Exhibit 2023
`E.I. du Pont de Nemours & Co. and
`Acher-Daniels-Midland Co. v. Furanix Technologies B.V.
`IPR2015-01838
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`4,338,462
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`SILVER-CATALYZED OXIDATION OF
`MEI'I-IACROLEIN TO METHACRYLIC ACID
`
`BACKGROUND OF THE INVENTION
`
`The oxidation of a,B-unsaturated aldehydes to the
`corresponding a,B-unsaturated carboxylic acids or car-
`boxylic acid salts is well known in the art. Improved
`yields of the desired acid are known to be obtainable by
`oxidation of the unsaturated aldehyde with an oxidizing
`gas in an aqueous alkaline solution in the presence of a
`silver catalyst. US. Pat. Nos. 2,930,801; 3,162,682 and
`3,839,437 disclose methacrylic acid production from
`methacrolein oxidation in a strongly alkaline medium
`catalyzed with silver as illustrated by the following:
`
`‘f”’
`5”“
`Cl-lz=C-CH ——-9 Cl-lz=C-COOH
`II0
`
`Active life of the silver catalyst is disclosed by U.S. Pat.
`No. 2,887,496 to be prolonged by conducting such oxi-
`dation in the presence of a mixture of triethanolamine
`and tetrasodium salt of ethylenediaminetetraacetic acid.
`Oxidation catalysts having copper (II) oxide alone or
`in combination with other metals and metal oxides,
`including silver, are also known. Polyacroleins may be
`oxidized to corresponding polyacrylic acids as de-
`scribed in U.S. Pat. Nos. 3,387,029 and 3,546,286. Polys-
`crolein and polymethaerolein oxidation is disclosed to
`be conducted in an aqueous alkaline solution maintained
`by an alkali hydroxide or its corresponding carbonate 0
`bicarbonate.
`'
`When methacrolein has been oxidized by the prior art
`alkaline solution silver catalyzed processes, production
`of the corresponding acid salt is accompanied by the
`formation of methallyl alcohol and isobutyrate salts as
`by-products. Formation of those by-products represents
`a diminution of yield of the desired methacrylate salt
`and further causes problems in purification of meth-
`acrylic acid formed upon acidification of the salt-form
`product.
`
`SUMMARY OF THE INVENTION
`
`It has been discovered that formation of methallyl
`alcohol and isobutyrate salt by-products are signifi-
`cantly suppressed by oxidizing methacrolein with an
`oxidizing gas in a strongly alkaline medium with a silver
`catalyst in the presence of a small amount of dissolved
`alkali metal carbonate.
`-
`
`DETAILED DESCRIPTION OF THE
`'
`INVENTION
`
`Quite unexpectedly, it has been found that the forma-
`tion of the by-products methallyl alcohol and isobutyr-
`ate salts is suppressed during the oxidation of methacro-
`lein with an oxidizing gas in the presence of finely di-
`vided silver in an aqueous alkaline medium by the addi-
`tion of small amounts of alkali metal carbonates to the
`alkaline medium. By-product methallyl alcohol and
`isobutyrate salts formed during this improved process
`are at very low levels, i.e., less than about 0.5 mole
`percent of methacrolein oxidized. The advantages of
`this improved process are readily apparent. Higher
`yields of methacrylate salts are realized and conven-
`tional means for purification of the methacrylic acid
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`produced upon acidification of the product mixture is
`greatly facilitated and simplified.
`The_ alkaline substances and the silver catalysts used
`in this improved methacrolein oxidation reaction are
`the same as those described in the prior art, especially
`the aforementioned U.S. Pat. Nos. 2,930,801; 3,162,682
`and 3,839,437. Sodium hydroxide is the preferred alka-
`line substance but other suitable substances are the hy-
`droxides of potassium lithium, barium, and calcium. The
`amount of alkaline substance dissolved in water to pre-
`pare the aqueous alkaline medium for the oxidation is in _
`excess of the stoichiometric amount of methacrolein to
`be oxidized. Any concentration of alkaline substance up
`to about 50% by weight of the aqueous solution may be
`used. Preferred concentrations are in the range of
`15-35% by weight. The aqueous solution of alkaline
`substance is then saturated with dimolved alkali metal
`carbonate to produce the aqueous alkaline medium for
`use in this improved oxidation process. The preferred
`alkali metal carbonate is sodium carbonate but lithium
`carbonate and potassium carbonate are also suitable. By
`virtue of its saturation in the aqueous alkaline medium,
`the actual concentration of the carbonate additive var-
`ies with the concentration of the alkaline substance and
`the particular alkali metal carbonate employed. In gen-
`eral, however, the carbonate concentration should be
`less than about 5% by weight of the medium and may be
`as low as 0.01% by weight. Excessively high carbonate
`concentrations are to be avoided because deactivation
`of the silver catalyst can result causing a decreased yield
`of methacrylate salt.
`The oxidizing gas employed is oxygen or oxygen
`mixed with inert gases. Air is a suitable oxidizing gas.
`The operating conditions for this improved oxidation
`process are similar to those disclosed in U.S. Pat. No.
`2,930,801. Oxidation 'may be carried out at a tempera-
`ture of from about 0' to 100' C. and the preferred tem-
`perature is about 20‘ to 80' C. The reaction may be
`conducted at atmospheric pressure or at super atmo-
`spheric pressures of oxygen or air. Suitable pressures
`are from 0 to 200 psig and preferably 0 to 150 psig. The
`pH of the aqueous reaction mixture should be main-
`tained above about ll.8, and preferably above 12.5, at
`all times during the oxidation.
`Methacrolein oxidation according to this process
`may also be conducted continuously by simultaneous
`continuous addition of the aqueous alkaline medium and
`methacrolein. The alkaline medium is added at a suffi-
`cient rate to always maintain a free hydroxide ion con-
`centration of about 1% by weight in the reaction mix-
`ture.
`
`On completion of the oxidation of methacrolein, the
`reaction mixture is filtered to remove the silver catalyst
`and the filter cake is washed with water. The filtrate
`and water washings are combined and treated with an
`acid stronger than methacrylic acid in order to free
`methacrylic acid from its salt. Suitable acids are mineral
`acids such as sulfuric acid, hydrochloric acid or nitric
`acid. Thus obtained methacrylic acid may then be iso-
`lated and purified by conventional means.
`The following examples serve to further illustrate the
`present invention which is not limited to the examples.
`EXAMPLE I
`
`A twenty percent by weight solution of sodium hy-
`droxide in water was saturated with sodium carbonate
`by stirring the solution with excess anhydrous sodium
`carbonate followed by filtration. The resulting solution
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`to maintain the pH of the reaction mixture above a
`value of 12.0. The temperature of the reaction mixture
`was maintained between 28' and 35' C. by means of the
`water bath. Filtration of the reaction mixture to remove
`the catalyst gave 320 grams of an aqueous solution
`containing 34.6 grams of sodium methacrylate (94%
`yield based on methacrolein), 0.l3 gram sodium isobu-
`tyrate (0.3% yield based on methacrolein), and 0.06
`gram methallyl alcohol (0.2% yield based on methacro-
`lein).
`What is claimed is:
`1. In the process for oxidizing methacrolein to a
`methacrylic acid salt with oxygen or oxygen mixed
`with an inert gas in a strongly alkaline medium at a
`temperature of 0° to 100' C. and in the presence of a
`finely divided silver catalyst and recovering‘ meth-
`acrylic acid by acidification, the improvement which
`comprises carrying out said oxidation at a pH of greater
`than 12.5 in the presence of from 0.01 to 5 percent by
`weight of dissolved alkali metal carbonate based on the
`‘ alkaline medium which has a hydroxide concentration
`of not more than 50 percent by weight.
`2. The process according to claim 1 wherein the
`oxidation temperature is about 20' to 80' C.
`3. The process according to claim 2 wherein the
`alkaline medium is an aqueous solution of sodium hy-
`droxide and sodium carbonate.
`4. The process according to claim 3 wherein the
`alkaline medium contains 15-35% by weight of an alkali
`metal hydroxide.
`5. The process according to claim 1 wherein the
`strongly alkaline medium comprises an aqueous solution
`of
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`contained about four percent by weight dissolved so-
`dium carbonate.
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`A one liter five necked flask equipped with a sintered
`glass gas diffusion disc in the bottom and a mechanical
`paddle-type stirrer was charged with 32 grams of silver
`catalyst, prepared by reducing silver oxide with hydro-
`gen peroxide and sodium hydroxide, and 250 grams of
`distilled water. The flask was then equipped with a
`reflex condenser, a thermometer, and an electrode for
`measuring the pH of the reaction mixture. Stirring was
`commenced and oxygen gas was introduced into the
`reaction mixture via the gas diffusion disc at a rate of
`about 30 liters per hour. The reaction mixture was
`heated to 50‘ C. by a water bath and the pH was ad-
`justed to 12.2 using the sodium hydroxide solution
`which was saturated with sodium carbonate. During a
`period of about eighty minutes, 34 grams of methacro-
`lein (0.49 mole) was‘ added to the reaction mixture con-
`tinuously from a syringe using a Sage syringe pump at a
`rate of 0.50 milliliters per minute. Simultaneously, with
`the addition of the methacrolein, 89 milliliters of the
`aqueous sodium hydroxide solution saturated with so-
`dium carbonate were added to the reaction mixture so
`as to maintain the pH of the reaction mixture above a
`value of 12.0. The temperature of the reaction mixture
`was maintained at 50° to 53° C. by means of the water
`bath.
`After completion-of the reaction, the reaction mix-
`ture was filtered to remove the catalyst. The resulting
`aqueous solution (495 grams) contained 5l.9 grams of 30
`sodium methacrylate for a yield of 97 percent based on
`methacrolein and 0.03 grams of sodium isobutyrate
`(0.04 percent yield based on methacrolein). The product
`mixture was acidified with a slight excess of sulfuric
`acid and was then extracted with diethyl ether. The
`extract was fractionally distilled in the presence of hy-
`droquinone to give 38.4 grams of methacrylic acid (0.45
`mole) for a yield of 92 percent based on methacrolein.
`EXAMPLE II
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`(a) at least one hydroxide selected from the group
`consisting of sodium hydroxide, potassium hydrox-
`ide, lithium hydroxide, barium hydroxide and cal-
`cium hydroxide, and
`(b) at least one carbonate selected from the group
`consisting of sodium carbonate, potassium carbon-
`ate and lithium carbonate.
`6. The process according to claim 1 wherein the
`alkaline medium is an aqueous solution saturated with
`dissolved alkali metal carbonate and contains a hydrox-
`ide selected from the group consisting of sodium hy-
`droxide, potassium hydroxide, Iithium hydroxide, bar-
`ium hydroxide and calcium hydroxide in an amount
`slighly in excess of the stoichiometric amount of meth-
`acrolein to be oxidized.
`7. The process according to claim 1 wherein methac-
`rolein and the strongly alkaline medium are continu-
`ously added to the reaction mixture at respective rates
`sufficient to maintain a free hydroxide ion concentra-
`tion of about 1% by weight of the reaction mixture.
`Q
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`The apparatus described in Example I was charged
`with 27 grams of silver catalyst and 200 grams of dis-
`tilled water. Stirring was commenced, and oxygen gas
`was introduced into the catalyst suspension at a rate of
`about 30 liters per hour. The pH of the reaction mixture
`was adjusted to 12.5 using a twenty percent by weight
`solution of sodium hydroxide which had been saturated
`with sodium carbonate. During a period of about sixty
`minutes 24 grams of methacrolein (0.34 mole) was
`added to the reaction mixture continuously from a sy-
`ringe using a Sage syringe pump at a rate of 0.48 milli-
`liters per minute. Simultaneously with the addition of
`the methacrolein. 62 milliliters of the twenty weight
`percent aqueous sodium hydroxide solution saturated
`with sodium carbonate were added to the reaction so as
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