ES2688090B2 - PROCEDURE FOR OBTAINING BIOSILICE FROM CASCARA DE ARROZ - Google Patents

Description

DESCRIPTION

PROCEDURE FOR OBTAINING BIOSYLLISM FROM RICE SHELL

Field of the Invention

The present invention falls within the general field of biomaterial synthesis and in particular it relates to a process for obtaining biosilicate from rice husk and the use of said biosilicate.

State of the art

Mesoporous silica is currently one of the most important industrial materials whose interest lies in its multiple applications, such as absorbent, insulator, sensor, as photovoltaic wafers, support in separation processes and catalysis among others. In recent years, it has also been used in the field of biomedicine for controlled drug release and as a biosensor. The use of this material as a support in catalysis provides stability and improvement in the conversion and selectivity of the desired products and in addition to allowing the catalyst to be recycled once the reaction cycle is finished, thereby increasing the efficiency of the process.

In recent years, biomass has become a source of resources in sustainable chemistry, with large applications in the synthesis of porous materials, chemical compounds and biofuels.

Silicon is the second most abundant element in the earth's crust. Despite this, the processes to synthesize siliceous nanomaterials are usually complex and expensive since they require high energy consumption.

To date, several methods have been developed to carry out the synthesis of these porous materials where in most cases a siliceous precursor, such as a silicon alkoxide (tetraetroxysilane) is used as a source of silica. These methods are effective for the synthesis of nanostructured materials since they allow the control of particle size, morphology and porosity. However, its main disadvantages are its high cost and its low sustainability.

The silicon alkoxides used in the design of nanostructured materials are synthesized from a series of stages that start from the carbothermal reduction of silica Rough, like sand, needing a lot of energy, they are not compatible with the environment. Due to these inconveniences, on the one hand, new, more economical and sustainable synthetic routes are being designed, and on the other, alternative sources are being used for the production of mesoporous silica, so that they are fundamental aspects for the advancement of the production of Siliceous materials with high performance to meet the increase in current demand for such materials.

Rice husk (RH) is a byproduct of biomass that is obtained after milling rice. This agricultural residue contains up to 20% by weight of silica, which is in the hydrated form (SiO ² , with 5-15% H ² O). Silicon is an important element for the growth of rice, which is present in the form of water-soluble silicic acid, to subsequently precipitate in the rice husk in the form of amorphous silica.

With a content of 20-25% silica in dry weight, the amounts of biomass obtained from this residue offer a great opportunity for the production of nanostructured siliceous materials for industrial applications. In 2012 alone, world rice production was approximately 738 million tons, which means that around 148-185 million tons of rice husk biomass were generated worldwide.

A determining factor when choosing rice husk as biomass for the production of high added value is that it is a waste product. The applications of the rice husk in the industry are limited due to its low nutritional value, its resistant nature and its high ash content after calcination. For all this, the recovery of this waste is a great alternative to its current storage, burning in boilers or its use as a bed for animals. Another advantage of using the rice husk in comparison to the use of ashes from agri-food waste is that it is not necessary to perform a heat treatment to obtain a final product with good characteristics, thus obtaining a product of excellent properties without energy expenditure and the production of contaminants derived from this treatment.

The mechanochemical process of milling, used in the synthesis of nanomaterials, has recently emerged as a very promising technology in which the energy generated during the milling process has shown that it is capable of breaking and forming bonds in chemical compounds as well. how to generate new surface species in the material synthesis. Likewise, microwave-assisted extraction is a determining technique for obtaining silica from rice husk. The best heating of microwave-assisted processes translates into greater conversion, smoother working conditions and shorter synthesis times.

The processes that have been used to obtain biosilica have a great simplicity, being clean, reproducible and versatile in the development of a wide range of advanced nanomaterials such as supported metals, metal oxide nanoparticles and nanocomposites with various applications in catalysis, synthesis organic, sensors, drug transporters or absorption processes.

Description of the invention

The present invention solves the problems described in the state of the art since, on the one hand, an added value product, mesoporous biosilicate is obtained and on the other hand, the recovery of a residue from the food industry is achieved, as is The rice husk.

Thus, in a first aspect, the present invention relates to a process for obtaining mesoporous biosilicate from rice husk (hereinafter, process of the present invention) comprising the following steps:

a) obtaining rice husk particles by milling and sieving the rice husk,

b) adding an acid solution to the particles obtained in step a), more particularly, the acid solution is hydrochloric acid of molarity between 0.25-0.5 M in water.

c) extraction of the biosilica by irradiation of the solution obtained in step b) in the microwave,

In a particular embodiment, the process of the present invention further comprises an additional step of washing, drying and calcining of the biosilica obtained in step c).

In a particular embodiment, step a) is repeated at least once.

In a more particular embodiment of the present invention, the grinding of step a) is carried out under conditions of at least 250 rpm, for at least 10 minutes. More particularly, it is performed between 250 rpm. Preferably at 350 rpm.

In a more particular embodiment of the present invention, the screening of step a) is carried out with a 0.2 mm-0.6 mm sieve.

In a more particular embodiment, the microwave irradiation of step c) is carried out at a temperature between 70-100 ° C for 30-60 min at 200-300 W.

In another particular embodiment, the washing and drying of biosilicate obtained in step c) is carried out at a temperature between 80-110 ° C-,

In another particular embodiment, the biosilicate calcining obtained in step c) is performed at a temperature between 400-800 ° C

In another aspect, the present invention relates to the use of mesoporous biosilicate obtained by the process of the present invention, for the production of nanomaterials.

In another aspect, the present invention relates to a process for obtaining a metallic nanomaterial comprising:

i) obtaining mesoporous biosilicate by the process of the present invention,

ii) grinding of the biosilica obtained in step i) together with a metal precursor

iii) calcination of the material obtained in ii) at a temperature of at least 300-500 ° C

In a more particular embodiment of the present invention, the milling of step ii) is carried out between 250-500 rpm, for 10-30 min.

Detailed description of the invention

First, the mesoporous biosilica was obtained from the recovery of the rice husk residue. The large size of the rice husk makes subsequent microwave extraction difficult, so the grinding process was necessary to reduce the particle size. The biosilica extraction was carried out by a microwave-assisted process. For this, a sample of rice husk was introduced into an acid solution that was subsequently heated in the microwave. This step was crucial to obtain the biosilica. The use of an acid solution eliminated the cations present in the rice husk, resulting in a pure silica. On the other hand, the use of the microwave provided us with constant and precise, controlled heating, which allowed us to shorten the extraction times. The processes of washing, drying and calcination are crucial to obtain a more homogeneous and more pure material.

After obtaining a mesoporous siliceous material through the recovery of the biomass residue, the synthesis of the catalyst was carried out. The technique used was mechanical-chemical grinding.

For the preparation of the catalyst, a precursor of the nanoparticle to be supported is used (for example, FeCh, in the case of depositing iron oxide nanoparticles), adjusting this precursor to the amount of metal that we want in the catalyst (0.5% , 1%, 3%. Etc.)

The metal precursor was introduced along with the mesoporous silica in a planetary ball mill where the mechanochemical process occurs during grinding. In this mechanism the activation of the surface of the material occurs resulting in dehydroxylation during milling, thus producing water molecules in the reaction medium. In the presence of water, the metal precursor is hydrolyzed to hydroxide during milling and subsequently high local temperatures (exclusively at localized points) facilitate the decomposition of hydroxides into oxide nanoparticles (NPs). By calcining the final material we obtain during grinding, we ensure that the intermediates of the hydroxide formed also become oxides, which are in the form of nanoparticles in the final material. Likewise, traces of HCl are obtained as a byproduct of the generation of the NPs of the RH-Si material.

Example 1: Obtaining mesoporous biosilicate from rice husk.

The rice husk was subjected to grinding in a Retsch-PM-100 planetary ball mill using a 125 ml container and eighteen stainless steel balls (10 mm diameter and 5 g weight each) under 350 grinding conditions rpm for 10-15 minutes. The material obtained from this process was screened using a 0.2 mm sieve and the same process is repeated with the material that remains un sieved.

To obtain the biosilica from this residue, microwave assisted extraction was carried out using the non-focused microwave ETHOS-ONE. The sieve of the rice husk was added to a solution of molarity HCl between 0.25-0.5 M in water and subsequently subjected to microwave irradiation at 100 ° C for 30-60 minutes with a power of 300 W. The solution The resulting was washed with distilled water, filtered and finally dried in an oven at 100-120 ° C between 6-24 hours. Finally the material It was calcined in a flask between 450-650 ° C for 4 hours to obtain the pure biosilica (RH-Silica).

Example 2: Support of iron nanoparticles on the mesoporous silica obtained in example 1.

For the preparation of a Fe / RH-Silica catalyst, RH-Silica underwent another grinding process in the same planetary ball mill (optimal grinding conditions, 350 rpm, 10-15 minutes) together with an appropriate amount of iron precursor (FeCh ■ 4 H ² O) to reach the theoretical% desired in the final material. After the grinding process was finished, the resulting material was calcined at 400-500 ° C for 4 hours.

Claims (9)

1. Procedure for obtaining mesoporous biosylic from rice husk comprising the following stages: a) obtaining rice husk particles by milling and sieving the rice husk, b) adding an acid solution to the particles obtained in step a), c) extraction of the biosilica by irradiation of the solution obtained in step b) in the microwave. 2. The method according to claim 1 comprising an additional step of washing, drying and calcining the biosilica obtained in step c). 3. Method according to any of the preceding claims, wherein the grinding is carried out under conditions of at least 250 rpm, for at least 10 minutes. 4. Method according to the preceding claims, wherein the sieving is carried out with a 0.2-0.6 mm sieve. 5. Method according to the preceding claims, wherein the microwave irradiation is carried out at a temperature between 70-100 ° C, for 30-60 minutes at 200-300W 6. Method according to claim 2, wherein the washing and drying is carried out at a temperature between 80-110 ° C. 7. Method according to claim 2, wherein the calcining is performed at a temperature between 400-800 ° C. 8. Procedure for obtaining a metallic nanomaterial comprising: i) obtaining mesoporous biosilicate by a method according to any of claims 1-7, ii) grinding of the biosilica obtained in step i) together with a metal precursor iii) calcination of the material obtained in ii) at a temperature of at least 300 ° C. 9. Method according to claim 8, wherein the grinding is carried out between 250-500 rpm, for 10-30 minutes.