WO2005108293A1

WO2005108293A1 - Improved process for production of pure amorphous mesoporous silica from quartz

Info

Publication number: WO2005108293A1
Application number: PCT/NO2005/000157
Authority: WO
Inventors: Birger Langseth; Christian Rosenkilde; Natalia Loboda
Original assignee: Promeks As
Priority date: 2004-05-12
Filing date: 2005-05-12
Publication date: 2005-11-17

Abstract

A process for production of amorphous silica from quartz includes the following steps: heating (calcinations step) of quartz with MgCl2, CaCl2 or other metal chlorides, commonly referred to as MeCl2, at a temperature of 800 - 1300 °C wherein the weight ratio of MeCl2 to quartz is greater than 2 and the presence of water vapour in excess of the stoichiometric amount needed; leaching at temperatures preferable between 50 and 130 °C of the produced calcium silicate with HCl to form a solution of MeCl2 with insoluble silica; separation of insoluble silica from the solution; recycling of MeCl2 to the heating step and the HCl solution to the leaching step; ageing the silica in an ageing reactor.

Description

IMPROVED PROCESS FOR PRODUCTION OF PURE AMORPHOUS MESOPOROUS SILICA FROM QUARTZ

The present invention relates to the production of pure amorphous silica from quartz or other SiO₂ based raw materials. Several types of silica can be produced by using the techniques described in this application. Common for most of them is the purity of the silica, which is higher than commercial silicas on the marked today. The silica content in the product silica might be as high as 99.98%. The various types of silica can be used for beer stabilization, insulation, catalysts and silicon rubber, and other applications that require pure silica. There are small differences during the production process for the various types of silica.

Amorphous silica is mainly produced by acidulation of a soluble silicate, commonly by addition of sulphuric or hydrochloric acid to a sodium silicate (water glass) solution. The products are either precipitated silica or silica gel depending upon details in the production process. Also other known processes (silicon tetrachloride/alkoxide reacts with hydrogen and oxygen to form fumed silica) are used commonly in the present silica industry.

Methods for preparation of amorphous silica from soluble silicates is well established, but suffer from the disadvantage that soluble alkali silicate and mineral acid are consumed in the production process. Furthermore, these silica products often contain rather high amounts of alkali metals, which is unwanted for many applications.

US patent No. 1 ,868,499 relates to a process for recovering alumina from silicious materials where silica is considered as an unwanted by-product and no further processing of this product is carried out.

Further, US patent No. 4689315 describes a method for the production of amorphous silica particles where the lime and the hydrochloric acid are consumed in the process. European patent, EP 1265812 B1 , relates to a process for the preparation amorphous silica where the raw materials are similar to the present invention, but where the process is limited with respect to the type of silica that can be produced, the purity of the silica product and that CaCI₂ is the only reagent used in the mixture with the raw materials.

Common for all prior art solutions is that no provisions are made with regard to the possibilities for the silica product, no description of the silica product is given and nothing is stated about the applications for the various types of pure silica products.

The silica product according to the present invention is very pure, having an amorphous silica content of more than 90%, and it can be used for several applications that never have been investigated before. The chemical impurities are at a much lower level than the commercial silica types, and the produced amorphous silica can have a very high surface area. The silica is produced from quartz or other SiO₂ based materials and all other reagents, chemicals like mineral acid and chlorides from all elements in the group II of the periodic table (Be-Mg-Ca-Sr-Ba-Ra), used in the process are recycled. Only minor amounts for make-up of these chemicals are required.

The invention according to the present invention will be further described in the following with reference to the attached drawing showing, by means of a flow diagram, the main steps of the process.

The process according to the invention for production of amorphous silica from quartz include the following steps:

Step 1. Heating the crushed (< 100 μm) quartz together with MgCI₂, CaCI₂ or other metal chlorides like BeCI₂, SrCI₂ and BaCI₂, commonly referred to as MeCI₂, to a temperature in the range 800 - 1300 °C preferably over a two stage calcinations step for a period of 0.5 to 3 hours, depending on the temperature, wherein the ratio of MeCI₂ to the quartz is greater than 2 and in the presence of water vapour in excess of the stoichiometric amount (preferable at least 7%) needed for the reaction: x MeCI₂ + y SiO₂ + x H₂0 ^ (MeO)x * (Si0₂)y + 2x HCI wherein x is greater than y in order to obtain a conversion of quartz to magnesium (or calcium) silicates in excess of 99.9%. The HCI produced during calcination is absorbed in a scrubber and via step 4 reused in step 2.

Step 2.

Leaching of the metal silicate with HCI, preferably an excess of HCI of at least 20%, to form a solution of MeCI₂ with insoluble silica.

Step 3.

Separating insoluble silica from the solution using filters (belt filter, press filter, filter press etc.) or another separation method. The solution contains an excess of HCI, MeCI₂ and impurities.

Step 4.

Recycling of the chloride solution to step 1 and the HCI solution to step 2 using a recovery system in order to separate the solutions. The impurities are removed prior to the reuse of the solutions in order to avoid build-up of impurities. Several techniques can be used to remove impurities depending on the amount impurities in the raw materials, but one way is to precipitate impurities as hydroxides at elevated pH.

Step 5.

Further treatment of the silica product or modifications in the process described in step 2 - 4 above in order to produce a silica product of a special quality for various applications.

The silica with a large pore size and volume is produced at step 5, which is the basic aging of silica gel. The basic aging is a way to transform microporous silica gel with a low oil absorption to the silica, which has pores large enough to be applied as a carrier, as a catalyst, as an insulation material etc. Three silica types which fit different applications (silica T- beer stabilizer, silica V - additive to insulation material in insulation panels, silica Z - carrier and free flowing agent), are produced by silica gel basic aging specially tailored for every application.

The silica gel structure collapses during the basic aging at a high temperature. The basic aging of wet silica gel (in the presence of NH OH (pH8-10), at temperatures 120°C-150°C, and various duration (from several minutes to several hours) results in xerogel with a variety of large pores/voids (about 100 micron according to mercury porosimetry). However, the basic aging arises serious problems in the filtration process: submicron silica particles formed during aging cause a loss of silica (to 40-50%). Spray drying of the aged silica suspension allows the production of spherical particles having a special structure formed due to a combination of porous silica and submicron (0.1-0.2 micron) particles.

In order to strengthen the silica structure and to prevent its collapse during aging, a freezing/thawing stage was included before the aging step. Freezing of wet silica at - 10°C-17°C and thawing in hot water or at room temperature considerably strengthen the silica pore structure and facilitates filtration after aging. Filtration is relatively fast, no loss of silica is observed.

The silica is dried in oven at 105°C-115°C up to a constant weight or spray dried. The spray drying can be made both from acidic (4-6% silica) and basic (20% silica) suspensions that also influences the silica porosity.

Example 1.

Silica T (beer stabilizer with good performance and high permeability) was made by aging of silica gel produced by leaching of calcium silicate made at step 1. Leaching. A calcium silicate slurry in water was prepared by addition of 40g calcium silicate to 72 ml water in a beaker under continuous stirring. The bake slurry was fed to the reactor by means of a peristaltic pump. Before the calcium silicate feeding, the reactor was filled with 184g water and 141.6 g 37%HCI to make 15.8% hydrochloric acid solution. The reactor was equipped with a condenser and a thermocouple. While mixing the solution (15.8%HCI), the calcium silicate slurry was slowly added to the reactor. Concentration of hydrochloric acid in the reactor is 13%, solid/liquid ratio was 1/10 (w/w). The slurry was heated until boiling (reflux) reached. Reflux was continued for 30 minutes. Then heating was stopped and the slurry was cooled down to 40°C -45°C. Concentration of silica in the leaching slurry was about 3%. Filtration and washing. The slurry was filtered on a Buchner funnel over fast filter paper until a cake was obtained. The cake was washed with distilled water (at least 3 portions of 200ml water over the cake) until the cake contained a pH>4. Aging. The filter cake was repulped in water and ammonium hydroxide was added to pH 9.5- 10.0. The ratio of dry silica to liquid was equal to 1/20. The reaction mixture was heated at 60°C for 6 hours. Then it was cooled and spray dried. D₅₀ of silica T was about 20 micron. The silica properties are given in Table 1. Table 1. Properties of silica T.

Example 2. Silica V (additive to fumed silica in insulation panels) made by aging of silica gel produced by leaching of calcium silicate produced at step 1. Leaching. Calcium silicate slurry in water was prepared by addition of 40g calcium silicate to 72 ml water in a beaker under continuous stirring. The bake slurry was fed to the reactor by means of a peristaltic pump. Before the calcium silicate feeding, the reactor was filled with 184g water and 141.6g 37%HCI to make 15.8% hydrochloric acid solution. The reactor was equipped with a condenser and a thermocouple. While mixing the solution (15.8%HCI), the calcium silicate slurry was slowly added to the reactor. Concentration of hydrochloric acid in the reactor was 13%, solid/liquid ratio was 1/10 (w/w). The slurry was heated to 70°C. The reaction duration was 60 minutes. Then heating was stopped and the slurry was cooled down to 40°C -45°C. Concentration of silica in the leaching slurry is about 3%. Filtration and washing were made as in Example 1. Aging. The filter cake was repulped in water, then ammonium hydroxide was added to pH 9.5- 10.0. The ratio of dry silica to liquid was equal to 1/20. The reaction mixture was heated at 150°C for 4 hours. Drying and Milling. The aged silica slurry was spray dried (D₅₀ is about 20 micron). The silica has rather low water uptake and after jet milling (D₅₀ is 4-5 micron) it can be applied in insulation. The milled silica V properties are given in Table 2. Table 2. Properties of silica V.

Example 3.

Silica Z (carrier, free flowing agent, filter aid, filter body, adsorber). Production of silica type Z proceeded in five stages: leaching of calcium silicate with hydrochloric acid, filtration and washing, freezing/thawing of the filter cake, its aging, and drying. Leaching of calcium silica, its filtration and washing were made as in Example 1. Freezing of the filter cake. The filter cake containing 92-94% water was frozen in a freezer. The freezing temperature was -12°C and the freezing time at this temperature was 2 hours. The frozen gel was thawed by addition of hot water. The amount of water added was calculated so that to get solid/liquid ratio equal to about 1/20. Aging. The suspension of silica in water was fed to the reactor. Ammonium hydroxide was added to the same reactor to adjust the pH to 9.5. The reactor was heated to 130°C. The suspension was heated at this temperature for 1 hr. After cooling the aged silica was filtered on a Buchner filter and washed with distilled water at least three times. Drying. The 19% suspension of the aged silica gel having pH 6 was prepared and dried in a spray dryer. The inlet/outlet temperature was 250°C /120°C.

The properties of the silica were as follows. The permeability of silica with D₅o=27micron is 0.072 darcy, specific surface area (BET) 205m2/g, pore volume (BET) 1.58cm3/g, pore radius (BET) 11.2nm, DBP 250ml/100g, oil absorption 380 ml/100g, 99.7-99.9% SiO2, pH (5%) 7-8.

After jet milling silica Z (particle size 3-5 micron) can be used as an insulation material.

Claims

1. Process for production of amorphous silica from quartz characterised by the following steps:

• heating (calcinations step) of quartz with MgCI₂, CaCI₂ or other metal chlorides, commonly referred to as MeCI₂, at a temperature of 800 - 1300 °C wherein the weight ratio of MeCI₂ to quartz is greater than 2 and the presence of water vapour in excess of the stoichiometric amount needed, • leaching at temperatures preferable between 50 and 130 °C of the produced calcium silicate with an excess of HCI under reflux to form a solution of MeCI₂ with insoluble silica, • separation of insoluble silica from the solution, • recycling of MgCI₂ to the heating step and the HCI solution to the leaching step, • ageing the silica in an ageing reactor with or without a preliminary freezing/thawing step • drying of the silica product.

2. Process in accordance with claim 1 , characterised in that the calcination is carried out in two steps where the temperature for the first step is below 1000 °C and for the second step the temperature might be as high as 1300 °C

Process in accordance with claims 1-2, characterised in that metal impurities such as Fe, Al and Ti are removed prior to reuse of the chlorine and acid solutions.

4. Process in accordance with claims 1-3, characterisied in that filter cake is aged in a reactor at pH>9 at a temperature < 100 °C (preferably 80 °C).

5. Process in accordance with claims 1-4, characterisied in that the aged silica suspension iis spray dried to get spherical particles of 20-60 micron

6. Process in accordance with claim 1 - 2 characterised in that, .in order to strengthen the silica structure and to prevent its collapse during aging, a freezing/thawing stage is included before the aging step.

7. Process in accordance with claim 6, characterised in that .the freezing of wet silica is performed at -10 °C to -17 °C and the thawing is performed in hot water or at room temperature.

8. Process in accordance with claims 1-3 and 6-7, characterisied in that filter cake is aged in a reactor at pH>9 at the temperature > 100 °C (preferably 130 °C).

9. Process in accordance with claims 1 -8 characterised in that silica after ageing is spray dried or dried in oven at 105°C-115°C up to a constant weight.

0. Process in accordance with claims 1-3 characterised in that a silica is prepared by a two stage process including leaching at 70 °C and aging for 1 - 7 hours at 150 °C and spray drying followed by jet milling.