Organic compounds -- part of the class 532-570 series – Organic compounds – Oxygen containing
Reexamination Certificate
1998-12-18
2001-12-04
Shippen, Michael L. (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Oxygen containing
C568S810000
Reexamination Certificate
active
06326521
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a process for the preparation of benzyl alcohol via hydrolysis of a benzyl ester with water in the liquid phase.
2. Description of the Related Art
NL-A-7614458 describes a process for processing a tar containing benzyl benzoate via a hydrolysis reaction in the liquid phase. The hydrolysis can be carried out in the presence of a strong acid, for example a mineral acid such as sulphuric acid or phosphoric acid, or in the presence of a basic solution, in particular an aqueous sodium hydroxide or soda solution. Both embodiments present the drawback that the reaction mixture has to be neutralized afterwards so that salts are formed. The processing and disposal of salts are not desirable from an economic and an environmental viewpoint. The use of a strong acid moreover presents the drawback that it is highly corrosive and as such imposes high demands on the material of the equipment.
DETAILED DESCRIPTION OF THE INVENTION
The aim of the present invention is to solve the aforementioned drawbacks.
This aim is achieved according to the invention by carrying out the hydrolysis of a benzyl ester with water in the liquid phase in the absence of a strong acid and in the absence of a base.
It has namely surprisingly been found that the hydrolysis of benzyl esters can be well effected under such mild reaction conditions, too.
The Journal of Supercritical Fluids, 1992, 5, 107-113 “Reactions of Supercritic Water with Benzaldehyde, Benzylidenebenzylamine, Benzylalcohol, and Benzoic acid”, describes an experiment in which benzyl benzoate is hydrolyzed with H
2
O without a catalyst under supercritical conditions, i.e. at a very high pressure (26.7 MPa) and temperature (400° C.). These supercritical conditions however involve an extreme safety problem and moreover high investments, which is not desirable in commercial exploitation. Under these conditions water moreover behaves as an aggressive acid, as a result of which higher demands have to be imposed on the material of the equipment. Another drawback is the relatively poor selectivity owing to a relatively high degree of decomposition of benzyl alcohol and benzoic acid and hence the formation of undesired by-products.
EP-A-778257 also describes the hydrolysis of benzyl acetate with the aid of a strong acid ion exchanger as a catalyst. The life of such ion exchangers depends on the purity of the fraction to be hydrolyzed. In practice they are usually deactivated by cationic impurities even occurring in a low concentration. The temperature is moreover a limiting parameter in such a process. A cosolvent, for example acetone, is moreover required for the hydrolysis of higher benzyl esters, for example benzyl benzoate, to turn the benzyl benzoate/water system into a homogeneous phase. However, the use of a cosolvent is economically unattractive because it must in turn be separated from the ultimate product. As a result, extra process steps are required, which of course imply extra investments.
Examples of benzyl esters that are suitable for use in the process of the present invention are benzyl esters of organic carboxylic acids, for example benzyl formiate, benzyl acetate, benzyl propionate and benzyl benzoate.
Such benzyl esters are formed for example during the oxidation of monoalkylbenzene compounds, for example toluene, with molecular oxygen. The oxidation of toluene can take place either in the liquid phase or in the gas phase. In practice the resultant reaction mixture often contains benzoic acid; by-products with boiling points lower than that of benzoic acid, for example benzyl alcohol, benzaldehyde and light benzyl esters such as benzyl formiate, benzyl propionate and benzyl acetate; and products with boiling points higher than that of benzoic acid, such as benzyl benzoate, which are summarized under the heading tar residue. After recovery of benzoic acid and upgrading of the reaction mixture a tar containing benzyl benzoate often remains, which may still contain benzoic acid and/or a fraction with a boiling point lower than that of benzoic acid, which, in addition to benzoic acid, contains light benzyl esters such as benzyl formiate, benzyl propionate and benzyl acetate. Both the tar containing benzyl benzoate and the light fraction can be used as a starting material for the process according to the invention.
The hydrolysis of benzyl esters proceeds according to an equilibrium reaction. Because the hydrolysis reaction can be performed with a high degree of conversion of the benzyl ester, for example a degree of conversion of more than 90%, preferably more than 98%, for example via a favourable ratio of reactants or the removal of reaction product, a process stream can be obtained from which very pure benzyl alcohol can be recovered in a simple manner.
The benzyl ester/water molar ratio may vary within a wide range, for example between 50:1 and 1:500. Preferably the molar ratio varies between 1:1 and 1:200, in particular between 1:10 and 1:100.
The temperature and the pressure at which the hydrolysis reaction takes place may vary within a wide range. The temperature may for example vary from 40° C. to 320° C., preferably 80° to 300°. When the aim is the hydrolysis of higher benzyl esters, for example benzyl benzoate, a temperature higher than 150° C., for example between 180° and 320° C., in particular between 220° and 300° C., is preferably chosen. The autogenous pressure is preferably used as the pressure at which the hydrolysis reaction takes place. The pressure for example varies between 0.1 and 10 MPa, preferably between 1 and 10 MPa, in particular between 2 and 8 MPa.
The hydrolysis reaction according to the invention can be carried out in different types of reactors, for example a batch reactor, a plug-flow reactor, a continuously stirred tank reactor or combinations of different reactors.
The residence time in the reactor depends strongly on the type of reactor, the temperature and the corresponding pressure, the miscibility and degree of mixing of the system, the water/benzyl esters molar ratio and the composition of the feed. The residence time in the reactor may vary within a wide range, depending on the parameters chosen, for example between 1 minute and 10 hours, preferably between 2 minutes and 2 hours, in particular between 5 and 60 minutes. A person skilled in the art will be able to determine the optimum residence time in a simple manner on the basis of the desired degree of conversion of benzyl esters and the selectivity to benzyl alcohol.
A weak acid, for example an acid with a pK
a
of more than 3 and less than 7, may optionally be used in the hydrolysis reaction according to the invention. The determination of pK
a
used here is described in the ‘Handbook of Chemistry and Physics’, 60th ed. D 155-167. Preferably an acid formed during the hydrolysis reaction is added, for example formic acid, acetic acid, propionic acid or benzoic acid. In the hydrolysis the acid that corresponds to the acid residue of the benzyl ester is preferably added. As a result of this the reaction rate increases. The amount of acid to be added is not particularly critical. A person skilled in the art will be able to determine the optimum amount of acid to be added in a simple manner on the basis of the desired reaction rate, homogeneity of the system and the desired degree of conversion. The acid can be added at any moment, preferably at the beginning of the hydrolysis reaction. Preferably the amount of acid used and the chosen reaction conditions, for example the temperature, are controlled so that a homogeneous phase is obtained at the end of the hydrolysis.
The process according to the invention is particularly suitable for upgrading a tar containing benzyl benzoate. It results in conversion of the benzyl benzoate, which has a high boiling point and which is difficult to separate from certain tar components through distillation, into benzyl alcohol and benzoic acid, which have much lower boiling points and can easily be separated from one another. The benzyl benzo
Peet Abram
Plantema Otto G.
Rozie Hendricus J.
Stoelwinder Christiaan J. C.
van Soolingen Jacob
DSM N.V.
Pillsbury & Winthrop LLP
Shippen Michael L.
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