Method of producing saturated C3-C20-alcohols

Details Method of producing saturated C3-C20-alcohols Method of producing saturated C3-C20-alcohols

2002-11-14

2004-07-20

Richter, Johann (Department: 1621)

Organic compounds -- part of the class 532-570 series

Organic compounds

Oxygen containing

C568S876000, C568S878000, C568S880000, C568S882000, C568S883000, C568S884000, C568S885000

Reexamination Certificate

active

06765119

ABSTRACT:

The present invention relates to a process for the preparation of saturated C
3
-C
20
-alcohols in which a liquid hydrogenation feed comprising at least one C
3
-C
20
-aldehyde is passed over a bed of a hydrogenation catalyst in the presence of a hydrogen-containing gas.
The catalytic hydrogenation of aldehydes in order to obtain alcohols is a process which has been carried out on an industrial scale for decades and in which a multiplicity of catalysts, which generally consist of elements from sub-groups VI to VIII and I of the Periodic Table, in particular of the elements chromium, manganese, iron, cobalt, nickel and/or copper, are employed. Such catalysts are described, for example, in DE-A 32 28 881, DE-A 26 28 987 and DE-A 24 45 303. The alcohols prepared by these processes find broad use, for example as solvents or as plasticizer alcohols.
In the hydrogenation, in particular at high hydrogenation temperatures, undesired side reactions, such as acetalization or aldolization, the Tischtschenko reaction or ether formation, occur in addition to the desired hydrogenation of the aldehyde to the alcohol. These side reactions result in a reduction in the product yield and require increased effort during purification of the hydrogenation product in order to obtain the relevant alcohol in the desired purity.
In order to avoid side reactions of this type, DE-A 26 28 897 recommends adding water to the hydrogenation feed. However, this measure has a number of disadvantages; for example, the energy necessary for purification of the resultant alcohols by distillation increases significantly.
Another possibility for reducing the formation of by-products comprises increasing the hydrogen pressure in the hydrogenation, which increases the rate of the hydrogenation reaction, while the reaction rate of the side reactions which are independent of the hydrogen pressure remains the same. Overall, the selectivity with respect to the desired hydrogenation product thus increases.
However, an increase in the hydrogen pressure is associated with high equipment complexity, since, for safety reasons, pressurized reactors with thicker walls must be used and further safety precautions have to be taken.
German patent 16 43 856 describes the hydrogenation of aldehydes by means of a copper- and/or nickel-containing catalyst whose surface has been adjusted to a pH of from 6 to 10 by treatment with alkali metal hydroxides. This publication is expressly directed to the use of the catalysts pretreated in this way in gas-phase hydrogenation. Their use in liquid-phase hydrogenation is only possible to a limited extent. The alkali metal hydroxide is usually washed out by the liquid hydrogenation feed or the liquid hydrogenation products and removed from the reaction system, and consequently the advantages of the surface treatment of the catalyst are only short term.
JP 172 838 A relates to the hydrogenation of C
5
- and higher aldehydes on a nickel/chromium catalyst in the presence of a tertiary aliphatic amine.
JP 171 447 A relates to the hydrogenation of C
4
-aldehydes to butanol on a nickel/chromium catalyst in the presence of a tertiary aliphatic amine. In both the last-mentioned processes, the added amine is separated off from the hydrogenation product by subsequent distillation and advantageously fed back into the hydrogenation. However, pure amine is not recovered in the distillation, but instead a mixture of the amine with so-called high boilers, i.e. the by-products which boil higher than the target alcohol and are formed in the hydrogenation of aldehydes, is obtained. The recycling of the amine/high boiler mixture requires that a ballast of high boilers is always circulated through the hydrogenation and distillation. Since, in order to avoid increases in concentration, a part of the high-boilers which corresponds to the formation rate of the high boilers must always be removed from the circuit, amine losses are unavoidable and represent an additional economic burden for the process.
WO 96/26173 describes a process for the purification of C
3
-C
10
-alcohols by distillation, where the distillation is carried out in the presence of an alkali metal hydroxide. This publication makes no mention of the addition of a salt-like base to a liquid hydrogenation feed.
It is an object of the present invention to indicate a process for the preparation of saturated alcohols from aldehydes by liquid-phase hydrogenation in which the formation of undesired by-products is suppressed, in particular at hydrogenation temperatures of 150° C. or above, and which is free from the disadvantages of the known hydrogenation processes.
We have found that this object is achieved by a process in which a liquid hydrogenation feed comprising at least one C
3
-C
20
-aldehyde is passed over a bed of a hydrogenation catalyst in the presence of a hydrogen-containing gas, which comprises adding to the hydrogenation feed an amount, homogeneously soluble therein, of a salt-like base [M
+
]
n
[A
n−
], in which [M
+
] is an alkali metal ion or the equivalent of an alkali earth metal ion; [A
n−
] is an anion of an acid having a pK
s
value of greater than 2, and n is the valency of the anion.
The effect of the addition of base to the hydrogenation feed is that the side reactions outlined at the outset are substantially suppressed even at hydrogenation temperatures of 150° C. or above, and very pure alcohols are obtained even at these hydrogenation temperatures.
The type of salt-like base used is generally not crucial so long as the salt-like base used is homogeneously soluble in the hydrogenation feed, at least in low concentration, and does not undergo any undesired side reactions with the aldehyde. Accordingly, a multiplicity of salt-like bases can successfully be employed in the process according to the invention.
The bases employed in accordance with the invention are salt-like, i.e. they are built up from cations and anions; they comprise at least one alkali metal or alkaline earth metal cation, such as lithium, sodium, potassium, magnesium or calcium ions, and a basic anion. The corresponding acid of the basic anion has a pK
a
value of greater than 2, preferably greater than 4, in particular greater than 8. The pK
a
value used for the characterization of the acid strength of the corresponding acid is the negative decimal logarithm of the dissociation constant of the acid in dilute aqueous solution. The pK
a
values of numerous acids have been tabulated and are given, for example, in CRC Handbook of Chemistry and Physics, 76
th
Edn., 1995, CRC Press; Organikum, various authors, 16
th
Edn., VEB Deutscher Verlag der Wissenschaften 1986, p. 138; Sykes P., Reaktionsmechanismen der Org. Chemie, 8
th
Edn. 1982, p. 307.
Suitable basic anions are hydroxide (14), carbonate (10.33), hydrogencarbonate (6.35), phosphate (12.35), amide (35), hydride (39); alkoxides, in particular C
1
-C
4
-alkoxides, such as methoxide (16), ethoxide, n- and isopropoxide and butoxide; phenoxide (10), carboxylates, such as acetate (4.76) or benzoate (4.21); carbanions, such as butyl (50), cyclopentadienyl or phenyl (40). The values in brackets indicate the pK
S
value of the respective corresponding acid. Besides the hydride ion itself, complex hydrides are also suitable; these can be regarded as adducts of the hydride ion and their basicity is essentially due to the, hydride ion, for example complex hydrides such as [BH
4
]
−
or [BHR
3
]
−
(where R=C
1
-C
4
-alkyl, for example s-butyl).
In general, hydroxide or carbonate is preferred.
Advantageous salt-like bases are, in particular, alkali metal hydroxides and/or carbonates, such as lithium carbonate, potassium carbonate, sodium carbonate, lithium hydroxide, sodium hydroxide and potassium hydroxide. In general, sodium hydroxide and/or potassium hydroxide are preferred. However, sodium alkoxides and/or potassium alkoxides, such as the methoxide or ethoxide, or the alkoxide of the alcohol which is the hydrogenation

Affiliated with

Also associated with

Rating

Method of producing saturated C3-C20-alcohols does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Method of producing saturated C3-C20-alcohols, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method of producing saturated C3-C20-alcohols will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-3247431