Organic compounds -- part of the class 532-570 series – Organic compounds – Carboxylic acids and salts thereof
Patent
1986-04-30
1989-08-08
Lone, Werren B.
Organic compounds -- part of the class 532-570 series
Organic compounds
Carboxylic acids and salts thereof
C07C 51097, C07C 5302
Patent
active
048554960
DESCRIPTION:
BRIEF SUMMARY
The present invention provides a process for the production of formic acid from carbon dioxide and hydrogen using an integrated series of process steps.
Our European patent application Nos. 0095321 and 84301772.4 respectively describe a method for the production of a trialkylammonium formate from a tertiary amine, carbon dioxide and hydrogen and a method for converting the trialkylammonium formate into another formate salt which is thermally decomposable to formic acid.
An integrated process has now been devised which allows formic acid to be prepared from carbon dioxide and hydrogen feedstocks only.
Accordingly, the present invention provides an integrated process for the production of formic acid from carbon dioxide and hydrogen characterised in that reacted together in the presence of a catalyst to produce a formate salt of the nitrogenous base. nitrogenous base and any low boilers and recycled to the first stage; from the low boilers. with a base having a high boiling point to produce the nitrogenous base and the formate salt of the base having a high boiling point. point is decomposed to the higher boiling base and formic acid.
By the term nitrogenous base is meant a nitrogenous base containing a tertiary nitrogen atom. The nitrogenous base containing a tertiary nitrogen atom maay suitably be of formula ##STR1## or of formula: ##STR2## wherein in the formulae, R.sup.1, R.sup.2 and R.sup.3, which may be the same or different, are hydrocarbyl groups or substituted hydrocarbyl groups or any two or all of R.sup.1, R.sup.2 and R.sup.3 may form part of a ring, R.sup.4 is a hydrocarbyl group or substituted hydrocarbyl group and R.sup.5 is a divalent organic group or R.sup.4 and R.sup.5 may form part of a ring. Suitably the hydrocarbyl group is an aliphatic, cycloaliphatic, aryl, or alkaryl group. Substituted hydrocarbyl groups may contain for example nitrogen or oxygen. Preferably the organic base is a trialkylamine, even more preferably a lower trialkylamine, for example a C.sub.1 to C.sub.10 trialkylamine. Examples of suitable trialkylamines are trimethylamine, triethylamine, tripropylamine and tributylamine. Examples of other nitrogenous bases which may be employed are 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) and 1,4-diazabicyclo[2.2.2]octane (DABCO), pyridines and picolines. Mixtures of nitrogenous bases may also be used.
The formate salt produced in the first stage of the process corresponds to the nitrogenous base used in this stage. Thus using triethylamine the product is triethylammonium formate.
As regards the base having a high boiling point, this is suitably also a nitrogenous base and is selected so that process. the boiling point of the nitrogenous base used in the first stage of the process, and of the process.
It will be seen from these criteria that the exact choice of such a base will depend upon which nitrogenous base is used in the first stage of the process.
Preferably the second base has a pKa in the range 4.0 to 9.0 and is an imidazole of the general formula: ##STR3## where R.sub.1 is a monovalent hydrocarbon group containing 1 to 12 carbon atoms and R.sub.2 is a hydrogen atom or an R.sub.1 group, the total number of carbon atoms and R.sub.1 and R.sub.2 conveniently being not more than 20 and preferably from 4 to 12.
Suitable hydrocarbon radicals on the imidazole derivatives (I) are, in general, alkyl groups of 1 to 8 carbon atoms, cyclopentyl, cyclohexyl, phenyl and methylphenyl groups. Amongst the above, imidazole derivatives where R.sup.1 is n-1-alkyl of 4 to 10 carbon atoms and R.sup.2 is hydrogen or methyl are particularly suitable. Examples of such compounds are 1-(n-1-butyl)-imidazole (pKa 5.9), 1-(n-1-pentyl)-imidazole (pKa 5.9), 1-(n-1-decyl)-imidazole (pKa 5.75), 1-(n-1-butyl)-2-methylimidazole (pKa 7.0) and 1-(n-1-pentyl)-2-methylimidazole (pKa 6.85).
In addition to imidazoles, quinoline and other heterocyclic nitrogenous bases can be used.
For a definition of the pKa values, which are a measure of the base strength, reference may be made, for example to Landoldt-Bornstein, 6
REFERENCES:
patent: 4218568 (1980-08-01), Hohenschutz et al.
patent: 4474959 (1984-10-01), Drury et al.
Anderson et al., Australian Patent Abstract, vol. 54, No. 35, Sep. 20, 1984.
Anderson Jeffrey J.
Drury David J.
Hamlin John E.
Kent Alexander G.
BP Chemicals Limited
Lone Werren B.
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