Organic compounds -- part of the class 532-570 series – Organic compounds – Oxygen containing
Reexamination Certificate
2000-01-10
2001-03-13
Padmanabham, Sreeni (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Oxygen containing
C568S754000, C568S385000, C568S311000
Reexamination Certificate
active
06201157
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an improved method for production of phenol and acetone by decomposition of cumene hydroperoxide to phenol, acetone, and &agr;-methylstyrene in the presence of an acidic catalyst. The improvement comprises neutralization of the acidic catalyst after substantial completion of the decomposition by addition of a substituted amine.
2. Related Background Art
One of the predominant commercial processes for manufacture of phenol is the cumene oxidation process, in which cumene is oxidized in air to produce cumene hydroperoxide (CHP). The CHP is then cleaved to phenol and acetone in the presence of an acidic catalyst. This process also produces &agr;-methylstyrene (AMS), along with other byproducts, including acetophenone, dimethylphenylcarbinol, and cumylphenols. Typically, the acidic catalyst is a strong, and not heavily corrosive inorganic acid, such as sulfuric or phosphoric acid. The acidic catalyst must be removed or neutralized to prevent further, unwanted reactions in the downstream purification steps that produce the phenol and acetone products.
Typically, commercial processes for manufacture of phenol from CHP use inorganic bases, ion exchange resins, or a combination thereof to remove acidity from the crude product stream. Since ion exchange resins are temperature sensitive, the crude product stream must be cooled substantially prior to contact with the resin. The need to cool the product stream increases energy costs significantly because the crude product stream must then be re-heated prior to downstream purification operations. A further drawback of ion exchange resins is that they must be regenerated frequently, a labor-intensive and costly process which also results in formation of large amounts of aqueous waste. Moreover, ion exchange resins give a highly variable final pH in the crude product stream, adversely affecting final product yields, and can also release alkali salts which cause fouling of equipment.
The use of a strong base, such as sodium hydroxide or potassium hydroxide to neutralize the acidic catalyst is not desirable because it is difficult to achieve accurate pH control in a neutralization reaction between a strong acid and a strong base. Moreover, metal hydroxides generate salts that have a propensity to deposit on heat exchange surfaces, causing fouling and decreasing efficiency.
The use of ammonia to neutralize the acidic catalyst is disclosed in U.S. Pat. No. 5,254,751 to Zakoshansky. In the process described in this reference, neutralization with ammonia is performed during the CHP decomposition, rather than after the decomposition. The disclosure states that the ammonium salts produced from addition of ammonia to the reaction mixture act as acidic catalysts for the remainder of the CHP decomposition reaction. This reference suggests that hydrazine and alkylamines having one to five carbon atoms are suitable for neutralization during CHP decomposition, but that ammonia is preferred, especially for neutralizing sulfuric acid. Zakoshansky also suggests a maximum operating temperature of 110° C.
SUMMARY OF THE INVENTION
The present invention is directed to an improved method for production of phenol and acetone from cumene hydroperoxide by decomposition of cumene hydroperoxide in the presence of an acidic catalyst, wherein the improvement comprises neutralization of the acidic catalyst after substantial completion of the decomposition by addition of a substituted amine selected from the group consisting of: (i) a secondary or tertiary amine having from 4 to 21 carbon atoms and not having hydrolytically unstable substituents or acidic substituents; and (ii) a primary amine of formula
wherein R
1
and R
2
are independently hydrogen or C
1
-C
12
alkyl, and R
3
is hydrogen, C
1
-C
12
alkyl or C
1
-C
12
alkyl substituted by hydroxyl, amino or dimethylamino, provided that at least two of R
1
, R
2
and R
3
are not hydrogen.
DETAILED DESCRIPTION OF THE INVENTION
The term “alkyl” is used herein to refer to a saturated acyclic hydrocarbyl substituent group which may be linear or branched. The term “alkylene” is used herein to refer to an acyclic hydrocarbyl substituent group having at least one carbon-carbon double bond, and which may be linear or branched. The term “secondary or tertiary amine” is used herein to refer to an amine in which there is at least one nitrogen atom directly bonded to at least two carbon atoms.
The term “acidic substituents” is used herein to refer to substituents having a pKa value in aqueous media of less than about 5. Examples of acidic substituents include the acid forms of carboxylates, nitrates, phosphates, phosphonates, sulfates and sulfonates. The term “hydrolytically unstable substituents” is used herein to refer to those substituents that undergo substantial hydrolysis and/or condensation reactions at a pH in the range from about 3.5 to about 1.5 and a temperature in the range from about 30° C. to about 180° C. in a period of about two hours. Examples of hydrolytically unstable groups are esters, anhydrides, amides, acid halides, amidines, aminals, enamines, aldehydes, ethers, acetals, hemi-acetals, ketals, hemi-ketals, epoxides and alkynes. Preferably, a substituted amine employed in the present invention contains no elements other than carbon, hydrogen, nitrogen and oxygen, and no functional groups containing nitrogen or oxygen other than amine and hydroxyl groups.
The substituted amine employed in the present invention allows neutralization of product streams from decomposition of cumene hydroperoxide at elevated temperatures with minimal formation of byproducts from reactions between the amine and organic constituents of the product stream, e.g., acetone. Performing the neutralization at elevated temperatures, i.e., temperatures near the normal process temperature for decomposition of the hydroperoxide, eliminates the need to cool the process stream prior to neutralization, and then reheat prior to performing purification operations. The preferred temperature range for the neutralization process of this invention is from about 30° C. to about 180° C., more preferably from about 60° C. to about 160° C., and most preferably from about 120° C. to about 160° C.
Neutralization with relatively unsubstituted amines which are highly basic, relatively unsubstituted and sterically relatively unhindered, as suggested in the literature, e.g., ammonia, is not efficient, especially at elevated temperatures. This is believed to be due to consumption of the amine in reactions with acetone or other components of the process stream. As shown below in Example 33, addition of ammonium hydroxide to a typical product mixture at 140.3° C. produces a much smaller change in pH than the same amount added at 22.5° C., indicating that a substantial amount of the ammonia is consumed in side reactions. Even at 100.2° C., the pH is significantly lower than that observed at 22.5° C. Addition of the relatively unsubstituted amines DYTEK®-A, hexamethylene diamine, or n-propylamine also produces a much smaller change in pH at high temperatures, as shown below in Examples 1-3.
In contrast, the amines employed in the present invention exhibit a final pH at a high temperature that is much closer to the final pH observed at low temperature. These amines are more sterically hindered or are more highly substituted on the nitrogen. Without being bound to theory, it is believed that these amines do not undergo reactions with organic constituents of the product stream as readily due to the aforementioned characteristics, and are thus more efficient neutralizing agents, especially at high temperatures.
The method of the present invention allows better control of the post-neutralization pH of the product stream than conventional methods, especially when the neutralization is conducted at elevated temperatures. Preferably, the target final pH is in the range from about 2.0 to about 3.5, most preferably from about 2.2 to about 2.8.
In a preferred embodiment of the invention
Koons, Jr. Robert A.
McWilliams Matthew P.
Padmanabham Sreeni
Pepper Hamilton LLP
Sunoco Inc. (R&M)
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