CN112390260A - Method for producing mesoporous porous silica from biomass - Google Patents
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Abstract
The present invention relates to a method for producing mesoporous porous silica from biomass, and more particularly, to a method for producing mesoporous silica in which the surface area and the size of pores (pores) of mesoporous silica produced from biomass can be controlled.
Description
Technical Field
The present invention relates to a method for producing mesoporous silica from biomass, and more particularly, to a method for producing mesoporous silica in which the surface area and pore (pore) size of mesoporous silica produced from biomass can be controlled.
Background
It is known that significant amounts of silica are present in biomass, especially lignocellulosic biomass, especially in rice hulls or straw, including about 10% by weight silica.
Various uses of such biogenic silica are being studied as silicon raw materials (J.A. Amick, J.electrochem. Soc.129,864 (1982); L.P.Hunt, J.electrochem. Soc.131,1683(1984)), silicon carbide raw materials (R.V. Krishnarao, J.Am.chem. Soc.74,2869(1991)), cement additives (Jose James, et. al, J.Sci.Ind.Res.51,383(1992)), and the like.
In addition, in order to obtain silica from biomass, research and development of techniques for removing organic substances (cellulose, hemicellulose, lignin, and the like) of biomass have been continuously conducted, and typically, a method of obtaining silica by treating rice hulls or straws with acid and then treating the treated rice hulls or straws at high temperature has been used.
However, these conventional methods focus on the production of silica only, and it is difficult to control the structure of the produced silica such as the area of pores formed on the surface of the silica, and thus the methods have limitations in terms of industrialization and commercialization.
Further, plant bodies such as rice hulls are extremely low density materials having a density of about 0.1g/mL, and are extremely small in mass but extremely large in volume, and therefore the process volume becomes large, and an excessive amount of water is used when washing and chemical treatment are performed.
In this case, not only the amount of water increases and thus the volumes of the reactor and the scrubber increase, there are difficulties in handling (handling) due to the large volume when processing the plant bodies in the washing process, and with the large scale of the related facilities, there is a problem that the equipment cost increases, and there is a problem that it is not suitable for the engineering of the commercial scale.
Documents of the prior art
Patent document
(patent document 0001) Korean patent laid-open publication No. 10-1703849
Disclosure of Invention
The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a method for producing mesoporous porous silica, which can control the surface area and the size of pores (holes) of mesoporous porous silica produced from biomass.
The above and other objects and advantages of the present invention will become apparent from the following description illustrating preferred embodiments.
The object can be achieved by a method for producing porous silica comprising the steps of: a first step of heating the biomass to perform a heat treatment in such a manner as to reduce the volume and mass of the biomass; a second step of reacting the heat-treated biomass with any one of an acidic solution, an ionic liquid, and a microbial fermentation broth to remove metal ions from the biomass to produce a silicon-rich (Si-rich) biomass; a third step of filtering and separating the silicon-rich biomass, and then heating the separated biomass to produce white silica; a fourth step of adding an aqueous alkali solution to the white silica and then heating the mixture to produce a silicate solution; a fifth step of adding a surfactant and an acidic solution to the silicate solution and stirring to manufacture (co-assembly) silica having the surfactant incorporated therein; and a sixth step of aging (marking) the silica combined with (co-assembly) a surfactant and then calcining (calcination) the silica to remove the surfactant and produce porous silica.
In this case, the biomass in the first step may be at least one selected from rice bran, rice hull, straw, reed, corn leaf, and corn stalk, and the biomass may be heated at a temperature of 450 to 750 ℃ in the first step.
And, the acidic solution in the second step may be a sulfuric acid solution or a hydrochloric acid solution, and the ionic liquid in the second step may include an ionic liquid selected from the group consisting of 1-allyl-3-methylimidazolium chloride, 1, 3-dimethylimidazolium chloride, 1-butyl-3-methylimidazolium dicyanamide, 1-butyl-3-methylimidazolium hexafluoroantimonate, 1-butyl-3-methylimidazolium hexafluorophosphate, 1-butyl-3-methylimidazolium bicarbonate, 1-butyl-3-methylimidazolium bisulfate, 1-butyl-3-methylimidazolium methylsulfate, 1-butyl-3-methylimidazolium tetrachloroaluminate, and mixtures thereof, 1-butyl-3-methylimidazolium tetrachloroborate, 1-butyl-3-methylimidazolium thiocyanate, 1-dodecyl-3-methylimidazolium iodide, 1-ethyl-2, 3-dimethylimidazolium chloride, 1-ethyl-3-methylimidazolium bromide, 1-ethyl-3-methylimidazolium chloride, 1-ethyl-3-methylimidazolium hexafluorophosphate, 1-ethyl-3-methylimidazolium tetrafluoroborate, 1-hexyl-3-methylimidazolium tetrafluoroborate and 1-butyl-4-methylpyridinium chloride.
In the third step, the white silica is preferably produced by heating at 850 to 950 ℃.
And, the aqueous alkali solution in the fourth step may be an aqueous sodium hydroxide solution, and the surfactant in the fifth step may be selected from the group consisting of Pluronic P-123(Pluronic P-123, EO)20PO70EO20) Hexadecyltrimethylammonium bromide (CTAB: cethyltetramethonium bromide) and trimethylbenzene (TMB: trimethylbenzene), and the acidic solution in the fifth step may be at least one selected from the group consisting of an acetic acid solution, a sulfuric acid solution, and a hydrochloric acid solution.
In the sixth step, it is preferable that the aging treatment is performed at a temperature of 60 to 120 ℃ and the calcination is performed at a temperature of 450 to 650 ℃.
According to the present invention, the heat treatment step is performed at the initial stage of the silica production process, so that the organic matter of the biomass can be decomposed, and the washing process can be omitted to reduce the amount of water used, thereby reducing the process volume and the process time.
In addition, a surfactant is combined with (co-assembly) silica in the silica production process and then removed, whereby porous silica having a plurality of mesoporous pores formed therein can be produced.
However, the effects of the present invention are not limited to the above-mentioned effects, and other effects not mentioned can be clearly understood by those skilled in the art from the following description.
Drawings
Fig. 1 is a view schematically showing a method for manufacturing porous silica according to an embodiment of the present invention.
FIG. 2 shows the results of SEM-EDS ((a) initial rice husk, (b) RH-SiO)2))。
FIG. 3 shows RH-SiO2XRD (a), SEM (b), TEM (c-d), and N (e)2Isotherms, (f) results of pore size distribution.
FIG. 4 shows TEM images of OMS-1(a to c), OMS-2(d to f), OMS-3(g to i) and OMS-4(j to l).
FIG. 5 shows (a) N in the examples and production examples2Isotherms, and (b) pore size distribution results.
FIG. 6 shows SAXS patterns ((a) OMS-1, (b) OMS-2, (c) OMS-3, (d) OMS-4, (e) RH-SiO2) A graph of (a).
FIG. 7 is a graph showing the results of (a) XRD pattern and (b) SEM-EDS of example 1.
Detailed Description
The present invention will be described in detail below with reference to embodiments of the present invention and the accompanying drawings. These embodiments are merely exemplary for the purpose of more specifically illustrating the present invention, and it will be apparent to those having ordinary skill in the art that the scope of the present invention is not limited to these embodiments.
Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs, and the description of the specification including definitions herein takes precedence when viewed in a contrary manner.
In order to clearly explain the invention proposed in the drawings, portions irrelevant to the explanation are omitted, and like reference numerals are given to like portions throughout the specification. In addition, when a component is referred to as being "included" in a certain portion, unless otherwise stated, it means that other components may be included without excluding other components that are not stated. In the specification, "unit" means a unit or a block that performs a specific function.
In each step, a reference numeral (first, second, etc.) is used for convenience of description, and the reference numeral does not describe the order of each step, and each step may be performed in an order different from the described order unless a specific order is explicitly described in the text. That is, the steps may be performed in the same order as described, may be performed substantially simultaneously, or may be performed in the reverse order.
Fig. 1 is a view schematically showing a method for manufacturing porous silica according to an embodiment of the present invention. Referring to fig. 1, a method for manufacturing porous silica according to an embodiment of the present invention includes the steps of: a first step of performing a heat treatment by heating the biomass to reduce the volume and mass of the biomass; a second step of reacting the heat-treated biomass with one of an acidic solution, an ionic liquid and a microbial fermentation broth to remove metal ions from the biomass, thereby manufacturing a silicon-rich (Si-rich) biomass; a third step of filtering and separating the silicon-rich biomass, and then heating the separated biomass to produce white silica; a fourth step of adding an aqueous alkali solution to the white silica and then heating the mixture to produce a silicate solution; a fifth step of adding a surfactant and an acidic solution to the silicate solution and stirring to manufacture (co-assembly) silica having the surfactant incorporated therein; and a sixth step of subjecting the (co-assembly) surfactant-bonded silica to aging treatment (aging) and then calcination (calcination) to remove the surfactant and produce a porous silica. In the present invention, by using a surfactant as a method for producing porous silica from biomass, a large number of pores can be formed on the surface of silica as compared with conventional methods, and the surface area can be increased. Thus, it can be used as an additive in various industrial fields such as semiconductors and cosmetics. In the present specification, biomass is a concept including not only raw material substances but also organic substances such as cellulose decomposed by an acid solution or the like.
The first step is a heat treatment step that heats the biomass to reduce the volume and mass of the biomass. The biomass may be at least one selected from rice bran, rice hull, straw, reed, corn leaf, and corn stalk as a raw material for producing silica. Preferably, the biomass is heated at a temperature of 450 to 750 ℃. In the case where the heating temperature is lower than 450 c, there is a possibility that the volume reduction effect is not high due to poor removal of organic matter and the metal cation attached to the organic matter is not removed well, and in the case where the heating temperature exceeds 750 c, it is converted into SiC form instead of silica form, thereby causing a decrease in purity of the produced silica. The present invention reduces the volume of biomass through a thermal decomposition step at the initial stage of the process, makes the subsequent process easier, and decomposes organic substances through thermal decomposition at the initial stage, thereby making it possible to omit unnecessary warm water washing process.
The second step is a step of reacting the heat-treated biomass with one of an acidic solution, an ionic liquid, and a microbial fermentation broth to remove metal ions from the biomass, thereby producing a silicon-rich (Si-rich) biomass.
At this time, the acidic solution is not particularly limited. Preferably, a sulfuric acid solution or a hydrochloric acid solution is used. Specifically, in the case of using a sulfuric acid solution, the following steps may be included in order: mixing the heat-treated biomass with sulfuric acid with the purity of 70-75 wt% and reacting for 1 hour; adding distilled water to adjust the concentration of sulfuric acid to 2-5 wt%; a step of decomposing organic substances such as cellulose, hemicellulose and lignin by reacting for one hour in a high-temperature high-pressure reactor at 115-125 ℃ and allowing metal ions to permeate out; and a step of filtering the mixture to remove decomposed organic substances and exuded metal ions, washing the washed product with distilled water, and drying the product at about 60 ℃ for 22 to 26 hours to produce a silicon-rich (Si-rich) biomass.
And, in case of using a hydrochloric acid solution as the acidic solution, the following steps may be sequentially included: mixing the heat-treated biomass with hydrochloric acid with the purity of 8-15 wt% and reacting for 1 hour; a step of decomposing organic substances such as cellulose, hemicellulose and lignin by reacting for one hour in a high-temperature high-pressure reactor at 115-125 ℃ and allowing metal ions to permeate out; and a step of filtering the mixture to remove decomposed organic substances and exuded metal ions, washing the washed product with distilled water, and drying the product at about 60 ℃ for 22 to 26 hours to produce a silicon-rich (Si-rich) biomass.
Ionic liquids may be used instead of acidic solutions. Ionic liquid (ionic liquid) means a liquid consisting of ions only, usually consisting of giant cations including nitrogen and smaller anions. With this structure, the lattice energy of the crystal structure can be reduced, and as a result, it will have a low melting point and high thermal stability.
In the case of bringing the ionic liquid and the biomass into contact, hydrogen bonds of hydroxyl groups present in the biomass are weakened by the ionic liquid, so that the crystalline portion is transformed into non-crystallinity, which eventually promotes hydrolysis reaction of cellulose, hemicellulose, lignin, and the like.
That is, the anion of the ionic liquid binds to the hydrogen of the hydroxyl group, and the cation binds to the oxygen of the hydroxyl group, thereby hindering the complicated hydrogen bond between the hydroxyl groups, and finally dissolving the dietary fiber of the biomass.
In the case of using such an ionic liquid, not only is it more environmentally friendly than using a strong acid, but also since the decomposition of biomass is performed under milder conditions, the structure of the silica produced can be easily controlled by adjusting the synthesis conditions such as the heat treatment temperature or time.
In order to have high thermal stability while promoting decomposition of biomass, preferably, the ionic liquid includes: a) a cation selected from the group consisting of substituted or unsubstituted imidazolium, pyridinium, ammonium, phosphonium, sulfonium, pyrazolium and pyrrolidinium, and b) a cation selected from the group consisting of BF4 -、PF6 -、Cl-、Br-、I-、OH-、NO3 -、SO4 2-、CF3CO2 -、CF3SO3 -、AlCl4 -、SCN-、(CF3SO2)2N-、CH3CO2 -And CH3SO4 -At least one anion of (a).
More specifically, the ionic liquid may include one or more ionic liquids selected from the group consisting of 1-allyl-3-methylimidazolium chloride, 1, 3-dimethylimidazolium chloride, 1-butyl-3-methylimidazolium dicyanamide, 1-butyl-3-methylimidazolium hexafluoroantimonate, 1-butyl-3-methylimidazolium hexafluorophosphate, 1-butyl-3-methylimidazolium bicarbonate, 1-butyl-3-methylimidazolium hydrogen sulfate, 1-butyl-3-methylimidazolium methyl sulfate, 1-butyl-3-methylimidazolium tetrachloroaluminate, 1-butyl-3-methylimidazolium tetrachloroborate, 1-allyl-3-methylimidazolium tetrachloroborate, and mixtures thereof, 1-butyl-3-methylimidazolium thiocyanate, 1-dodecyl-3-methylimidazolium iodide, 1-ethyl-2, 3-dimethylimidazolium chloride, 1-ethyl-3-methylimidazolium bromide, 1-ethyl-3-methylimidazolium chloride, 1-ethyl-3-methylimidazolium hexafluorophosphate, 1-ethyl-3-methylimidazolium tetrafluoroborate, 1-hexyl-3-methylimidazolium tetrafluoroborate and 1-butyl-4-methylpyridinium chloride.
Specifically describing the reaction of biomass and ionic liquid, the method can sequentially comprise the following steps: mixing 0.5-2L of ionic liquid with 100g of biomass; reacting at 100-200 ℃ for 24-72 hours to decompose organic matters such as cellulose, hemicellulose and lignin and enable metal ions to seep out; the biomass is filtered to remove decomposed organic substances and exuded metal ions, washed with distilled water, and reacted at about 60 ℃ for 10 to 13 hours to produce a silicon-rich (Si-rich) biomass. In this case, in order to improve the reaction efficiency, it is preferable to carry out the second step under stirring at 100 to 400 rpm.
Also, in order to remove metal ions from the biomass and produce a silicon-rich biomass, a microbial fermentation broth may be used instead of the acidic solution. In the case of using a microbial fermentation broth, since a strong acid such as sulfuric acid may not be used, there may be an effect that stability can be more ensured. Specifically, the method may sequentially include the following steps: mixing 0.5-2L of microbial fermentation liquor with 100g of biomass; reacting for 1-5 hours under the reaction condition of 120-200 ℃ and 1-5 atm in the atmosphere of carbon dioxide to decompose organic matters such as cellulose, hemicellulose, lignin and the like and enable metal ions to seep out; the biomass is filtered to remove decomposed organic substances and exuded metal ions, washed with distilled water, and reacted at about 60 ℃ for 10 to 13 hours to produce a silicon-rich (Si-rich) biomass. Alternatively, in order to shorten the reaction time, the microorganism fermentation broth may be mixed and then reacted for 30 minutes to 2 hours under the reaction conditions of 120 to 200 ℃ and 250 to 1200atm in an air atmosphere to decompose organic substances such as cellulose, hemicellulose, and lignin and to allow metal ions to permeate out.
In this case, the microbial fermentation broth is preferably a fermentation broth of a phytopathogenic (phytopathogenic) filamentous fungus or a saprophytic (saprophytic) filamentous fungus, which is known to discharge various effective components capable of decomposing plant cell walls.
In particular, in a filamentous fungus of tree root including oxaloacetate hydrolase (oxaloacetate hydrolase) as a cytoplasmic enzyme (cytoplasmic enzyme), the hydrolase discharges an effective component such as organic acid (oxalacetic acid or the like) capable of decomposing organic substances such as cellulose, hemicellulose, lignin or the like in a fermentation process, thereby further promoting the removal of impurities from biomass. Various filamentous fungi having oxaloacetate hydrolase (oxaloacetate hydrolase) can be used, and as an example, Aspergillus niger (Aspergillus niger), Paxillus convolvulus (Paxillus invoolutus), and the like can be used. In this case, in order to improve the decomposition efficiency of other organic substances such as cellulose, hemicellulose and lignin, it is preferable to culture filamentous fungi at a pH of 5-6 using a hexose as a carbon supply source.
The third step is a step of filtering the silicon-rich biomass to separate it and then heating it to produce white silica, and white silica (white silica) can be produced by pouring out the acidic solution, the ionic liquid or the microbial fermentation liquid, washing it with water, drying it for 24 hours, and burning it at 850 to 950 ℃ for about 12 hours.
The fourth step is a step of adding an aqueous alkali solution to white silica and then heating the mixture to produce a silicate solution, and an aqueous alkali solution in which an alkaline substance such as sodium hydroxide, lithium hydroxide, calcium hydroxide, or sodium carbonate is dissolved in water may be used. By taking sodium hydroxide as an example, when an aqueous sodium hydroxide solution is added to white silica and then heated, a silicon component is extracted from biomass to produce sodium metasilicate (Na)2SiO3) Or a form in which sodium metasilicate is combined with crystal water (Na)2SiO3·nH2O), and the like. In this case, 100 to 200mL of an aqueous alkaline solution is preferably added to 100g of biomass.
The fifth step is a step of adding a surfactant and an acidic solution to the silicate solution and stirring to manufacture a co-assembly silica having a surfactant. At this time, a surfactant is used as a structure-directing agent, and an acidic solution is used to adjust pH. The preparation method comprises the steps of forming a neutral pH or alkaline pH condition by using an acidic solution, mixing a surfactant, and stirring at the temperature of 20-60 ℃ for more than 1 hour, so that a meso-structure is formed, and a silica framework (framework) and a structure directing agent are combined at the same time. The porous silica is formed by removing the surfactant in the following sixth step.
The surfactant is preferably selected from Pluronic P-123(Pluronic P-123, EO)20PO70EO20) Hexadecyltrimethylammonium bromide (CTAB: cethyltetramethonium bromide) and trimethylbenzene (TMB: trimethylbenzene), but the present invention is not limited thereto, and other polymers that perform similar functions may be used. As an example, poly (ethylene glycol) -b-poly (propylene glycol) -poly (ethylene glycol) (PEG-PPG-PEG: poly (ethylene glycol) -b-poly (propylene glycol) -poly (ethylene glycol) as a triblock copolymer may be used, and specifically, at least one selected from the group consisting of non-ionic (non-ionic) triblock copolymers of Pluronic type, Kolliphor type, polyoxamer type, and synperonic type may be used.
The acidic solution may be at least one selected from the group consisting of an acetic acid solution, a sulfuric acid solution, and a hydrochloric acid solution, but is not limited thereto. Since the acidic solution may be splashed at the time of addition, it should be safely added in a small amount at a time, and sulfuric acid having a purity of 90% or more may be added in order to reduce the reaction time.
The sixth step is a step of aging (aging) the silica having the surfactant bonded thereto and then calcining (calcining) the silica to remove the surfactant, thereby producing the porous silica, and is preferably a step of aging (aging) the silica at a temperature of 60 to 120 ℃ for 6 to 48 hours and then calcining (calcining) the silica at a temperature of 450 to 650 ℃ for 4 hours or more, in order to effectively form mesopores by removing the surfactant. The surfactant bonded to the silica is removed by high-temperature heat treatment, thereby forming pores at sites (spots) where the surfactant is bonded, and finally, the mesoporous silica having a large surface area can be produced.
Hereinafter, the constitution of the present invention and the effects thereof will be described in more detail by way of specific examples and comparative examples. However, the present embodiment is only for explaining the present invention more specifically, and the scope of the present invention is not limited to these embodiments.
[ production example ]
Material preparation
Rice hulls were purchased from polished rice plants in the south of the korean celebration. Sulfuric acid (72%, Daejung Chemicals)&Metals), sodium hydroxide (97%, Aldrich), acetic acid (99.7%, Kanto Chemical), 1-butanol (99.4%, Aldrich), Pluronic P-123 (EO)20PO70EO20Aldrich), cetyltrimethylammonium bromide (CTAB, 99%, Aldrich), trimethylbenzene (TMB, 98%, Aldrich) were used.
Manufacture of silicate solutions
The hulls were washed three times with distilled water to remove physically adhering impurities and dried overnight in an air circulating oven at 80 ℃. Dried rice hulls (100g) were washed with 72% H2SO4(1,000mL) for one hour, and then H was added slowly with distilled water2SO4The concentration of (3) was adjusted to 4%. 4% of H2SO4The rice husk ash (rice husk ash) contained in (1) was reacted at 121 ℃ for one hour to remove flux materials (flux materials) such as alkali and alkaline earth metal oxides.
At the time of pouring H2SO4Thereafter, white silica (RH-SiO) was produced by washing with water and drying at 80 ℃ for 24 hours, followed by burning (under air) at 900 ℃ for 12 hours2). The manufactured white silica was poured into a 5M NaOH solution so that each 1mL of NaOH included 0.5g of SiO2Thereafter, this solution was heated to 150 ℃ in a reflux beaker to produce a sodium silicate solution.
[ example 1]
9.8g of P-123 and an amount of acetic acid equivalent to the hydroxide content of the silicate solution (about 4.5mL) were mixed in 400mL of distilled water. After P-123 was completely dissolved, 11.2mL of TMB was added at 60 ℃. Thereafter, 400mL of distilled water mixed with 16mL of a silicate solution was added, followed by stirring for 12 hours. After the resulting solution was aged (aging) at 100 ℃ for 24 hours, the product was filtered and calcined at 550 ℃ for 4 hours to produce porous silica (example 1, OMS-1).
[ example 2]
Porous silica (example 2, OMS-2) was produced in the same manner as in example 1, except that 400mL of distilled water mixed with 32mL of a silicate solution was added without using TMB.
[ example 3]
1.6g CTAB was dissolved in 8mL of distilled water. Next, 0.8mL of 1-butanol, 6.5mL of the silicate solution, and 10mL of 1.2M H were added in this order2SO4. The resulting solution was stirred vigorously at room temperature for 12 hours. After aging (aging) at 100 ℃ for 24 hours, the product was filtered and calcined at 550 ℃ for 4 hours to produce porous silica (example 3, OMS-3).
[ example 4]
For comparative observation with examples 1 to 3, the amount of white silica added was reduced in the production example to obtain 0.1g of SiO per 1mL of NaOH2Then, a sodium silicate solution produced by heating the solution to 150 ℃ in a reflux beaker was used. To compensate for SiO2The contents of (a) were varied, and a part of the additives were adjusted to manufacture example 4. Specifically, acetic acid (about 17mL) in an amount corresponding to 7.8g of the hydroxide content of the P-123 and silicate solutions was mixed to 160mL of distilled water. After P-123 was completely dissolved, 4.5mL of TMB was added at 60 ℃. Then, 130mL of a solution of distilled water mixed with 45mL of a silicate solution was added thereto, and the mixture was stirred for 12 hours. Aging the resulting solution at 100 deg.CAfter 24 hours, the product was filtered and calcined at 550 ℃ for 4 hours to produce porous silica (example 4, OMS-4).
[ Experimental example ]
Experimental methods
The composition of rice hulls was analyzed according to the National Renewable Energy Laboratory Procedure (National Renewable Energy Laboratory Procedure). Using a moisture analyzer (50-3C, Kern)&Sohn GmbH, Germany) determined the moisture content of the rice hulls. Dissolving rice hull in H2SO4Carbohydrates, acid soluble lignin and extracts were determined using an Agilent 1200 series HPLC with a refractive index detector (Agilent Technologies, USA), equipped with Aminex HPX-87P and HPX-87H chromatography columns (BioRad, USA). Solvent flow rate of 0.6mL/min, 0.5 wt% H at HPX-87H2SO4And water in the case of HPX-87P. To determine the content of acid-insoluble lignin and rice ash (ash), the solids were transferred to a crucible and left for 24 hours at 575 ℃ in a muffle furnace. The rice ash (ash) and acid-insoluble lignin content was calculated according to the experimental procedures of the U.S. Renewable Energy research institute (National Renewable Energy Laboratory Procedure).
The inorganic chemical composition of the silica was determined using inductively coupled plasma optical emission spectroscopy (ICP-OES; Optima 5300DV, PerkinElmer, USA). The X-ray diffraction pattern (XRD) was measured using a Rigaku D/Max2500/PC diffractometer (Japan). Material morphology was studied using scanning electron microscopy (SEM, Oxford, X-Max T50) and transmission electron microscopy (TEM, JEOL, JEM-2000EX, Japan). An Energy Dispersive Spectrometer (EDS) attached to an SEM analysis apparatus was used for elemental analysis.
Nitrogen gas (N) was obtained at 77K using an ASAP 2420 system (Micromeritics Inc., USA)2) Physical adsorption isotherms. The surface area was calculated from the measured isotherms according to the method of Brunauer-Emmett-Teller (BET), at P/P0The pore volume was taken at a single point of-0.995. The pore size distribution of the material was calculated from the adsorption branch of the isotherm (branch) by the Barrett-Joyner-Halenda (BJH) method.
Results of the experiment
2Extraction of high purity Silica (SiO) from rice hulls
Table 1 shows the composition of the initial rice hulls used in the production of the examples, and Table 2 shows the initial rice hulls, white silica RH-SiO2And the inorganic component of example 1 (OMS-1). Rice hulls were analyzed according to the National Renewable Energy Laboratory Procedure. The ratio of rice ash (ash) corresponding to the inorganic component of rice husk was 14.5 wt%. In particular, it was confirmed that almost 95% of the rice ash (ash) was composed of silica (see table 2). Accordingly, it was confirmed that rice hulls can be effectively used as precursors of silicon-based materials.
[ Table 1]
| Water content | Rice ash | Cellulose, process for producing the same, and process for producing the same | Hemicellulose | Organic extract | Lignin | |
| wt％ | 4.93 | 14.52 | 29.97 | 10.61 | 10.76 | 20.32 |
[ Table 2]
In the experiment, cellulose, hemicellulose and inorganic components contained in rice hulls were dissolved and removed by sulfuric acid treatment in addition to silica. Thereafter, the solid product was thermally decomposed to completely remove the residual lignin and organic components, and white silica powder was obtained (see fig. 1). Silica (RH-SiO) from rice hulls2) The purity of (C) was as high as 99.8% (see Table 2). SEM-EDS analysis showed that other impurities in the purified rice hulls were removed (see FIG. 2). Accordingly, it was confirmed that high purity silica can be successfully obtained by chemical treatment using sulfuric acid and thermal decomposition.
In the case of amorphous silicon dioxide, RH-SiO2The XRD pattern of (a) shows broad diffraction around the typical 20 deg. (a of fig. 3). By electron microscopy and N2Physical adsorption isotherm to study RH-SiO2The form of (1). RH-SiO2Has an irregular overall morphology and no specific microstructure or nanostructure (see fig. 3 (b) to (d)). In RH-SiO2A partial mesoporous pore is observed, which appears to be generated when organic components or inorganic impurities are removed. Such characteristics are reflected in the shape of the isotherm and the pore size distribution (see (e) to (f) of fig. 3). RH-SiO2The physical adsorption isotherm of (A) is at P/P0Hysteresis loops of the H3 type are shown at 0.4 to 0.99, which can be observed in particle aggregates with typical irregular slit porosity. The size of the air holes is widely distributed in the range of 2-30 nm, and is quite consistent with a TEM image. RH-SiO2Respectively, surface area and pore volume of 88m2G and 0.13cm3(ii) in terms of/g. Therefore, it was confirmed that high purity could be obtained from rice hullsRH-SiO of2However, it is known that an additional step is required to synthesize high-value added silica having a finer nanostructure and a high specific surface area.
2Synthesis of various porous silicas using white Silica (SiO)
To obtain a macroporous mesoporous silica (OMS-1), P-123 polymer and TMB additive were used as structure directing agents. Above the critical micellization temperature, P-123 forms micelles with a hydrophobic core composed of polypropylene oxide (PPO) segments and a hydrophilic shell composed of polyethylene oxide (PEO) segments. Hydrophobic TMB is able to interact with PPO to expand the core of the micelle, and thus, the size of the pores may increase. As shown in (a) - (c) of FIG. 4, OMS-1 has a uniform mesoporous pore structure having a pore size of about 30nm, and OMS-2 using only P-123 without TMB forms mesoporous silica having a pore size smaller than that. As can be confirmed by (d) to (f) of FIG. 4, OMS-2 shows a pore size of about 10nm and a pore structure of a hexagonal system, and since the ratio of P-123 to silicate is changed and TMB is not used, a hexagonal mesoporous structure of MSU-H type is obtained unlike OMS-1 and the pore size is reduced. In OMS-3, CTAB was used as a structure directing agent. Although CTAB also forms micelles in aqueous solution, the formation of small mesoporous pores is induced due to the relatively short hydrophobic alkyl chains. OMS-3 has a uniform hexagonal pore structure with a pore size of about 3nm (see FIGS. 4 (g) to (I)). OMS-3 is composed of irregular morphology and discrete particles (discrete particles) of several hundred nanometers in size.
In OMS-4, large pores were unexpectedly observed in the TEM image (see (j) to (i) of FIG. 4). OMS-4 has a mesoporous pore (mesoporous foam) structure, particle morphology, and overall size similar to OMS-1, but can be confirmed to have a pore size tens of nm larger than OMS-1. The average pore size of OMS-4, which can be confirmed from (1) of FIG. 4, is about 60nm, which is slightly larger than the upper limit (50nm) defined by mesoporous pores (mesopores). The main difference in experimental conditions between the synthesis of OMS-1 and OMS-4 was the amount of NaOH and acetic acid. The reaction solution of OMS-4 contained a greater amount of sodium ions and acetate ions than the reactant solution for OMS-1. It is predicted that the large amount of acetic acid promotes the condensation of silica (i.e., increases the hydrophobicity of silica) and induces pore expansion of OMS-4.
By N2The pore structure of the examples was analyzed by physical adsorption isotherm (see fig. 5) and small angle X-ray scattering (SAXS) (see fig. 6). All examples show typical type IV isotherms of mesoporous materials classified according to IUPAC (see fig. 5 (a)). And, with RH-SiO in a random form without scattering peaks2(see fig. 6 (e)), the example shows a characteristic SAXS pattern of a mesoporous material having regular pores (see fig. 6 (a) to (d)). The isotherms of OMS-1 and OMS-4 are at high P/P0Hysteresis of the H1 type is shown, which is associated with mesoporous cellular foam structures having large-sized pores exceeding 30 nm. The SAXS results of OMS-1 are in good agreement with the pattern of uniform and monodisperse spherical pores typically present in mesoporous-morphology silica resulting from good growth of mesoporous pores (see fig. 6 a). OMS-4 shows a relatively unclear scattering peak (see FIG. 6 (d)) as seen in a TEM image (see FIG. 4 (l)) and a pore size distribution (see FIG. 5 (b)) due to the uneven and wide size distribution of spherical pores. OMS-2 is in the middle P/P due to the relatively small pores0Hysteresis of type H1 is shown. H4 hysteresis of the isotherm of OMS-3 shows the presence of slit-shaped pores. Both OMS-2 and OMS-3 had well-resolved SAXS peaks and were indexed to highly ordered hexagonal (p6mm) mesoporous structures (see FIGS. 6 (b) - (c)). Pore size distributions calculated from the adsorption curves of the isotherms were shown as major pore sizes of about 30nm, about 8nm and about 3nm in OMS-1, OMS-2 and OMS-3, respectively (see FIG. 5 (b)). This result is almost consistent with the pore structure and size observed in SAXS results (see fig. 6) and TEM images (see fig. 4). In the case of OMS-4, the adsorption volume is at a very high P/P0>0.97 (refer to (b) of fig. 5), thereby showing giant pores (macrophores,>50 nm). Due to the fact thatThe pores are in a size range in which it is difficult to completely fill the pores with the gas-adsorbing substance at atmospheric pressure, and thus N cannot pass through2Physical adsorption was fully evaluated. This makes it difficult to accurately calculate the pore size from the adsorption isotherm, and causes a small amount of deviation from the TEM image (refer to (j) - (l) of fig. 4). However, TEM and N of OMS-42Physical adsorption isotherm analysis demonstrated the existence of large mesopores and macropores undoubtedly.
The surface area and pore volume of the examples are shown in table 3 below.
[ Table 3]
All examples have a thickness of 250m2Large surface area of more than g and 0.8cm3Pore volume in the atmosphere above g. At low relative pressure (P/P)0<0.1) adsorption volume has a close correlation with the micropore volume of OMS. Compared with mesoporous pores and giant pores, micropores can make a greater contribution to surface areas and have a great effect on large surfaces. FIG. 5 (a) shows that as the main gas hole size of the OMS increases, at P/P0<0.1 adsorption of N2The volume of (a) is reduced. This trend is in order of OMS surface area (OMS-3)>OMS-2>OMS-1>OMS-4) was very consistent.
In contrast, it is confirmed that0When calculated about 0.99, OMS with large pores (OMS-1 and OMS-4) had significantly larger pore volumes than OMS with small pores (OMS-2 and OMS-3).
Although the present specification illustrates only a few of various embodiments performed by the present inventors, it is apparent that the technical idea of the present invention is not limited or restricted thereto, and can be implemented in various ways by being modified by those skilled in the art.
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| CN116692884B (en) * | 2023-06-13 | 2024-01-16 | 金三江(肇庆)硅材料股份有限公司 | Silica microsphere with low oil absorption value and high viscosity as well as preparation method and application thereof |
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