WO2005021475A1

WO2005021475A1 - Method for preparing sugar alcohols by catalytic hydrogenation of sugars

Info

Publication number: WO2005021475A1
Application number: PCT/KR2004/002233
Authority: WO
Inventors: Byong-Sung Kwak; Byoung-In Lee; Tae-Yun Kim; Jin-Woong Kim; Sang-Il Lee
Original assignee: Sk Corporation
Priority date: 2003-09-03
Filing date: 2004-09-03
Publication date: 2005-03-10

Abstract

Disclosed a method of producing sugar alcohols through the hydrogenation of sugars using a catalyst in which ruthenium is supported on a carrier comprising silica, zirconia, or a mixture thereof. The method includes hydrogenating sugar under relatively moderate reaction conditions using a catalyst in which ruthenium is supported on a carrier including silica, zirconia, or a mixture thereof, with the metal dispersion of 10% or more, and in which the chlorine content is less than 100ppm. Sugar alcohol is produced through a continuous process under moderate conditions of low temperature and pressure at a high yield, thereby generating few by products or wastes and producing sugar alcohol without a complicated separation process.

Description

METHOD FOR PREPARING SUGAR ALCOHOLS BY CATALYTIC HYDROGENATION OP SUGARS

Technical Field

The present invention relates to a method of producing sugar alcohols by the hydrogenation of sugars using a catalyst in which ruthenium is supported on a carrier including silica, zirconia, or a mixture thereof. More particularly, the present invention relates to a method of producing sugar alcohol, which comprises hydrogenating sugar at low temperature and pressure using a catalyst in which ruthenium is supported on a carrier including silica, zirconia, or a mixture thereof, with the metal dispersion of 10 % or more, and in which a chlorine content is less than 100 ppm.

Background Art Sugar alcohols such as xylitol, sorbitol, mannitol, or maltitol have been widely used as useful materials applied to food additives, medical supplies, cosmetics and the like. Typically, sugar alcohol is produced by the hydrogenation of its corresponding sugar, which is exemplified by the following process. A method of producing xylitol, in which xylose is hydrogenated in a batch reactor using a Raney nickel catalyst, is disclosed in U.S. Pat. No. 3,586,537 and 4,008,285. The method is problematic in that it is necessary to conduct complicated separation-purification and catalyst recovery processes since byproducts are generated in large amounts, and metals leach in a solution, and the catalyst is deactivated. Recently, a continuous hydrogenation process using a nickel-based catalyst has been suggested to avoid the disadvantages of the batch reactor. U.S. Pat. No. 6,414,201 discloses a process of producing xylitol yielding 98 %, in which sugar such as xylose is continuously hydrogenated at 120°C under hydrogen pressure of 150 kg/cm² using a Raney nickel- alumina catalyst. However, this process has a disadvantage in that reactivity is decreased over time.

Furthermore, U.S. Pat. No. 6,124,443 discloses a method for the continuous hydrogenation of xylose using a nickel-iron- zirconia alloy catalyst. The continuous hydrogenation method is advantageous in that xylose is hydrogenated at 60°C under hydrogen pressure of 300 kg/cm², and then crystallized to be converted into xylitol having a purity of 99.6 %. However, the method is disadvantageous in that a reaction device capable of enduring high pressure is required, and the catalyst must be produced and treated without exposure to atmospheric air. U.S. Pat. No. 6,177,598 discloses the production of sugar alcohol having a purity of 99 % without the problem of leaching of metals in the reaction, in which sugar is hydrogenated using a catalyst in which a group VIII transition metal including ruthenium is supported on a carrier such as alumina having mesopores of 2 - 50 nm and acropores of 50 - 10,000 nm in a proper ratio. However, this method is problematic in that high- pressure devices are required, a separation-purification process is required to obtain highly pure products, and the catalyst is deactivated.

Furthermore, WO 02/100537 discloses a method of hydrogenating xylose at 100°C under hydrogen pressure of 50 kg/cm², in which a catalyst is dried then reduced using a halogen-free ruthenium precursor in amorphous silica without calcination. However, the method is disadvantageous in that ruthenium precursor is relatively expensive material in comparison with ruthenium chloride of the present invention, and it is required to conduct a separation-purification process after the reaction is completed since the selectivity of xylitol is a low 97 %. U.S. Pat. No. 6,570,043 discloses a method of hydrogenating sugar at 100°C and 100 bar using a titania- supported Ruthenium catalyst. However, the selectivity of sugar alcohol is low even though the conversion efficiency is high.

Meanwhile, besides hydrogenation, technologies of converting sugar such as xylose into xylitol using the fermentation process have been suggested. U.S. Pat. No. 5,998,181 discloses a method of producing xylitol by fermentation using a strain of Candida tropicalis for 48 hours. The method using the fermentation has an advantage in that a separation-purification process is relatively easily conducted in comparison with a batch-type hydrogenation process. However, it is problematic in that it takes a long time and productivity is low.

Disclosure of the Invention

Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, and an object of the present invention is to provide a method of producing highly _.pure sugar alcohol through a simple process without a complicated purification process, in which sugar is selectively hydrogenated using a heterogeneous catalyst having high activity and long life under conditions that are more moderate than in the conventional technology, thereby generating few byproducts or wastes .

In order to accomplish the above object, the present invention provides a method of producing sugar alcohol, which includes hydrogenating sugar at a reaction temperature of 20 - 150°C and a hydrogen pressure of 5 - 300 kg/cm² using a catalyst in which ruthenium is supported on a carrier including silica, zirconia, or a mixture of silica and zirconia, with the metal dispersion of 10 % or more and in which a chlorine content is less than 100 ppm.

Best Mode for Carrying Out the Invention Hereinafter, the invention will become more apparent from the following description. Unlike a conventional method, in the present invention, sugar is hydrogenated using a catalyst in which ruthenium is supported on a carrier including silica, zirconia, or a mixture thereof, to have high dispersion. Accordingly, sugar alcohol is effectively produced in relatively moderate reaction conditions at a high yield without an additional separation process. Generally, VIII to XI group transition elements of the periodic table can be used in hydrogenation. Particularly, it is known that ruthenium and nickel have high activity against the hydrogenation of sugar. However, they are problematic in that byproducts are generated due to a high-pressure reaction condition, isomerization, decomposition, and polymerization, and in that the catalyst is deactivated. Taking all the above into consideration, in the present invention, silica, zirconia, or a mixture thereof, which is stable in reaction solution and has a high mechanical strength, is used as a carrier. Additionally, a catalyst is used wherein ruthenium is supported .on the carrier in high dispersion. Sugar is hydrogenated in relatively moderate reaction conditions using the catalyst in which ruthenium is supported on the carrier such as silica, zirconia, or a mixture thereof, thereby producing sugar alcohol at a high yield. Furthermore, the activity of the catalyst is stably maintained by controlling the chlorine content in the catalyst.

In the present invention, silica or zirconia may be used alone as the carrier. Alternatively, a mixture of silica and zirconia may be used as the carrier. At this time, the content of silica, zirconia, or the mixture of silica and zirconia is 50 wt% or more, and more preferably, 90 wt% or more of the total weight of the carrier. If necessary, the rest of the components of the carrier may be selected, however, it is preferable that the content of each impurity such as iron or sulfur in the carrier is less than 0.2 wt% . Illustrative, but non-limiting examples of silica used in the present invention may include natural silica, synthetic silica, silica gel, and pyrogenic silica (commercial name: Aerosil, Carbosil) . Additionally, examples of zirconia may include monoclinic, tetragonal, and amorphous zirconia. It is preferable to use a carrier having a surface area of 10 - 500 m²/g. When the surface area of the carrier is less than 10 m²/g, it is difficult for the metal to be uniformly dispersed. When the surface area of the carrier is more than 500 m²/g, the pore size is reduced, resulting in lowered reactivity. The carrier is shaped in the proper size depending on the length and the diameter of the reactor so as to desirably conduct continuous hydrogenation employing a fixed-bed reactor. The catalyst of the present invention wherein ruthenium is supported on silica, zirconia, or a mixture thereof is produced according to the following procedure. Ruthenium in a salt form is dissolved in a small amount of water, and then supported on the carrier such as silica, zirconia, or a mixture of silica and zirconia, according to a conventional production method. In the course of producing the catalyst including ruthenium according to the present invention, a ruthenium salt such as ruthenium chloride, ruthenium nitrosyl nitrate, or ruthenium acetylacetonate may be employed. Ruthenium chloride is preferred. With respect to the control of the chlorine content significantly affecting the activity of the catalyst, even though the precursor such as ruthenium nitrosyl nitrate and ruthenium acetylacetonate contains no chlorine, it is necessary to control the chlorine content of the catalyst because chlorine may exist in the carrier or the like during the production of the catalyst. The catalyst containing the ruthenium salt is dried at 90 - 150^°C, calcined under an inert gas atmosphere, such as nitrogen or helium, or under atmospheric air at 200 - 600°C for 3 hours or more to decompose the salt, and then stored. When the calcining temperature is less than 200°C, the calcining is accomplished incompletely, thereby resulting in poor decomposition of the metal precursor during supporting of the ruthenium. When the calcining temperature is more than 600°C, since the metal dispersion is reduced, the catalyst becomes deactivated. The catalyst is reduced in a reducing agent atmosphere such as hydrogen at 100 - 500°C before it is applied to the hydrogenation. In an embodiment of the present invention, it is preferable that the dispersion of ruthenium in the carrier be maintained at 10 % or more. When the dispersion of ruthenium is less than 10 %, the activity of the catalyst is low. The metal dispersion is the percentage of the number of metal atom being exposed at the surface of the catalyst based on the total number of metal atoms contained in the catalyst. The number of exposed metal atoms is measured by the chemisorption of carbon monoxide . The amount of ruthenium metal dispersed in a support, such as silica, zirconia, or a mixture thereof, is 0.1 - 10 wt% . When the amount of ruthenium metal is less than 0.1 wt%, hydrogenation activity is poor. When the amount is more than 10 wt%, costly precious metals are used in excess, thereby resulting in reduced economic efficiency.

Furthermore, it is preferable to control the chlorine content through calcining and/or washing processes so that the chlorine content in the catalyst including ruthenium is less than 100 ppm in the course of producing the catalyst. In the case of using the catalyst containing 100 ppm or more of chlorine, deactivation of catalyst is progressed rapidly, thereby undesirably generating an excess amount of byproducts. As described above, sugar is hydrogenated under moderate conditions using the catalyst, in which ruthenium is supported on silica, zirconia, or the mixture thereof with the metal dispersion of 10 % or more, to produce highly pure sugar alcohol . The hydrogenation of the present invention may be performed in a batch process or in a continuous process, and it is preferable to perform a continuous reaction using a tubular fixed-bed reactor in consideration of operating costs and reaction efficiency. Sugars to be hydrogenated according to the present invention are selected from the group consisting of erythrose, xylose, arabinose, glucose, galactose, mannose, fructose, lactose, lactulose, maltose, isomaltulose, talose, rhamnose, sucrose, starch sugar, starch hydrolyzate, cellulose hydrolyzate, hemicellulose hydrolyzate, and a mixture thereof.

Generally, since sugar is in a solid form at room temperature, it is preferable that sugar be used while being dissolved in a proper solvent so as to improve reaction efficiency. Any solvent, which is capable of simultaneously dissolving sugar as a raw material and sugar alcohol as a product, may be used as the solvent to improve reaction efficiency. Preferably, water or alcohol may be used alone, or a mixture of them may be employed. Examples of alcohol include methanol, ethanol, propanol, isopropanol, or a mixture thereof.

More preferably, water is used alone, or a mixture of water and ethanol is used. In the case of using the solvent, the concentration of sugar in the solution is not limited, but is preferably 1 - 60 wt% . In the present invention, it is preferable to carry out the hydrogenation of sugar at 20 - 150°C. More preferably, the hydrogenation is performed at 30 - 130°C. When the temperature is less than 20°C, a reaction activity becomes lower. When the temperature is more than 150°C, occurrence of side reactions is increased and a coloration problem occurs. It is preferable to conduct the hydrogenation of sugar according to the present invention at a pressure of 5 - 300 kg/cm². More preferably, the hydrogenation is performed at 10 - 200 kg/cm². When the pressure is less than 5 kg/cm², the reaction rate becomes slower. When the pressure is more than 300 kg/cm², the reaction is accomplished without any problem, however, equipment costs is increased due to the high pressure, thus reducing economic efficiency. Furthermore, it is preferable that the amount of hydrogen in the hydrogenation be 1 - 50 times the amount of sugar used, expressed as a molar ratio. When the hydrogenation is carried out in the continuous reaction system, it is preferable that a weight hourly space velocity (WHSV) of sugar be about 0.05 - 10 h^"1. At this time, the WHSV is excessively low, operation costs is increased, thereby resulting in reduced economic efficiency. If the WHSV is very high, the hydrogenation undesirably occurs. As described above, in the present invention, sugar alcohol is selectively produced under moderate conditions of low temperature and pressure in a continuous process, in comparison with conventional method. Thereby, an environmentally friendly process is realized, in which few byproducts and wastes are generated, and sugar alcohol having a purity of 99.5 % or more is effectively and economically produced without a complicated separation process. A better understanding of the present invention may be' obtained through the following examples and comparative examples which are set forth to illustrate, but are not to be construed as the limit of the present invention.

EXAMPLE 1

Ruthenium chloride was uniformly supported on silica pellets having a size of 2 mm so that a ruthenium content was 3 wt%, dried at 110°C for 6 hours, and calcined in a nitrogen atmosphere at 500°C for 5 hours to produce a ruthenium catalyst having the ruthenium dispersion of 45 % and a chlorine content of 54 ppm. 2 g of catalyst thus produced was packed into a fixed-bed tubular reactor made of stainless steel, and reduction was subsequently conducted at 350°C for 6 hours in the presence of hydrogen flowing at a rate of 50 cc per minute. After the reduction was completed, the flow rate of hydrogen was controlled so that it was 6 times the amount of xylose used, expressed as a molar ratio. After a temperature and pressure of the reactor were set to 50°C and 50 kg/cm², a reactant was fed at a weight hourly space velocity (WHSV) of 0.18 h^_1 (on the basis of xylose) to initiate a reaction. 40 wt% solution of xylose dissolved in distilled water was used as the reaσtant, and the product was analyzed using liquid chromatography provided with a refractive index detector. After the reaction was carried out for 100 hours, the average conversion of xylose was 99.9 % and the selectivity of xylitol was 99.9 %. Reactivity was not reduced even though the reaction was continuously performed for 3,000 hours or more.

EXAMPLE 2

The procedure of example 1 was repeated except that the reaction temperature was 60°C and the WHSV was 0.24 h^"1. After the reaction was conducted for 100 hours, the average conversion of xylose was 99.9 % and the selectivity of xylitol was 99.8 %. Reactivity was not reduced even though the reaction was continuously performed for 1,000 hours or more.

EXAMPLE 3 The procedure of example 1 was repeated except that glucose was used as a reactant. After the reaction was conducted for 100 hours, the average conversion of glucose was 99.9 % and the selectivity of sorbitol was 99.9 %. Reactivity was not reduced even though the reaction was continuously performed for 1,000 hours or more.

EXAMPLE 4 Ruthenium chloride was uniformly supported on zirconia pellets having a size of 3 mm, so that a ruthenium content was 3 wt%, dried at 110°C for 6 hours, and calcined under a nitrogen atmosphere at 500°C for 5 hours to produce a ruthenium catalyst having the ruthenium dispersion of 40 % and a chlorine content of 50 ppm. 6 g of catalyst thus produced were packed into a fixed-bed tubular reactor made of stainless steel, and the reduction was subsequently conducted at 350°C for 6 hours in the presence of hydrogen flowing at a rate of 50 cc per minute. After the reduction was completed, the flow rate of hydrogen was controlled so that it was 6 times the amount of xylose used, expressed as a molar ratio. After the temperature and pressure of the reactor were set to 60°C and 50 kg/cm , a reactant was fed at the WHSV of 0.10 h^_1 (on the basis of xylose) to initiate a reaction. 40 wt% solution of xylose dissolved in distilled water was used as the reactant, and the product was analyzed using liquid chromatograph provided with a refractive index detector. After the reaction was conducted for 100 hours, the average conversion of xylose was 99.9 % and the selectivity of xylitol was 99.8 %. Reactivity was not reduced even though the reaction was continuously performed for 1,000 hours or more. EXAMPLE 5

The procedure of example 4 was repeated except that glucose was used as the reactant. After the reaction was conducted for 100 hours, the average conversion of glucose was 99.9 % and the selectivity of sorbitol was 99.8 %. Reactivity was not reduced even though the reaction was continuously performed for 1,000 hours or more.

EXAMPLE 6

The procedure of example 4 was repeated except that the sugar containing 80 % xylose, 9 % arabinose, 5 % galactose, and 6 % glucose was used as a reactant. After the reaction was conducted for 100 hours, the average purities of hydrogenated sugar alcohols were 79.8 %, 9.2 %, 5 %, and 5.9 % for xylitol, arabitol, galactitol, and sorbitol, respectively. Reactivity was not reduced even though the reaction was continuously performed for 1,000 hours or more.

EXAMPLE 7 The procedure of example 4 was repeated except that silica-zirconia consisting of 90 wt% silica and 10 wt% zirconia was used as a carrier to produce a 3 wt% ruthenium catalyst having the ruthenium dispersion of 42 % and a chlorine content of 60 ppm. After the reaction was conducted for 100 hours, the average conversion of xylose was 99.9 % and the selectivity of xylitol was 99.8 %. Reactivity was not reduced even though the reaction was continuously performed for 1,000 hours or more. COMPARATIVE EXAMPLE 1

The procedure of example 1 was repeated except that silica was used as a carrier to produce 3 wt% of ruthenium catalyst having the ruthenium dispersion 2.8 %. After the reaction was conducted for 100 hours, the average conversion of xylose was 82.1 % and the selectivity of xylitol was 99.9 %. The production efficiency per time was reduced because the dispersion was low.

COMPARATIVE EXAMPLE 2

The procedure of example 1 was repeated except that 3 wt% of ruthenium was dispersed with the ruthenium dispersion of 3.0 % in an alumina carrier, which had 85.3 % mesopores of 2 - 50 nm and 14.7 % macropores of 50 - 10,000 nm based on a pore volume thereof, to produce a catalyst. After the reaction was conducted for 10 hours, the average conversion of xylose was 82.1 % and the selectivity of xylitol was 99.8 %. The catalyst was deactivated over time and the conversion of xylose was 72.1 % after 48 hours.

COMPARATIVE EXAMPLE 3

The procedure of example 1 was repeated except that silica was used as a carrier to produce a 3 wt% ruthenium catalyst having the ruthenium dispersion of 10 % or more and a chlorine content of 1,000 ppm. After the reaction was conducted for 20 hours, the average conversion of xylose was 99.9 % and the selectivity of xylitol was 99.9 %. The catalyst was slowly deactivated over time and the conversion of xylose was 96.3 % after 270 hours.

COMPARATIVE EXAMPLE 4 The procedure of example 4 was repeated except that zirconia was used as a carrier to produce a 3 wt% ruthenium catalyst having the ruthenium dispersion of 10 % or more and a chlorine content of 1,000 ppm. After the reaction was conducted for 20 hours, the average conversion of xylose was 99.9 % and the selectivity of xylitol was 99.8 %. The catalyst was deactivated over time and the conversion of xylose was 95.5 % after 270 hours.

Industrial Applicability

As described above, in the present invention, sugar alcohol is selectively produced through a continuous process under moderate conditions of low temperature and pressure using a catalyst in which ruthenium is dispersed in a carrier such as silica, zirconia, or a mixture thereof with the metal dispersion of 10 % or more, and in which the chlorine content is less than 100 ppm. Thereby, an environmentally friendly method is provided, in which few byproducts or wastes are generated, and highly pure sugar alcohol is efficiently and economically produced without an additional complicated separation process.

Claims

1. A method of producing sugar alcohols, comprising: hydrogenating sugars at a reaction temperature of 20 -

150°C and a hydrogen pressure of 5 - 300 kg/cm² using a catalyst in which ruthenium is supported on a carrier including silica, zirconia, or a mixture of silica and zirconia, with the metal dispersion of 10 % or more and in which a chlorine content is less than 100 ppm.

2. The method as set forth in claim 1, wherein the carrier comprises 50 wt% or more of silica, zirconia, or the mixture of silica and zirconia.

3. The method as set forth in claim 1, wherein the carrier has a surface area of 10 - 500 m²/g.

4. The method as set forth in claim 1, wherein the ruthenium is contained in an amount of 0.1 - 10 wt% based on a weight of the catalyst.

5. The method as set forth in claim 1, wherein the catalyst is produced so that the dispersion of the ruthenium is 11 - 100 %.

6. The method as set forth in claim 1, wherein the sugar is selected from the group consisting of erythrose, xylose, arabinose, glucose, galactose, mannose, fructose, lactose, lactulose, maltose, isomaltulose, talose, rhamnose, sucrose, starch sugar, starch hydrolyzate, cellulose hydrolyzate, hemicellulose hydrolyzate, and a mixture thereof.

7. The method as set forth in claim 1, wherein the sugar is used while being dissolved in a solvent, and the solvent is selected from the group consisting of water, alcohol, and a mixture thereof.

8. The method as set forth in claim 7, wherein the alcohol is methanol, ethanol, propanol, isopropanol, or a mixture thereof.

9. The method as set forth in claim 1, wherein the reaction temperature is 30 - 130°C.

10. The method as set forth in claim 1, wherein the hydrogen pressure is 10 - 200 kg/cm².

11. The method as set forth in claim 1, wherein when the hydrogenation of the sugar is continuously carried out, a weight hourly space velocity of the sugar is 0.05 - 10 h^-1.