WO2012074190A1

WO2012074190A1 - Continuous preparation method for furfural from xylose

Info

Publication number: WO2012074190A1
Application number: PCT/KR2011/007094
Authority: WO
Inventors: Ki Hyun Park; Hyo Kyu Lee; Sang Min Lee; Sung Rak Joo; Saet Byul Kim; Eun Duck Park
Original assignee: Kolon Industries, Inc.
Priority date: 2010-11-30
Filing date: 2011-09-27
Publication date: 2012-06-07
Also published as: CN103339119B; CN103339119A; KR20120059251A; KR101192576B1

Abstract

Disclosed is a method for preparing furfural continuously prepared from xylose. In detail, the method for preparing furfural continuously prepared from xylose according to the exemplary embodiments of the present invention can improve the selectivity of furfural, minimize the generation of by-products during the reaction process, and obtain the excellent economic efficiency by performing the liquid-phase dehydration reaction on the xylose melted in the solvent using the continuous tubular reactor without using the heterogeneous catalyst.

Description

CONTINUOUS PREPARATION METHOD FOR FURFURAL FROM XYLOSE

The present invention relates to a continuous preparation method for furfural from xylose.

Furfural (C₅H₄O₂), which is typical liquid aromatic aldehyde, is known as furan-2-carbaldehyde, fural or furfuraldehyde. The furfural itself has a value as a final product and has very high applicability. As a result, the furfural has been used as precursor and nylon of spandex, an adhesive, a pesticide, and synthetic polymers, or the like.

Using a commercial process, the furfural can be prepared from a natural material compound that is currently in competition with crude oil, or the like. Actually, the furfural has been prepared from various organic farming wastes since 1920. In theory, the furfural is prepared using plants containing pentosan, for example, corn cob, as a raw material through a two-stage process and a reaction path may be represented by reaction equations 1 and 2.

[Reaction Equation 1]

Pentosan + water → pentose (C₅H₈O₄)n + nH₂O → nC₅H₁₀O₅

[Reaction Equation 2]

Pentose → water + furfural (C₅H₁₀O₅) → C₅H₄O₂ + 3H₂O

In the case of synthesizing the furfural through a path through reaction Equations 1 and 2, the diffusion of furfural from a solid matrix to water is very slow and thus, residence time in a reactor is long, thereby causing yield reduction reaction. A representative example of yield reduction reaction may include polymerization reaction of furfural and condensation reaction with pentose that is a precursor. By-products such as acetaldehyde, ethanol, methanol, acetic acid, formic acid, 5-methylfurfural, furyl methyl ketone are generated due to side reaction during a decomposition process from a matrix.

In addition, since hydration reaction prefers low temperature but dehydration reaction as endothermic reaction prefers high temperature, there is a need to develop a process system capable of improving reactivity and selectivity of furfural using sufficient temperature, pressure, and/or concentration of xylose, and an acid catalyst

Therefore, the dehydration from the xylose to the furfural may be prepared using a liquid-type acid catalyst and a solid-type acid catalyst in a liquid phase. A representative example may include sulfuric acid, hydrochloric acid, hydrofluoric acid, acetic acid, phosphoric acid, or the like.

A method for preparing furfural may use a batch process or a continuous process but adopts the batch process based on a Quaker Oats technology developed in 1920. The batch process is known to be significantly inefficient. That is, the theoretical furfural yield is about 30 to 40%, the residence time in the reactor is significant long as 4.5 to 5.5 hours, water of 50MT per 1MT of furfural is consumed, and a significant amount of harmful substance is included in effluents. In addition, costs consumed for working are considerably increased.

In order to overcome the disadvantages and increase the yield, selectivity, and stability of products, a continuous liquid phase process has been developed.

US Patent No. 6,642,396 describes a process of preparing furfural from lignosulfonate waste liquid containing pentose. The pressure state is constantly maintained so as to maintain a sufficient time for converting the pentose into the furfural and remove the reaction with the pentose, the lignosulfonate, or the furfural itself.

US Patent No. 4,401,514 discloses a continuous liquid phase process using sulfite, acetic acid, and a formic acid aqueous solution as the liquid-type acid catalyst.

US Patent No. 4,533,743 discloses a method for synthesizing the furfural within a temperature of 220 to 300℃ in a tubular reactor by using mineral acid, for example, sulfuric acid, hydrochloric acid, or the like, of, for example, a concentration of 0.05 to 0.2 N.

However, when using the liquid acid catalyst, the process corrosion and the acid wastes are generated, such that it is difficult to separate, recover, and recycle a non-reactive raw material and the acid catalyst. Further, the economic efficiency of the process may be very vulnerable according to the increase in investment costs of process facility and low product yield and environmental toxicity, recovery, and recycle may be complicated even in the process of using an organic solvent.

KR Patent No. 10-0295738 discloses a supercritical fluid process technology principle using the sold-type acid catalyst. In detail, KR Patent No. 10-0295738 discloses a method for synthesizing the furfural at high yield in a high conversion yield area by using supercritical carbon dioxide and sulfated solid acid catalyst, in detail, sulfation reformed titania containing 0.1 to 10 wt% of sulfur, zirconia, alumina, clay catalyst, or the like.

However, when the reaction is performed by using the solid acid that is a heterogeneous catalyst, the performance of the catalyst is degraded by staying a reactant, intermediate products, final products, and side reactants in a pore structure in the used catalyst and shielding an active point.

As such, the catalyst system in the continuous liquid phase process of the related art has a big limitation to secure the economic efficiency in the process. Therefore, a method for overcoming the limitation is urgently needed.

An object of the present invention is to provide a continuous preparing method of furfural continuously prepared from xylose capable of improving selectivity of furfural, minimizing generation of by-products during a reaction process, and obtaining excellent economic efficiency.

An exemplary embodiment of the present invention, there is provided a method for preparing furfural using xylose, including: performing liquid phase dehydration reaction on an aqueous solution containing the xylose under a temperature of 190 to 210℃ and a pressure of 2.5 to 6 MPa without using a catalyst.

The aqueous solution containing the xylose may have pH of 5 to 9.

The aqueous solution containing the xylose may have a concentration of xylose of 0.02 to 0.20 M.

After the aqueous solution containing the xylose is subjected to the liquid phase dehydration reaction, only a peak of xylose may be shown in 11.5 to 12.1 min at the time of a measurement of high performance liquid chromatography (HPLC) under the following analysis conditions.

Column: Hi-Plex H, Temperature-60℃

Refractometer Detector: Sensitivity-512, Temperature-40℃, Filter factor-1

Wavelength Absorbance Detector: Wavelength-280 nm, Sensitivity-2

The liquid phase dehydration reaction may be performed in a continuous tubular reactor.

A liquid hour space velocity (LHSV) of the aqueous solution containing the xylose in the continuous tubular reactor may be in 0.01 to 100 h^-1.

As set forth above, the method for preparing furfural continuously prepared from xylose according to the exemplary embodiments of the present invention can improve the selectivity of furfural, minimize the generation of by-products during the reaction process, and obtain the excellent economic efficiency by performing the liquid-phase dehydration reaction of the xylose dissolved in the solvent using the continuous tubular reaction without using the heterogeneous catalyst.

FIG. 1 is a graph analyzing an aqueous solution containing xylose after performing liquid phase dehydration reaction without using a catalyst according to an exemplary embodiment of the present invention using HPCL.

FIG. 2 is a graph analyzing an aqueous solution containing xylose after the liquid phase dehydration reaction with a β-zeolite catalyst using HPLC.

The foregoing and additional aspects of the exemplary embodiment of the present invention will be more apparent through exemplary embodiments of the present invention described with reference to the accompanying drawings. Hereinafter, the exemplary embodiments of the present invention will be described in detail so as to be easily understood and reproduced by a person skilled in the art to which the present invention pertains.

According to an exemplary embodiment of the present invention, a method for preparing furfural using xylose includes performing liquid phase dehydration reaction on an aqueous solution containing the xylose under a temperature of 190 to 210℃ and a pressure condition of 2.5 to 6 MPa without using a catalyst.

When the exemplary embodiment of the present invention performs the liquid phase dehydration reaction in the aqueous solution without any heterogeneous catalyst in a continuous tubular reactor using the xylose as a starting material, it can achieve higher selectivity of xylose than using a batch reactor, in particular, minimize generation of by-products during a reaction process.

The liquid phase dehydration reaction is performed under a temperature of 190 to 210℃ and a pressure condition of 2.5 to 6 MPa.

When the reaction temperature is less than 190℃, reaction activity is low and reaction time and contact time are also increased, thereby a yield of furfural is degraded. When the reaction temperature exceeds 210℃, condensation reaction of furfural is generated, thereby reducing the selectivity of furfural and suddenly increasing the process pressure so as to maintain the liquid phase. As a result, performing the reaction within the range is advantageous in preparing the furfural that is a targeted object at high yield and high selectivity.

Since a pressure above a vapor pressure is applied so as to maintain the liquid phase at high temperature within the reactor performing the reaction, when the reaction pressure is below 2.5 MPa, the liquid phase dehydration reaction does not generated and when the reaction pressure exceeds 6 MPa, it is difficult to handle the process. As a result, it is preferable to perform the reaction within the range.

In this case, a pre-treatment process, performing heating treatment of the aqueous solution containing the xylose before it is added to a high-temperature reactor may be performed. The pre-treatment process is to apply heat in advance in consideration of a condition in which a heating rate is slow and sufficient heat conduction is not generated when a room-temperature aqueous solution is added within the high-temperature reactor.

It is preferable that the temperature of the pre-treatment process is in the range of 100 to 140℃ in that the aqueous solution before the reaction needs to be sufficiently heated.

It is preferable that the aqueous solution containing the xylose has pH that is in a range of 5 to 9, preferably, 6 to 8. When the pH is less than 5, a high-price reactor needs to be used and a waste acid treatment needs to be additionally performed because the corrosivity of the aqueous solution is increased. In addition, when the pH exceeds 9, the reactivity may be remarkably degraded.

It is preferable that a concentration of the aqueous solution containing the xylose is in the range of 0.02 to 0.20 M, preferably, 0.1 to 0.10 M. When the concentration of xylose is in the range, the selectivity of furfural is advantageous and the furfural that is a targeted object can be obtained at a high generation rate. When the concentration of xylose is less than 0.02 M, cost to separate products may be excessively consumed and when the concentration of xylose exceeds 0.20M, the side reaction may be excessively performed.

After the liquid phase dehydration reaction is terminated, the aqueous solution containing the xylose, the high performance liquid chromatography (HPLC) under the following analysis conditions is performed and only a peak of the xylose is shown in 11.5 to 12.1 min at the time of the measurement of the HPLC.

Column: Hi-Plex H, Temperature-60℃

Refractometer Detector: Sensitivity-512, Temperature-40℃, Filter factor-1

Wavelength Absorbance Detector: Wavelength-280 nm, Sensitivity-2

FIG. 1 is a graph analyzing the aqueous solution containing the xylose after performing the liquid phase dehydration reaction without using a catalyst under the continuous process reaction conditions according to an exemplary embodiment of the present invention using the HPCL.

D-xylose concentration=0.2M, Preheating T=140℃

Reaction T=200℃

Pressure=3MPa, F_feed=0.032ml/min

FIG. 2 is a graph analyzing the aqueous solution containing the xylose after the liquid phase dehydration reaction with a β-zeolite (SiO₂/Al₂O₃=25) catalyst under the following continuous process reaction conditions using the HPLC.

D-xylose concentration=0.2M, Preheating T=140℃,

Reaction T=200℃

Pressure=3MPa, F_feed=0.032ml/min

Catalyst=0.1g β-zeolite(SiO₂/Al₂O₃=25)

It can be appreciated from FIG. 1 that the peak of xylose is shown near 12 min. when the liquid phase dehydration reaction is performed on the aqueous solution containing the xylose without the catalyst. However, it can be appreciated from FIG. 2 that a peak of lyxose that is an isomer of the furfural other than the peak of xylose is shown when the same conditions as FIG. 1, excepting the catalyst is used, are performed with the catalyst.

The lyxose is shown as the reaction by-products when the reaction is performed using the catalyst. When the lyxose is generated, many problems such as the reduction in selectivity of furfural and the increase in reaction time may occur.

The exemplary embodiment of the present invention can obtain the high-purity furfural without generating the reaction by-products such as the lyxose by performing the liquid phase dehydration reaction on the aqueous solution containing the xylose under the optimal reaction conditions without using the catalyst.

The liquid phase dehydration reaction that is dehydrated from the starting material, that is, the xylose is performed in the continuous liquid phase, preferably, the continuous tubular reactor, thereby obtaining the high selectivity of furfural, but is not limited thereto.

Liquid hour space velocity (LHSV) of the aqueous solution containing the xylose within the continuous tubular reaction may be 0.01 to 100 h^-1, preferably, 0.1 to 10 h^-1.

The liquid hour space velocity is a value obtained by dividing a volume flow rate introduced into an inlet by a volume of the reactor. When the liquid hour space velocity is less than 0.01 h^-1, it is difficult to secure the economic efficiency due to very low space velocity and when the liquid hour space velocity exceeds 100 h^-1, a conversion rate is very low and thus, cost consumed for the separation process is excessively increased.

Meanwhile, in applying the method for preparing furfural according to the exemplary embodiment of the present invention, the preferred specifications are as follows. However, the exemplary embodiment of the present invention is not limited thereto.

Generally, in order to maximally increase the yield of furfural, the reaction may be performed while removing by-products such as acetaldehyde, ethanol, methanol, acetic acid, formic acid, 5-methylfurfural, furyl methyl ketone from the reactor. The known method, that is, the method of progressing balance toward generating furfural by controlling a equilibrium constant of Equation 2 (see the background art of the present invention) may be applied to the exemplary embodiment of the present invention. In this case, the selectivity of furfural may be increased using a hydrophobic solvent in addition to water, in detail, toluene as a part of　the　solvent of　the aqueous solution containing　the xylose.

The above-mentioned method for preparing furfural performs the reaction under the conditions in which pH of the reactant is 5 to 9 without using any heterogeneous catalyst within the continuous tubular reactor, which may result in overcoming reactor corrosion due to the liquid phase acid catalyst, environmental pollution, complexity of a recycle process, non-activity of the catalyst due to the solid acid catalyst, difficulty due to a catalyst recycle that have been reported from the past. By using the catalyst, the high selectivity of furfural may be achieved at a relative lower reaction temperature range, in particular, the generation of by-products during the reaction process may be minimized.

In particular, the method for preparing furfural according to the exemplary embodiment of the present invention can increase the selectivity of furfural. Describing this in detail, as a measure of evaluating the synthesis results of furfural, there are two factors such as the conversion rate of xylose and the selectivity of furfural. The conversion rate of xylose means a measure on how much the xylose aqueous solution supplied to the system is converted into other products. The selectivity of furfural means a ratio of furfural among products generated in the xylose aqueous solution.

The conversion rate (X_Xylose) of xylose and the selectivity (S_Furfural) of furfural may be obtained by calculation as the following Equations 1 and 2.

X_Xylose = (C_Xylose,_in ― C_Xylose,_out )÷C_Xylose,_in

S_Furfural= C_Furfural ÷ (C_Xylose,in ― C_Xylose,_out )

(In Equation, C_Xylose,_in is an initial concentration of xylose, C_Xylose,_out is a concentration of xylose after the reaction, and C_Furfural is a concentration of furfural after the reaction)

The conversion of xylose may be easily controlled by the change in reaction conditions, the use of catalyst, or the like. However, several kinds of other products in addition to the furfural are included in the products due to the conversion of xylose. Therefore, the selectivity of furfural is more important than the conversion rate of xylose in that the high-purity furfural is selectively prepared. In the exemplary embodiment of the present invention, the selectivity of furfural can be improved by the above-mentioned preparing method.

Hereinafter, preferred examples of the present invention and comparative example will be described. However, the following examples are only the preferred examples of the present invention and therefore, the present invention is not limited to the following examples.

Example 1

The reaction was performed at a pressure of 3 MPa in the tubular reactor made of a stainless material and having a length of 15.2 cm and an inner diameter of 5.5 mm. The reactor was vertically disposed in a heating furnace maintained at the reaction temperature. The aqueous solution (hereinafter, referred to as 'reactant') containing the xylose of 0.2 M was maintained so as to have a volume flow rate of 0.016 ml/min (space velocity 0.266h^-1). In order to perform the uniform reaction on the products at the temperature of the reactor, the reactor was maintained at a temperature of at least 140℃ prior to passing through the reactor. A molar flow rate of xylose was maintained so as to be 192μmol·h^-1. The duration time of the reaction experiment was about 3 days and the sample was recovered at an interval of about 8 hours. The products after the reaction is performed were subjected to the dehydration reaction of xylose by the recovering process through a trap maintained at a temperature of 20℃. The results are shown in the following Table 1.

Table 1

Reaction Temperature (℃)	Conversion Rate of xylose (%)	Selectivity of furfural (%)
140	19.53	48.30
150	22.89	55.86
160	27.84	56.28
170	34.38	62.56
180	44.92	65.69
190	55.34	73.67
200	66.59	79.28
210	77.36	66.99
220	88.14	60.40
230	89.51	54.11
240	97.27	43.92

As shown in Table 1, when the experiment is performed under the concentration conditions of xylose of 0.2 M within the reactant, the conversion rate of xylose was increased according to the increase in the reaction temperature. In addition, it could be appreciated that the selectivity of xylose was increased according to the increase in the reaction temperature and when the reaction temperature is 190℃, the selectivity of xylose was remarkably increased. However, it could be appreciated that over 220℃, the selectivity of furfural was remarkably reduced, which depends on the polymerization reaction of furfural.

From this, it could be appreciated that when the aqueous solution containing the xylose is subjected to the liquid phase dehydration reaction without using a catalyst, the optimal temperature range was in 190 to 210℃.

Example 2

The method for synthesizing furfural was performed by performing the dehydration reaction of xylose in the same method as Example 1 other than the volume flow rate of reactant is changed to 0.032 ml/min (space velocity 0.532h^-1), which is the concentration condition of xylose of 0.2 M. A molar flow rate of xylose was maintained so as to be 384mol·h^-1. The results were shown in the following Table 2.

Table 2

Reaction Temperature (℃)	Conversion Rate of xylose (%)	Selectivity of furfural (%)
190	45.04	62.06
195	49.86	62.67
200	50.29	81.64
205	57.05	73.66
210	62.80	75.21

It could be appreciated from Table 2 that the selectivity of xylose is excellent at the same level as Table 1 within a temperature range of 190 to 210℃.

Example 3

Except that the concentration conditions of xylose are different within the reactant and the volume flow rate is changed to 0.032 ml/min, the method for synthesizing furfural was performed by performing the dehydration reaction of xylose at 200℃ by the same method as Example 1. The results were shown in the following Table 3.

Table 3

Concentration of xylose (M)	Conversion of xylose (%)	Selectivity of furfural (%)
0.01	46.81	100.00
0.02	57.39	86.92
0.05	56.75	75.35
0.10	58.65	64.53
0.15	57.78	66.81
0.20	60.03	63.81
0.50	64.15	52.15
1.00	64.21	41.35

It could be appreciated from Table 3 that the conversion rate of xylose was increased with the increase in the concentration of xylose but the selectivity was reduced, in particular, the selectivity of xylose was suddenly degraded over 0.50 M.

From this, it could be appreciated that when the aqueous solution containing the xylose is subjected to the liquid phase dehydration reaction without using a catalyst, the optimal concentration range of xylose was in 0.01 to 0.20 M.

Example 4

Except that the pH of the reactant is different using a diluted sulfuric acid solution or an ammonia solution and the volume flow rate thereof is changed to 0.032 ml/min, the method for synthesizing furfural was performed by performing the dehydration reaction of xylose at 200℃ by the same method as Example 1. The results were shown in the following Table 4.

Table 4

pH of Reactant	Conversion rate of xylose (%)	Selectivity of furfural (%)
6(acetic acid)	63.20	57.87
7	60.03	63.81
8(ammonia solution)	62.17	59.09

It could be appreciated from Table 4 that the conversion rate of xylose and the selectivity of furfural are excellent in a range of pH of 6 and 7, in particular, pH of 7 at the same level as Tables 1 to 3.

Comparative Example 1

The reaction was performed in inactive atmosphere by introducing 30 ml of aqueous solution of xylose of 0.2 M into the batch reactor having 100 ml capacity and nitrogen into the reactor for 10 minutes. The pressure was performed under the atmosphere based on normal temperature and the influence on the reaction temperature was analyzed. The results were shown in the following Table 5.

Table 5

Reaction Temperature (℃)	Conversion Rate of xylose (%)	Selectivity of furfural (%)
160	14.54	51.83
180	42.05	59.32
220	97.85	48.10

It could be appreciated from Table 5 that the selectivity of furfural was degraded, when comparing with the results at the same reaction temperature at the liquid phase continuous tubular reaction of the aqueous solution of xylose of 0.2 M of Table 1 in Example 1.

Except that the concentration of reactants is changed, the method for synthesizing furfural was performed by performing the dehydration reaction of xylose at 200℃ for 1 hour by the same method as Comparative Example 1. The results were shown in the following Table 6.

Table 6

Reaction Concentration (M)	Conversion Rate of xylose (%)	Selectivity of furfural (%)
0.2	83.93	60.05
0.4	87.10	57.95
0.6	87.14	57.61

It could be appreciated from Table 6 that as the concentration was increased, the selectivity of furfural was reduced, similar to the results of the liquid phase continuous tubular reaction of the aqueous solution of xylose of Table 3 in Example 3. In addition, comparing with the results of the continuous tubular reaction, it was confirmed that the conversion rate of xylose was increased, while the selectivity thereof was degraded.

Except that the use of the catalyst and the reaction temperature were changed, the method for synthesizing furfural was performed by performing the dehydration reaction of xylose for 1 hour by the same method as Comparative Example 1. 0.3g of β-zeolite(SiO₂/Al₂O₃=25) was used as the catalyst and the results were shown in the following Table 7.

Table 7

Reaction Concentration (℃)	Conversion Rate of xylose (%)	Selectivity of furfural (%)
170	90.20	44.00
200	96.65	44.69

It could be appreciated from Table 7 that the use of catalyst increased the conversion rate of xylose or the selectivity of furfural was reduced due to other side reactions.

From the examples and the comparative examples, it could be appreciated that when the furfural was prepared by performing the reaction on the aqueous solution without using any catalyst in the continuous tubular reactor, the higher selectivity of xylose as compared with using the batch reactor was shown.

In addition, although exemplary embodiments of the present invention have been illustrated and described, the present invention is not limited to the above-mentioned embodiments and various modified embodiments can be made by those skilled in the art within the scope of the appended claims of the present invention. In addition, these modified embodiments should not be seen as separate from the technical spirit or prospects outlined herein.

Claims

A method for preparing furfural using xylose, comprising:

performing liquid phase dehydration reaction on an aqueous solution containing the xylose under a temperature of 190 to 210℃ and a pressure of 2.5 to 6 MPa without using a catalyst.
The method of claim 1, wherein the aqueous solution containing the xylose has pH of 5 to 9.
The method of claim 1, wherein the aqueous solution containing the xylose has a concentration of xylose of 0.02 to 0.20 M.
The method of claim 1, wherein after the aqueous solution containing the xylose is subjected to the liquid phase dehydration reaction, only a peak of xylose is shown in 11.5 to 12.1 min at the time of a measurement of high performance liquid chromatography (HPLC) under the following analysis conditions.

<Analysis Conditions>

Column: Hi-Plex H, Temperature-60℃

Refractometer Detector: Sensitivity-512, Temperature-40℃, Filter factor-1

Wavelength Absorbance Detector: Wavelength-280 nm, Sensitivity-2
The method of claim 1, wherein the liquid phase dehydration reaction is performed in a continuous tubular reactor.
The method of claim 5, wherein a liquid hour space velocity (LHSV) of the aqueous solution containing the xylose in the continuous tubular reactor is in 0.01 to 100 h^-1.