[DESCRIPTION]

[Invention Title]

METHOD FOR PRODUCING XYLOSE FROM BAMBOOS

[Technical Field]

The present invention relates to a method for producing xylose from bamboo. More specifically, the present invention relates to a method for producing xylose from bamboo, which provides a solution to the economic and environmental problems occurring in the prior art and is used to recover xylose as resources from hemicellulose dissolved during prehydrolysis and digestion steps in a process of producing high-quality dissolving pulp.

Up to recently, xylose has been produced primarily from birch wood. In addition, xylose may be produced by the separation of xylose from components dissolved during digestion of various wood species and herbaceous plants with organic solvents.

[Background Art]

The present invention relates to a method for producing xylose from bamboo, and more particularly to a method for producing xylose from bamboo,

which provides a solution to the economic and environmental problems occurring in the prior art and is used to recover xylose as resources from hemicellulose dissolved during prehydrolysis and digestion steps in a process of producing high-quality dissolving pulp. Up to recently, xylose has been produced primarily from birch wood. In addition, xylose may be produced by the separation of xylose from components dissolved during digestion of various wood species and herbaceous plants with organic solvents.

The aforementioned methods have focused only the production of xylose from raw materials, and therefore unfortunately suffer from various disadvantages in terms of efficient and economic utilization of resources, thereby increasing production costs of xylose.

In addition, xylose may also be produced by acid hydrolysis of unbleached and bleached chemical pulp prepared via various methods or by alkaline extraction and enzymatic treatment of pulp.

However, due to the main purpose for the production of xylose, these methods also have similar shortcomings such as non-effective and uneconomic utilization of resources suffered by previous methods, upon considering the current circumstances there have been actively proposed and developed various legal regulations and movements for greenhouse gas reduction and global environment protection as people are increasingly paying attention to the severity of global environmental deterioration.

Meanwhile, even though xylose is also partially recovered from the digestion waste liquor generated during a dissolving pulp manufacturing process using wood, it is difficult to produce sufficient amounts of xylose due to strict regulations on forest conservation. Unfortunately, this situation unavoidably will only get worse with time.

[Disclosure] [Technical Problem]

Therefore, the present invention has been made in view of the above problems, and it is an object of the present invention to provide a method for producing xylose from bamboo, and more particularly a method for producing xylose from bamboo, which provides a solution to the economic and environmental problems occurring in the prior art and is used to recover xylose as resources from hemicellulose dissolved during prehydrolysis and digestion steps in a process of producing high-quality dissolving pulp.

[Technical Solution]

In accordance with an aspect of the present invention, the above and other objects can be accomplished by the provision of a method for producing xylose as a raw material of gum from bamboo, comprising the steps of 1) removing leaves from

bamboo; 2) splitting bamboo culms at a regular interval of 1.5 to 3 mm in a longitudinal direction; 3) cutting the longitudinally-split culms to a length of 10 to 30 mm in a horizontal direction to produce bamboo chips; 4) screening debris and impurities from the cut bamboo chips; 5) water-washing to remove impurities, foreign materials and dust from the cut bamboo chips; 6) subjecting the washed bamboo chips to prehydrolysis using water or steam, followed by addition of a suitable amount of a catalyst depending upon a desired degree of prehydrolysis to facilitate prehydrolysis to dissolve hemicellulose components; 7) concentrating the solution separated from the bamboo chips by a heat exchange system or waste heat; 8) subjecting the concentrated solution to alkanol precipitation to precipitate xylose by adding methanol, ethanol, or a mixture of methanol and ethanol in a 50 to 150% volume of the solution; 9) separating the precipitated xylose by filtration or centrifugation; and 10) purifying the separated xylose by acid hydrolysis.

In accordance with another aspect of the present invention, there is provided a method for producing xylose as a raw material of gum from bamboo, comprising the steps of 1) removing leaves from bamboo; 2) splitting bamboo culms at a regular interval of 1.5 to 3 mm in a longitudinal direction; 3) cutting the longitudinally-split culms to a length of 10 to 30 mm in a horizontal direction to produce bamboo chips; 4) screening debris and impurities from the cut bamboo chips; 5) water-washing to remove impurities, foreign materials and dust from the cut bamboo chips; 6) subjecting the washed bamboo chips to prehydrolysis using water or steam, followed by addition of a suitable amount of a catalyst depending

upon a desired degree of prehydrolysis to facilitate prehydrolysis to dissolve hemicellulose components; 7) introducing the bamboo chips into a digester, and softening and pulping the bamboo chips by high-temperature digestion using a liquid chemical consisting of water, alkali and anthraquinone in a liquor ratio of 3.5 to 6.0 : 1 (weight ratio of liquid chemical : bamboo); 8) subjecting the digested materials to neutralization and precipitation with a supply of carbon dioxide gas to dissolve xylose; 9) adding a mixture of water, alcohol and methylisobutylketone to the resulting precipitates, followed by phase separation of the homogenous mixture with appropriate control of a water proportion; and 10) adding alcohol to the separated aqueous solution to thereby precipitate xylose.

[Best Mode]

The present invention is similar to a conventional art in terms of providing a method for producing pulp.

However, unlike the conventional art, the present invention is significantly characterized by the production of xylose from bamboo as a nonwoody plant, extraction of xylose in the prehydrolysis and digestion steps during the production of pulp, and consequently no need for global tree felling and deforestation with provision of remarkably high-quality xylose produced from the bamboo. Hereinafter, individual steps for production of xylose from bamboo will be described in more detail.

In the present invention, the method for producing dissolving pulp from bamboo includes removal of leaves from bamboo, as a first step.

That is, bamboo leaves contain various components unnecessary for the production of pulp, but are substantially less in a quantity of fibers. In other words, bamboo leaves may result in increased consumption of chemicals rather than provision of beneficial effects in pulp production. Therefore, elimination of the bamboo leaves is done prior to introduction of bamboo into the production process of the dissolving pulp.

That is, bamboo pulp production in accordance with the present invention employs only bamboo culms without inclusion of bamboo leaves.

Next, the second step includes splitting of the bamboo culms at a regular interval of 1.5 to 3 mm in a longitudinal direction.

Unlike wood, it is very difficult to achieve penetration of chemicals into the bamboo due to a dense structure thereof. Therefore, production of pulp involves a process of grinding and shredding.

For this purpose, the bamboo culms are split into halves, followed by re-splitting of the split bamboo culms into a narrower width.

Preferably, the bamboo culms are split into a width of 1.5 to 3 mm.

Vertical cutting (splitting) is a substantially characteristic process in the present invention. Nondirectional random splitting of the bamboo may be highly susceptible to disintegration of fibers rather than achieving uniform cutting of the resulting fibers.

Consequently, such nondirectional random splitting also weakens the strength of the produced pulp to thereby result in deterioration of the fiber quality.

For this reason, the method of the present invention uses the bamboo material which is processed to have a narrow width by application of multiple vertical splitting.

Alternatively, the bamboo material may be collectively cut into small pieces using a multi-blade cutting apparatus.

The third step includes horizontal cutting of the longitudinally-split culms to a length of 10 to 30 mm to produce bamboo chips. That is, for production of small-sized bamboo chips and consequently easy filling and packing of the chips into a digester, the bamboo material is also cut into a size of 10 to 30 mm in the horizontal direction using a cutting machine.

Where the length of the bamboo chip is excessively long, it is difficult to efficiently pack the chips into the digester. On the other hand, where the length of the bamboo chip is excessively short, this may bring about considerable damage to fibers, thereby resulting in weakening of the pulp strength.

The fourth step includes screening of debris and impurities from the cut bamboo chips.

Even though debris, generated during splitting and cutting of bamboo, may be used in the production of pulp, the resulting pulp suffers from weak strength due to destruction of fiber structures, as well as high possibility of increases in consumption of chemicals.

Foreign materials accompanying the cutting process are also useless in the production of pulp.

Therefore, it is necessary to remove the foreign materials by screening, since the use or incorporation of debris or foreign materials in the production of pulp is not beneficial to a yield of pulp (productivity of pulp) and also exhibits detrimental effects on the pulp quality.

Next, the fifth step includes water-washing to remove impurities, foreign materials and dust sticking to the bamboo chips.

That is, the foreign materials and dust adhering to the bamboo chips are removed by water.

This removal step reduces wasteful and unnecessary consumption of chemicals in the digestion process, and enables to obtain pure pulp, thereby improving the quality of the resulting pulp.

Next, the sixth step includes subjecting the washed bamboo chips to prehydrolysis using water or steam, followed by addition of a suitable amount of a catalyst depending upon a desired degree of prehydrolysis to facilitate prehydrolysis to dissolve hemicellulose components.

That is, hydrolysis is carried out to dissolve hemicellulose while achieving a maximum yield of the dissolving pulp in the bamboo chips. For this purpose, hydrolysis is conventionally carried out as a liquid water or steam phase prehydrolysis, or in the presence of a catalyst such as sulfuric acid.

More specifically, the catalyst that can be used in prehydrolysis may be selected from the group consisting of sulfuric acid, hydrochloric acid, sulfurous acid and formic acid.

Since the purpose for carrying out the prehydrolysis is to dissolve hemicellulose components in the bamboo chips, a single use of acid may lead to excessive acid hydrolysis, thereby posing the risk of destroying cellulose components.

For this reason, the acid should be used in a suitable ratio depending upon various operation parameters. Herein, a liquor ratio, i.e. an addition ratio of liquid water+catalyst: bamboo chip is preferably adjusted in a range of 1.5 to 7:1, depending upon a desired degree of hydrolysis.

That is, prehydrolysis is carried out at a 1.5 to 7:1 liquor ratio of the water- containing liquor and the bamboo chip. It should be noted that hemicellulose among chemical components of the bamboo during the prehydrolysis step decomposes with evolution of organic acids, and the resulting organic acids lead to hydrolysis of the bamboo.

Therefore, taking advantage of the property that an increasing liquor ratio results in sluggish hydrolysis, the liquor ratio should be adjusted to an appropriate level depending upon a desired polymerization degree and a desired hydrolysis degree of hemicellulose.

In other words, the liquor ratio refers to a 1.5 to 7 volume of the aqueous solution (the state where chemicals were dissolved in water if chemicals such as a catalyst were included), assuming that the bamboo chip (based on the oven dry weight) is 1. The purpose of adjusting the liquor ratio to within the above-specified range is to 1) facilitate intimate contact between the bamboo chip and the liquid chemical during reaction of the bamboo chip, and 2) control a degree of the reaction by varying the strength (concentration) of the liquid chemical in contact with the bamboo chip, depending upon the liquor ratio to be established. In addition, prehydrolysis temperature and time may be preferably set to a range of 90 to 150 ^° C and a range of 60 to 250 min, respectively, even though there may be slight differences depending upon the required quality with decomposition conditions in the prehydrolysis step.

Of course, these prehydrolysis conditions were demonstrated through various intensive and extensive experiments by the present applicant.

As used herein, the term "oven dry weight" refers to a weight of the pure bamboo chip with exclusion of moisture, because the bamboo chip contains large amounts of moisture.

In order to calculate the production yield, a moisture content of the bamboo chip is determined and then the weight of the pure bamboo chip is calculated based on the thus-obtained value.

Then, the seventh step includes concentration of the solution separated from the bamboo chips by a heat exchange system or waste heat.

That is, the solution concentration is carried out by elevating the temperature to evaporate the water vapor. Next, the eighth step includes precipitation of xylose via alkanol precipitation of the concentrated solution by addition of methanol, ethanol, or a mixture of methanol and ethanol in a 50 to 150% volume of the solution.

Next, the ninth step includes separation of the precipitated xylose by a filtration or centrifugation method. That is, filtration or centrifugation is carried out to extract xylose in the precipitated state.

Through such a process, pure xylose is extracted.

Finally, the tenth step includes purification of the thus-extracted xylose by acid hydrolysis treatment. In order to enhance the purity of xylose, acid hydrolysis is carried out to purify xylose.

Examples of the acid that can be used in the acid hydrolysis treatment may also include sulfuric acid, hydrochloric acid, and formic acid.

The thus-produced xylose is used as a raw material for gum or as a sweetening agent.

In addition to the aforementioned extraction method of xylose through concentration and precipitation of prehydrolyzate liquor, followed by filtration and

purification, the present invention is also directed to an extraction method of xylose in the digestion step following the prehydrolysis step.

Therefore, the latter method also follows the same steps 1 to 6 of the former method. However, the latter method includes different steps from the seventh step to the tenth step.

Specifically, the seventh step includes introducing of the bamboo chips into a digester, and softening and pulping of the bamboo chips by high-temperature digestion using a liquid chemical consisting of water, alkali and anthraquinone in a liquor ratio of 3.5 to 6.0 : 1 (weight ratio of liquid chemical : bamboo).

That is, use of a conventional sulfurous acid method in digestion of the bamboo chips suffers from problems such as weakening of fiber strength and a low pulp yield.

For these reasons, the present invention involves application of a soda-AQ pulping in order to facilitate delignification, and prevent decomposition of alpha- cellulose simultaneously with realization of improved pulp yield.

That is, this soda-AQ process is carried out by adding a liquor containing alkali (largely using NaOH), anthraquinone and water in a liquor ratio of 3.5 to 6.0:1, based on the oven dry weight of the bamboo chip. Preferably, in the soda-AQ process, an amount of the alkali (in terms of

Na ₂ O) added to water is 10 to 30%, and anthraquinone (AQ) is 0.01 to 2%, based on

the oven dry weight of the bamboo chip (net weight of the bamboo chip with exclusion of moisture contained therein).

Preferably, the digestion step is carried out at a temperature of 140 to 180 ^° C for 90 to 200 min. Such digestion conditions may be adjusted depending upon the quality of pulp to be produced, including a degree of polymerization.

Next, the eighth step includes neutralization and precipitation of the digested materials with a supply of carbon dioxide gas to dissolve xylose.

That is, this step is carried out to precipitate and separate xylose for facilitated extraction of xylose. Next, the ninth step includes addition of a mixture of water, alcohol and methylisobutylketone to the resulting precipitates, followed by phase separation of the homogenous mixture with appropriate control of a water proportion.

That is, the phase separation process is necessary to separate xylose from the mixture because the precipitates obtained in the previous step also contain lignin. Lignin is soluble in organic solvents, whereas hemicellulose and xylose are soluble in aqueous solutions.

For phase separation, the mixture of water, alcohol and methylisobutylketone is added to the resulting precipitates, followed by homogenous mixing and phase separation with appropriate control of a water proportion. Once phase separation occurred, an organic solvent fraction and an aqueous fraction are separated from each other.

Finally, the tenth step includes addition of alcohol to the separated aqueous solution to thereby precipitate xylose.

That is, the added alcohol is separated and recovered again by distillation.

[Mode for Invention]

EXAMPLES

Now, the present invention will be described in more detail with reference to the following examples. These examples are provided only for illustrating the present invention and should not be construed as limiting the scope and spirit of the present invention.

Example 1

Myanmar Bamboo was split to a width of about 2 mm and cut into small pieces having a size of 15 to 25 mm. The split and cut bamboo pieces were screened through a 60-mesh screen provided on a trough to remove foreign materials and bamboo debris, followed by washing.

400 g (oven dry weight) of the washed bamboo was introduced into a digester which was then filled with water to make a liquor ratio of 6:1. Then, a stainless weight was applied such that the bamboo can be sufficiently soaked in water.

The digester was covered and screwed, followed by hydrolysis at 170 ^° C for 90 min.

After hydrolysis was complete, the separated solution and wash water were concentrated, followed by precipitation and separation via alkanol precipitation.

The washed prehydrolyzed bamboo chips were re-introduced into the digester, to which 16% active alkali (in terms Of Na ₂ O) and 0.1% anthraquinone were added. After the liquor ratio was adjusted to 4:1, digestion was carried out at 170 ^° C for l20 min.

The digestion waste liquor and wash liquid were concentrated, followed by neutralization and precipitation with an addition of carbon dioxide.

The resulting precipitates were separated from the alkaline solution, and a mixture of water, alcohol and methylisobutylketone was added to dissolve the precipitates. Phase separation was carried out with an addition of water. Characteristics of the thus-obtained pulp are given in Table 1 below.

Table 1

Ex erimental results on reh dro l sis and ul in of bamboo 1

Example 2

Bamboo treatment and most of conditions were the same as in Example 1, and prehydrolysis conditions were set as follows.

That is, a liquor ratio was adjusted to 4:1, and prehydrolysis was carried out at a temperature of 170 ^° C for 100 min. Characteristics of the thus-obtained pulp are given in Table 2 below.

Table 2

Ex erimental results on rehydrolysis and pulping of bamboo (2)

[ Industrial Applicability ]

As apparent from the above description, the invention allows efficient use of natural resources by recovering xylose generated as a byproduct in a process of producing dissolving pulp from bamboo that do not significantly influence the environment and, at the same time, can be stably supplied as a raw material, and using the recovered xylose as high- value added resources. Also, the invention allows recovery of xylose at significantly lower costs, as compared to a conventional method of producing xylose from wood or pulp.

In particular, management of xylose contained in the prehydrolyzate liquor fraction and the digestion waste liquor via the separate process enables selective application of the recovered xylose depending upon consideration of efficient and economic utilization of resources. As such, resource recovery and recycling for utilization of wastes generated in a process of producing dissolving pulp is beneficial for improvement in economic utilization of resources, and may bring about reduction in production costs of xylose that is used as a raw material for producing xylitol, sweetening agents, pharmaceutical products and the like. Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.