RU2772830C1 - Method for producing silicon dioxide - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to a method for producing silicon dioxide from cellulose-containing material, including preliminary processing of initial material by acid hydrolysis and subsequent isolation of silicon dioxide. The method is characterized by that acid hydrolysis is carried out at pH<5, temperature of 140-240°C and increased pressure in the presence of at least one monosaccharide protector protecting them from the impact of high temperatures and pressure, with subsequent separation of lignin reaction products by deposition on a filter and monosaccharides by protector distillation. The residue, after the removal of a liquid phase, is burnt at a temperature of 350-750°C in a zonal furnace to obtain silicon dioxide.

EFFECT: obtaining a method for producing silicon dioxide.

7 cl, 1 tbl, 1 dwg, 7 ex

Description

The invention relates to a technology for the deep processing of agricultural waste, municipal waste and other types of waste (sawdust, wheat straw, rice straw, etc., rice husk and sunflower husk, bagasse of fast-growing grasses, sedimentary sludge from urban sewage treatment plants, etc.), that is, to the field of processing cellulose-containing materials, in order to extract silicon dioxide and organic substances contained in such materials, for their further use in various fields of technology. So, the silicon dioxide extracted in this case can be used in the tire industry (as a filler), the production of rubber products and plastics, the chemical and food industries, mechanical engineering, electronics and the electrical industry.

State of the art

Rice hulls are used as the most common plant-derived silica feedstock. In this case, two different technologies are used - without pre-treatment of the source material (rice husks) and with pre-treatment.

Methods for obtaining silicon dioxide without pre-treatment of the feedstock are simply roasting rice husks at high temperatures. Examples of such a method are German patent No. 2416291, class. C04B and UK patent No. 150 8825, MKI S01B 33/12 where the rice husk is fired, varying the firing temperature in the range of 200°C-900°C. The main disadvantage of this method of obtaining silicon dioxide is the production of this product with a low degree of purity, as well as the release into the atmosphere of up to 80% or more of the mass of the husk in the form of gases.

The second type of technology uses pre-treatment of the feedstock before the firing stage with dilute solutions of mineral or organic acids, washing with water and then stepwise annealing of the residue in the temperature range of 300°C-1100°C (patents US 7998448 B2 and US 9403688 B1). However, even when using it, a lot of waste is large (at the preliminary stage of processing, lignin is not removed, but only partially cellulose and hemicellulose) and one type of product is obtained, silicon dioxide, which is in the amorphous phase.

Thus, although the use of pretreatment of feedstock in the production of silicon dioxide by roasting gives a better result compared to methods without pretreatment of feedstock, however, it has two significant drawbacks. Firstly, the multi-stage processes with the use of large volumes of liquids and various equipment, which leads to high energy costs. Secondly, they do not allow for the complex processing and use of all potentially useful accompanying substances of cellulose-containing materials. Rice husk contains only about 15-20% of silicon dioxide (like many other cellulose-containing materials and waste), and in existing technologies, the remaining 80-85% of the substances that make up the material are irretrievably lost - these are cellulose, polysaccharides, lignin and a number of other valuable substances that are destroyed.

More effective is the method of obtaining silicon dioxide (patent US 8178067 B2) from waste forestry, agricultural raw materials or materials containing hexose and/or pentose and SiO ₂ , where before the roasting process to obtain silicon dioxide, acid hydrolysis is carried out (in the presence of organic acid) of the original cellulose-containing material in two stages using increased pressure. In this case, it is possible to reduce the content of components containing hexoses and pentoses in the starting material to 10 wt % and 20 wt %, respectively. At the same time, the content of polyphenols (in particular, lignin) in the residue after the hydrolysis stage reaches 40 wt %, which complicates and increases the cost of the process of roasting the residue. Annealing of the residue after hydrolysis is carried out at a temperature of from 400°C to 1200°C.

The essence of the invention

The objective of the present invention is to provide a method for producing silicon dioxide by burning cellulose-containing material that has undergone preliminary preparation aimed at removing (maximum reduction) of its carbon part before the combustion process. Another object of the invention is to provide such a process, in which, in addition to obtaining silicon dioxide as the final target product, other useful products, monosaccharides (hexose and pentose), as well as pure non-sulfonated lignin, can be extracted from the feedstock.

These and other related tasks, in particular, reducing the cost of pre-treatment of raw materials and reducing the amount of gaseous products formed during the stage of roasting raw materials that have undergone preliminary processing, when obtaining silicon dioxide, are solved by the present invention through the use of a raw material pre-treatment technology, including:

acid hydrolysis of raw materials at pH<5, temperature 140-240°C and elevated pressure, separation of lignin and monosaccharides from reaction products.

The selection of silicon dioxide is carried out by burning the solid part of the hydrolysis residue at a temperature of 350-750°C.

To increase the yield of monosaccharides as one of the by-products along with silicon dioxide, it is advisable to carry out hydrolysis in the presence of at least one of the protectors that protect monosaccharides from exposure to high temperatures and pressure. As such, ketones or oxygen-containing heterocycles can be used.

It is also advisable to carry out the following additional operations:

to reduce the carbon content, wash the hydrolysis residue with a solvent;

to reduce the content of metal oxides, treat the hydrolysis residue with 1N hydrochloric acid;

with an increased content of lignin in the feedstock, subject it (raw materials) to alkaline pulping.

It is advisable, but not necessary, to use rice husk as a raw material.

When pre-treatment of raw materials is carried out in accordance with the present invention, it becomes possible to extract as much as possible from the bulk of the raw material the carbon component in the form of industrially useful products (lignin, monosaccharides) in an amount of up to 80% of the total mass. The hydrolysis (mineral) residue is about 20% of the feedstock and contains mainly silicon dioxide with impurities of metal oxides and minor carbon residues.

The above characteristics and advantages of the invention will become clearer from the following detailed description of it, given by way of non-limiting embodiments of the invention, with reference to the accompanying drawing.

Brief description of the drawing

In FIG. 1 shows a variant of the technological scheme for the implementation of the method in accordance with the invention.

Detailed description of the invention

Let us turn to the consideration of Fig. 1, which shows the flow chart of the method.

The source material enters the "grinder" - dispenser M (or without preliminary grinding, as in the case, for example, of using primary sedimentary sludge from treatment facilities). From the dispenser M, the solid material with particles 0.5–1.0 mm in size enters the mixer 2. A solution for hydrolysis (GR) is also supplied through the dispenser 1. The reaction mass is supplied alternately from mixers 2 and 1 through a dosing pump 3 and check valve K to the reactor 4. Reactor 4 is equipped with a heating jacket not shown in the diagram, temperature and pressure sensors, a safety valve, a siphon connected to the top valve (throttle) for discharge of reaction products, a lower valve (throttle) for discharge of reaction products, (as well as a valve for introducing steam directly into apparatus 4, if necessary, for quickly heating the reaction mass and introducing part of the required amount of water for the hydrolyzing solution or for preliminary steaming of the feedstock before treatment with hydrolyzing solutions, if necessary).

The reaction mass is heated and the reaction products are discharged from the reactor 4 through the valves (throttles) of apparatus 4 into hydrocyclone 5, where they are rapidly cooled and volatile by-products are separated, which, in turn, are discharged through valve 6 from cyclone 5 into the accumulator (not shown). Then, through filters 7 and 15, on which the solid components of the reaction mass are separated, the solution of the reaction products enters the distiller 8, where the protectors (or at least one) are separated. The protectors are returned to the mernik - dispenser 1 for the preparation of GH. The residue is fed to the filter (or hydrocyclone) 9, where the separation of lignin takes place, and then enters the "neutralizer" 10, equipped with a pH meter (11), a neutralizing solution measuring device (12). Neutralized products (an aqueous solution of sugars) are collected through a filter 13 into a receiving tank 14 and then sent for fermentation.

The solid residue from the filters 15 and 7 is sent to the accumulator 16, where (if necessary) it is treated with acetone to remove residual lignin, then with a 1 N HCl solution and washed with water on the filter 17. The solid residue is fed to the dryer 18, and from there to the zone furnace 19, where zones are set with a certain solid residue combustion temperature, depending on the quality of silicon dioxide that needs to be obtained for a particular application. The resulting silica contains a total carbon of <0.02 wt %, indicating complete removal of carbon from the original cellulosic material in the form of useful by-products.

For some cellulose-containing materials, where the amount of lignin is high enough, it is possible to pre-treat such raw materials, for example, by "alkaline cooking" in a dilute alkali solution, for example, 4% aqueous NaOH solution. In this case, a preprocessing block is added to the technological scheme (Scheme 1, pos. 20). The crushed product in this case enters through the dispenser M into the "digester" (not shown), where it is treated with an alkaline solution (T=95°C-100°C; 2 hours) and the main part of the lignin contained in the original substrate is boiled out. Then, the alkali is washed off the solid substrate on the filter, and it enters the technological chain of scheme 1 through pos. 2 and the alkaline lignin solution is sent to a settling tank (not shown) where the lignin precipitates. Alkali is returned to the technological cycle, and the lignin sediment is removed from the process through a centrifuge (or hydrocyclone).

The scheme also allows multiple processing of a dose of the starting material with new portions of the hydrolyzing liquid. In this case, the reaction mixture with a sample of cellulose-containing material from mixer 2 is first fed into the reactor through a dosing pump and, after holding, the liquid reaction products are discharged through the top valve (throttle) into cyclone 5. The solid sample being processed remains in the autoclave. Fresh hydrolyzing liquid is supplied from the mixer 1 by the dosing pump 3, which switches (possibly automatically) to this mixer. For one sampling with a sample from mixer 2, there are 2 samplings of pure hydrolyzing solution from mixer 1. The valves for “resetting” products also work in turn: for 2 resets through the upper valve (throttle), one “reset” occurs through the lower valve (throttle) , while the third processing of the remnants of the material sample takes place.

Below are examples of the invention using various starting materials (including those based on rice husks) and various monosaccharide protectors. The overall results are presented in Table 1.

Example 1

The reactor was loaded with 130 g of primary sedimentary sludge from city treatment facilities with a moisture content of 30% (100 g of dry source material), which was treated three times for 5 minutes at T=180°C and pH=1.87 with a hydrolyzing solution (GR), at the ratio of the starting material / hydrolyzing solution 1:10 and the ratio of protector / water in the hydrolyzing solution 4: 1 (protector - acetone). GR was introduced through a check valve with a dosing pump, and the reaction products were removed through the upper and lower autoclave throttles into hydrocyclones, as described above (Scheme 1).

After filtration, the hydrolysis residue of the original sludge was dried to a constant weight (32 g). From the combined hydrolysis solutions, after filtration, the protector was removed by distillation in a water jet pump vacuum. The precipitated lignin was separated by filtration. The settled lignin was washed off and dried from the walls of the stripping flask. The total yield of lignin was 28.6 g. The residue (an aqueous solution of sugars) was neutralized to pH=6.1 with "calcium milk" (CaO), the precipitate was filtered off. The concentration of sugars in the aqueous solution was determined by saccharimeter. The yield of sugars was 32.5 g. The volatile reaction products were collected in storage tanks through cyclone valves. Their approximate content is 6.9 g (Table 1, p. 1).

The hydrolysis residue containing silica is treated with acetone to dissolve the remaining traces of lignin, which remained in the solid residue after filtration. This reduces the content of total carbon by about 3.5 wt%. After washing the residue with a 1N HCl solution, the total content of metal oxides decreases to 0.80 wt%. Further, after drying in air, the residue is sent to the zone furnace. Annealing the residue at T=600°C leads to the production of silicon dioxide with a total carbon content of <0.02 wt%. The yield of amorphous silicon dioxide is 96.5 wt%. The output of silicon dioxide 29, 5% of the feedstock in terms of absolutely dry feedstock.

Example 2

Three times autoclave treatment was subjected to 146 g of bagasse with a moisture content of the original sample of 46% (100 g of dry sample) at pH=2.5; at a temperature of 150-190°C (preferably 180°C); the duration of each treatment is 5 minutes. The ratio of GR / sample and protector / water, similar to example 1. Protector mixture of methyl ethyl ketone with acetone at a ratio of 1:1. The processing method is similar to example 1. The rest of the sample after autoclave hydrolysis was 18 g. The yield of sugars and lignin was 62 g and 18 g, respectively (Table 1, p. 2). The content of volatile products 2, the Residue after hydrolysis is processed by analogy with example 1 and then enters the zone furnace for combustion. Silicon dioxide obtained at T=750°C contains <0.02 wt% of total carbon. Yield of amorphous silica 96.1% (pure silica 98%). The output of silicon dioxide 16, 7% of the feedstock in terms of absolutely dry feedstock.

Example 3

A sample of wheat straw 110 g with a moisture content of 4.82% was placed in an autoclave and treated three times, lasting 4 minutes each, at T=190°C; pH=1.6. The ratio of GR / sample and protector / water, similar to example 1. Protector methyl ethyl ketone. The processing method is similar to example 1. The rest of the sample after hydrolysis is 18.2 g. The yield of sugars and lignin is 62.66 g and 20.2 g, respectively (Table 1, p. 3). The content of volatile products is 3.64 g. After washing with acetone to remove lignin residues and an aqueous solution of hydrochloric acid (1N) to reduce the total content of metal oxides in the residue to 0.88 wt%, the hydrolysis residue was annealed in a zone furnace at T=750°C. The resulting silica contained <0.02 wt% total carbon and was 97% pure. The output of amorphous silicon dioxide is 96.5% and 17.0% of the feedstock in terms of absolutely dry feedstock.

Example 4

A sample of wheat straw was pre-treated with 4% NaOH solution at a temperature of 97-100°C for two hours ("alkaline cooking"). Then, the sample was filtered from the solution, washed on the filter from the remnants of the alkaline solution and dried. With this treatment, most of the lignin is released from the straw sample (the lignin residue in the straw can be about 11%) and part of the hemicellulose. The rest of the straw after processing averages 41.7% of the original sample taken for processing. Some of the pentose sugars can be recovered from the filtrates, if necessary.

The treated straw sample (as described above) weighing 110 g with a moisture content of 10% is placed in an autoclave, where it is processed three times (4 min each) at T=180°C; pH=2.1; GR with the ratio protector: water=1:1 (protector - methyl ethyl ketone) and at the ratio Sample: GR=1:10. The combined hydrolysates were placed in a "titrator" (as described above in the second embodiment of the process) and the pH was adjusted to 10 and the solution allowed to settle to form a lignin precipitate.

Lignin was separated by filtration and dried (10 g). From the filtrate, after neutralization, methyl ethyl ketone was removed by distillation in a vacuum water jet pump. The yield of sugars was 64.2 g. The residue of the straw sample after hydrolysis was 17.68 g, and after treatment with a solvent and an aqueous acid solution, 17.0 g (Table 1, p. 4). By burning the residue, by analogy with examples 1 - 4, in a zone furnace, amorphous silicon dioxide is obtained with a yield of 98.8%, a basic substance content of 98% and a yield of 17.0% from absolutely dry feedstock.

Example 5

A sample of sawdust of coniferous trees 100 g (in terms of a dry sample) was subjected to three autoclave treatments (6 minutes each) at T=170-190°C (preferably 180°C); pH=1.87 with a solution containing a mixture of acetone/water in a ratio of 4:1 at a dilution similar to the previous examples. The selection of reaction products was carried out according to a method similar to example 1. The yield of volatile products 6.2, the yield of monosaccharides amounted to 35.6 g; 30 g of lignin. The conversion of the initial sample reached 71.6% (Table 1, p. 5). Before burning in a zone oven (750° C.), the residue (28.4 g) was treated in analogy to the above examples. The yield of amorphous silicon dioxide is 90%.

Example 6

A portion of rice husks 97.1 g (in terms of dry sample) was subjected to autoclaving similar to the procedure of Example 1. The yield of monosaccharides was 57.7% of the weight of the starting material (56.03 g) at a conversion of 80% (Table 1, item 6). Lignin yield 14.6%, by-products 7.7%. Residue after hydrolysis 19.42 g (20%). Before burning in a zone furnace, the residue was treated in analogy to the above examples. The output of amorphous silicon dioxide 97.1% when annealing in a zone furnace at 600°C.

Example 7

Rice husk weighed 100 g (in terms of dry sample) was autoclaved similarly according to the method of Example 1. products 7.9%. Residue after hydrolysis 19.0 g. Before burning in a zone furnace, the residue was treated in analogy to the above examples. The output of amorphous silicon dioxide 96.0% when annealing in a zone furnace at 750°C.

The content of residual carbon in silicon dioxide did not exceed 2% at the annealing temperature of the hydrolysis residue of 350°C and 0.02% at temperatures of 600 and 750°C.

Industrial Applicability

The method in accordance with the present invention makes it possible to obtain high quality silica from various types of cellulose-containing materials, from waste from the woodworking industry and bagasse to primary sedimentary sludge from sewage treatment plants, that is, it is quite versatile.

This ensures a high yield of not only silicon dioxide, but also fuel monosaccharides, which are easily fermented by yeast into alcohol and lignin as a valuable product for industry. It makes it possible to reduce the amount of flue gases released during the process of burning the hydrolysis residue, to practically use the heat of the latter in the hydrolysis process, and to significantly reduce the cost of silicon dioxide due to the production of industrially useful by-products.

Claims (7)

1. A method for producing silicon dioxide from a cellulose-containing material, including pre-treatment of the starting material by acid hydrolysis and subsequent isolation of silicon dioxide, characterized in that acid hydrolysis is carried out at pH<5, a temperature of 140-240°C and elevated pressure in the presence of at least one protector of monosaccharides protecting them from exposure to high temperatures and pressure, followed by separation from the reaction products of lignin by precipitation on a filter and monosaccharides by distillation of the protector, the residue after removal of the liquid phase is burned at a temperature of 350-750°C in a zone furnace to obtain silicon dioxide. 2. The method according to p. 1, characterized in that the acid hydrolysis is carried out at a temperature of 170-190°C. 3. The method according to p. 1, characterized in that the hydrolysis residue before burning is washed from lignin residues with a solvent to reduce the carbon content. 4. The method according to p. 1, characterized in that the hydrolysis residue after combustion is treated with a 1N hydrochloric acid solution to reduce the total content of metal oxides. 5. The method according to any one of paragraphs. 1-4, characterized in that at least one of the chemical compounds selected from ketones and oxygen-containing heterocycles is used as a monosaccharide protector. 6. The method according to any one of paragraphs. 1-5, characterized in that with an increased content of lignin in the feedstock, the feedstock is subjected to alkaline pulping before hydrolysis. 7. The method according to any one of paragraphs. 1-6, characterized in that rice husks are used as feedstock.

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