DE1077204B - Process for the production of glycerine and glycols from sugar alcohols - Google Patents

Description

GERMAN

It is known to split glycerin and glycols and to produce catalytic hydrogenation of sugar alcohols. The known methods are at temperatures carried out up to about 300 ° C and pressures of at most 300 at. The conventional hydrogenation catalysts, especially supported nickel, are used. It has already been suggested been, this reaction in weakly acidic, more neutral or to be carried out in an alkaline aqueous solution.

The disadvantages of the known methods are that the yields of glycerol, the most valuable Reaction product, are low and that a more or less large amount of sugar alcohols through uncontrollable side reactions such as decomposition, secondary condensation and resinification are destroyed becomes or is lost.

It is also known that in the splitting off of sorbitol at about 200 ° C in methanolic solution and with Copper on diatomaceous earth as a catalyst the glycerine yield increases with increasing hydrogen pressure, however, an increase in pressure above 180 atm no longer brings any improvement in the yield.

It has now been found that higher glycerol yields can be obtained obtained by processes known per se for the cleavage and hydrogenation of sugar alcohols Performs at much higher pressures than were previously common.

The present invention relates to a process for the preparation of glycerol and glycols from sugar alcohols by cleavage and catalytic hydrogenation of the sugar alcohols at elevated temperatures and elevated pressure in an aqueous alkaline solution, characterized in that at temperatures from 200 to 300 ^! ° C and hydrogen pressures of 500 to 1000 in a solution at p _H 8 hydrogenated to 10 and splits.

As in the known processes, the catalyst used is advantageously nickel on a carrier, for example pumice stone or kieselguhr. Other known hydrogenation catalysts can also be used. The _pH value of the reaction mixture can be adjusted with calcium hydroxide in a simple manner.

Theoretically, the cleavage and catalytic hydrogenation of sugar alcohols has not yet been clarified. It it has now been found that in the procedure according to the invention, the reaction rate with increasing Pressure decreases slightly. Sales are also falling. However, these disadvantages can be found in Taken as a purchase, since the increase in pressure improves the glycerol yield and the losses Sugar alcohols are significantly reduced by side reactions.

It was also found that the decomposition of the process of manufacture of glycerine and glycols

from sugar alcohols

Applicant:

INVENTA A. G. for research

and patent exploitation,

Lucerne (Switzerland)

Representative: Dr.-Ing. Dr. jur. H. Mediger, patent attorney, Munich 9, Aggensteinstr. 13th

Claimed priority: Switzerland of November 16, 1957

Dr. Fritz Conradin, Tamins, Giuseppe Bertossa, Domat-Ems,

and Dr. Johann Giesen, Haldenstein, Chur (Switzerland), have been named as the inventor

Glycerine becomes lower due to secondary reactions with increasing pressure and is almost avoided above about 600 at. It was also found that at high pressures of the _pH-value constant the reaction mixture and remains higher. If an initial _pH value of about 11 chosen, this value falls very rapidly and then remains fairly constant. At a pressure of 100 at the _pH value during the reaction is about 8, however, at about 8.8 to 9, at pressures of 600 to 800 indicating that less acids are formed. It is known that the cleavage of the sugar alcohols proceeds better and more clearly in an alkaline medium. The activity of the catalyst also decreases more slowly at high pressures.

The reaction temperature can be about 200 to 300 ° C be, about 220 to 250 ° C. are advantageous. The rate of reaction increases with increasing temperature to, d. This means that higher reaction temperatures reduce the reaction rate can compensate, which is caused by the pressure increase.

If you use reaction temperatures of more than 250 ° C, it is difficult to introduce the necessary amount of heat into the reaction vessel. In this case you can burn some of the hydrogen by injecting oxygen in the reaction vessel and

909 759/426

thus generate the necessary heat in situ. Depending on the desired temperature, up to 15 ^ff / o of the total hydrogen is burned. This modification of the process according to the invention is particularly advantageous if the process is to be carried out continuously at temperatures of about 270.degree.

The injection of oxygen also has the advantage that the catalyst becomes less resinous and lasts longer remains active.

Wood sugar alcohols can also be hydrogenated and cleaved using the present process. Such are obtained by the hydrogenation of wood sugars, which are obtained from the hydrolysis of wood with mineral acids attack.

example

In an autoclave of 5 1 Content 1.1 kg of sorbitol and 2.41 of water are mixed with as much calcium oxide, that the solution has a _pH value of about. 11 Using a stirrer, 250 g of catalyst are distributed as finely as possible in the mixture. The catalyst consists of kieselguhr with a content of about 20 to 30% metallic nickel. Now hydrogen is pressed into the autoclave and this is heated to the reaction temperature. The temperature and pressure are kept at the values given in the table below for about 3 to 5 hours. During the reaction the _pH value of the mixture is about 8.5 to 9, depending on the applied pressure.

After cooling and letting down the autoclave, the reaction mixture is filtered and in the usual way, for example by distillation, broken down into the individual components.

The table below contains the pressures (in at) and the temperatures (in ° C) during the reaction, this is followed by the percentage of the residue in the filtered anhydrous reaction mixture. This The residue consists mainly of sorbitol and a little erythritol; you can use fresh sorbitol again be split. The following column indicates the conversion as a percentage of the sorbitol used, then follow the proportions of the reaction products and losses in percent., based on sales. The losses are composed of unidentifiable resins, gases, lower alcohols, acids, etc.

pressure Tempe
rature Back
was standing sales Glycerin Glycols losses 10
100
600
800 220
220
220 3.7
47.6
64.5 96.3
52.4
35.5 19.5
45.4
57.0 36.0
43.0
38.2 44.6
11.5
4.8

The first transverse row of the table contains values that are obtained at 100 at. They are only listed here so that the results at this low pressure with the results with the invention high pressures can be compared. It should also be noted that the unreacted sorbitol in can be easily separated and recycled to the hydrogenation.

Claims (3)

Patent claims: 1. A process for the preparation of glycerol and glycols from sugar alcohols by cleavage and catalytic hydrogenation of the sugar alcohols at elevated temperatures and elevated pressure in an aqueous alkaline solution, characterized in that one presses at temperatures of 200 to 300 ° C and hydrogen from 500 to 1000 at hydrogenated in a solution of _pH-value 8 to 10 and splits. 2. The method according to claim 1, characterized in that the catalyst used is nickel on a Carrier, in particular diatomaceous earth, used. 3. The method according to claim 1 or 2, characterized in that during the hydrogenation and cleavage by means of supplied oxygen burns up to about 15% of the hydrogen. © 909 759/426 3.60 '