CN1446784A - Method for producing xylitol by using bracteal leaf of maize - Google Patents

Abstract

The invention discloses a method for producing xylitol from corn bracts. The method mainly uses corn bracts to hydrolyze xylose to produce xylose, and then hydrogenates the xylose to produce xylitol. The method is characterized in that , the catalyst used for hydrolysis is hydrochloric acid, which saves half of the catalyst compared with the use of sulfuric acid; neutralizes the hydrochloric acid in the xylose liquid with cation exchange resin, reduces the ash in the xylose liquid, and improves the quality of the xylose liquid; The invention uses powdery and granular activated carbon as a decolorizing agent, which greatly enhances the decolorizing effect, and because the pigment content in corn bracts is low, it also saves the amount of activated carbon and reduces production costs. In addition, hydrolysis is in Carrying out under normal pressure saves equipment investment, therefore, the present invention can reduce the production cost of xylitol and improve the quality of xylitol.

Description

A kind of method of producing xylitol with corn husk

technical field

The invention relates to a method for producing xylitol, in particular to a method for producing xylitol from corn bracts.

Background technique

At present, the mature process of producing xylitol (C ₅ H ₁₂ O ₅ ) uses corn cob or bagasse as raw material, its specific surface area is 4cm/g, which is relatively small, prolongs the catalytic time, and is pressurized hydrolysis; The neutralization method uses calcium carbonate (CaCO ₃ ) as a neutralizing agent, which increases the ash and colloids in the hydrolyzed solution, reduces the quality of the solution, and increases the burden on the next step of purification, especially when it evaporates, causing serious damage. Scaling affects the normal progress of evaporation and greatly increases the consumption of steam for evaporation. In addition, it will also produce a side effect of the neutralization process, that is, the over-alkaline area during neutralization, which will deepen the color of the neutralization solution and increase the concentration of sugar. Decomposition and loss, especially when the temperature is high and the time is long, are more serious; the purification in this process adopts the recrystallization method; since corncobs are used as raw materials, the pigment content of corncobs is obviously greater than that of corn bracts, and the color of corncobs The average chromaticity of corn bracts is 1.1 Stern Meer, and the average chromaticity of corn bracts is 0.6 Sten Meer. Due to the high pigment content of corncobs, the decolorizing agent in the decolorization process, that is, the amount of activated carbon is large, and the production cost remains high. ; In addition, sulfuric acid (H ₂ SO ₄ ) is generally used as the catalyst for hydrolysis, and the catalytic activity of sulfuric acid is not very high.

Contents of the invention

The purpose of the present invention is to solve the problems of high cost and poor product quality existing in the existing xylitol production process, and provide a method for producing xylitol with corn husks with low production cost, high efficiency and small investment method.

The process steps and principle of the method are as follows:

(1) crushing corn husks, and removing impurities therein before and after crushing;

(2) Washing the pulverized corn husks for the first time, pickling, and washing for the second time, this process can remove dust impurities in the raw material and relatively improve the purity of the hydrolyzed solution;

(3) Hydrolyzing the treated corn bracts to produce xylose, the process conditions during hydrolysis are: temperature 100-130°C, wherein 100-125 is the preferred temperature, 100-106 is the optimum temperature; the time is 2 ~3 hours; the catalyst is hydrochloric acid (HCl), the concentration of hydrochloric acid is 1%, the solid-liquid ratio is 1: 10, and the pressure is normal pressure; the principle of hydrolysis is: corn bract contains pentosan, and its structural formula is:

This can be regarded as a polymer formed by the dehydration condensation of the hemiacetal group of one cyclopentose molecule and the hydroxyl group on the four carbon atoms of another cyclopentose molecule, that is, hemicellulose, and the polypentose is insoluble In addition to water, it has no sweet taste. It will dissolve and further hydrolyze when heated in an acidic aqueous solution, that is, it will be decomposed into many single-molecule pentose sugars, namely xylose. The reaction formula is as follows:

(4) Utilize anion exchange resin to remove the acid in the xylose liquid, this anion exchange resin adopts melamine-guanidine-formaldehyde resin, adopts ammoniacal liquor during regeneration, makes regeneration waste liquid contain ammonium chloride, to do agricultural irrigation;

(5) Utilize activated carbon to remove the pigment and a part of nitrogen-containing substances in the xylose solution, so as to avoid catalyst poisoning during the subsequent catalytic hydrogenation; The amount of activated carbon is 10% (relative to sugar), and the quality of the decolorizing solution is more than 80% of light transmittance; the activated carbon is a mixture of powder and granules; the powder accounts for 63.6% to 66.7%;

(6) Evaporating and removing the moisture in the xylose liquid; the process conditions are: temperature below 60°C, vacuum degree above 0.85atm, and the time is 6 to 9 hours;

(7) purify and purify the xylose after evaporation with ion resin, the xylose purity after general evaporation only has about 85%, in order to ensure the purity of xylose for hydrogenation, it is purified to a purity of more than 95%;

The anion resin used is: melamine resin (AH-1), the exchange capacity is 2.4 mg/g, the specific volume is 2.2-2.8 ml/g, and the particle size is 0.3-2.0 mm;

The cationic resin used is 732 ^# sulfonic acid resin (styrene-divinylbenzene strong acid resin), with an exchange capacity of 1.1 to 1.5 milliequivalents/gram and a particle size of 0.25 to 2.0 millimeters;

(8) Xylose hydrogenation produces xylitol, and its reaction formula is:

The technological conditions of the reaction are: pressure: 6.5-8.0Mpa, reaction temperature: 110-130°C; the catalyst is Raney nickel, and its addition is 3-6%; the pH value of the solution is 7.5-8, and the reaction time is 60 minutes ; The optimal process conditions are: temperature is 120°C, pressure is 7.5Mpa, reaction time is 60 minutes, catalyst dosage is 6%, the average conversion rate of xylose is 99.23%, and the average yield is 90.59%.

Advantage and positive effect of the present invention:

1. The content of raw material pigment is low: In my country, the traditional raw material for xylitol production is mainly corn cobs. Since the average color of corn cobs is 1.1 Sten Meer, the average color of corn bracts is 0.6 Sten Meer. Mill, the difference in pigment content between the two greatly reduces the amount of decolorizing agent in the decolorization process, which reduces the burden on the purification of the subsequent process. At present, the price of decolorizing agent is relatively high, and in the production of enterprises, the cost of decolorizing agent accounts for almost 50% of the total raw material cost. It can be seen that taking corn bracts as raw materials obviously improves the economic benefits of the enterprise.

2. The influence of temperature and pressure: This method is hydrolyzed under the condition of normal pressure and temperature of 100-130°C, while the traditional production is carried out under pressure. The color of xylose solution changes with the temperature. The rise of the temperature becomes a 10-fold increase, the temperature remains unchanged, the concentration of the acid increases, although the color increases, but the increase is small, and the quality of the hydrolyzed solution is better. Therefore, the acid concentration should be higher than the temperature. Therefore, normal pressure hydrolysis can greatly reduce the amount of decolorizing agent. In addition, the equipment investment for pressurized hydrolysis is also greater than that for normal pressure hydrolysis equipment.

Three, the influence of raw material specific surface area: there is big difference between the specific surface area of raw material corncob and corn bract leaf, and the specific surface area of corncob is 4cm/g, and the specific surface area of corn bract leaf is 220cm/g, in pretreatment and In the hydrolysis process, it has different effects significantly. The specific surface area of corn husk leaves is large, and when it acts with the catalyst, it is easy to be hydrolyzed, and the mass and heat transfer effect is obvious, which can shorten the catalytic time.

4. Although it is believed that hydrochloric acid (HCI) is more corrosive to equipment than sulfuric acid (H ₂ SO ₄ ), the catalytic activity of hydrochloric acid (HCI) is far greater than that of sulfuric acid (H ₂ SO ₄ ). , the concentration of hydrochloric acid (HCI) is 1/2 of the concentration of sulfuric acid (H ₂ SO ₄ ), and the selling price of the two is almost the same, so the hydrolysis of hydrochloric acid (HCI) is economically advantageous.

5. Differences in neutralization methods: The traditional neutralization method uses _CaCO3 as a neutralizer. This method increases the ash and colloid in the hydrolyzed solution, reduces the quality of the solution, and increases the burden on the next step of purification. Especially during evaporation, serious fouling occurs, which affects the normal operation of evaporation and greatly increases the consumption of steam for evaporation. In addition, there will be side effects of the neutralization process, that is, the over-alkaline area during neutralization, which will deepen the color of the neutralization solution and increase the decomposition and loss of sugar, especially when the temperature is high and the time is long. The law of exchange avoids these problems.

Detailed ways

Embodiment 1 of the present invention

(1) crushing corn bracts into 1.5×0.5cm ² , and removing impurities therein;

(2) Take an appropriate amount of crushed corn husks, wash them with water, then wash them with 1% hydrochloric acid solution, and then wash them with water;

(3) The corn husks after the above treatment are sent into a hydrolysis tank for hydrolysis, adding 1% hydrochloric acid, the solid-to-liquid ratio is 1:10, the reaction temperature is 100° C., and the time is 2.5 hours; the pressure is normal pressure; The reaction decomposes into xylose liquid;

(4) utilize melamine-guanidine-formaldehyde resin to remove the acid of xylose liquid;

(5) Utilize powdery and granular activated carbon to decolorize the xylose solution. The process conditions are: temperature 80°C, heat preservation and stirring speed 37 rpm, activated carbon consumption 10% (relative to sugar), and the quality of the decolorization solution is the light transmittance. More than 80%;

(6) Evaporating and removing the moisture in the xylose liquid; the process conditions are: temperature below 60°C, vacuum degree above 0.85atm, and the time is 6 to 9 hours;

(7) Purify xylose with melamine resin (AH-1);

(8) xylitol is produced by hydrogenation of xylose, the technological conditions of reaction are: pressure 6.5Mpa, reaction temperature is 110 ℃, catalyst is Raney nickel, and its addition is 3%, and the pH value of solution is 7.5.

Example 2

Carry out embodiment 1 repeatedly by the same step as described, but difference is,

The process conditions of step (3) are: temperature 130°C, hydrolysis time 3 hours;

The time in step (6) is 9 hours;

The resin used in the step (7) is 732 ^# sulfonic acid type (styrene-divinylbenzene strong acid resin);

The process conditions in the step (8) are: the pressure is 8.0Mpa, the reaction temperature is 130°C, the addition of Raney nickel is 5%; the pH value of the solution is 8.

Example 3

Carry out embodiment 1 repeatedly by the same step described, but difference is,

The technological condition of step (3) is temperature 106 ℃, and hydrolysis time is 2 hours;

The evaporation time in step (6) is 7.5 hours;

The process conditions in the step (8) are: the pressure is 7.5Mpa, the reaction temperature is 120°C, the reaction time is 60 minutes, and the addition of Raney nickel is 6%;

Example 4

Carry out embodiment 3 repeatedly by described same step, but difference is that the resin used in step (7) is 732 ^# sulfonic acid type resin (styrene-divinylbenzene strong acid resin).

In the above four examples, the average conversion rate of xylose is 99.23%, and the average yield is 90.5%.

Claims (10)

1, a method for producing xylitol with corn bracts, the method may further comprise the steps in sequence: (1) crushing corn husks, and removing impurities therein before and after crushing; (2) Water-acid-water treatment of the pulverized corn bracts; (3) hydrolyzing the treated corn bracts to produce xylose, the catalyst used is hydrochloric acid; (4) utilize anion exchange resin to remove the acid in the xylose liquid; (5) Utilize active carbon to remove the pigment and a part of nitrogenous substances in the xylose solution; (6) evaporation removes the moisture content in the xylose liquid; (7) Purify and purify the evaporated xylose with ion resin; (8) Xylose is hydrogenated to produce xylitol. 2. The method for producing xylitol from corn husks according to claim 1, characterized in that: the process conditions for hydrolysis in the step (3) are: temperature 100-130°C, hydrolysis time 2-2 3 hours; the concentration of hydrochloric acid is 1%, the solid-liquid ratio is 1:10, and the pressure is normal pressure. 3. A method for producing xylitol from corn husks according to claim 2, characterized in that the hydrolysis temperature is 100-106°C. 4, according to the method that a kind of corn husk produces xylitol according to claim 1, it is characterized in that: the melamine-guanidine-formaldehyde resin of the anion exchange resin used in the described step (4), regeneration When using ammonia water. 5. A method for producing xylitol from corn husks according to claim 1, characterized in that: the process conditions in the step (5) are: temperature 80°C, heat preservation and stirring speed 37 rpm, The dosage of activated carbon is 10%, and the quality of the decolorizing solution is more than 80% of light transmittance. 6. A method for producing xylitol from corn husks according to claim 1, characterized in that: the process conditions in the step (6) are below 60° C. of temperature, above 0.85 atm of vacuum, and the time is 6 to 9 hours. 7. The method for producing xylitol from corn bracts according to claim 1, characterized in that: the ion resin used in the step (7) is melamine resin or 732 ^# sulfonic acid resin . 8. A method for producing xylitol from corn husks according to claim 1, characterized in that: the reaction process conditions in the step (8) are: pressure: 6.5-8.0Mpa, reaction temperature: 110 ～130 DEG C; the catalyst is Raney nickel, and its addition amount is 3～6%; the pH value of the solution is 7.5～8, and the reaction time is 60 minutes. 9. A method for producing xylitol from corn husks according to claim 8, characterized in that: the optimum process conditions for the reaction are as follows: temperature is 120°C, pressure is 7.5Mpa, and reaction time is 60 minutes , The amount of Raney nickel added is 6%. 10. A method for producing xylitol from corn husks according to claim 1, characterized in that: the activated carbon is a mixture of granules and granules, wherein the powder accounts for 63.6%-66.7%.