KR20000019598A - Process of changing microscopic structure of cellulosic materials by multiple explosion treatments with supercritical carbon dioxide - Google Patents

Abstract

PURPOSE: A process for changing the structure of all cellulosic materials, including cellulosic material having a high alpha-fraction is provided which enhances its affinity to the processing solvents or the reactants without using expensive and/or corrosive chemicals and with less loss of molecular weight and provides raw material for producing sugars and alcohols. CONSTITUTION: A process for changing the structure of all cellulosic materials, including the cellulosic materials having a high alpha-fraction to enhance its affinity to processing solvents or reactants without using expensive and/or corrosive chemicals and with less loss of molecular weight comprises: (a)pretreating the cellulosic materials with caustic soda or ammonia water; (b)drying them totally or partially; (c)making supercritical carbon dioxide penetrate into cellulose chains at 35-200°C under 200-500 atm; and (d)subjecting them to the repeated chain explosion treatments more than twice. Also are disclosed the methods of producing cellulose solutions or the feedstock of reducing sugars or alcohols. The resulting materials can be used as raw material for cellulose solution or the feedstock for the production of reducing sugars or alcohols.

Description

A method of microstructure transformation by supercritical carbon dioxide multiple aeration of chemically pretreated fibrous materials.

Natural fibrous materials are commonly used to produce cellulose dope through physicochemical dissolution processes or to produce sugars or alcohols through chemical conversion reactions. However, in order to accelerate the processing speed in the above physicochemical and chemical processes and to improve the conversion yield, the contact and affinity between the fibrous material and the chemical should be enhanced. The present invention relates to a novel technique for efficiently inducing structural morphological changes in order to enhance the affinity and the physicochemical processability of fibrous polymer materials having various sources and uses, ie, cellulose and hemi-cellulose. . The technology can be applied to natural renewable resources such as cellulose, hemicellulose-containing wood, pulp, sawdust, paper, rice straw and corn by-products. By chemically pretreatment of fibrous material with supercritical carbon dioxide in a dried or partially dried raw state, repeated aeration once or several times, disrupting the crystal structure and reducing the size of crystal grains (or crystal fibers) In this patent, the technical contents for improving processability and chemical affinity are included.

In order to lower the crystallinity of the fibrous materials, various methods are used, such as using an acid and a base, an organic solvent and ice water in order, and applying microwave and ultrasonic waves. As a typical method, the acid or alkali simple treatment method uses a strong acid or strong alkali, thereby causing process corrosion and waste acid or waste alkali, thereby causing secondary environmental pollution. Due to the nature of the process, the recovery and recovery of the treatment medium is extremely difficult, and the cost of equipment investment is excessively demanded. In the case of applying an organic solvent or a complex forming chemical, there are problems such as high corrosion resistance, environmental toxicity, and absence of a recovery method. External energy application methods, such as microwaves and ultrasounds, are costly to process energy and can add to equipment investment. On the other hand, the effect is difficult to reproduce constantly.

Although a method of chain explosion of a polymer chain using nitrogen, water vapor, ammonia, etc. has been introduced, the explosion process using the above materials has disadvantages in terms of adopting corrosion resistant materials, energy cost, aeration efficiency, and molecular weight loss. . Carbon dioxide can easily reach its critical conditions from room temperature and atmospheric pressure, and has a strong penetration into the polymer chain in the supercritical fluid state. Since the density of the medium can be controlled very sensitively according to the macro process variables of temperature and pressure, it has been considered as an explosive medium and used as a pretreatment method for starch and some fibrous materials. However, it has been experimentally observed that the simple explosive method in the above supercritical carbon dioxide medium has a very limited effect on a fibrous polymer material having a relatively high molecular weight and a very high crystallinity, that is, a high α fraction.

All of the fibrous materials, including those with very high alpha fractions, do not use expensive corrosive chemicals, but have very low molecular weight loss, resulting in improved affinity for processing solvents, reactants, and fibrous solutions or sugars. Or a raw material for producing an alcohol.

Figure 1 is a comparison of the XRD type of untreated α-cellulose and feed depleted therefrom.

Figure 2 (a) is a change in crystal structure of the α-cellulose due to the simple explosion of the chemical pretreatment is omitted.

Figure 2 (b) is a change in the crystal structure of the α-cellulose by three times aeration, without chemical pretreatment.

Figure 3 (a) is a change in crystal structure after a one-time aeration of α-cellulose pretreated with caustic soda water.

Figure 3 (b) is a change in crystal structure after the three times the explosion of α-cellulose pretreated with caustic soda water.

Figure 4 (a) is a diagram showing the crystal structure change after a one-time decay of α-cellulose pretreated with ammonia water.

Figure 4 (b) is a change in crystal structure after the three times the explosion of α-cellulose pretreated with ammonia water.

The fibrous material is pretreated with caustic soda or ammonia water to dry or partially dry the supercritical fluid in the fibrillar polymer chain at 200 to 500 atm and 35 to 200 ° C., followed by repeated aeration.

(Specific embodiment of invention)

Fibrillar polymer chains are placed in a strong long-range interaction field due to the interchain / intra-chain hydrogen bonding force. The crystallization region of fibrin formed by this interaction is difficult to access other chemicals, and the reactivity is extremely reduced. In order to enhance physical processability and chemical reactivity, a method of exploding by steam and ammonia has been conventionally applied to fibrous crystals. In recent years, Avicel has introduced a technology that uses a supercritical carbon dioxide to explode, change its structure, and convert it into glucose with high efficiency.

Fibrous materials are divided into α, β and γ fractions based on their solubility in 17.5% caustic soda solution. α-cellulose has the typical molecular structure and crystal form of pure cellulose, and the chain structure is rigid. It shows a high degree of crystallinity compared to other fiber fractions and very few incomplete crystallizations. Therefore, the fibrous materials containing a large amount of α are very difficult to be physically and chemically processed due to their intrinsic crystalline structure. Natural cellulose has a cellulose-Ⅰ structure, which is converted to a cellulose-Ⅱ structure through a conventional mercerization process, and used for physical processing and chemical reactions. In the present invention, the chemically pretreated samples are bombarded with supercritical carbon dioxide to enable efficient microcrystal structure conversion. These attenuation effects were compared and confirmed through X-ray diffraction (XRD) and scanning electron microscopy (SEM).

After immersing α-cellulose in an 18wt% caustic soda solution, which is 3 to 5 times its own weight, for about 2 hours, mercerized cellulose with cellulose-II structure is produced. After washing on the filter cloth with the washing water and dried using a vacuum dryer or the like to make a dry sample or a wet non-aqueous sample including water. Samples pretreated with ammonia are prepared in the form of dry or non-aqueous samples by washing mercerized cellulose three times or more with 35 wt% ammonia water, equivalent to half the weight of the sample on a filter cloth.

The explosion facility may be divided into a supercritical carbon dioxide supply facility part, a static pressure, a constant temperature maintenance facility part, a rapid depressurization facility part, and a stirring vessel or nozzle part in which the explosion is substantially performed. The detonation plant system is designed to protect itself from high pressure conditions that maintain supercritical conditions and mechanical shock resulting from sudden pressure changes. Such aeration equipment can be operated batchwise, semi-continuously, or continuously. Sudden media expansion causing a burst occurs by rapidly opening the valve or flowing between convergent-diffusing nozzles. It is necessary to expose the substrate to the supercritical carbon dioxide fluid for a predetermined time or more before the aeration so that the detonating medium can penetrate deep into the fibrous substrate. Fibrous materials pretreated by the aforementioned chemical methods are capable of multiple explosions, one or more times, in a batch, semi-continuous, continuous aeration plant.

The efficiency of the detonation is approximately proportional to the density change of the medium before and after the detonation. Therefore, it is desirable to maintain initial supercritical fluid conditions to maximize density differences. This usually leads to higher pressures and lower temperatures above the critical temperature. When exploding non-aqueous samples, the explosive trajectory can be interpreted on the pressure-temperature state diagram of carbon dioxide and water, and in most cases, the explosive trajectory passes through the phase boundary where water freezes. This means that a small amount of water penetrates into the interior close to the surface of the fibrous crystal and freezes the water that partially swells the fibrous body, and the frozen water serves as a wedge that collapses the crystal structure. This structural change effect is more pronounced in the multiple explosives. It is possible to apply a modifier that can improve the explosive efficiency while being present in a small amount, such as water, by using alcohol, amine, fatty acid series, etc. to promote the structural change of the fibrous material and control the behavior of the structural change. It is possible. The new cellulose depletion technology introduced in the present invention has a great effect on a sample having a very large α fraction, and thus is equally applicable to rice straw, sawdust, pulp, paper, wood, etc., which have a small α fraction. It can change the structure.

Chemically pretreated samples can be bombarded with a supercritical carbon dioxide medium to directly observe crystal structure changes by X-ray diffraction (XRD) analysis and scanning electron microscopy (SEM). Indirect methods can be used to measure and compare the dissolution rate, solubility, etc. for a particular solvent. By using this explosive effect, an increase in the reaction rate in the sugar conversion reaction and the alcohol conversion reaction, an improvement in the reaction yield, and the like can be obtained.

Examples of the present invention are listed below. The following examples illustrate the technical details and features of the present invention, but the scope and content of the present invention are not limited to the examples.

Example

Examples will be described in detail but this does not limit the technical scope of the present invention.

Example 1

18 wt% caustic soda water 5 with respect to alpha cellulose 1 was added to a high pressure container, and the dried sample was exposed to 10 minutes at 50 ° C. and 350 atm in the presence of a supercritical carbon dioxide (99.9 wt%) medium. Then repeated three times.

After dissolving the sample in a mixed solvent of 4.5 wt% of ritimchloride and dimethylacetamide, the mixture was stirred at 25 ° C. for 24 hours, and then the solvent was removed and dried. The experimental results are shown in Table 1.

Example 2

In Example 1, the caustic soda water treatment sample was washed with 35 wt% ammonia water and used in the same manner as in Example 1. The results are shown in Table 1.

Table 1.

Sample Number Condition Relative dissolution rate Remarks One Untreated Sample (α-cellulose) 1.000 Control 2 18 wt% caustic soda water treatment 1.100 3 Crush 2 samples 3 times 1.927 Water system 4 Treatment of sample 2 with ammonia water 1.109 5 Amplify sample 4 three times 1.946 Water system

Example 3

In Example 1, the same procedure as in Example 1 was carried out except that water or ethanol or benzylethylamine or dimethylamine or monochloride was added to the supercritical carbon dioxide medium.

Example 4

The same procedure was followed as in Example 1 except for replacing hemicellulose or wood or pulp or sawdust or paper or rice straw or corn dispersion in Example 1.

Example 5

It carried out similarly to Example 1 except having bombed twice in Example 1 instead of three times.

Example 6

In Example 1, 100 degreeC instead of 50 degreeC was implemented like Example 1 except having replaced 400atm instead of 350atm.

Example 7

In Example 1, 150 degreeC instead of 50 degreeC was implemented like Example 1 except having replaced 450atm instead of 350atm.

As described and exemplified above, the molecular weight loss of the fibrous material is low, the use of expensive corrosive chemicals is economical, and even the fibrous material having a very high alpha fraction can convert the microstructure. In addition to the solubility increase and the glucose (or total sugar) conversion yield characteristic described in the above examples, when applied to a process for producing alcohol, the increase in sugar yield is increased because the concentration of alcohol is proportional to the concentration of sugar as a raw material. Leads to an increase in yield. Therefore, when the technique of the present invention is applied directly to the alcohol production process, it is possible to produce alcohol in a higher yield than the alcohol yield possible in the prior art.

Claims (17)

Chemically pretreatment of the fibrous material, and then dried or partially dried is repeatedly aerated in a high-temperature, high-pressure supercritical fluid medium and a high-pressure container, characterized in that the method of microstructure conversion of the fibrous material. The method of claim 1, wherein the chemical pretreatment is caustic soda water. The method of claim 1, wherein the chemical pretreatment is ammonia water. The method of converting the microstructure of a fibrous material according to claim 1, wherein the high temperature and the high pressure are 35 ° to 200 ° C and 200 to 500 atm. The method of claim 1, wherein the fibrous material is cellulose. The method of claim 1, wherein the fibrous material is hemicellulose. The method of claim 1, wherein the fibrous material is wood. The method of claim 1, wherein the fibrous material is pulp. The method of claim 1, wherein the fibrous material is sawdust. The method of claim 1, wherein the fibrous material is paper. The method of claim 1, wherein the fibrous material is rice straw. The method of claim 1, wherein the fibrous material is corn by-products. The method of claim 1, wherein the repetitive explosion is two or more times. 2. The method of claim 1, wherein the supercritical fluid medium is a mixture of supercritical carbon dioxide alone or at least one of water, alcohols, amines and fatty acids in supercritical carbon dioxide. 15. The method of claim 14, wherein the alcohol is ethanol. 15. The method of claim 14, wherein the amine is benzylethylamine. 15. The method of claim 14, wherein the fatty acid is monochloride acetic acid.