane with the product mixture under conditions which produce a permeate comprising the dialkyl carbonate, preferably dimethyl carbonate.
Additional objects, advantages and novel features of the invention will be set forth in part in the description and examples which follow, and in part will become apparent to those skilled in the art upon examination of the following, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
As used herein and in the claims, the term “lower polarity” when referring to a fluid (e.g., liquid and/or gas) means that the fluid with lower polarity is of relatively lower polarity as compared to at least one other fluid of higher polarity in a mixture of fluids. For example, assume a fluid mixture contained fluid 1, fluid 2, fluid 3, and fluid 4 and that each successively listed fluid was of higher polarity than the preceding listed fluids (i.e., as to polarity: fluid 1<fluid 2<fluid 3<fluid 4). Then each of fluids 1 through 3 could qualify as a fluid of lower polarity, because at least one fluid 4 in the mixture of four fluids is of a higher polarity than each of fluids 1 through 3.
The present invention is a method for separating a mixture of organic fluids (e.g., liquids and/or gases) based upon their relative polarity. More specifically, it is a method for selectively separating a liquid or liqu
Altman Lawrence J.
Buchanan J. Scott
Diehl John W.
ExxonMobil Chemical Patents Inc.
McKane Joseph K.
Small Andrea D.
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