Process for the extraction of silica

Abstract

Disclosed is a process for the extraction of silica from lignocellulosic plant matter, including the steps of: a) fractionating the lignocellulosic plant matter in the presence of an acid solution, so as to obtain a solid fraction including cellulose; b) extracting the silica from the solid fraction obtained in step a) with a basic solution, at a pH between 10 and 13 and at a temperature between 70° C. and 90° C., so as to obtain a liquid phase including silica and a solid phase; c) separating the liquid phase and of the solid phase which are obtained in step b); and d) precipitating the silica which is included in the liquid phase, at a pH between 5 and 6.

Claims

1. A process for an extraction of a silica from lignocellulosic plant matter, comprising the steps of: a) fractionating the lignocellulosic plant matter in a presence of an acid solution, so as to obtain a solid fraction comprising cellulose, b) extracting the silica from the solid fraction obtained in step a) with a basic solution, at a pH between 10.5 and 11.5 and at a temperature between 70° C. and 90° C., so as to obtain a liquid phase comprising the silica and a solid phase, c) separating the liquid phase and the solid phase which are obtained in step b), d) precipitating the silica which is comprised in the liquid phase, at a pH between 5 and 6, wherein the precipitated silica comprises silica particles have an apparent mean diameter of 1-10 micrometers obtained at the pH between 10.5 and 11.5 in step b), and wherein the apparent mean diameter is achieved without the need to use sonication or other additional steps to reduce the size of the silica particles.

2. The process for an extraction of a silica according to claim 1, wherein the fractionating step a) comprises the steps of: a1) bringing the lignocellulosic plant matter into contact with the acid solution, so as to obtain a solid fraction comprising cellulose and a liquid fraction, a2) separating the solid fraction and the liquid fraction which are obtained in step a1).

3. The process for an extraction of silica according to claim 2, wherein the precipitating step d) is carried out with the acid solution obtained by recycling the liquid fraction obtained subsequent to the separating step a2).

4. The process for an extraction of a silica according to claim 3, wherein the acid solution of the fractionating step a) is a solution of organic acid.

5. The process for an extraction of a silica according to claim 3, wherein the acid solution of the fractionating step a) is a solution of formic acid and/or of acetic acid.

6. The process for an extraction of a silica according to claim 2, wherein the acid solution of the fractionating step a) is a solution of organic acid.

7. The process for an extraction of a silica according to claim 2, wherein the acid solution of the fractionating step a) is a solution of formic acid and/or of acetic acid.

8. The process for an extraction of silica according to claim 1, wherein the acid solution of the fractionating step a) is a solution of organic acid.

9. The process for an extraction of a silica according to claim 1, wherein the acid solution of the fractionating step a) is a solution of formic acid and/or of acetic acid.

10. The process for an extraction of a silica according to claim 1, wherein the basic solution of the extracting step b) comprises 1.5% by weight of NaOH.

11. The process for an extraction of a silica according to claim 1, wherein the lignocellulosic plant matter is cereal straw and/or chaff.

12. The process for an extraction of a silica according to claim 1, comprising a step of concentrating the liquid phase after the separating step c) and before the precipitating step d).

13. The process for an extraction of a silica according to claim 1, comprising a step of filtration of the silica precipitated in step d).

Description

FIGURE

(1) FIG. 1 is a partial and diagrammatic view of the process and installation according to the invention.

(2) The lignocellulosic plant matter is introduced via the pipe 1 into the reactor 3, in which the lignocellulosic plant matter is brought into contact with an acid solution in order to obtain a solid fraction comprising cellulose and a liquid fraction comprising lignin and sugar. The acid solution is introduced into the reactor 3 via the pipe 2. The combination comprising the liquid and solid fractions is transferred into a press 4 in order to separate the two fractions. The reactor 3 and the press 4 form the fractionating unit 3,4.

(3) The liquid fraction is sent to a recycling unit 16 via the liquid fraction outlet 5. The liquid fraction is treated therein by evaporation in order to obtain a recycled acid solution. This solution is recovered via the pipe 17. The other constituents of the liquid fraction, such as the lignin or sugar, can also be recovered via the outlet 18 and purified.

(4) The solid fraction is sent to an extraction reactor via the pipe 6. The solid fraction is brought into contact therein with a basic extraction solution introduced via the pipe 8. This extracting step is carried out at a pH of between 10.5 and 11.5 at a temperature between 70° C. and 90° C. The silica present in the solid fraction then dissolves in the extraction solution, forming a liquid phase comprising silica and a solid phase comprising cellulose and depleted in silica.

(5) The combination consisting of the solid phase and the liquid phase is subsequently introduced into a press 9 in order to separate them. The extraction reactor 7 and the press 9 form the extracting unit 7,9.

(6) The solid phase thus separated is recovered via the pipe 10. This solid phase can be subjected to various treatments in order to recover in value the cellulose which it comprises.

(7) The liquid phase is concentrated in the unit 12 and then precipitated in the precipitating unit 13 by adjustment of the pH to a pH between 5 and 6. The adjustment of the pH is carried out by the recycled acid solution originating from the pipe 17.

(8) The precipitated silica is subsequently filtered in the filtration unit 14.

(9) The silica is recovered via the pipe 15.

EXAMPLE

Materials and Methods

(10) The fractionating step was carried out with a solution of acetic acid/formic acid/water for a period of time of 3 hours, at a temperature of 105° C. and at pH 3.

(11) The extracting step was carried out with a 12% by weight sodium hydroxide solution, for a period of time of 60 min, at a temperature of 80° C. and at pH 10.5 or at pH 12.5.

(12) The precipitating step was carried out with a 1% acetic acid solution, for a period of time of 10 min, at a temperature of 25° C. and at pH 5.5.

Results

(13) The results obtained are combined in Table 1 below.

(14) TABLE-US-00001 TABLE 1 Extraction at Extraction at Silica particles pH 10.5 pH 12.5 Mean diameter by laser particle 4.8 μm 176 μm sizing Specific surface by the BET 155.93 m.sup.2/g 413.46 m.sup.2/g method Cumulative pore volume by the 0.28 cm.sup.3/g 1.21 cm.sup.3/g BJH adsorption method Mean pore diameter by the BJH 8.2282 nm 11.0661 nm adsorption method Median pore diameter 0.9441 nm 0.9326 nm
These results show that the size of the silica particles decreases greatly with the pH of the extraction solution.