Classifications

• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B33/00—Silicon; Compounds thereof
  • C01B33/113—Silicon oxides; Hydrates thereof
  • C01B33/12—Silica; Hydrates thereof, e.g. lepidoic silicic acid
  • C01B33/18—Preparation of finely divided silica neither in sol nor in gel form; After-treatment thereof
  • C01B33/187—Preparation of finely divided silica neither in sol nor in gel form; After-treatment thereof by acidic treatment of silicates
  • C01B33/193—Preparation of finely divided silica neither in sol nor in gel form; After-treatment thereof by acidic treatment of silicates of aqueous solutions of silicates
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
  • C01P2002/00—Crystal-structural characteristics
  • C01P2002/02—Amorphous compounds
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
  • C01P2006/00—Physical properties of inorganic compounds
  • C01P2006/12—Surface area
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
  • C01P2006/00—Physical properties of inorganic compounds
  • C01P2006/14—Pore volume
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
  • C01P2006/00—Physical properties of inorganic compounds
  • C01P2006/16—Pore diameter

Definitions

• the present invention relates to controlled-pore amorphous silicas and to a process for manufacturing the same.
• the present invention more specifically relates to amorphous silicas having pore diameters of at least 1 ,000 Angstroms which are particularly useful as enzyme support in biocatalysis.
• Enzyme supports play an essential role in biocatalysis.
• the effect of pore diameter and surface on enzyme efficiency is well known (see for example Use of
• Surface area is determined by standard nitrogen adsorption methods of Brunauer, Emmett and Teller (BET) using a multi point method with an ASAP 2400 apparatus supplied by Micrometrics of the USA. The samples are outgassed under vacuum at 120°C for at least 1 hour before measurement. Surface area is calculated from the adsorption data measured in the P/Po region from 0.05 to 0.3. The calculation is restricted to the linear region of the BET plot within this pressure range.
• BET Brunauer, Emmett and Teller
• the porosity of materials with pore sizes greater than about 500 Angstroms (50 nm) cannot be analysed using nitrogen sorption analysis because of severe theoretical and practical limitations of the method.
• the maximum pore diameter that can be measured by nitrogen is about 1000 Angstroms and this would be insufficient to allow complete characterisation of a 500 Angstrom pore size material if it had a normal pore size distribution.
• the best alternative method for the characterisation of such macroporous materials is mercury porosimetry which has an analytical range from about 300 microns to 35 Angstroms.
• Porous materials have a number of regions of porosity when measured using mercury intrusion analysis.
• the two main identifiable regions are the inter- and intra-particle regions which can be identified from the cumulative intrusion curves.
• the inter-particle porosity is dependant on the particle size of the material, the particle shape and the packing geometry.
• the intra-particle porosity is the porosity of interest in the present invention and this too can have more than one component depending on the nature of the material. Such porosity can exist in micro, meso, or macro pore sizes, as defined by the IUPAC convention.
• the Intra-particle Pore Volume is defined as the volume of pores in the region less than 5 microns as measured by mercury porosimetry and the Macropore Volume (MPV) is defined as the contribution to the intra-particle pore volume in the region between 5 microns and 0.05 microns (500 Angstroms) as measured by mercury porosimetry.
• the pore size of particular relevance in the present invention is in the macropore region, namely greater than 500 Angstroms (or 50 nm).
• Macropore Diameter is determined as the pore diameter position of the maximum of the first differential of the cumulative intrusion curve plotted between 5 microns and 500 Angstroms.
• D of N Degree of Neutralisation
• D of N Degree of Neutralisation
• a controlled-pore amorphous silica having a surface area of between 10 m 2 /g and 900 m 2 /g, a Macropore Diameter of between 1 ,000 and 10,000 Angstroms, the Surface
• SA SA Area
• MPD Macropore Diameter
• the controlled-pore amorphous silica of the invention has a surface area of between 52 m 2 /g and 900 m 2 /g.
• the controlled-pore amorphous silica of the invention has an
• Intra-particle Pore Volume of between 1 and 3.5 cc/g.
• the controlled-pore amorphous silica of the invention has a
• the Macropore volume of between 1 and 3.0 cc/g. Most preferably, the Macropore volume represents at least 80% of the Intra-particle Pore Volume. It has been found that the amorphous silica of the invention can be used as a metal support in catalysis. When metals are deposited on a support, due to the high price of the metals used, great attention is paid to the fact that only a limited amount of metal is deposited on sites which are not going to be accessible during the reaction. Therefore, it is important to avoid, as much as possible, the deposition of metal in micropores. It has been found that it was possible to calcine the amorphous silica of the invention, thence eliminating the micropores while keeping the macropores intact.
• the amorphous silica of the invention presents a surface area of between 52 m 2 /g and 200 m 2 /g, preferably below 150 m 2 /g.
• the electrolyte is sodium chloride but sodium sulphate, potassium chloride and potassium sulphate have also been used.
• the washed and dried product is subsequently calcined by heating in air at a temperature between 70ff and 1000°C, preferably between 700° and 800 C C.
• a hydrothermal ageing step can be optionally introduced between the gelation and electrolyte addition steps, the electrolyte addition and the second acid addition steps, between the second acid addition and filtration and washing steps and/or any combination of these ageing steps.
• the most interesting products for the proposed applications are those made at relatively high silica concentration and low D of N.
• the sol presents, before the electrolyte addition, a Degree of Neutralisation of 25% to 30% and a silica content of 12% to 15% by weight. These materials set within a few hours to form an easily processable solid. This is then slurried with an equal volume of electrolyte solution (eg 200g/1 NaCI) and stirred at room temperature for a few minutes.
• the electrolyte is added such that the concentration of cations is between 1 and 3.5 Molar with respect to the cation. It should be noted that the electrolyte concentration referred to in the examples is expressed as the concentration in the liquid which is added to the gel in order to form a processable slurry and not the concentration in the final slurry.
• the electrolyte may be added either as a solution to the milled gel or as a dry solid to the gel after slurrying. The electrolyte causes the gel to form localised clusters which create the macropore matrix.
• the electrolyte also promotes the formation of siloxane bonding and increased strength through sodium ion bridging while the gel is in the alkaline condition and thus these wide pores have significant wall strength and do not collapse easily on drying.
• Macropore Diameters achieved through this process vary between a few hundred and 10,000 Angstroms (measured by mercury intrusion).
• the surface areas of the products can be much higher than might be predicted on the basis of the porosity alone using the well known (4,000 * Pore volume/Surface Area) rule. In the examples which have been prepared the surface area covers a wide range.
• the surface area is a feature of the smaller pore structures in the walls that surround the macropores.
• Sulphuric acid and sodium silicate (Na-,0 : 3 Si0 2 ) were mixed together by pumping the acid and silicate through an in line high speed, high shear mixer head (in line Silverson mixer).
• the flow rates and solution concentrations were such that the resultant sol had a silica concentration of 15 % (wt/wt) and a D of N of 30%.
• the sol was allowed to set and had a gel time of about 15 minutes. The gel time is defined as the point at which the resultant sol behaves as a single mass rather than a viscous suspension/solution. It can be identified using a small sample collected in a beaker.
• the sol was allowed to set and harden up for 48 hours before being coarsely broken up by forcing it through a 3.5 mm stainless steel mesh.
• a weighed amount of the disintegrated gel was added to an equal weight of demineralised water and solid sodium chloride was added slowly over a period of about 10 minutes with continuous stirring. The amount of salt added was sufficient to create a 200g/1 solution in the added water.
• the resultant slurry was stirred for 10 minutes at ambient temperature before adding sufficient sulphuric acid solution to complete the neutralisation and achieve a pH of 3.
• the white particulate solid that results was isolated and washed with demineralised water using a plate and frame filter press.
• the material obtained was freeze dried by cooling the sample quickly in liquid nitrogen and placing the frozen solid in an SB4 laboratory freeze drier supplied by Chemlab Instruments. The water was then removed from the sample by sublimation at reduced pressure over a period of 72 hours.
• a second sample of the filter cake was dried over night in a laboratory fan oven at 120°C.
• the freeze dried material had a total intra-particle pore volume of 2.38 cc/g, a macropore volume of 2.09 cc/g and a macropore diameter of 7000 Angstroms and a BET surface area of 674 nrf/g.
• the oven dried material had a total intra-particle pore volume of 2.17 cc/g, a macropore volume of 1.87 cc/g, and a macropore diameter of 4800 Angstroms and a BET surface area of 536 rrf/g.
• a sample was prepared as above with a silica concentration in the gel of 15% and a D of N of 20%.
• the gel time was 3 hours 15 minutes and the material was allowed to harden for 24 hours.
• 400 g of the gel broken into particles was slurried with 400g of a 200g/1 sodium chloride solution. After stirring for 10 minutes the excess alkali was neutralised and the pH adjusted to 3 before filtering and washing using a Buchner filter.
• the resultant product was freeze dried and had a macropore diameter of 4200 Angstroms and a total intra-particle pore volume of 3.22 cc/g, a macropore volume of 2.64 cc/g, and a BET surface area of 306 rrfVg.
• Example 3
• Example 4 This preparation was the same as in Example 2 above with a silica concentration in the gel of 15% and a D of N of 20% but after contact with the sodium chloride solution the slurried gel was aged in a stirred vessel under reflux at 90C for 1 hour.
• the resulting material after washing and freeze drying had a total intra-particle pore volume of 3.28 cc/g, a macropore volume of 2.98 cc/g, a macropore diameter of 5000 Angstroms and a BET surface area of 78 rrfVg.
• Example 4 Example 4
• This material was prepared as in Example 1 above with a silica concentration in the gel of 15% and a D of N of 30%.
• the gel was slurried with a solution of sodium chloride at 100 g/1 and then aged in a stirred vessel at ambient temperature for 1 hour before completing the neutralisation.
• the product after filtering, washing and oven drying had a total intra-particle pore volume of 1.64 cc/g, a macropore volume of 1.40 cc/g, a macropore diameter of 3000 Angstroms and a BET Surface Area of 704 m 2 /g.
• a freeze dried sample of the material had a total intra-particle pore volume of 2.43 cc/g, a macropore volume of 2.11 cc/g, a macropore diameter of 3000 Angstroms and a BET Surface Area of 857 rrf/g.
• An alkaline gel was prepared as described in Example 1 above with a silica concentration of 15% and a D of N of 30%. The gel was allowed to harden for 10 days before contacting with electrolyte solution. 250 g of roughly milled gel was slurried with 250 g of demineralised water and 50 g of sodium chloride was added. The slurry was stirred at ambient temperature for 1 hour before adjusting to pH 3 with sulphuric acid. The solid was filtered off using a Buchner filter and washed by reslurrying 3 times with demineralised water and filtering. The solid produced was split into two samples and part freeze dried and part oven dried at 120°C.
• the freeze dried material had a total intra-particle pore volume of 1.36 cc/g, a macropore volume of 1.11 cc/g, a macropore diameter of 3300 Angstroms and a BET surface area of 475 rrrVg.
• the oven dried material had a total intra-particle pore volume of 1.14 cc/g, a macropore volume of 1.03 cc/g, a macropore diameter of 4200 Angstroms and a BET surface area of 99 rrf/g.
• the freeze dried material had a total intra-particle pore volume of 1.89 cc/g, a macropore volume of 1.74 cc/g, a macropore diameter of 5000 Angstroms and a BET surface area of 580 rrf/g.
• the oven dried material had a total intra-particle pore volume of 1.78 cc/g, a macropore volume of 1.64 cc/g, a macropore diameter of 5000 Angstroms and a BET surface area of 99 ⁇ f/g.
• Example 8 This sample was prepared as described in Example 5 above but the sodium chloride was omitted and replaced by 60.72g of sodium sulphate.
• the freeze dried material had a total intra-particle pore volume of 1.83 cc/g, a macropore volume of 1.63 cc/g, a macropore diameter of 5100 Angstroms and a BET surface area of 463 rrf/g.
• the oven dried material had a total intra-particle pore volume of 1 .80 cc/g, a macropore volume of 1 .65 cc/g, a macropore diameter of 5200 Angstroms and a BET surface area of 487 rrfVg.
• Example 9 250 kg of alkaline gel, with 30% degree of neutralisation and 15% silica, was made into 210 litres kegs by mixing a 9.5% (wt/wt) solution of sulphuric acid, at a flow rate of 0.172 litre/min, with a 19.6% (as SiO, wt/wt) sodium silicate (3.3 ratio) solution, at a flow rate of 0.49 litre/min. This was left for 24 hours before an equal volume of water was added to each keg and the gel was broken up with a paddle. The resulting slurry was added to a 400 litres vessel and the vessel agitator (straight six-blade turbine) was used to break the gel down into a slurry.
• a 9.5% (wt/wt) solution of sulphuric acid at a flow rate of 0.172 litre/min
• a 19.6% (as SiO, wt/wt) sodium silicate (3.3 ratio) solution at a flow rate of 0.49 litre
• the material After calcination at 700°C the material had a total intra-particle pore volume of 2.19 cc/g, a macropore volume of 1 .96 cc/g, a macropore diameter of 1300 Angstroms and a BET surface area of 163 rrf/g.
• the material After calcination at 800°C the material had a total intra-particle pore volume of 1.86 cc/g, a macropore volume of 1 .81 cc/g, a macropore diameter of 1700 Angstroms and a BET surface area of 34 rrf/g.

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• 1996
  • 1996-12-10 GB GBGB9625630.0A patent/GB9625630D0/en active Pending
• 1997
  • 1997-12-01 CA CA002274099A patent/CA2274099A1/en not_active Abandoned
  • 1997-12-01 BR BR9713899-1A patent/BR9713899A/pt not_active Application Discontinuation
  • 1997-12-01 EP EP97945995A patent/EP0960068A1/de not_active Withdrawn
  • 1997-12-01 WO PCT/GB1997/003305 patent/WO1998025851A1/en not_active Ceased
  • 1997-12-01 AU AU51305/98A patent/AU5130598A/en not_active Abandoned

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