GB2188310A - A process for the preparation of silica particles - Google Patents
A process for the preparation of silica particles Download PDFInfo
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- GB2188310A GB2188310A GB08607697A GB8607697A GB2188310A GB 2188310 A GB2188310 A GB 2188310A GB 08607697 A GB08607697 A GB 08607697A GB 8607697 A GB8607697 A GB 8607697A GB 2188310 A GB2188310 A GB 2188310A
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- particles
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- silica particles
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J21/00—Catalysts comprising the elements, oxides, or hydroxides of magnesium, boron, aluminium, carbon, silicon, titanium, zirconium, or hafnium
- B01J21/06—Silicon, titanium, zirconium or hafnium; Oxides or hydroxides thereof
- B01J21/08—Silica
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- 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
- C01B33/16—Preparation of silica xerogels
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- Inorganic Chemistry (AREA)
- Engineering & Computer Science (AREA)
- Materials Engineering (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Silicon Compounds (AREA)
Abstract
A process for the preparation of silica particles which comprises: a. preparing a silica hydrosol by mixing an aqueous solution of an alkali metal silicate with an aqueous solution of an acid and allowing the reactants to react, b. converting the hydrosol into droplet form, c. shaping the droplets in air or in a liquid which is not miscible with water, d. partially pre-drying the hydrogel particles by contacting the hydrogel particles with a water miscible organic solvent (e.g. an alcohol, ester or ketone) at a temperature below 100 DEG C and allowing to extract a part of the water from the hydrogel, e. subjecting the partially pre-dried particles to a hydrothermal treatment, f. decreasing the cation content of the hydrogel particles and g. drying and optionally calcining the silica particles. o
Description
SPECIFICATION
A process for the preparation of silica particles
The present invention relates to a processforthe preparation of silica particles, to silica particles prepared by means ofthis process and to catalysts made from the silica particles.
In European Patent Application 82200382 (Publication 67459) is disclosed a process for the preparation of silica particles, in which process a silica hydrosol is prepared by mixing an aqueous solution of an alkali metal silicate with an aqueous solution of an acid, the obtained hydrosol is converted into droplet form, the droplets are shaped in air or in a liquid which is not misciblewith water, the hydrogel particles are partially pre-dried, subsequently subjected to a hydrothermal treatment and their cation content is then decreased.
Finally they are dried and optionally calcined.
It has been found that the processability of the silica may be improved.
Accordinglythe present invention relates to a process for the preparation of silica particles which comprises:
a. preparing a silica hydrosol by mixing an aqueous solution of an alkali metal silicate with an aqueous solution of an acid and allowing the reactants to react,
b. converting the hydrosol intodropletform, c. shaping the droplets in air or in a liquid which is not miscible with water,
d. partially pre-drying the hydrogel particles by contacting the hydrogel particles with a water miscible organic solvent at a temperature below 100 "C and allowing to extract a part ofthe water from the hydrogel,
e. subjecting the partially pre-dried particles to a hydrothermal treatment,
f. decreasing the cation of the hydrogel particles and
g. drying and optionally calcining the silica particles.
In the German Patent Application 2,633,198 is disclosed a processforthe preparation of silica particles, in which a treatment with an organic solvent on a silica hydrogel at a temperature above 100 C is carried out.
However the treatment is very severe and partial drying, if any, seems difficu It to control. Moreoverthe process is complicated. Very fine silica particles are prepared.
The silica hydrosol can be prepared conveniently by mixing an aqueous solution of an alkali metal silicate with an aqueous solution of an acid. Suitable alkali metal silicates comprisethe so-calledwaterglasses, based on Na2O/SiO2 having a sodium :silicon molar ratio between 1 and 0.2. Suitable acids comprise hydrochloric acid, nitric acid and especially sulphuric acid. Good results have been obtained using a mqlar ratio in the range 0.5-1.2 acid/waterglass, especially using a molar ratio in the range 0.6-0.8 acid/waterglass. The reactants can be used in various molar concentrations. Preferably, waterglasses are used in molarconcentrations between 0.5 and 1.3 and the acid can be chosen accordingly.
The process of mixing may be performed suitably by leading the starting solutions separately via capillaries into tubular mixing chambers. Thorough mixing which appears to be importantto produce uniform particles is established by carefully controlling the flow conditions in and outside the appropriate nozzles.
After the silica hydrosol has been formed, it is converted into droplet form by carefully controlling the break-up of the emerging stream which allows the formation of particles of uniform predetermined size and uniform shape. This may be achieved by gelling the hydrosol in a liquid which is immiscible, orsubstantially immisciblewith water such asan oil, e.g. a paraffinicoil. This maybe performed suitably by introducing the hydrosol into the upper end of a vertically disposed tu be filled with oil. Best results are obtained when a relatively short sol-gel transformation time is applied, e.g. lessthan 15 seconds. It is also possible to spray the droplets in air.
The gelled particles thus obtained may be caught in an aqueous phase such as water or, preferably, an aqueous solution of a salt such as sodium sulphate, particularly a salt solution having substantially the same salt concentration as that present in the hydrogel particles. The hydrogel particles arethen separated from the aqueous phase, e.g. by filtration or centrifugation. It is also possible to separatethem directlyfrom the oil phase but that is more cumbersome in view offurther steps in the preparation ofthe final particles. If desired the hydrogels obtained may be leftfor some time during which shrinkage oftheirvolume maygradually occur.The hydrogel particles thus obtained contain large amounts of waster and also contain, apartfrom sillica, water-soluble sodium salts as well as chemically bonded sodium ions.
The process according to the present invention allows for the preparation of silica particles of various sizes and shapes such as spheres, granules and extrudates. The process is especially suitable for the preparation ofsilica spheres which combine a number of advantageous properties such as high intrinsic strength,virtu- ally no formation offines when used in fixed or moving bed catalytic reactions as well as optimal transport characteristics. The present process allows not only particles, especially spheres of different sizes but also having at the same time similar pore volumes and yet different but uniform pore diameters and vice versa.
For instance, porous structures suitablefor hydrodemetallization normally have pore diameterswhich are several times higherthan those used in the hydration of ethylene whereas the diameter of the particles may be the same and their porevolume may differ more than 100%. The combination of partially pre-drying the hydrogel particles obtained and a hydrothermal treatment adjusted for the type of product required produces final particles having optimal performance parameters.
It has been found that pure strong silica particles can be obtained when the amount of water present in the hydrogel is reduced very carefully, not onlywith respect ot the temperature applied but also with respectto the amountofwaterwhich should remain in the then partially dried particles priortothe hydrothermal treatment. This is not only necessary to prevent the formation of cracks in the particles which might occur at forced or prolonged drying but also to determine the texture of the particles which is dependent on moisture contentandtemperature.
The amount of water to be removed from the hydrogel particles obtained is preferably between rather narrow ranges, e.g. between 30 %w and 75%w, calculated on the amount of water initially present in the hydrogel. It has been found thatvery good results can be obtained when the amount of water remaining in the pre-dried particles is between 12 %w and 70 %w, calculated on the solid content in the pre-dried particles.
The partial pre-drying of the hydrogel particles is carried out by contacting the hydrogel particles with a water miscible organic solvent at a temperature below 100 "C and allowing to extract a part of the waterfrom the hydrogel. The hydrogel particles are mixed with the solvent and the mixture is allowed to stand for a short time, necessaryto extract part of the water out of the hydrogel particle. Then the hydrogel particles are separated from the solvent and are now ready for hydrothermal treatment. Suitable organic solvents are aliphatic esters, aliphatic ketones or aliphatic alcohols. Preferred alcohols are C1 to C6-alcohols, such as butanol-1, butanol-2, 2-methylpropanoi-1, pentanol-2, pentanol-3, 2-methylbutanol-3, isobutanol.Preferred esters are methyl acetate, ethylacetate, propylacetate and isopropylacetate. Preferred ketones are acetone, methylpropylketone and ethyl n-propyl ketone. The organic solvents may comprise water.
The temperature applied during the solvent treatment is preferably between 10 0C and 80 "C, more preferably between 20 "C and 65 "C.
It appears to be especially the amount of water remaining in the partially dried hydrogel which determines the pore volume. The flexibility of the process according to the present invention is particularly vested in the unique property that once the pore volume has been set, the pore diameter can still be chosen. This allows, for instance, the preparation of silica particles having large pore volumes, e.g. > 1.2 ml/g as well as large pore diameters, e.g. even as high as 70 nm or even higher. The advantage of particles having large pore volumes is that higher loading of catalytically active materials can be applied.
The pre-dried silica particles are next subjected to a hydrothermal treatment, i.e. a treatment at elevated temperature with liquid water and/orwater vapour. This treatment results in a controllable growth of the
pore diameterwhiistthe porevolume is substantially retained. It is necessary to perform the hydrothermal treatment in the presence of one or more compounds selected from the group of compounds of the elements
Li, Na, K, Cs, Rb, Ca, Sr, Ba as well as NR1R2R3R4 compounds wherein R1, R2, R3 and R4which may bethesame or different and each represents a hydrogen atom or a hydrocarbyl group, e.g. an alkyl group having up to 12 carbon atoms, and NH3.
Since the partially-dried hydrogels still contain alkali ions, there is no special need to add one or more of the compounds mentioned hereinbefore. In the event that the alkalimetal salts had been removed from the
hydrogel,fresh amounts of such compound or of any compound referred to hereinabove would haveto be
added prior to the hydrothermal treatment.
When the hydrothermal treatment is effected by treating the partially-dried silica particles with liquid water
at elevated temperature, in general a treating temperature between 50 "C and 374 0C is chosen. Preferred treating temperatures are between 80 "C and 350 "C and in particular between 100 "C and 300"C. When using a treating temperature above 100"C, the treatment has to be carried out in a closed vessel underautogenous
pressure. The treating times generally range between 15 minutes and 24 hours. The volume of liquid waterto
be applied is preferably chosen such that during thetreatmentthe partially-dried silica particles are com
pletely surrounded by water.When using treating temperatures below 100 "C it is sufficientto employ a
quantity of liquid water substantially equal in volume to that of the silica particles to be treated. This also
holds when the treatment is carried out at a temperature above 100 "C in a closed vessel under autogenous
pressure, provided that the volume of the closed vessel is sufficiently larger than the volume of the silica
particles and the volume of water to be applied. When the treatment is carried out at a temperature above 100 "C in a closed vessel whose volume is considerably largerthan twice the volume of the silica particles to be
treated, a largervolume of liquid water has to be used.
When the hydrothermal treatment is carried out by treating the partially-dried silica particles with water
vapour at an elevated temperature, the treating temperature is generally chosen between 100 "C and 500 'C, preference being given to temperatures in the range of from 100 "C to 300 C. The water partial pressure
applied is preferably chosen between 1 and 40 bar. The heating times generally range between 15 minutes
and 24 hours. The treatment may be effected either by keeping the silica particles in a closed vessel in contact
with a certain quantity of satu rated water vapour or by continuously passing saturated watervapour overthe
silica particles.
The amount of one or more compounds selected from the group of compounds ofthe elements Li, Na, K,
Cs, Rb, Ca, Sr, Ba as well as NR1R2R3R4 compounds and NH3 present in the partially-dried silica particles to be
subjected to hydrothermal treatment mayvary between wide ranges, e.g. an amount of from 0.1 gram ofthe compound concerned upta 25g of the compound per 100 gram of the silica in the particles to be hydrotherm
allytreated. Preference is given to the use of compounds in the amountoffrom 0.5to 15 g per 100 g of silica in the particles to be treated. Good results have been obtained using silica particles still containing part or all of the alkali ions, e.g. sodium ions present therein because of the formation ofthe hydrosol as discussed here
inbefore.
The process according to the present invention thus combines the possibility of primarily setting the pore volume by a controlled partial drying of the hydrogel and of primarily setting the pore diameter by a hydrothermal treatment which make it very flexible with respect to the silica to be prepared.
The hydrothermal treatment will be followed by a treatmentto decreasethe cation of the silica particles, preferably to less than 10 %w, more preferably less than 5 %w, calculated on dry material. Normally, the cations present are sodium ions originating from the waterglass constituent in the formation of the hydrosol.
It is also possible that the cations are present since they were added to facilitate the hydrothermal treatment.
The decrease in the amount of cation can be conveniently performed by washing the silica particles one or several times with water or with an aqueous solution of ammonia so that the concentration is reduced to the desired level. Depending on the intended use of the final silica particles the amount of cation may be reduced to, say, 7% or less, calculated on dry material when an alkaline carrier is desired, orto less than 1 %when neutral carriers are required. In the latter case it may be advantageous to subject the silica particles to a treatment with an inorganic or organic acid in order to remove cation bound to the silica particlesthemse Ives.
Finally the hydrogel particles thus obtained are dried and calcined. Drying may be carried out by methods known in the art. Since the structure parameters have been firmly set by the process according to the present invention, the final drying conditions appear not be be crucial. The hydrogel particles can be dried smoothiy by heating them at a temperature of about 100 "C at reduced pressure or by heating them at atemperature above 100 "C in a stream of air. Butother methods are also applicable. Normally drying is carried outfor several hours attemperatures upto 200 "C.
Calcining may be carried out by methods known in the art. Itwill be appreciated that highercalcining temperatures have to be used when the dried hydrogel contains ammonium ions as described hereinbefore.
The temperature atwhich the calcination occurs may very between wide ranges. Normally temperatures up to 600 "C can be used but higher temperatures are not excluded. It may even be advantageousforcertain applications, such as hydration reactions to subject the dried hydrogel to a calcination at a temperature between 800 "C and 1000 "C. Normally calcining will be carried out during relatively short periods, e.g. periods of up to one hour, but longer periods may also be used.
The silica particles prepared by the process according to the present invention may be applied e.g. as catalysts, catalyst carriers, absorbents, drying agents and ion exchangers. They are of particular importance as carriers for one or more metals or metal compounds with catalytic activity. Catalysts comprising the present silica particles as carrier may be applied in various processes in the chemical and petroleum industries. The preparation of the catalysts may be carried out by any technique for the preparation ofsuppor- ted catalysts known in the art, e.g. by impregnating the silica particles with an aqueous solution comprising salts of the catalytically active metals concerned, followed by drying and calcining of the composition.A suitable way of preparing the present catalysts is one in which the catalytically active metals are incorporated into the carrier in an early stage of the carrier preparation, e.g. when the latter is still in the hydrogel form.
This may have an impact on the porosity ofthe ultimate carrier to be made and it also renders the additional drying and calcining steps required after separate impregnation optional.
Silica particles, and particularly silica spheres prepared according to the process according to the present invention are of particular importance as carriers for catalysts which are normally used in the hydrodemetallization of heavy hydrocarbon oils, the epoxidation of olefinically unsaturated compounds with or- ganic hydroperoxides and in the hydrations of olefinically unsaturated compounds to producethe corresponding alkanols.
Example
An aqueous sodium waterglass solution comprising 12 %w SiO2 and having a Na2O/SiO2 molar ratio of 0.3 was mixed continuously in a mixing chamber with an aqueous 1.2 N sulphuric acid solution in a volume ratio acid solution/waterglass of 0.75. After a residence of a few seconds in the mixing chamber the hydrosol obtained was converted into droplet form and the hydrosol droplets allowed to fall through a vertically disposed cylindrical tube with a length of 1.8 m filled with a paraffinic hydrocarbon oil at25 "C. During thefall through the tube gelation occurred. The globular hydrogel particles were caught at the bottom ofthe tube in water of 25 C. After the globular hydrogel particles had been separated by filtration they were washed with water.The water content of the hydrogel particles prior to furthertreatment amounted to 90 %w, as determined using a standard test (heating a sample in three hours from ambient temperature to 600 "Cand thereafter keeping the same thus heated at 600 'C for one hour).
5 g of the hydrogel particles (diameter 4.6 mm) thus obtained was treated with 250 ml solvent during 5 minutes, then the particles were separated from the solvent. The used solvent, the temperature and the percentage of weight-loss are given in the following Table:
Table
Solvent Temperature C % ofWeight-loss
Butanol-1 20 37
40 65
60 68 (88%w)+12%wH2O 40 % w) + 12 %w H2O 40 36 (88%w)+12%wH2O 60 %w) + 12 %w H2O 60 63 Butanol-2 60 69
Iso-butyl alcohol 60 67
Thereafter the hydrosol particles thus treated were subjected to a hydrothermal treatment in an autoclave.
An amount of water was added so that the volume ratio of water: bulk hydrogel particles (partially dried)was 0.7. This mixture was heated in 4 hours to 180 C and then kept atthistemperaturefor 2 hours whereafterthe mixture was cooled down gradually. The hydrogel particles thus treated were treated with an aqueous solution of sulphuric acid at ambienttemperature until the sodium content of the particles had been decreased to less than 0.2 %w, calculated on the dry material. After drying for 2 hours at 150 C the silica sphereswere subjected to a final calcination at 900 C.
Claims (11)
1. A process forthe preparation of silica particles which comprises:
a. preparing a silica hydrosol by mixing an aqueous solution of an alkali metal silicate with an aqueous solution of an acid and allowing the reactants to react,
b. converting the hydrosol into droplet form,
c. shaping the droplets in airorin a liquid which is not miscible with water,
d. partially pre-drying the hydrogel particles by contacting the hydrogel particles with a water miscible organic solvent at a temperature below 100 C and allowing to extract a part of the water from the hydrogel,
e. subjecting the partially pre-dried particles to a hydrothermal treatment,
f. decreasing the cation content of the hydrogel particles and
g. drying and optionally calcining the silica particles.
2. A process according to claim 1,wherein the amount of water be removed from the hydrogel particles is between 30 %w and 75 %w, calculated on the amount of water initially present in the hydrogel.
3. A process according to claim 1 or 2, wherein the hydrothermal treatment is carried out at a temperature between 80 C and 350 C.
4. A process according to any one ofthe claims 1-3, wherein the cation content ofthe hydrogel particles is decreased by treating the hydrogel particles with an aqueous solution of ammonia.
5. A process according to any one of the claims 1-4, wherein the water miscible organic solvent of step d.
is an alcohol containing 1 to 6 carbon atoms.
6. A process according to claim 5, wherein the alcohol is butanol-1, butanol-2 or iso-butyl alcohol.
7. A process according to claim 1,5 or 6, wherein the temperature is between 10 'C and 80 "C, preferably between 20'Cand 65 'C.
8. A process according to any one of claims 1 -7, wherein the dried hydrogel is subjected to a calcination at a temperature in the range offrom 800 C to 1000 C.
9. A process as claimed in claim 1, as hereinbefore described with special reference to the example.
10. Silica particles prepared by means of a process according to any one of the claims 1 -9.
11. Catalysts comprising one or more metals or metal compounds with catalytic activity on silica particles according to claim 10 or silica particles prepared by means of a process according to any one of the claims 1-9.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB08607697A GB2188310A (en) | 1986-03-27 | 1986-03-27 | A process for the preparation of silica particles |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB08607697A GB2188310A (en) | 1986-03-27 | 1986-03-27 | A process for the preparation of silica particles |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| GB8607697D0 GB8607697D0 (en) | 1986-04-30 |
| GB2188310A true GB2188310A (en) | 1987-09-30 |
Family
ID=10595368
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB08607697A Withdrawn GB2188310A (en) | 1986-03-27 | 1986-03-27 | A process for the preparation of silica particles |
Country Status (1)
| Country | Link |
|---|---|
| GB (1) | GB2188310A (en) |
Citations (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB1284087A (en) * | 1968-10-11 | 1972-08-02 | Nat Distillers Chem Corp | Preparation of silica gels |
| GB1284086A (en) * | 1968-08-06 | 1972-08-02 | Nat Distillers Chem Corp | Preparation of silica gels |
| GB1431975A (en) * | 1972-11-29 | 1976-04-14 | Phillips Petroleum Co | Dehydration of hydrogens |
| GB1596660A (en) * | 1977-11-09 | 1981-08-26 | Purdue Research Foundation | Prepaation of aluminium hydroxide gel |
| EP0067459A1 (en) * | 1981-04-13 | 1982-12-22 | Shell Internationale Researchmaatschappij B.V. | Silica particles and method for their preparation |
-
1986
- 1986-03-27 GB GB08607697A patent/GB2188310A/en not_active Withdrawn
Patent Citations (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB1284086A (en) * | 1968-08-06 | 1972-08-02 | Nat Distillers Chem Corp | Preparation of silica gels |
| GB1284087A (en) * | 1968-10-11 | 1972-08-02 | Nat Distillers Chem Corp | Preparation of silica gels |
| GB1431975A (en) * | 1972-11-29 | 1976-04-14 | Phillips Petroleum Co | Dehydration of hydrogens |
| GB1596660A (en) * | 1977-11-09 | 1981-08-26 | Purdue Research Foundation | Prepaation of aluminium hydroxide gel |
| EP0067459A1 (en) * | 1981-04-13 | 1982-12-22 | Shell Internationale Researchmaatschappij B.V. | Silica particles and method for their preparation |
Also Published As
| Publication number | Publication date |
|---|---|
| GB8607697D0 (en) | 1986-04-30 |
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| WAP | Application withdrawn, taken to be withdrawn or refused ** after publication under section 16(1) |