KR102077699B1 - Method of extract silica from rice husk - Google Patents

Abstract

The present invention is a method of extracting silica from the chaff comprising the step of immersing the chaff in an alkaline solution at a temperature of 20 ℃ to 95 ℃ in a ratio of solid solution (volume of liquid to weight of solids) 1: 3 to 1:20. To provide. In the method of extracting silica from the chaff according to the present invention, since the chaff is extracted by using an alkaline solution at low temperature, the occurrence of dissolution of lignin and other organic substances is low, and thus, precipitation and purification of silica are relatively easy. There is.

Description

Method of extracting silica from rice husks {Method of extract silica from rice husk}

A method for extracting silica from chaff.

Chaff is a major agricultural by-product, generating about 100 million tons worldwide, and about 800,000 tons annually in Korea. Most of the biomass resources consist of cellulose, hemicellulose, and lignin, and the rest consists of minerals and extracts. In the case of chaff, the content of minerals except cellulose, hemicellulose, and lignin is about 15% to 20%. The content is very high and more than 90% of the inorganic material is made of silica.

Rice is stored and stored in a grain state after drying after harvesting. The high silica content of the rice hull surface constituting the outer skin of the rice is characterized by maximizing resistance to microorganisms of the rice to facilitate storage. After that, rice is sold just before being sold, and the rice husk generated is characterized by relatively low utility.

Chaff is produced at the time of sale of stored rice, and it is generated mainly in the rice grain processing plant. Unlike other biomass, rice bran is produced in a constant amount without any seasonal effect. Although the morphological, physical, and chemical properties are constant, the processability is very excellent as an industrial raw material, but due to excessive silica content in the outer shell, the workability of grinding and materialization is poor, and the ignition characteristics and heat generation capacity are low as a fuel material.

In general, it is mainly used for low-grade applications such as livestock rugs, and has a relatively non-corrosive property and low nutritional components, which are not suitable for compost or feed.

Silica present in rice husk has high purity and has amorphous characteristics compared to mineral-based silica which is commonly used as rice is ecologically absorbed in the form of silicic acid in soil and accumulates on the skin of rice husk.

Particularly, in the case of mineral silica, silicate silicate, which is a soluble silica, is prepared through extraction process under high temperature of 1,500 ° C. in order to extract or manufacture silica having high purity due to high content of various metal components and impurities such as boron and phosphorus. Although there is a disadvantage in producing a variety of silica particles on the basis, the silica present in the chaff relatively easy to purify because of the relatively small presence of such impurities and having an amorphous amorphous structure.

Due to the lack of proper utilization, a considerable amount of chaff, which occurs every year, is an important issue around the world, especially due to the high industrial resources value of the high volume and continuous characteristics of the chaff. The development and research of various techniques for the use of the method and its use have been conducted.

In general, methods for extracting or separating silica from chaff have been mainly developed to remove organic matter from chaff and to obtain inorganic silica. To this end, methods for continuously removing chaff organic matter by burning or carbonizing at high temperature have been continuously developed. And methods for utilizing microorganisms or enzymes have also been developed. In addition, various studies have been conducted to extract silica using a variety of complex and highly advanced processes (Yafei, S., Rice husk silica derived nanomaterials for sustainable applications, Renewable and sustainable energy reveiws 80: 453-466 (2017).

Korean Patent Registration No. 10-0396457 discloses a method for preparing porous silica, porous silica molded body, and nano-sized silica particles prepared from chaff. The prior patent discloses a method of extracting silica by acidifying the ash after carbonizing the rice hull in an oxygen-free atmosphere, but for the application of this technique, a carbonization treatment at a temperature of 500 ° C. or higher is required to remove the organic matter of the rice husk. In the case of improper carbonization treatment, the crystallinity of the chaff silica is increased, making it difficult to extract and purify the chaff silica, and also lower the utilization value.

Korean Patent No. 10-1048410 discloses a method of applying a biorefining technology based on chemical treatment as a method for overcoming the disadvantage of silica extraction through combustion or carbonization of rice hulls. Methods of making have been disclosed. In the above patent, a method of dissolving rice hull silica and lignin to separate the rice hull fiber by heating the rice hull at high temperature and high pressure of 170 ° C. or higher in a high alkali solution has been developed. This method also has the disadvantage of high energy costs and cost for building facilities for extracting the silica of the chaff under high temperature and high pressure conditions.

In addition, US Patent Publication No. 2015-0121979 describes the use of silica produced by immersion in calcium silicate as a plant nutrient. Specifically, the chaff is soaked in 20% potassium hydroxide (KOH), which is a high alkaline solution, for about 6 hours, and then used to spray the extracted liquid on the leaves. When the immersion as described in the prior patent, as well as silica lignin, hemicellulose and various low molecular weight components are dissolved, there is a problem that the extraction purity of the silica itself is low, and the neutralization and purification for the precipitation of high purity silica later There is a very inefficient problem.

As such, various existing techniques developed for extracting or separating chaff silica from chaff generally require high energy, high temperature treatment, complex process steps, and are inefficient for the precipitation of high purity silica. Have. In particular, there are no patents for eluting and utilizing silica through low energy extraction methods for rice hulls.

Accordingly, the present inventors studied a method of extracting silica from chaff, and as a method of extracting silica present in the shell of the chaff surrounded by lignin, the chaff silica accumulated by the lignin was partially dissolved and softened. We developed a method of dissolving efficiently, and in this way, not only chaff lignin but also other organic components such as cellulose of the endothelium are burned or pyrolyzed and then silica is extracted from the chaff or cooked at high temperature. Unlike the existing methods of inducing dissolution of silica by dissolving in large part, it was confirmed that the method can achieve high efficiency silica extraction and separation with low energy and completed the present invention.

It is an object of the present invention to provide a method for extracting amorphous silica present in chaff at high efficiency under low energy conditions.

In addition, another object of the present invention to provide a silica extraction method using the chaff not treated with a separate heat, combustion or chemicals in the extraction of silica from the chaff.

Furthermore, another object of the present invention is to efficiently dissolve and extract silica concentrated in the shell by partially dissolving and softening the lignin in the rice hull shell, unlike the conventional decomposition and dissolution of chaff lignin in extracting silica from rice husk. To provide a way.

In order to achieve the above object, the present invention

Provided is a method for extracting silica from chaff, which comprises immersing chaff in an alkaline solution at a temperature of 20 ° C. to 95 ° C. in a ratio of solid to liquid ratio (volume of liquid to weight of solids) 1: 3 to 1:20. .

In addition, the present invention

Extracting the silica by immersing the rice hulls in an alkaline solution at a temperature of 20 ° C. to 95 ° C. in a ratio of solid solution ratio (volume of liquid to weight of solids) 1: 3 to 1:20 (step 1);

Separating the silica extract produced in step 1 from the rice husks (step 2);

Neutralizing the extract separated in step 2 (step 3);

Recovering the precipitate in the extract neutralized in step 3 (step 4); And

It provides a method for producing silica from chaff comprising the step (step 5) of obtaining a silica by heat-treating the precipitate recovered in step 4 above.

In the method of extracting silica from the chaff according to the present invention, since the chaff is extracted using an alkaline solution at low temperature, the incidence of dissolution of lignin and other organic substances is low, and thus the precipitation and purification of silica are relatively easy. There is.

1 to 5 and 7 to 9 are graphs showing the amount of silica extraction after silica extraction performed in Examples 1 to 44 and Comparative Examples 1 to 4;
Figure 6 is a photograph showing a color change comparison of the supernatant according to the degree of purification of the silica extraction solution performed in Example 25, Comparative Example 2 and Comparative Example 3 when the silica precipitated.

The present invention

Provided is a method for extracting silica from chaff, which comprises immersing the chaff in an alkaline solution at a temperature of 20 ° C. to 95 ° C. in a ratio of 1: 3 to 1: 100 in solids ratio (volume of liquid to weight of solids). .

Hereinafter, a method of extracting silica from the chaff according to the present invention will be described in detail.

Conventionally developed techniques for extracting silica from rice husk are inefficient in the high energy, high cost method of combustion, dissolution or cooking of organic matter other than chaff silica. On the contrary, in the present invention, a method of extracting silica from chaff of low energy and high efficiency has been developed based on consideration of morphological characteristics of chaff and distribution of silica in chaff.

The chaff serves as an outer protective or epidermal layer that protects the grain, which can be divided into the outer shell and the inner shell. Almost all of the chaff's silica is present in the outer shell. Silica present in the husk hull is surrounded by the lignin of the chaff, the removal of this lignin structure is essential for the elution of chaff silica. To this end, conventional methods induce the dissolution of silica by burning or thermally decomposing not only chaff lignin but also other organic components such as endothelial cellulose and extracting chaff silica or by cooking at high temperature to dissolve most chaff lignin. Methods have been used.

However, in the present invention, the chaff silica, which is concentrated with lignin in the epidermal layer of the rice husk, is extracted through immersion of a low temperature alkali solution, and the method proposed in the present invention can achieve high efficiency silica extraction and separation with low energy. It proved to be economical and environmentally friendly.

The method of extracting silica from the rice hulls according to the present invention comprises the steps of immersing the rice hulls in an alkaline solution at a temperature of 20 ° C. to 95 ° C. in a ratio of 1: 3 to 1:20 in a liquid-liquid ratio (volume of liquid to weight of solids). It is characterized by including.

In the method of extracting silica from the chaff according to the present invention, the chaff is immersed in an alkaline solution in a ratio of 1: 3 to 1:20 in a solid solution ratio (volume of liquid to weight of solid).

As a specific example, the alkaline solution may be a sodium hydroxide solution, potassium hydroxide solution, ammonia solution or a mixed solution thereof.

In addition, the concentration of the alkaline solution is preferably at least 1%, may be 1% to 15%, may be 2% to 15%, may be 2% to 10%, may be 2% to 5% , 3% to 15%, 3% to 10%, 3% to 5%, 5% to 15%, and 5% to 10%. The concentration of the alkaline solution represents the amount of the alkaline substance when the total solution is 100 (see Equation 1 below).

[Equation 1]

Further as an example, the ratio of the solid solution of the chaff and the alkaline solution is preferably in the ratio of 1: 3 to 1:20, may be 1: 3 to 1:10, may be 1: 5 to 1:20, 1 : 5 to 1:10, and may be 1:10 to 1:20. In one example, it may be most preferably 1:10 or less. Preference is given to minimizing and using alkaline solutions containing alkaline substances.

As a specific example, when the chaff is not pre-treated chaff, the high ratio of the chaff and the alkaline solution is preferably 1:10 to 1: 100, 1:10 to 1:30, chaff is physically ground chaff In this case, it is preferable that the solid-liquid ratio of chaff and an alkaline solution is 1: 3-1: 30, 1: 3-1: 10.

In the method of extracting silica from the rice hulls according to the present invention, the rice hulls are immersed in an alkaline solution at a temperature of 20 ° C to 95 ° C. Unlike the extraction method of cooking at a high temperature of 100 ° C. or more, the present invention is immersed at a relatively low temperature of 100 ° C. or less. In this case, production is possible by applying relatively simple equipment without using expensive equipment including pressure equipment. Through this, only part of the lignin in the husk husk can be dissolved to extract silica concentrated in the hull with high efficiency.

The extraction temperature is preferably 20 ° C to 95 ° C, may be 20 ° C to 90 ° C, may be 50 ° C to 95 ° C, 50 ° C to 90 ° C, 60 ° C to 95 ° C, It may be from 60 ℃ to 90 ℃, may be from 65 ℃ to 95 ℃, may be from 65 ℃ to 90 ℃, may be from 70 ℃ to 95 ℃, may be from 70 ℃ to 90 ℃.

Further, for example, the immersion is preferably performed in less than 1 hour, may be performed for 30 minutes to 3 hours, may be performed for 30 minutes to 1 hour, may be performed for 30 minutes to 2 hours, It may be performed for 1 to 2 hours, and may be performed for 1 to 3 hours.

In the present invention, the chaff which is the target of silica extraction may be unpretreated chaff, ground chaff and swollen chaff. The method of extracting silica from the rice husk presented in the present invention is a method of extracting the silica of the rice hull with low energy efficiency.

Furthermore, the present invention

Extracting the silica by immersing the rice hulls in an alkaline solution at a temperature of 20 ° C. to 95 ° C. in a ratio of solid solution ratio (volume of liquid to weight of solids) 1: 3 to 1:20 (step 1);

Separating the silica extract produced in step 1 from the rice husks (step 2);

Neutralizing the extract separated in step 2 (step 3);

Recovering the precipitate in the extract neutralized in step 3 (step 4); And

It provides a method for producing silica from chaff comprising the step (step 5) of obtaining a silica by heat-treating the precipitate recovered in step 4 above.

Hereinafter, a method for producing silica from rice hulls according to the present invention will be described in detail for each step.

First, in the method for producing silica from the chaff according to the present invention, step 1 is 20 to 95 ℃ in a ratio of 1: 3 to 1:20 in the liquid solution ratio (volume of the liquid to the weight of the solid) of the chaff in an alkaline solution The silica is extracted by immersion at a temperature of.

Step 1 is a step of extracting silica from the chaff, it is possible to extract the silica from the chaff in a low energy high efficiency by the extraction method proposed in the present invention as described above.

Next, in the method for producing silica from the chaff according to the present invention, step 2 is a step of separating the silica extract and chaff generated in step 1 above.

The silica extracted in step 1 is dissolved in the extract, and in step 2, the extract in which a large amount of silica is dissolved is separated through solid-liquid separation.

Next, in the method for producing silica from the chaff according to the present invention, step 3 is a step of neutralizing the extract separated in step 2.

In step 3, the extract separated in step 2 may be neutralized, and the silica dissolved in the silica extract may be precipitated through neutralization.

As a specific example, the neutralization treatment of step 3 may be performed under the condition of pH 6 to pH 8 by adding a strong acid or weak acid. The strong acid or weak acid may be sulfuric acid, nitric acid, hydrochloric acid, or the like, and may be neutralized by inducing application and dissolution of carbon dioxide (CO ₂ ) gas.

Next, in the method for producing silica from chaff according to the present invention, step 4 is a step of recovering the precipitate in the extract solution neutralized in step 3.

In step 4, the silica precipitated by neutralization in step 3 is recovered.

As a specific example, the step 4 may be separated from the extract and the precipitate by centrifugation, the precipitate obtained in the gel state may include metal salt impurities such as sodium, potassium, etc. derived from the alkaline solution used in step 1 in addition to silica. Therefore, the washing process consisting of washing water input and centrifugation may be performed one or more times, preferably 3 to 10 times.

Next, in the method for producing silica from rice hulls according to the present invention, step 5 is a step of heat-treating the precipitate recovered in step 4 to obtain silica.

As a specific example, the heat treatment of step 5 may be performed at a temperature of 300 ℃ to 700 ℃.

Hereinafter, the present invention will be described in detail by the following Examples and Experimental Examples.

However, the following Examples and Experimental Examples are only illustrative of the present invention and the scope of the invention is not limited by the Examples and Experimental Examples.

Example 1-33 Extraction of Silica from Chaff 1

The chaff was immersed in a sodium hydroxide (NaOH) solution to extract silica, and the solid solution ratio of the immersed chaff and sodium hydroxide solution, the concentration of the sodium hydroxide solution, the immersion temperature and the immersion time are shown in Tables 1 to 5 below.

High cost ratio (w / v) Sodium hydroxide
Concentration of solution (%) Temperature (℃) Hour (hr) Example 1 1:10 5 25 One Example 2 1:10 5 25 2 Example 3 1:10 5 25 4 Example 4 1:10 5 25 6 Example 5 1:10 5 25 12 Example 6 1:10 5 25 24 Example 7 1:10 5 25 72 Example 8 1:10 5 25 168 Example 9 1:10 5 25 336

High cost ratio (w / v) Sodium hydroxide
Concentration of solution (%) Temperature (℃) Hour (hr) Example 10 1:10 10 25 One Example 11 1:10 10 25 2 Example 12 1:10 10 25 4 Example 13 1:10 10 25 6 Example 14 1:10 10 25 12 Example 15 1:10 10 25 24

High cost ratio (w / v) Sodium hydroxide
Concentration of solution (%) Temperature (℃) Hour (hr) Example 16 1:10 5 50 One Example 17 1:10 5 60 One Example 18 1:10 5 70 One Example 19 1:10 5 80 One Example 20 1:10 5 90 One

High cost ratio (w / v) Sodium hydroxide
Concentration of solution (%) Temperature (℃) Hour (hr) Example 21 1:10 0.25 70 One Example 22 1:10 0.5 70 One Example 23 1:10 0.75 70 One Example 24 1:10 One 70 One Example 25 1:10 2 70 One Example 26 1:10 4 70 One

High cost ratio (w / v) Sodium hydroxide
Concentration of solution (%) Temperature (℃) Hour (hr) Example 27 1:10 5 70 0.25 Example 28 1:10 5 70 0.5 Example 29 1:10 5 70 0.75 Example 30 1:10 5 70 2 Example 31 1:10 5 70 3 Example 32 1:10 5 70 4 Example 33 1:10 5 70 12

Example 34-44 Extraction of Silica from Chaff 2

The chaff was crushed to use a classification between 40 and 100 mesh. The ground chaff was immersed in a sodium hydroxide (NaOH) solution to extract silica, and the solid solution ratio of the immersed chaff and sodium hydroxide solution, the concentration of the sodium hydroxide solution, the immersion temperature and the immersion time are shown in Tables 6 to 8 below.

High cost ratio (w / v) Sodium hydroxide
Concentration of solution (%) Temperature (℃) Hour (hr) Example 34 1: 3 5 70 One Example 35 1: 5 5 70 One Example 36 1:10 5 70 One

High cost ratio (w / v) Sodium hydroxide
Concentration of solution (%) Temperature (℃) Hour (hr) Example 37 1: 3 0.5 70 One Example 38 1: 3 One 70 One Example 39 1: 3 2 70 One

High cost ratio (w / v) Sodium hydroxide
Concentration of solution (%) Temperature (℃) Hour (hr) Example 40 1: 3 5 70 0.25 Example 41 1: 3 5 70 0.5 Example 42 1: 3 5 70 0.75 Example 43 1: 3 5 70 2 Example 44 1: 3 5 70 3

Comparative Example 1

Rice husk was added to 30% potassium hydroxide (KOH) at a solid solution ratio of 1:10 at 150 ° C. for 1 hour to extract silica.

 Comparative Example 2-3

The chaff was immersed in sodium hydroxide (NaOH) solution to extract silica, and the solid solution ratio of the soaked chaff and sodium hydroxide solution, the concentration of the sodium hydroxide solution, the immersion temperature and the immersion time are shown in Table 9 below.

High cost ratio (w / v) Sodium hydroxide
Concentration of solution (%) Temperature (℃) Hour (hr) Comparative Example 2 1:10 2 100 One Comparative Example 3 1:10 2 130 One

< Experimental Example  1> Evaluation of Silica Extraction Characteristics of Chaff

In order to confirm the extraction amount of the silica extracted through the method of extracting silica from the chaff according to the present invention, the silica extraction amount after the silica extraction performed in Examples 1 to 44 and Comparative Examples 1 to 4 was analyzed.

The amount of silica extracted was calculated as a ratio of the amount of ash removed by dipping by comparing the amount of ash before the immersion and after washing the rice hull immersed in the alkaline solution.

(1) Evaluation of Silica Extraction Characteristics at Room Temperature

Silica extraction amount was analyzed after the silica extraction performed in Examples 1 to 15, and the results are shown in Figures 1 and 2.

As shown in Figure 1 and Figure 2, when looking at the silica extraction amount at room temperature 25 ℃ it can be seen that the extraction of about 10% in the case of Example 1 and Example 10 extracted for 1 hour, after about 168 hours or more extracted about 80% You can see that. It was confirmed that the amount of silica extraction was almost similar when exceeding 168 hours.

(2) Evaluation of Silica Extraction Characteristics According to Temperature

Silica extraction amount after silica extraction performed in Example 1 and Examples 16 to 20 was analyzed, and the results are shown in FIG.

As shown in FIG. 3, the extraction amount was about 10% when silica extraction was performed at room temperature of Example 1, and the extraction amount was about 53% when silica extraction was performed at a temperature of 50 ° C. of Example 16. When silica extraction was performed at a temperature of 60 ℃ of Example 17 the extraction amount was about 66%.

In particular, when silica extraction was carried out at a temperature of 70 ℃ or more of Examples 18 to 20 it was confirmed that the extraction amount represents about 80% or more.

(3) Evaluation of Silica Extraction Characteristics According to Alkali Concentration

Silica extraction amount was analyzed after the silica extraction performed in Example 18 and Examples 21 to 26, the results are shown in FIG.

As shown in FIG. 4, the silica extraction amount in Example 21 having a concentration of 0.25% sodium hydroxide as an alkaline solution represents about 10%, and the silica extraction amount in Example 22 having 0.5% represents about 27%, 0.75 It was confirmed that the silica extraction amount in Example 23, which is%, was about 59%, and the silica extraction amount in Example 24, which was 1%, was about 76%.

In particular, in the case of Example 23, Example 24, and Example 18 in which the concentration of sodium hydroxide as the alkaline solution was 2% or more, it was confirmed that the silica extraction amount was about 80% or more.

(4) Evaluation of Silica Extraction Characteristics over Time

Silica extraction amount was analyzed after silica extraction performed in Example 18 and Examples 27 to 33, the results are shown in FIG.

As shown in FIG. 5, in Example 27 having a immersion time of 15 minutes, it was confirmed that the silica extraction amount was about 68%, and in Example 28 having 30 minutes, the silica extraction amount was about 79%, In the case of Example 29 which was 45 minutes, it was confirmed that the silica extraction amount was about 82%.

In particular, in the case of Example 18 and Examples 30 to 33 where the immersion time is 1 hour or more, it was confirmed that the silica extraction amount was about 80% or more.

< Experimental Example  2> Evaluation of Lignin Dissolution Characteristics of Rice Hull

In order to confirm the amount of silica extracted through the method of extracting silica from the chaff according to the present invention, the content of lignin dissolved after silica extraction performed in Example 25, Comparative Example 2 and Comparative Example 3 was analyzed, The results are shown in Table 10 below. Lignin content analysis was performed according to TAPPI Standard Method T222 om-98. The lignin content of the chaff applied in this experiment was 25%, but the lignin content of the extracted residue was reduced when the silica was extracted under each condition because the reduced lignin was dissolved into the extract during silica extraction. The amount of lignin dissolved in this extract was calculated by the following equation.

[Equation 2]

Residual lignin content (%) of residue after extraction Lignin Dissolution by Extraction (%) Example 25 22.3 9.9 Comparative Example 2 19.9 32.7 Comparative Example 3 14 58.5

As shown in Table 10, looking at Example 25 according to the present invention, the lignin dissolution amount is 9.9% at a temperature of 70 ℃, Comparative Example 2 and Comparative Example 3, 32.7% at a temperature of 100 ℃, 130 ℃ It was confirmed that the amount of lignin dissolved was very high when the rice hull soaking temperature was 58.5% at a temperature of 100 ℃ or more. If the chaff immersion temperature is higher than 100 ℃, the content of impurities in the chaff immersion liquid increases, it can be expected to increase the purification step in the purification process, increase the water consumption and waste water generation, and related energy consumption and production cost increase .

At this time, as a result of confirming the silica extraction amount of Example 25, Comparative Example 2 and Comparative Example 3, all of the silica extraction amount was found to be similar to 80% or more.

Determining the amount of lignin dissolved and the amount of silica extracted comprehensively, silica extraction under high temperature conditions of 100 ℃ or more can cause problems that the economic efficiency of the extract is greatly reduced and the economic efficiency is greatly reduced as the elution of lignin and organic substances increases. You can see that there is.

< Experimental Example  3> Comparison of Extract Purification Effect According to Extraction Conditions

In order to confirm the effect of the method of extracting silica from the chaff according to the present invention, the change in the state of the extract in the step of washing the distilled water for purification of silica during the silica extraction process performed in Example 25, Comparative Example 2 and Comparative Example 3 Was evaluated and the results are shown in FIG.

Extraction temperature conditions were 70 ℃ (Example 25), 100 ℃ (Comparative Example 2), 130 ℃ (Comparative Example 3) was immersed in NaOH 2% aqueous solution for 1 hour. The sulfuric acid silica extract obtained under each condition using sulfuric acid was titrated to pH 8, and silica was precipitated. Then, the precipitated silica was precipitated from the precipitated rice husk silica immersion liquid using a centrifugal separator to perform solid-liquid separation. At this time, the solid-liquid separation condition using a centrifuge was 3000 rpm, 1 minute each time. After centrifugation, the supernatant was removed, and the precipitated rice hull silica was washed with distilled water and the centrifugal washing was repeated. At this time, the characteristics of the supernatant were compared and evaluated for each washing step. In the case of lignin, as the chromophore is present, the higher the lignin content in the supernatant is, the darker the brown color is.

In the case of chaff extract obtained under the low temperature of less than 100 ℃ according to the present invention, the content of impurities such as lignin is low, so that the lignin is easily removed in the washing step, the color of the supernatant is lightened, and the purification efficiency of chaff silica increases. In the fourth purification step, it could be seen that it began to become transparent.

< Experimental Example  4> silica purity evaluation

In order to confirm the effect of the method of extracting silica from the chaff according to the present invention, silica precipitation was performed in the immersion liquid after the silica extraction performed in Example 18. The precipitated silica was heat-treated at 500 ° C. and 800 ° C. to remove residual organic materials, and then silica content analysis was performed. Impurities Al, Na, K, Mg, Ca, Zn, Pb, and Cd, which are typically included in rice hull silica, were analyzed by ICP-MS, and the degree of silica was evaluated by applying the order method. Purity evaluation results of the silica heat-treated at 500 ℃ and 800 ℃ for each temperature showed a purity of about 99%.

Through this, it was judged that a high enough silica could be obtained by simple heat treatment. The purity difference of the silica obtained at the heat treatment temperature of 500 degreeC and 800 degreeC showed little. It was determined that the decomposition of organic impurities present in rice hull silica almost occurred at 500 ° C.

element Content evaluation after 500 ℃ heat treatment (%) Content evaluation after 800 ℃ heat treatment (%) Si 98.7 98.6 Al 0.0 0.0 Na 1.2 1.1 K 0.1 0.2 Mg 0.0 0.0 Ca 0.0 0.0 Zn 0.0 0.0 Pb - - CD - -

< Experimental Example  5> Evaluation of solid and ash content of extract

In order to confirm the effect of the method of extracting silica from the chaff according to the present invention, the solid content, ash content, ash content of the solid content of the extract obtained according to the silica extraction performed in Example 18 and Comparative Example 1 And the results are shown in Table 12 below.

Solid content (%) Ash content (%) Ash content relative to solids (%) Example 18 6.3 5.7 90.4 Comparative Example 1 5.2 3.2 56.4

As shown in Table 12, when the method of extracting silica from the chaff according to the present invention can be confirmed that the ash content of the solids content is very high as 90.4%. On the other hand, Comparative Example 1, which was carried out under conventional cooking conditions (KOH 30%, solid solution ratio 1:10, temperature condition of 150 ° C., immersion time: 1 hour), was found to have a significantly lower ash content of 56.4% compared to solids. .

This is because, in the case of Comparative Example 1, in addition to the silica contained in the rice husk, lignin, hemicellulose, etc. are eluted together, the solid content is not significantly different, but the ash content is greatly different, and the method of Comparative Example 1 is highly purified. It can be confirmed that there is a problem that a high cost is generated because of the treatment required.

< Experimental Example  6> Confirmation of Silica Extraction Characteristics from Ground Chaff

In order to confirm the extraction characteristics in the case of using crushed chaff in the method of extracting silica from the chaff according to the present invention, the amount of silica extraction after silica extraction performed in Examples 34 to 44 was analyzed.

The amount of silica extracted was calculated as a ratio of the amount of ash removed by dipping by comparing the amount of ash before the immersion and after washing the rice hull immersed in the alkaline solution.

(1) Evaluation of Silica Extraction Characteristics by High Liquid Ratio

Silica extraction amount was analyzed after silica extraction performed in Examples 34 to 36, and the results are shown in FIG.

As shown in Figure 7, it was confirmed that the silica extraction amount of the silica extraction performed in Examples 34 to 36 is about 85% or more.

(2) Evaluation of Silica Extraction Characteristics According to Alkali Concentration

Silica extraction amount was analyzed after the silica extraction carried out in Example 34 and Examples 37 to 38, the results are shown in FIG.

As shown in FIG. 8, the silica extraction amount in Example 37 having a concentration of 0.5% sodium hydroxide as an alkaline solution was about 31%, and the silica extraction amount in Example 38 having 1% was about 65%. Could.

In particular, in the case of Example 38 and Example 34 in which the concentration of sodium hydroxide as the alkaline solution is 2% or more, it was confirmed that the silica extraction amount was about 80% or more.

(3) Evaluation of Silica Extraction Characteristics over Time

Silica extraction amount after silica extraction performed in Example 34 and Examples 40 to 44 was analyzed, and the results are shown in FIG. 9.

As shown in FIG. 9, in Example 40 having an immersion time of 15 minutes, it was confirmed that the silica extraction amount was about 75%.

In this case, in the case of Example 34 and Examples 41 to 44 having an immersion time of 30 minutes or more, it was confirmed that the silica extraction amount was about 80% or more.

As described above, in the method of extracting silica from the rice hulls according to the present invention, since silica is extracted from the rice hulls using an alkaline solution at low temperature, the incidence of dissolution of lignin and other organic substances is low. It can be confirmed that there is an easy effect.

Claims (8)

A temperature of 20 ° C. to 70 ° C. in a ratio of 1: 3 to 1:20 in a liquid-liquid ratio (volume of liquid to weight of solid) in an alkali solution containing silica surrounded by lignin in a concentration of 2% to 10%. Extracting silica by dipping in a method of extracting silica from the chaff.
The method of claim 1,
The immersion is a method for extracting silica from chaff, characterized in that carried out at a temperature of 65 ℃ to 70 ℃.
delete delete The method of claim 1,
The chaff is a method of extracting silica from the chaff, characterized in that at least one selected from the group consisting of untreated chaff, milled chaff and swollen chaff.
A temperature of 20 ° C. to 70 ° C. in a ratio of 1: 3 to 1:20 in a liquid-liquid ratio (volume of liquid to weight of solid) in an alkali solution containing silica surrounded by lignin in a concentration of 2% to 10%. Extracting silica by immersion in (step 1);
Separating the silica extract produced in step 1 from the rice husks (step 2);
Neutralizing the extract separated in step 2 (step 3);
Recovering the precipitate in the extract neutralized in step 3 (step 4); And
Method for preparing silica from chaff comprising the step (step 5) of heat-treating the precipitate recovered in step 4 to obtain silica.
The method of claim 6,
After performing step 4, washing the recovered precipitate; further comprising a method of producing silica from chaff.
The method of claim 6,
The heat treatment of step 5 is a method for producing silica from chaff, characterized in that carried out at a temperature of 300 ℃ to 800 ℃.

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