JPH0457654B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a continuous hydrogenation process using a Raney-nickel catalyst.

Raney-nickel catalysts have been widely used since they exhibit high activity as hydrogenation catalysts for aldehydes, but they have the disadvantage that their activity decreases in a short period of time when used repeatedly or continuously. In order to regenerate the catalyst, the deactivated catalyst is washed with an alkaline solution, a new Raney alloy is added, and the catalyst is heated in the alkaline solution (Japanese Patent Application Laid-Open No. 51-84792).
Although such methods have been devised, they require complicated operations such as separation and recovery of the catalyst, treatment with a strong alkaline solution, and washing with water, and are not fully satisfactory as a method for regenerating catalysts, especially those used in continuous reactions.

The present inventor has investigated a method for producing butanediols by continuously hydrogenating an aqueous solution containing 4-hydroxybutyraldehyde and 2-methyl-3-hydroxypropionaldehyde obtained from a hydroformylated product of allyl alcohol. However, we learned that the Raney-nickel catalyst used in such continuous reactions has a relatively short activation retention time, which poses a problem. If the amount of new catalyst charged is increased, the activation retention time will be extended, but since the extension is approximately proportional to the amount charged, there is an advantage of avoiding interruption of continuous reaction, but it does not improve the catalyst cost.

After further investigation, we found that if a portion of the new catalyst used (a product developed by Raney Nickel) was added during the reaction, the catalytic activity, which had begun to decline, could be restored to almost the same level as the initial activity. The present invention was completed based on the discovery that the compound retains high activity for a significantly longer period of time than the conventional method.

The amount of new catalyst added is 1/50 to 1/2, preferably 1/10 to 1/3 of the initially charged catalyst, which is sufficient.
This is an extremely simple method that does not require any operations other than addition, such as alkali treatment. Therefore, even during continuous operation, by adding new catalyst into the reactor using the slurry pump injection method, isopressure method, etc.
Since it is possible to measure the recovery of activity, there is no need to stop operation, which is very efficient and industrially advantageous. The timing to add the new catalyst during the reaction is preferably at the stage when the conversion rate begins to decrease and it is known when measures to maintain activity should be taken. It is not preferable in terms of quality control of the hydrogenated product to carry out the process after the activity has decreased and is almost completely deactivated.

The hydrogenation reaction of aldehydes using a Raney-nickel catalyst is usually carried out under conditions of 1 to 110 atmospheres and room temperature to 125°C.

Known reaction conditions can also be used in the case of hydroformylation of allyl alcohol and hydrogenation of an aqueous aldehyde solution obtained by water extraction. In this case, hydrogen pressure is
A pressure of 20 to 80 atmospheres and a temperature of 70 to 120°C are preferred. Although there is no problem with the reaction when the hydrogen pressure is 80 atmospheres or more, it is not very advantageous from the point of view of equipment cost. In addition to ordinary Raney nickel, the catalyst may also contain trace amounts of other metals (Ti, Cr, Mo, Mn, etc.) ("Catalyst Preparation" edited by Takayasu Shirasaki and Naoyuki Todo, p. 80)
83, Kodansha, S49), usually developed with aqueous caustic soda solution. The initial charge amount of the catalyst is preferably 0.5 to 10%, preferably 2 to 7% in liquid concentration.

When an aldehyde is hydrogenated in an aqueous solution containing a large amount (for example, 50% or more) of water, the solution tends to be acidic. In some cases, as in the production of sorbitol, it is possible to add an alkali, but in many cases, adding an alkali causes a condensation reaction of aldehydes, which is disadvantageous. In the present invention, when such an aqueous solution of aldehyde is continuously hydrogenated, for example, 4-
Hydroxybutyraladehyde and 2-methyl-3-
An aldehyde aqueous solution obtained by water extraction of a reaction solution containing hydroxypropionaldehyde is continuously hydrogenated using a Raney-nickel catalyst to obtain 1,4-
It is particularly useful in methods for obtaining butanediols. The present invention will be explained below using specific examples.

Reference Example 1 Into an autoclave with an internal volume of 500 ml equipped with hydrogen gas, a liquid inlet, a filtered liquid outlet, and a magnetic stirrer, 4.7 g of Raney-nickel catalyst developed at 90°C with an aqueous solution of caustic soda was added, and 1% propionaldehyde and 3-hydroxyl were added. An aqueous solution containing 1.5% of -2-methylpropionaldehyde and 12% of 4-hydroxybutyraldehyde was charged at a rate of 315 ml/hr, and the reaction was carried out at 100°C. Hydrogen gas was supplied so that the total pressure was maintained at 50 Kg/cm ² . As shown in Figure 1, the aldehyde conversion rate is low for up to 34 hours.
The activity was above 99.9%, but the activity decreased rapidly thereafter. The duration of activity per gram of catalyst is 7.23 hours.

Example 1 When the reaction was carried out under the same conditions as in Reference Example 1 except that the amount of Raney nickel was changed to 9.45 g, the activity lasted for 74 hours (7.83 hours/g), but after that it rapidly decreased (Fig. 2). point A). When 2g of new catalyst was added to this reaction solution, the activity recovered (point B).
Furthermore, it continued for 92 hours until point C (46 hours/g amount added midway). When 2 g of new catalyst was added again, the activity recovered (point D) and lasted for 94 hours. (47 hours/g) Figures 3 and 4 share the time axis with Figures 1 and 2. Isobutyl alcohol by-product rate (mol%)
This figure shows that the recovery of catalytic activity by adding new catalyst is also effective in suppressing the production of by-products.

[Brief explanation of the drawing]

FIGS. 1 and 2 are diagrams showing the conversion rate of aldehyde hydrogenation reaction over time, and FIGS. 3 and 4 are diagrams showing the isobutyl alcohol by-product rate over time.