KR101192576B1 - Continuous Preparation Method for Furfural from Xylose - Google Patents

Abstract

The present invention relates to a method for producing furfural continuously produced from xylose, and specifically, by liquid phase dehydration reaction of xylose dissolved in a solvent using a continuous tubular reactor without using a heterogeneous catalyst. It can improve the selectivity of furfural, minimize the production of by-products during the reaction process, and obtain excellent economic effects.

Description

Continuous Preparation Method for Furfural from Xylose

The present invention relates to a method for producing furfural continuously produced from xylose.

Furfural (C ₅ H ₄ O ₂ ) is a typical liquid aromatic aldehyde, known as furan-2-carbaldehyde, fural or furfuraldehyde. Furfural is in itself a valuable end product and a very versatile product that is used as a precursor for spantex and as an intermediate for the synthesis of nylon, adhesives, pesticides and plastics.

In the commercial process, furfural can now be produced from natural compounds that are in competition with crude oil and has actually been produced from various agricultural organic waste since the 1920s. Theoretically, furfural is produced in a two-step process using a plant such as pentosan, for example, corn cob, as a raw material, and the reaction route may be represented by the following schemes (1) and (2).

[Reaction Scheme 1]

Pentosan + water → pentose (C ₅ H ₈ O ₄ ) _n + nH ₂ O → nC ₅ H ₁₀ O ₅

Scheme 2

Pentose → water + furfural (C ₅ H ₁₀ O ₅ ) → C ₅ H ₄ O ₂ + 3H ₂ O

In the case of the synthesis of furfural through the pathways according to Schemes 1 and 2, the diffusion of furfural from the solid substrate to the water is very slow, which leads to a long residence time in the reactor, resulting in a yield reduction reaction. Typical yield reduction reactions are the polymerization of furfural and the condensation of the precursor pentose. Side reactions in the process of decomposition from the substrate produce by-products such as acetaldehyde, ethanol, methanol, acetic acid, formic acid, 5-methylfurfural and furyl methyl ketone.

In addition, because the hydration reaction favors low temperatures while the dehydration reaction favors high temperatures for endothermic reactions, a process that improves reactivity and selectivity of furfural through sufficient temperatures, pressures and / or concentrations of xylose and acid catalysts. Development of the system is required.

Thus, dehydration from xylose to furfural can be prepared using an acid catalyst in liquid form and an acid catalyst in solid form in liquid phase. Typical examples are sulfuric acid, hydrochloric acid, hydrofluoric acid, acetic acid and phosphoric acid.

Batch or continuous processes may be used for furfural production, but batch processes based on Quaker Oats technology, developed in the 1920s, are employed. This batch process is known to be quite inefficient, the theoretical furfural yield is about 30-40%, the residence time in the reactor is quite long, 4.5-5.5 hours, and 50 MT of water per MT of furfural produced is required and a considerable amount of effluent. It is known to contain harmful substances. In addition, the cost of the operation is a significant disadvantage.

In order to overcome these shortcomings and to improve the yield, selectivity and stability of high products, continuous liquid phase processes have been developed.

US Pat. No. 6,642,396 describes a process for the production of furfural from lignosulfurate waste liquor including pentose. Sufficient time is maintained for converting pentose to furfural and includes maintaining a constant pressure state to eliminate reacting with pentose, lignosulfurate or furfural itself.

U. S. Patent No. 4,401, 514 discloses a continuous liquid phase process using an aqueous sulfite, acetic acid and formic acid solution as an acid catalyst in liquid form.

U.S. Patent No. 4,533,743 discloses a method for synthesizing furfural in a tubular reactor in a tubular reactor using mineral acids, such as sulfuric acid or hydrochloric acid at a concentration of 0.05-0.2 N.

However, the use of liquid acid catalysts generates process corrosion and acid waste, and it is difficult to separate and recover the acid catalyst and unreacted raw materials. In addition, the economic feasibility of the process is very weak due to the increase in the investment cost of the process equipment and the low product yield, and the environmental toxicity of the solvent, the complexity of the recovery and recycling process, and the like also become a problem in the process using the organic solvent.

Korean Patent No. 10-0295738 discloses a supercritical fluid process technology principle using an acid catalyst in a solid form, specifically, a supercritical carbon dioxide and a sulfated solid acid catalyst, specifically 0.1-10% by weight A method for synthesizing furfural in high yield in a high conversion region by using sulfurized modified titania, zirconia, alumina, clay catalyst, and the like containing sulfur is proposed.

However, when the reaction is performed using a solid acid, which is a heterogeneous catalyst, reactants, intermediate products, end products, and side reactants remain in the pore structure inside the catalyst used and shield the active point, thereby degrading the performance of the catalyst. .

As such, the catalyst system in the conventional liquid continuous process has a number of limitations to ensure the process economics. Therefore, there is an urgent need for measures to overcome these limitations.

The present invention is to provide a method for producing furfural continuously produced from xylose to improve the selectivity of furfural, minimize the production of by-products during the reaction process, and obtain an excellent economic effect.

In one embodiment of the present invention is a method for producing furfural using xylose, the aqueous solution containing the xylose in a liquid phase at a temperature of 190 to 210 ℃ and 2.5 to 6MPa under a catalyst It is a method for producing furfural comprising the step of dehydration reaction.

Another embodiment of the present invention is an aqueous solution containing xylose is a method for producing furfural having a pH of 5 to 9.

Another embodiment of the present invention is an aqueous solution containing xylose is a method for producing furfural having a concentration of xylose of 0.02 to 0.20M.

According to another embodiment of the present invention, after the liquid phase dehydration reaction of the aqueous solution containing xylose is terminated, a peak of xylose is measured in HPLC (High Performance Liquid Chromatography) measurement under the following analysis conditions. Only is a method for producing furfural which appears in 11.5 to 12.1 (min.).

<Analysis condition>

Column: Hi-Plex H, Temperature-60 ℃

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

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

Another embodiment of the present invention is a liquid dehydration reaction is a method for producing furfural carried out in a continuous tubular reactor.

Another embodiment of the present invention is a liquid space velocity (LHSV) of the aqueous solution containing xylose in the continuous tubular reactor is a method for producing furfural of 0.01 to 100 h ^-1 .

The method for producing furfural continuously produced from xylose according to the present invention selects furfural by performing liquid phase dehydration reaction of xylose dissolved in a solvent using a continuous tubular reactor without using a heterogeneous catalyst. It is possible to improve the efficiency, minimize the production of by-products during the reaction process, and obtain an excellent economic effect.

1 is a graph of HPLC analysis of an aqueous solution containing xylose after liquid phase dehydration reaction under a non-catalyst according to a preferred embodiment of the present invention.
2 is a graph of HPLC analysis of an aqueous solution containing xylose after liquid phase dehydration reaction under β-zeolite catalyst.

According to one embodiment of the present invention, in the method for producing furfural using xylose, the aqueous solution containing xylose is subjected to a temperature of 190 to 210 ° C. and a pressure of 2.5 to 6 MPa under a catalyst. It is to provide a method for producing furfural comprising the step of performing a liquid dehydration reaction under.

In the present invention, when xylose is used as a starting material and the liquid phase dehydration reaction is carried out in an aqueous solution without any heterogeneous catalyst in a continuous tubular reactor, high selectivity of xylose is achieved, especially in the course of the reaction. The production of by-products can be minimized.

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

If the reaction temperature is less than 190 ℃ reaction activity is low, the reaction time or contact time also increases, so the yield of furfural is lowered, and if it is above 220 ℃, the furfural selectivity is generated by the condensation reaction of furfural Since it is reduced, and the process pressure for maintaining the liquid phase is rapidly increased, it is advantageous to carry out the reaction within the above range to produce the desired furfural with high yield and high selectivity.

In order to maintain the liquid phase at the high temperature in the reactor in which the reaction proceeds, a pressure higher than the vapor pressure must be applied. When the reaction pressure is less than 2.5MPa, the liquid phase dehydration reaction does not occur. When the reaction pressure is more than 6MPa, the handling of the process is difficult, and it is preferable to carry out the reaction within the above range.

At this time, before the aqueous solution containing xylose is added to the high temperature reactor, the pretreatment step may be performed to heat the solution. The pretreatment process is to pre-treat by applying heat in advance in consideration that the temperature rise rate is low and the thermal conductivity does not occur sufficiently when the aqueous solution of room temperature in the high temperature reactor.

The temperature of the pretreatment step is preferably in the range of 100 to 140 ° C in that the aqueous solution must be sufficiently heated before the reaction.

The aqueous solution containing xylose is preferably in the range of 5 to 9, preferably 6 to 8 pH. If the pH is less than 5, the solvent used in the aqueous solution containing xylose increases the corrosiveness of the solvent, which requires the use of an expensive reactor, and additionally, waste acid treatment, and if the pH exceeds 9, the reactivity is remarkably high. There is a disadvantage of deterioration.

The aqueous solution containing xylose is preferably in the range of the concentration of xylose is 0.02 to 0.20M, preferably 0.1 to 0.10M. When the concentration of xylose is within the above range, it is advantageous in terms of selectivity of furfural, and the desired product furfural can be obtained at a high production rate. If the concentration of xylose is less than 0.02M is excessively expensive to separate the product is uneconomical, there is a disadvantage that the side reaction proceeds excessively if the concentration of xylose exceeds 0.20M.

After completion of the liquid dehydration reaction of the aqueous solution containing xylose, HPLC (High Performance Liquid Chromatography) measurement of the peak (xylose) peak only 11.5 to 12.1 (min.) Under the following analytical conditions Appears in the.

<Analysis condition>

Column: Hi-Plex H, Temperature-60 ℃

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

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

1 is a graph of HPLC analysis of an aqueous solution containing xylose after liquid phase dehydration reaction under a non-catalyst under the reaction conditions of a continuous process according to a preferred embodiment of the present invention.

<Continuous process reaction condition>

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

Reaction T = 200 ℃

Pressure = 3MPa, F _feed = 0.032ml / min

FIG. 2 is a graph of HPLC analysis of an aqueous solution containing xylose after liquid phase dehydration reaction under a β-zeolite (SiO ₂ / Al ₂ O ₃ = 25) catalyst under the reaction conditions of the following continuous process.

<Continuous process reaction condition>

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

Reaction T = 200 ℃

Pressure = 3MPa, F _feed = 0.032ml / min

Catalyst = 0.1 g β-zeolite (SiO ₂ / Al ₂ O ₃ = 25)

As shown in FIG. 1, it can be seen that the peak of xylose appears in the vicinity of 12 (min.) When the aqueous solution containing the xylose under the non-catalyst was subjected to liquid phase dehydration. However, as shown in FIG. 2, when the catalyst is used under the same conditions as in FIG. 1, it can be seen that a peak of lyxose, which is an isomer of furfural, appears in addition to the xylose peak.

Such lyxose appears when the reaction is carried out using a catalyst as a reaction by-product. When lyxose is produced, there are many problems because the selectivity of furfural and the increase of reaction time are required.

In the present invention, it is possible to obtain an effect of obtaining high-purity furfural without generating a reaction by-product such as lyxose by performing liquid phase dehydration reaction of an aqueous solution containing xylose under optimum reaction conditions without using a catalyst.

Dehydration of the liquid phase from the starting material xylose is preferably carried out in a continuous liquid phase, preferably in a continuous tubular reactor, in that the high selectivity of furfural is obtained, but is not limited thereto.

The continuous liquid space velocity (LHSV) of containing the xylose in the tubular reactor an aqueous solution that is from 0.01 to 100 h ^-1, preferably from 0.1 to 10h ^-1 is preferred.

The liquid space velocity is a value obtained by dividing the volume flow rate flowing into the inlet by the volume of the reactor. When the liquid space velocity is less than 0.01 h ^-1, it is difficult to secure economic feasibility due to a very low space velocity, and when the liquid space velocity exceeds 100 h ^-1 , the conversion rate is very low, resulting in excessive cost in the separation process.

On the other hand, preferred specifications in the application of the furfural production method according to the invention are as follows. However, the present invention is not limited thereto.

Typically, in order to maximize the yield of furfural, the reaction may be performed while removing by-products such as acetaldehyde, ethanol, methanol, acetic acid, formic acid, 5-methylfurfural, and furyl methyl ketone to the outside of the reaction system. A method of adjusting the equilibrium constant of Scheme 2 (see Background of the Invention), a known method, to advance the equilibrium towards producing furfural can be applied in the present invention. In this case, the selectivity of furfural may be increased by using a hydrophobic solvent, specifically toluene, in addition to water as a solvent used as an aqueous solution containing xylose.

The method for producing furfural described above proceeds in a continuous tubular reactor without any heterogeneous catalyst under the conditions of pH 5-9 of the reactants, which is a reactor corrosion, environmental pollution, and recycling of the liquid acid catalyst, which has been reported in the prior art. The complexity of the process and the difficulty of catalyst reactivation and catalyst regeneration of the solid acid catalyst can be overcome. Compared with the catalyst, improved furfural selectivity can be achieved at a relatively low reaction temperature range, and in particular, the production of by-products can be minimized during the reaction.

In particular, the method for producing furfural according to the present invention can obtain the effect of increasing the selectivity of furfural. Specifically, the conversion rate of xylose and the selectivity of furfural are measured as a measure for evaluating the synthesis result of furfural. You see two elements. The conversion rate of xylose refers to the measure of how much of the aqueous solution of xylose supplied to the system is converted to other products. Selectivity of furfural means to represent the ratio of furfural in the product produced in the aqueous solution of xylose.

_Xylose conversion (X _Xylose ) and furfural selectivity (S _Furfural ) can be obtained by calculating the following equations (1) and (2).

<Formula 1>

X _Xylose = (C _{Xylose , in} ? C _{Xylose , out} ) ÷ C _{Xylose , in}

S _Furfural = C _Furfural ÷ (C _{Xylose , in} ? C _{Xylose , out} )

( _{Wherein ,} C _{Xylose , in} Is the initial concentration of xylose, C _{Xylose , out} is the concentration of xylose after the reaction, and C _Furfural is the concentration of furfural after the reaction.)

By changing the reaction conditions, the use of a catalyst, the conversion of xylose can be easily controlled. However, the product resulting from the xylose conversion contains several other products in addition to furfural. Therefore, the selectivity of the furfural is more important than the conversion rate of xylose in the selective production of high purity furfural. In the present invention, it is possible to obtain the effect of improving the selectivity of the furfural by the above-described manufacturing method.

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

Example  One

A stainless steel tubular reactor having a length of 15.2 cm and an inner diameter of 5.5 mm was operated under a pressure of 3 MPa. This reactor is located perpendicular to the furnace maintained at the reaction temperature. An aqueous solution containing 0.2 M of xylose (hereinafter referred to as 'reactant') was maintained at a volume flow rate of 0.016 ml / min (space velocity 0.266 h ⁻¹ ). The reactants were allowed to be maintained at a temperature of at least 140 ° C. before passing through the reactor in order to proceed uniformly at the reactor temperature. The molar flow rate of the xylose was maintained to be 192 μmol · h ⁻¹ . The duration of the reaction experiment was about 3 days, and samples were collected at about 8 hour intervals. After the reaction was completed, the product was subjected to a dehydration reaction of xylose through the recovery process through a trap maintained at a temperature of 20 ℃, the results are shown in Table 1 below.

Reaction temperature (℃) Xylose Conversion Rate (%) Furfural Selectivity (%) 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 was carried out in the reaction conditions of xylose concentration of 0.2M in the reaction, the conversion of xylose increased with increasing reaction temperature. In addition, as the reaction temperature increases, the selectivity of xylose increases, but it can be seen that the selectivity of xylose increases significantly at 190 ° C. However, after 220 ℃ it can be seen that the selectivity of furfural is significantly reduced, it is due to the polymerization of furfural.

From this, it was found that the optimum temperature range is 190 to 210 ° C. when the aqueous solution containing xylose is subjected to liquid dehydration reaction under a non-catalyst.

Example  2

The furfural was synthesized by performing the xylose dehydration reaction in the same manner as in Example 1, except that the reactant having a 0.2M xylose concentration condition was changed to a volume flow rate of 0.032 ml / min (space velocity 0.532h ⁻¹ ). The method was performed. The molar flow rate of xylose was maintained to be 384 mol · h ⁻¹ . The results are shown in Table 2 below.

Reaction temperature (℃) Xylose Conversion Rate (%) Furfural Selectivity (%) 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

As shown in Table 2, it was found that the selectivity of xylose was excellent in the temperature range of 190 to 210 ℃ to the same level as in Table 1.

Example  3

A method of synthesizing furfural by proceeding the xylose dehydration reaction at 200 ° C. in the same manner as in Example 1 except for changing the concentration condition of xylose in the reactant and changing the volume flow rate to 0.032 ml / min. Was performed. The results are shown in Table 3 below.

Xylose concentration (M) Xylose Conversion Rate (%) Furfural Selectivity (%) 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

As shown in Table 3, as the concentration of xylose increases, the conversion rate of xylose increases, but it can be seen that the selectivity decreases, in particular, that the selectivity of xylose rapidly decreases after 0.50M. there was.

From this, it was found that the optimum concentration of xylose was 0.01 to 0.20 M when the aqueous solution containing xylose was subjected to liquid dehydration reaction under a non-catalyst.

Example  4

The xylose dehydration reaction was carried out at 200 ° C. in the same manner as in Example 1 except that the pH of the reactant was changed to pH using a diluted sulfuric acid solution or an aqueous ammonia solution and the volume flow rate was changed to 0.032 ml / min. A method of synthesizing fural was performed. The results are shown in Table 4 below.

PH of the reactants Xylose Conversion Rate (%) Furfural Selectivity (%) 6 (acetic acid) 63.20 57.87 7 60.03 63.81 8 (ammonia solution) 62.17 59.09

As shown in Table 4, it was found that the conversion level of xylose and selectivity of furfural were excellent in the range of pH 6 to 7, especially pH 7, at the same level as Tables 1 to 3.

Comparative example  One

30 ml of 0.2 M aqueous xylose solution was added to a 100 ml batch reactor, and the mixture was poured into the reactor with nitrogen for 10 minutes to carry out the reaction in an inert atmosphere. Based on the room temperature, the pressure was carried out under atmospheric pressure, and the effect on the reaction temperature was analyzed. The results are shown in Table 5 below.

Reaction temperature (℃) Xylose Conversion Rate (%) Furfural Selectivity (%) 160 14.54 51.83 180 42.05 59.32 220 97.85 48.10

As shown in Table 5, when compared with the results at the same reaction temperature in the liquid-phase continuous tubular reaction of 0.2M aqueous solution of xylose of Table 1 in Example 1, it can be seen that the furfural selectivity is reduced.

Except for changing the concentration of the reactants Xylose dehydration was carried out in the same manner as in Comparative Example 1 for 1 hour at 200 ℃ to perform a method for synthesizing furfural. The results are shown in Table 6 below.

Reaction concentration (M) Xylose Conversion Rate (%) Furfural Selectivity (%) 0.2 83.93 60.05 0.4 87.10 57.95 0.6 87.14 57.61

As shown in Table 6, it can be seen that the selectivity of furfural decreases with increasing concentration, similar to the result of the liquid phase continuous tubular reaction of the aqueous solution of xylose of Table 3 in Example 3. In addition, when compared with the results of the continuous tubular reaction, it was confirmed that the conversion of xylose was high while the selectivity was lowered.

Except for changing the use of the catalyst and the reaction temperature, the xylose dehydration reaction was performed for 1 hour in the same manner as in Comparative Example 1 to perform furfural synthesis. 0.3 g of β-zeolite (SiO ₂ / Al ₂ O ₃ = 25) was used as a catalyst and the results are shown in Table 7 below.

Reaction temperature (℃) Xylose Conversion Rate (%) Furfural Selectivity (%) 170 90.20 44.00 200 96.65 44.69

As shown in Table 7, the use of the catalyst increases the conversion of xylose, but it can be seen that the selectivity of furfural decreases due to other side reactions.

From the results of the above examples and comparative examples, it was confirmed that when furfural was prepared by reacting in an aqueous solution without any catalyst in a continuous tubular reactor, xylose selectivity was higher than that of a batch reactor.

All simple modifications or changes of the present invention can be easily carried out by those skilled in the art, and all such modifications or changes can be seen to be included in the scope of the present invention.

Claims (6)

A method for producing furfural using xylose, the method comprising: liquid-dehydrating a reaction of the xylose-containing aqueous solution under a catalyst at a temperature of 190 to 210 ° C. and a pressure of 2.5 to 6 MPa. Method for producing furfural. The method of claim 1, wherein the aqueous solution containing xylose has a pH of 5 to 9. The method according to claim 1, wherein the aqueous solution containing xylose has a concentration of xylose of 0.02 to 0.20M. According to claim 1, After the liquid phase dehydration reaction of the aqueous solution containing xylose, when the HPLC (High Performance Liquid Chromatography) measurement under the following analysis conditions only peaks of xylose (xylose) 11.5 To 12.1 (min.) A process for producing furfural.
<Analysis condition>
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 for preparing furfural according to claim 1, wherein the liquid phase dehydration reaction is carried out in a continuous tubular reactor. The method according to claim 5, wherein the liquid space velocity (LHSV) of the aqueous solution containing xylose in the continuous tubular reactor is 0.01 to 100 h ⁻¹ .

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