Process for preparing 1,4-butanediol by catalytic...

Details Process for preparing 1,4-butanediol by catalytic... Process for preparing 1,4-butanediol by catalytic...

1999-04-09

2001-07-17

Shippen, Michael L. (Department: 1621)

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

Organic compounds

Oxygen containing

Reexamination Certificate

active

06262317

ABSTRACT:

The present invention relates to a process for preparing 1,4-butanediol by catalytic hydrogenation of 1,4-butynediol with hydrogen in the presence of a solid hydrogenation catalyst at a pressure of from 1 to 200 bar and values of the volumetric liquid-side mass transfer coefficient k
L
a of from 0.1 s
−1
to 1 s
−1
, where the liquid forms the continuous phase and the hydrogen forms the dispersed phase.
The hydrogenation of 1,4-butynediol to give 1,4-butanediol via the individual steps shown in simplified form in the following scheme
has been carried out for decades and has been described many times. However, the known processes have the disadvantages of a low, uneconomical space-time yield (STY), ie. the amount of starting material used per reactor volume and unit time, when hydrogenation is carried out at pressures below 200 bar, low catalyst lives and low selectivity. In addition, when fixed-bed catalysts are used, the hydrogenation requires a high pressure of over 200 bar which is associated with high capital costs.
Furthermore, 1,4-butynediol, 1,4-butenediol and compounds derived therefrom, eg. the acetal from butanediol and hydroxybutyraldehyde which is formed by isomerization of butenediol, can be separated by distillation from 1,4-butanediol only with difficulty, if at all. However, for the further processing of 1,4-butanediol, it is critical for most applications that no incompletely hydrogenated products are present therein.
In chemical reactions, the selectivity generally decreases with increasing conversions. Efforts are therefore made to carry out the reaction, on the one hand, at as low as possible a temperature and, on the other hand, with a partial conversion in order to obtain selectivities which are as high as possible. In the hydrogenation of butynediol, complete conversion is essential with regard to the product quality achievable on work-up and the hydrogenation is therefore often distributed over a plurality of reactors which are operated under different conditions.
U.S. Pat. No. 5,068,468 discloses the hydrogenation of 1,4-butynediol over solid supported nickel/copper catalysts in which space-time yields of 0.3 kg of butanediol/l·h at a pressure of 250 bar.
BE-B 745 225 describes the use of fixed-bed Raney nickel catalysts at 259 bar, which achieve a space-time yield of 0.286 kg of butanediol/l·h in a two-stage process.
U.S. Pat. No. 4,153,578 discloses a two-stage process for the hydrogenation of 1,4-butynediol over suspended Raney nickel/molybdenum catalysts at a pressure of 21 bar. This process achieves space-time yields of 0.06 kg of butanediol/l·h.
DD-A 272 644 describes the suspension hydrogenation of aqueous butynediol over nickel/SiO
2
catalysts. Assuming that butynediol is as usual used in a concentration of from 39 to 50% by weight and assuming complete conversion, the space-time yield is calculated as from 0.15 to 0.25 kg of butanediol/l·h at a pressure of 15 bar. The catalyst used displays a loss in activity of 37% after only 50 hours.
For Example 1 of U.S. Pat. No. 2,967,893, a space-time yield of about 0.01 kg of butanediol/l·h can be calculated for the Raney nickel-copper-catalyzed hydrogenation of 1,4-butynediol.
RU-A 202 913 describes the hydrogenation of butynediol over a nickel/chromium catalyst at a space-time yield of 0.1 kg of butanediol/l·h.
EP-B 0 319 208, DE-A 19 41 633 and DE-A 20 40 501 disclose, inter alia, general hydrogenation processes which can be applied to 1,4-butynediol and in which the gas-circulation operating mode of the reactor is avoided by gas and liquid phases flowing in cocurrent from the bottom upwards through a fixed-bed catalyst. Here, gas and liquid phases flow through the catalyst in the form of the transition stream, with the liquid phase forming the continuous phase.
However, these processes have the disadvantage that in the case of high butynediol loadings in the hydrogenation feed the reaction mixture at the end of the reaction zone is depleted in hydrogen and as a result only an incomplete conversion of the 1,4-butynediol is achieved, thus leading to intermediates which can be separated from butanediol only with difficulty, if at all.
In the case of lower butynediol loadings, a complete conversion and satisfactory product quality can be achieved only if a significantly reduced space-time yield or higher operating pressure is accepted.
It is an object of the present invention to provide a process for the catalytic hydrogenation of 1,4-butynediol to 1,4-butanediol by means of which a high space-time yield together with high selectivity and high catalyst operating lives can be achieved at a pressure of below 200 bar even when using technical-grade 1, 4-butynediol.
We have found that this object is achieved by a process for preparing 1,4-butanediol by continuous catalytic hydrogenation of 1,4-butynediol, which comprises reacting 1,4-butynediol with hydrogen in the liquid continuous phase in the presence of a hydrogenation catalyst at from 20 to 300° C., preferably from 60 to 220° C. and particularly preferably from 120 to 180° C., a pressure of from 1 to 200 bar, preferably from 3 to 150 bar and particularly preferably from 5 to 100 bar, and values of the liquid-side volumetric mass transfer coefficient k
L
a of from 0.1 s
−1
to 1 s
−1
, preferably from 0. 2 s
−1
to 1 s
−1
,
a) using a catalyst suspended in the reaction medium, where if a packed bubble column is employed this is operated in the upflow mode and at a ratio of gas leaving the reaction vessel to gas fed to the reaction vessel of from 0.99:1 to 0.4:1, or
b) passing the liquid and gas in cocurrent in an upward direction through a fixed-bed reactor operated in the gas-circulation mode while maintaining a ratio of the gas fed to the reaction vessel to gas leaving the reaction vessel of from 0.99:1 to 0.4:1.
The process of the present invention gives 1,4-butanediol in high space-time yields together with high selectivity at a pressure below 200 bar by means of a single-stage or multistage hydrogenation. In addition, long catalyst operating lives can be achieved.
The liquid-side volumetric mass transfer coefficient between the gas phase and the liquid phase k
L
a is defined as
k
L
a=k
GL
×F
GL
,
where k
GL
is the mass transfer coefficient for gas-liquid mass transfer and F
GL
is the gas-liquid phase boundary area. The k
L
a value is, for example in Ullmanns Encyclopädie der technischen Chemie, Verlag Chemie, 4th edition (1973), Volume 3, pages 495 to 499, also described as the specific absorption rate.
The k
L
a value is determined experimentally by measuring the hydrogen absorption of a mixture of 50% by weight of butanediol and 50% by weight of water at the intended operating temperature. The procedure for the experimental determination of k
L
a has been described many times in the specialist literature, for example in P. Wilkinson et al.: “Mass Transfer and Bubble Size Distribution in a Bubble Column under Pressure”, Chemical Engineering Science, Vol. 49 (1994) No. 9, pp. 1417-1427, Ullmanns Encyclopadie der technischen Chemie, Verlag Chemie, Weinheim/Bergstr., 4th edition, 1973, Volume 3, pp. 495-499, H. Hoffmann: “Gepackte Aufstrom-Blasensäulen”, Chem.-Ing.-Tech. 54, (1982) No. 10, pp. 865-876 and A. Marquez et al.: “A Review of Recent Chemical Techniques for the Determination of the Volumetric Mass-transfer Coefficient k
L
a in Gas-liquid Reactors”, Chemical Engineering and Processing, 33 (1994) pp. 247-260.
According to the high k
L
a values which are employed in carrying out the process of the present invention, it is preferable to measure the hydrogen absorption under continuous operating conditions. As large as possible a stream of the liquid mixture is fed in, hydrogen-free and if appropriate together with suspended catalyst, at the desired temperature. The flow of the liquid mixture should be sufficiently high for the liquid contents of the reactor to be replaced at least within 2 minutes, preferably within 1 minute or less. At the same time, hydrogen-laden liquid mixture is taken o

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