Electrolysis: processes – compositions used therein – and methods – Electrolytic synthesis – Preparing inorganic compound
Reexamination Certificate
1999-06-22
2001-02-27
Gorgos, Kathryn (Department: 1741)
Electrolysis: processes, compositions used therein, and methods
Electrolytic synthesis
Preparing inorganic compound
C205S549000, C205S554000, C205S512000, C204S263000
Reexamination Certificate
active
06193872
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a process for treating an aqueous waste stream from a chemical production plant, more particularly an aqueous waste stream which contains at least one alkali metal carboxylate containing at least 3 carbon atoms, to produce a solution of an alkali metal hydroxide for recycle to the chemical production plant. In addition, the invention relates to a waste treatment plant for carrying out such a process.
2. Description of the Related Art
A number of types of chemical production plants produce a waste stream which contains at least one alkali metal carboxylate containing at least 3 carbon atoms up to about 22 carbon atoms. Normally, such an alkali metal carboxylate is a salt of an aliphatic acid. Examples of such chemical production plants include aldolisation plants in which a saturated aliphatic aldehyde, such as n-butyraldehyde or n-valeraldehyde, is converted by aldolisation followed by dehydration to an unsaturated aldehyde containing twice as many carbon atoms as the starting aldehyde, for example, 2-ethylhex-2-enal from n-butyraldehyde or 2-propylhept-2-enal from n-valeraldehyde. In such a process, the starting aldehyde may contain also a minor amount of the corresponding isomeric aidehyde, for example, iso-butyraldehyde or, in the case of n-valeraldehyde, also iso-valeraldehyde (2-methylbutyraldehyde) and 3-methylbutyraldehyde. The aldolisation-dehydration products, such as 2-ethylhex-2-enal and 2-propylhept-2-enal, find use as intermediates in the production of important plasticiser alcohols, such as 2-ethylhexanol and 2-propylheptanol.
An aldolisation-dehydration process is typically conducted in the presence of an aqueous solution of an alkali metal hydroxide as catalyst. When the starting aldehyde is n-butyraldehyde the reaction proceeds as follows:
A competing reaction is the Cannizzaro reaction which yields a mixture of the alcohol corresponding to the starting aldehyde and an alkali metal salt of the corresponding carboxylic acid. Thus, if the catalyst is sodium hydroxide, the Cannizzaro reaction is:
2CH
3
CH
2
CH
2
CHO+NaOH→CH
3
CH
2
CH
2
COONa+CH
3
CH
2
CH
2
CH
2
OH.
In order to limit the build up of the unwanted sodium carboxylate in the plant it is usual to purge a part of the aqueous liquor as a waste stream from the aldolisation plant. However, since this is alkaline and has a significant organic content, it cannot be discharged directly to the environment. Normally, the waste stream is neutralised and then subjected to appropriate biological treatment in order to reduce the oxygen demand of the waste stream to acceptable levels. The cost and inconvenience of importing to the plant site the acid used to neutralise the waste stream and the make up alkali needed to replace the alkali metal ions removed in the waste stream are drawbacks to the existing methods of operating an aldolisation plant. In addition, the capital cost of the necessary treatment plant required to reduce the oxygen demand to an acceptable level represents an undesirable additional expense, particularly since with increasing pressure to avoid pollution, plant operators are coming under increasing pressure to reduce the oxygen demand still further which requires even more capital expenditure.
Another process which produces an aqueous waste stream containing an alkali metal carboxylate is the conversion of iso-butyraldehyde to neopentyl glycol by reaction with formaldehyde. This proceeds by aldol condensation of formaldehyde with iso-butyraldehyde followed by a cross-Cannizzaro reaction between the intermediate &bgr;-hydroxyaldehyde, 2,2-dimethyl-3-hydroxypropanal, and formaldehyde according to the following equations:
In this case, the aqueous waste stream contains sodium formate; in addition, it contains sodium iso-butyrate formed as a result of a Cannizzaro reaction from iso-butyraldehyde according to one of the following reactions:
Another sodium salt in the waste liquor is sodium hydroxypivalate. This is formed by a Cannizzaro reaction of the intermediate &bgr;-hydroxyaldehyde, 2,2-dimethyl-3-hydroxypropanal, according to the following equation:
or according to the following equation:
Again, this process is typically conducted using an alkali metal hydroxide or carbonate solution as catalyst.
Neopentyl glycol finds application in a range of technologies, including waterborne and alkyd surface coatings, gel coatings for fibreglass-reinforced plastics, powder coatings, lube oil additives, plasticisers and polyurethanes; the aldol product is produced without any dehydration step.
1,1,1-trimethylol propane is also of value, inter alia, in the production of alkyl resin coatings and can be produced by the aldol condensation of formaldehyde with n-butyraldehyde followed by hydrogenation. The aldolisation proceeds according to the following equations:
CH
3
CH
2
CH
2
CHO+HCHO→CH
3
CH
2
CH (CHO)CH
2
OH
and
CH
3
CH
2
CH(CHO)CH
2
OH+HCHO→CH
3
CH
2
C(CHO)(CH
2
OH)
2
.
These reactions can be catalysed by a solution of an alkali metal hydroxide, such as sodium hydroxide. The hydrogenation reaction is:
CH
3
CH
2
C(CHO)(CH
2
OH)
2
+H
2
→CH
3
CH
2
C(CH
2
OH)
3
.
In a manner that is analogous to by-product formation in the synthesis of neopentyl glycol, there can be formed as byproducts by alkali-consuming side reactions, sodium butyrate, sodium formate and sodium 2,2-di(hydroxymethyl)-butyrate.
The conversion of 2,2-di(hydroxymethyl)-butyraldehyde to 1,1,1-trimethylol propane can be effected by a crossed Cannizzaro reaction using formaldehyde as the reducing agent in the presence of a basic catalyst. The reaction involved is:
CH
3
CH
2
C(CHO)(CH
2
OH)
2
+HCHO+NaOH→CH
3
CH
2
C(CH
2
OH)
3
+HCOONa.
In this case, at least one mole of sodium formate is produced per mole of neopentyl glycol produced.
Another important commercial chemical that finds its principal application in the surface coating industry as a raw material for oil-modified alkyd resins and synthetic drying oils is pentaerythritol. This can be produced by successive aldolisation steps followed by a hydrogenation or cross-Cannizzaro step, the starting materials being formaldehyde and acetaldehyde. The reactions involved are:
CH
3
CHO+HCHO→HOCH
2
CH
2
CHO;
HOCH
2
CH
2
CHO+HCHO→(HOCH
2
)
2
CH—CHO;
and
(HOCH
2
)
2
CH—CHO+HCHO→(HOCH
2
)
3
C—CHO.
There then follows either:
(HOCH
2
)
3
CH—CHO+HCHO+NaOH→(HOCH
2
)
4
C+HCOONa;
or
(HOCH
2
)
3
CH—CHO+H
2
→(HOCH
2
)
4
C.
A still further important commercial chemical is 2,2,4-trimethyl-1,3-pentanediol which is used, inter alia, as an intermediate in the production of unsaturated polyesters. This can be produced by aldolisation (or, as it may alternatively be termed, aldo-trimerisation) of iso-butyraldehyde followed by hydrogenation of the resulting intermediate aldolisation product, 2,6-di-iso-propyl-5,5-dimethyl-1,3-dioxan-4-ol, according to the following equations:
Certain hydrocarbon streams, for example C
10
to C
12
/C
13
olefin streams produced by the reaction of carbon monoxide and hydrogen according to the Fischer-Tropsch process, contain oxygenated materials such as carboxylic acids and phenolic materials. These acids and phenolic materials can be removed by washing with dilute aqueous alkali.
Another industrial process which produces an alkaline waste stream is esterification. Organic carboxylic acid ester streams produced in commercial esterification plants are often washed with aqueous alkali in order to remove any unreacted organic carboxylic acids.
Production of all of the above mentioned commercial chemicals results in formation of an alkaline waste stream containing at least one alkali metal carboxylate, usually a sodium carboxylate. In each case, neutralisation and biological treatment are the methods of choice in order to render the waste stream fit for discharge to the environment. Nevertheless, the waste stream will still contain sodium or other alkali metal values which may not alwa
Harrison George Edwin
Reason Arthur James
Spratt Richard Clive
Gorgos Kathryn
Kvaerner Process Technology Limited
Parsons Thomas H.
Senniger Powers Leavitt & Roedel
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