JPH02108682A - Production and concentration of furfural - Google Patents

Abstract

PURPOSE:To efficiently obtain highly concentrated furfural by extracting aqueous solution, etc., containing pentose such as xylose by using acid as catalyst and using supercritical fluid. CONSTITUTION:In a process producing furfural from aqueous solution containing pentose such as xylose or hemicellulose in plant body using acid as catalyst, a fluid having temperature and pressure exceeding critical temperature and critical pressure is made into contact with reacting liquid in reacting vessel and circulated, then furfural is extracted and recovered to outside of the reaction system. Preferably, the supercritical fluid containing furfural is circulated through a filling column having structure refluxing a part of concentrated liquid and the other concentrating column, thus concentration of furfural is enriched.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for efficiently producing and a-condensing furfural using a supercritical fluid in a furfural production process.

[Prior Art] A method for producing furfural from pentose or hemicellulose in vegetable matter using M as a catalyst is already known. In this process, the generated furfural is highly reactive, so it decomposes through side reactions or is consumed by forming condensates, resulting in a low yield. To prevent this, the concentration of furfural present in the reaction system must be reduced. It is necessary to reduce the reaction time or increase the reaction rate. Typical methods include (1) a method in which furfural is recovered together with the steam by blowing a large amount of steam into the reactor; (2)
A method of recovering furfural using an organic solvent with a high distribution ratio of furfural. (3) After reacting in a short time at high temperature using a back reactor, etc., the reaction solution is flashed and recovered together with water vapor. There are methods.

However, method (1) requires a large amount of water vapor, and the concentration of furfural in the recovered aqueous solution is low (usually on the order of several wt%), and in the vapor-liquid equilibrium of the furfural/water system, furfural is approximately 35 wt%. Since it has an azeotropic point and the difference from the boiling point of water is small, it also has the disadvantage that a large amount of thermal energy is required in the concentration process by azeotropic distillation.

Although the method (2) does not require latent heat during recovery, there are problems in that the solvent is expensive and that a large amount of thermal energy is required in the distillation process to separate the solvent and furfural.

Method (3) also has almost the same problem as (1).

[Problems to be Solved by the Invention] The present invention provides a method with low energy consumption and high yield in the process of producing furfural from an aqueous solution containing pentose such as xylose or hemicellulose in plants. Another object of the present invention is to provide an industrially advantageous method for concentrating an aqueous furfural solution to a high concentration.

As a result of extensive research into the furfural production process applying the supercritical extraction method, we have arrived at the present invention. [Means for solving the problems] That is, according to the present invention, an aqueous solution containing pentose or In the process of producing furfural from hemicellulose in plants, supercritical fluid is passed through one reactor to extract furfural, and furfural is recovered from the reaction system, resulting in a high yield and higher concentration than conventional methods. The present invention provides a method for obtaining furfural with less energy consumption and a method for efficiently recovering furfural from an aqueous furfural solution using a supercritical fluid.

Next, the production and concentration method of the present invention will be explained with reference to the drawings.

Figure 1 shows the vapor-liquid equilibrium of the furfural/water/supercritical carbon dioxide three-component system at a pressure of 200 kg/cn, and x - for the two components furfural/water excluding carbon dioxide.
It is shown in a y-diagram. A reactor was charged with pentose or hemicellulose and an acid as a catalyst, and the furfural production reaction was carried out at 140°C. Furfural was extracted by flowing supercritical carbon dioxide, and the furfural concentration in one reactor was maintained at 2 wt%. In this case, from Figure 1, the furfural concentration in the furfural/water binary component extracted into supercritical carbon dioxide is 38 wt% (this composition already exceeds the azeotropic composition of the furfural/water binary system). .

If this is introduced into a packed tower or other concentration tower whose top part is cooled to 80°C, and by applying appropriate reflux, the liquid phase composition in contact with supercritical carbon dioxide at the top part of the tower is maintained at 6 wt% or more.
Furfural with a concentration of 0 wt% or more can be obtained from the top of the tower. It is also possible to obtain even higher concentrations of almost anhydrous furfural by operating the condensation column at temperatures much lower than 80°C.

The furfural production reaction is carried out at 120 to 200°C, preferably 140°C or higher, and the pressure is 100 kg/cn when carbon dioxide is used as the supercritical fluid. Here,
Preferably it is 200 kg/- or more.

Fluids other than carbon dioxide can also be used as the supercritical fluid.

[Effects of the Invention] According to the present invention, high-concentration furfural can be efficiently recovered in the furfural production process without requiring a large amount of thermal energy unlike the conventional combination of steam blowing method and azeotropic distillation. Can be done.

In other words, since furfural is much easier to distribute into the supercritical fluid than water, furfural at a higher concentration can be recovered more efficiently than the steam injection method. Therefore, the concentration of furfural in the reaction solution can be kept low, side reactions can be prevented, and high yields can be obtained. Furthermore, by utilizing the vapor-liquid equilibrium characteristics of the supercritical fluid/furfural/water system and connecting a concentration column to a single reaction extractor, it is possible to recover furfural at a much higher concentration than in the distillation method. In the conventional method, in addition to using a large amount of steam by the steam blowing method, the resulting aqueous furfural solution of several wt% can only be concentrated to an azeotropic composition of about 35 wt% by azeotropic distillation, and the distillation column Since the temperature difference between the bottom and top of the column is only a few degrees Celsius, the concentration process also had the disadvantage of requiring a large amount of thermal energy, but the present invention eliminates these disadvantages and makes it possible to process furfural at a high concentration. can be obtained efficiently.

[Example] Next, the present invention will be explained in more detail with reference to Examples.

Example 1 At a temperature of 140°C, an IQ autoclave of 2.5
Pour 0.5Q of wt% furfural aqueous solution and pressure 10
The aqueous solution was extracted by passing 100 NQ of supercritical carbon dioxide at 0 to 200 kg/J, and the composition of the condensate obtained by reducing the pressure to atmospheric pressure and cooling was determined. The results are shown in FIG.

The higher the pressure, the higher the concentration of furfural obtained; 200
kg/(d) was about 35w%. This almost agrees with the vapor-liquid equilibrium 8111 constant result shown in Figure 1, and the concentration is nearly three times that of the steam injection method. It is clear that it can be extracted.

9
The furfural concentration after the reaction was 0.86 wt%, and the furfural yield was 49%.

Next, under the same conditions, 6 carbon dioxide was added at a pressure of 150 kg/Ci.
．． When the reaction was carried out for 4 hours by flowing from the bottom of the autoclave at a flow rate of 5 NQ/mjn, the furfural concentration in the reaction solution decreased to 0.4 wt% and the yield improved to 58%. In addition, the furfural concentration in the extract was 6.3w.
It was t%. The concentration of the recovered liquid when extracted by steam injection under these conditions is about 4 wt%.

From the above results, by extracting and recovering furfural produced using supercritical carbon dioxide, it is possible to maintain a low concentration of furfural in the reaction solution and improve the yield, as well as to increase the concentration of furfural in the reaction solution compared to the conventional method. It has become clear that it is possible to recover By increasing the extraction pressure to increase the extraction rate, and by appropriately selecting the reaction temperature, reactant concentration, acid concentration, acid type, etc., it is possible to recover even higher concentrations of furfural and further increase the yield. .

[Brief explanation of drawings]

Figure 1 shows a supercritical carbon dioxide/furfural/water ternary system at a pressure of 200 kg/aJ, a temperature of 80°C, and a temperature of 140"
The gas-liquid equilibrium relationship at C is shown as the relationship between the furfural concentration in the liquid phase excluding carbon dioxide and the gas phase. Figure 2 shows the furfural aqueous solution extracted using supercritical carbon dioxide at 140°C. This figure shows the relationship between extraction pressure and furfural concentration in the extract. Figure 1 Figure 2 Furfural concentration in liquid phase (wt%) (kg/a#)

Claims (4)

[Claims] (1) In the process of producing furfural from an aqueous solution containing pentoses such as xylose or from hemicellulose in plants using an acid as a catalyst, a fluid at a temperature and pressure exceeding the critical temperature and pressure (referred to as a supercritical fluid) is used. A method for producing furfural, which comprises extracting furfural by bringing it into contact with and circulating a reaction solution in a reactor and recovering it outside the reaction system. (2) A method for concentrating furfural, which comprises increasing the concentration of furfural by passing a supercritical fluid containing furfural through a packed tower having a structure in which a part of the concentrated liquid is refluxed or other concentration tower. (3) The method according to claim 2, characterized in that the concentration column is provided with a temperature gradient such that the temperature decreases from the bottom to the top of the column. (4) A method for producing and concentrating furfural, which is characterized by combining the method described in claim 1 with the method described in claim 2 or claim 3.