METHOD FOR PREPARING SUGAR ALCOHOLS USING RUTHENIUM ZIRCONIA CATALYST

Technical Field

[1] The present invention relates to a method of producing sugar alcohols by the hy- drogenation of sugars using a catalyst in which ruthenium is supported on a zirconia. More particularly, the present invention relates to a method of producing sugar alcohol, which comprises hydrogenating sugar at low temperature and pressure without dissolving catalyst components during hydrogenation using a catalyst in which ruthenium is supported on a zirconia with the metal dispersion of 10 % or more, and in which a chlorine content is less than 100 ppm.

[2]

Background Art

[3] 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.

[4] 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.

[5]

[6] 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/cm using a Raney nickel-alumina catalyst. However, this process has a disadvantage in that reactivity is decreased over time.

[7]

[8] 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/cm , 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 atmosphere.

[9]

[10] Meantime, several patents using ruthenium catalyst in hydrogenation have been disclosed in this art. U.S. Pat. No. 3,963,788 discloses a method for hydrogenating of sugars using ruthenium containing zeolite catalyst having silica / alumina mole ratio of at least 3. The catalyst is prepared by adding zeolite into aqueous ruthenium chloride solution, stirring it at 80°C in the form of slurry to substitute the ruthenium by ion exchange, filtering and washing it with distilled water to eliminate unsubstituted ruthenium chloride in the carrier, drying and reducing the formed catalyst. This patent insists that the used catalyst is regenerated by acid washing after hydrogenation. However, this method is disadvantageous in that ruthenium precursor is excessively dissolved caused by ion exchange method and it is difficult to control the ruthenium content in the catalyst. In addition, it is required to conduct additional catalyst regeneration process, and the yield is as low as about 97%, so that another separation process is required to produce high purity of sugar alcohol.

[H]

[12] U.S. Pat. No. 4,380,679 discloses a process for hydrogenating of sugars by using catalyst which a metal of Group D of periodic table such as ruthenium is supported on a carbonaceous pyropolymer composited inorganic oxide such as alumina. The carbonaceous pyropolymer support is prepared by treating inorganic oxide such as alumina with organic pyrolyzable compound at high temperature, and then by dissolving with acid or base. The catalyst is prepared by supporting a metal in the carbonaceous pyropolymer, caclinating and reducing the formed catalyst. This catalyst is advantageous in that the hydrothermal stability and reactivity of the catalyst is superior to conventional alumina support catalyst. Comparing to using gamma alumina support, the solubility of support during hydrogenation relatively improved. However, it is still disadvantageous in that aluminum is detected in an amount of several ppm and reaction selectivity is low.

[13]

[14] U.S. Pat. No. 4,950,812 relates to a process for conversion of polysaccharide to polyhydric alcohols performing simultaneous hydrolysis and hydrogenation, in which the catalyst being highly dispersed ruthenium formed by ion exchanging with ruthenium amine complex salt into acidic support such as zeolite is used. This method comprises adding zeolite substituted with ammonium ion in aqueous hexamine ruthenium chloride solution, filtering and washing it to remove residual ruthenium salt and ammonium chloride compounds, drying it at ambient temperature and reducing the catalyst in hydrogen atmosphere to apply hydrogenation. This method is advantageous in that the ruthenium is highly dispersed by ion exchange with ruthenium amine

complex salt and hydrolysis and hydrogenation is performing at the same time using acidic carrier. However, it is disadvantageous in that when hydrolysis is conducted, the reaction temperature is relatively high, resulting isomerization, thereby it is difficult to produce sugar alcohols selectively. In addition, it is disadvantageous in that silicon and aluminum in a carrier is dissolved during reaction and costly ruthenium amine complex salt is used comparing to ruthenium chloride.

[15]

[16] 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 hy- drogenated 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 macropores 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.

[17]

[18] Furthermore, WO 02/100537 discloses a method of hydrogenating xylose at 100°C under hydrogen pressure of 50 kg/cm , 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 silicon in a carrier is dissolved during hydrogenation. Also it is required to conduct a separation- purification process after the reaction is completed since the selectivity of xylitol is a low 97 %.

[19]

[20] 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.

[21]

[22] 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.

[23]

Disclosure of Invention

Technical Solution

[24] 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 without dissolving catalyst component during hydrogenation 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.

[25]

[26] 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 reaction pressure of 5 - 300 kg/cm ² using a catalyst in which rut henium is supported on a zirconia with the metal dispersion of 10 % or more and in which a chlorine content is less than 100 ppm.

[27]

Best Mode for Carrying Out the Invention

[28] Hereinafter, the invention will become more apparent from the following description.

[29]

[30] Unlike a conventional method, in the present invention, sugar is hydrogenated using a catalyst in which ruthenium is supported on a zirconia to have high dispersion. Accordingly, sugar alcohol is effectively produced in relatively moderate reaction conditions at a high yield without an additional separation process.

[31]

[32] Generally, VIE 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.

[33]

[34] Taking all the above into consideration, in the present invention, zirconia 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 a zirconia in high dispersion. Sugar is hydrogenated in relatively moderate reaction conditions without dissolving catalyst component during hydrogenation using the catalyst in which ruthenium is supported on a zirconia, 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.

[35]

[36] In the present invention, zirconia may be used as a carrier. At this time, the content of zirconia is 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%. When zirconia in the carrier is less than 90wt%, the amounts of the rest of the component of the carrier such as silica and alumina, and clay are increased so that the catalyst is easy to break or the activity is dramatically decreased since the carrier components are dissolved in reaction. Moreover, if the amounts of the component such as titania and sulfur etc., which are not dissolved well in reaction, are increased in the carrier, the surface area of carrier is dramatically decreased or poisoned.

[37]

[38] Examples of zirconia used in the present invention may include monoclinic, tetragonal, and amorphous zirconia. It is preferable to use a carrier having a surface area of 10 - 500 m Ig. When the surface area of the carrier is less than 10 m /g, it is difficult for the metal to be uniformly dispersed. When the surface area of the carrier is more than 500 m /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.

[39] The catalyst of the present invention wherein ruthenium is supported on a zirconia is produced according to the following procedure.

[40] Ruthenium in a salt form is dissolved in a small amount of water, and then supported on a zirconia according to a conventional impregnation method. In the course of producing the catalyst including ruthenium according to the present invention, a ruthenium salt such as ruthenium chloride, ruthenium nitrate, 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.

[41]

[42] The catalyst containing the ruthenium salt is dried at 90 - 150°C. If necessary, the dried catalyst is calcinated in nitrogen, helium or air at 200 - 600°C. Dried or calcined catalyst is reduced in a reducing agent atmosphere such as hydrogen at 100 - 500°C. This reduced catalyst is sufficiently washed with distilled water, aqueous ammonia, or

inorganic basic aqueous solution such as sodium hydroxide, and potassium hydroxide to eliminate chlorine and subsequently re-dried. If necessary, the calcined catalyst is washed before applied to reduction. Thus obtained catalyst, if necessary, is applied to reduction again before hydrogenation and then used.

[43]

[44] As described in the above, it is advantageous in that washing is performed after reduction or calcination so that the chlorine is eliminated and the ruthenium metal is uniformly dispersed in the carrier. However, if the supported catalyst is directly washed without reduction or calcination, the ruthenium, which is not strongly absorbed in the carrier, is excessively dissolved. Washing solution used in the present invention may include distilled water, and aqueous ammonia or inorganic basic aqueous solution such as sodium hydroxide and potassium hydroxide. More preferably, aqueous ammonia, which has excellent chlorine removal and low residual, is used. For the case of washing with basic aqueous solution except distilled water, if necessary, additional washing is conducted using distilled water. The concentration of washing solution required in washing is preferably 0.1 - 50wt% except distilled water, and the employed amount of washing solution is 10 - 1,000 times based on the catalyst.

[45]

[46] It is preferable to control the chlorine content by washing and/or calcining so that the chlorine content in the catalyst which ruthenium is supported on zirconia is less than 100 ppm. 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.

[47]

[48] In an embodiment of the present invention, it is preferable that the dispersion of ruthenium in zirconia be maintained at 10 % or more. When the dispersion of ruthenium is less than 10 %, the activity of the catalyst is low, the high purity of sugar alcohol products can not be simply produced and the temperature is increased to improve activity of catalyst with low dispersion, thereby resulting in increasing the byproducts. 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.

[49]

[50] The amount of ruthenium metal dispersed in zirconia is 0.1 - 10 wt%. When the amount of ruthenium metal is less than 0.1 wt%, hydrogenation rate is slower. When the amount is more than 10 wt%, costly precious metals are used in excess, thereby resulting in reduced economic efficiency.

[51]

[52] As described above, sugar is hydrogenated under moderate conditions using the catalyst, in which ruthenium is supported on a zirconia with the metal dispersion of 10 % or more, to produce highly pure sugar alcohol.

[53]

[54] 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.

[55]

[56] 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.

[57]

[58] 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%.

[59]

[60] 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.

[61]

[62] It is preferable to conduct the hydrogenation of sugar according to the present invention at a pressure of 5 - 300 kg/cm . More preferably, the hydrogenation is performed at 10 - 200 kg/cm . When the pressure is less than 5 kg/cm , the reaction rate becomes slower. When the pressure is more than 300 kg/cm , the reaction is accomplished without any problem, however, equipment costs is increased due to the high pressure, thus reducing economic efficiency.

[63]

[64] 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.

[65]

[66] 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 - 1O h ^"1 . At this time, if the WHSV is excessively low, the operation cost is increased, thereby resulting in reduced economic efficiency. If the WHSV is very high, the hydrogenation undesirably occurs.

[67]

[68] 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.

[69]

[70] 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.

[71]

[72] EXAMPLE 1

[73] Ruthenium chloride was uniformly supported on 99 wt% of zirconia pellets having a size of 3 mm so that a ruthenium content was 3 wt%. The supported catalyst was dried at 110°C for 6 hours, and then reduced in a hydrogen flow at 350°C for 6 hours. The reduced catalyst was sufficiently washed with 5 wt% of aqueous ammonia using the amount of 100 times based on the catalyst to remove the chlorine ion. After washing, the washed catalyst was re-dried at 110°C for 6 hours, so that ruthenium catalyst was obtained with 40% of ruthenium dispersion and 50 ppm of chlorine content. 6 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 60°C and 50 kg/cm , a reactant was fed at a weight hourly space velocity (WHSV) of 0.10 h ^" (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 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 99.8 %. Reactivity was not reduced even

though the reaction was continuously performed for 3,000 hours or more. After hy- drogenation, even 1 ppm of zirconium and ruthenium was not detected in the product solution.

[74]

[75] EXAMPLE 2

[76] The procedure of example 1 was repeated except that the glucose as a reactant was used. 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. After hydrogenation, even 1 ppm of zirconium and ruthenium was not detected in the product solution.

[77]

[78] EXAMPLE 3

[79] The procedure of example 1 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. After hydrogenation, even 1 ppm of zirconium and ruthenium was not detected in the product solution.

[80]

[81] EXAMPLE 4

[82] Ruthenium chloride was uniformly supported on 99 wt% of zirconia pellets having a size of 3 mm, so that a ruthenium content was 3 wt%. The supported catalyst was dried at 110°C for 6 hours, and then calcined under a nitrogen atmosphere at 500°C for 5 hours. The calcined catalyst was sufficiently washed with 5 wt% of aqueous ammonia using amount of 100 times based on the catalyst to remove the chlorine ion, and then re-dried at 100°C for 6 hours. Subsequently it was reduced in a hydrogen flow at 350°C for 6 hours to produce ruthenium catalyst having 30 % of ruthenium dispersion and 40 ppm of chlorine content. 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 3 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 ^" (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 99.7 %. Reactivity was not reduced even though the reaction was continuously performed for 1,000 hours or more. After hydrogenation, even 1 ppm of zirconium and ruthenium was not detected in the product solution.

[83]

[84] EXAMPLE 5

[85] Ruthenium chloride was uniformly supported on 99 wt% of zirconia pellets having a size of 3 mm, so that a ruthenium content was 3 wt%. The supported catalyst was dried at 110°C for 6 hours, and then calcined under a nitrogen atmosphere at 500°C for 5 hours. The calcined catalyst was reduced in a hydrogen flow at 350°C for 6 hours and then sufficiently washed with 5wt% of aqueous ammonia using amount of 100 times based on the catalyst to remove the chlorine. The washed catalyst was re-dried at 110°C for 6 hours to produce catalyst having 28% of ruthenium dispersion and 35 ppm of chlorine content. 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 3 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 99.7 %. Reactivity was not reduced even though the reaction was continuously performed for 1,000 hours or more. After hydrogenation, even 1 ppm of zirconium and ruthenium was not detected in the solution.

[86]

[87] COMPARATIVE EXAMPLE 1

[88] The procedure of example 1 was repeated except that zirconia was used as a carrier to produce 3 wt% of ruthenium catalyst having 4% of ruthenium dispersion and 60 ppm of chlorine content. After the reaction was conducted for 100 hours, the average conversion of xylose was 80.0 % and the selectivity of xylitol was 99.8 %. The high purity of sugar alcohols was not obtained due to the low dispersion and it was required to recycle reaction since the production efficacy was low.

[89]

[90] COMPARATIVE EXAMPLE 2

[91] The procedure of example 1 was repeated except that ruthenium chloride was

uniformly supported, dried at 100 °C for 6 hours, and subsequently reduced at 350°C for 6 hours without washing to produce ruthenium catalyst of 3wt% having 30% of ruthenium dispersion and 1,000 ppm of chlorine content. After the reaction was conducted for 20 hours, the average conversion of xylose was 99.9 % and the selectivity of xylitol was 99.7 %. The catalyst was deactivated over time and the conversion of xylose was 95.5 % after 270 hours.

[92]

[93] COMPARATIVE EXAMPLE 3

[94] The procedure of example 1 was repeated except using catalyst with ruthenium dispersion of 3% and chlorine content of 70 ppm, in which 3wt% of ruthenium was dispersed in an alumina carrier having 85.3 % mesopores of 2 - 50 nm and 14.7 % macropores of 50 - 10,000 nm based on a pore volume thereof. After the reaction was conducted for 10 hours, the average conversion of xylose was 82.1 % and the selectivity of xylitol was 99.7 %. The catalyst was deactivated over time and the conversion of xylose was 72.1 % after 48 hours. After reaction, even 1 ppm of ruthenium was not detected. However, 60 ppm of aluminum was detected, so that it was assumed that the carrier component was dissolved during reaction.

[95]

[96] COMPARATIVE EXAMPLE 4

[97] The procedure of example 1 was repeated except that silica was used as a carrier to produce a 3 wt% ruthenium catalyst with ruthenium dispersion of 2.8 % and chlorine content of 50 ppm. After the reaction was conducted for 100 hours, the average conversion of xylose was 76.0 % and the selectivity of xylitol was 99.8 %. Production efficacy was decreased over the time due to the low dispersion. After reaction, even 1 ppm of ruthenium was not detected. However, 60 ppm of silicon was detected, so that it was assumed that the carrier component was dissolved during reaction.

[98]

Industrial Applicability

[99] As described above, in the present invention, sugar alcohol is selectively produced through a continuous process under moderate conditions of low temperature and pressure without dissolving catalyst component during the hydrogenation using a catalyst in which ruthenium is dispersed in a zirconia 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.

[100]