CA2069705A1 - Process for the removal of chloride ions from a fine-particle titanium dioxide, such fine-particle titanium dioxide freed from chloride ions and its use - Google Patents
Process for the removal of chloride ions from a fine-particle titanium dioxide, such fine-particle titanium dioxide freed from chloride ions and its useInfo
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- CA2069705A1 CA2069705A1 CA002069705A CA2069705A CA2069705A1 CA 2069705 A1 CA2069705 A1 CA 2069705A1 CA 002069705 A CA002069705 A CA 002069705A CA 2069705 A CA2069705 A CA 2069705A CA 2069705 A1 CA2069705 A1 CA 2069705A1
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- titanium dioxide
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Classifications
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- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61Q—SPECIFIC USE OF COSMETICS OR SIMILAR TOILETRY PREPARATIONS
- A61Q17/00—Barrier preparations; Preparations brought into direct contact with the skin for affording protection against external influences, e.g. sunlight, X-rays or other harmful rays, corrosive materials, bacteria or insect stings
- A61Q17/04—Topical preparations for affording protection against sunlight or other radiation; Topical sun tanning preparations
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- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61K—PREPARATIONS FOR MEDICAL, DENTAL OR TOILETRY PURPOSES
- A61K8/00—Cosmetics or similar toiletry preparations
- A61K8/18—Cosmetics or similar toiletry preparations characterised by the composition
- A61K8/19—Cosmetics or similar toiletry preparations characterised by the composition containing inorganic ingredients
- A61K8/29—Titanium; Compounds thereof
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
- C01G23/00—Compounds of titanium
- C01G23/04—Oxides; Hydroxides
- C01G23/047—Titanium dioxide
- C01G23/0475—Purification
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
- C08K3/00—Use of inorganic substances as compounding ingredients
- C08K3/18—Oxygen-containing compounds, e.g. metal carbonyls
- C08K3/20—Oxides; Hydroxides
- C08K3/22—Oxides; Hydroxides of metals
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- C—CHEMISTRY; METALLURGY
- C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
- C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
- C09D7/00—Features of coating compositions, not provided for in group C09D5/00; Processes for incorporating ingredients in coating compositions
- C09D7/40—Additives
- C09D7/48—Stabilisers against degradation by oxygen, light or heat
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- 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
- C01P2006/22—Rheological behaviour as dispersion, e.g. viscosity, sedimentation stability
Abstract
Abstract The invention relates to a process for the removal of chloride ions from a fine-particle titanium dioxide A titanium dioxide sol containing at least 100 g/l TiO2 is mixed, at a temperature between 40°C and the boiling point, with an aqueous alkaline solution up to a pH of between 4 0 and 11.0 while stirring without generating high shear, resulting essentially in a tangential to radial flow of the liquid; the fine-particle titanium dioxide is flocculated in this procedure, subsequently it is filtered and washed with an aqueous electrolyte solution The flocculated mixture has a low viscosity which results in short filtration and washing times and in an improved removal of chloride. The titanium dioxide sol can be produced by reacting titanium dioxide hydrate with alkali, decomposing the titanate formed and peptising with hydrochloric acid, the mixture washed free of sulphate or by heating and/or partially neutralizing an aqueous TiC14 solution.
The invention also relates to the fine-particle titanium dioxide freed of chloride ions that is obtainable in the process of this invention and to its use as a rutilisation seed in the production of rutile from titanyl sulphate solutions, as a UV absorber and for the generation of special optical effects in paints.
The invention also relates to the fine-particle titanium dioxide freed of chloride ions that is obtainable in the process of this invention and to its use as a rutilisation seed in the production of rutile from titanyl sulphate solutions, as a UV absorber and for the generation of special optical effects in paints.
Description
20~7~
Process for the removal of chloride ions from a fine-particle titanium dioxide, -uch fine-particle titanium dioxide freed from chlor$de ions and its use Description 5 The invention relates to a process for the remoYal of chloride ions from a fine-particle titanium d~oxide that was produced using hydrochloric acid, titanium tetrachloride and/or the products of its reaction with water and which contain~ seeding crystals consisting o~ titanium dioxide of the rutile crystal modification, to such fine-particle titanium dioxide freed from chloride ions and obtainable by said process and to its use in various fields of application In this patent application, ~fine-particle titanium dioxide~ is unaerstood to be titanium dioxide of a particle ~ize below that lS which i~ normAl and optically eff-ctive in titanium dioxide plgmentJ~ ~aid titanium dioxide may contain hydroxyl groups and/or water bonded like in a usual product denoted as titanium dioxide hydr~te A ~nown process for producing titanium dioxide consists of ~u~ecting ~ titanyl sulphate solution to a thermal hydrolysis, which result~ in a titanium dioxide hydrate from which titanium __ __ : __r.~l--dlo~ide i~ produced by calc.nation This process is often termed -_ r__~sulphate process~ Titanium ~ioxide of the anata~e crystal form is deve:oped from ~uch titanium dioxide hydrate by ca'cining it at temperatures where there i~ -ot yet an excese'~e par~'cle croh~h and at which the pigmentary properties are maintained To produce titanium dioxide of the rutile crystal form ~hereinafter referred to 08 ~rut$1e titanium dioxide~), one adds, prior to calcination, 20697~5 small amounts of a seed which promotes the transformation of the first formed anatase into the rutile modification ~hereinafter this seed being referred to as ~rutilisation seed~). The rutilisation ~eed is mostly used in the form of a t$tanium dioxide sol containing seeding crystals of rutile titanium dioxide.
Since such seeding erystals consisting of rutile titanium dioxide are preferably formed in solutions which contain only univalent acid radicals, e.g. chloride ions, the proce~ses used to produce the titanium dioxide sol containing seeding cry~tals of rutile titanium dioxide are preferably those in which hydrochloric acid, titanium tetrachloride and/or the products of lts reaction with water are used as the compounds furnishing chloride lons.
According to J. Barksdale, ~Titanium~, 2nd edition, The Ronald Press Company, 1966, Pages 341-345, for instance, such a titanium dioxide ~ol is produced by ~reating with hydrochloric acid an alkali titanate washed free of sulphate. This ac~d treatment decomposes the alkali titanate, whereby seeding crystal~ of rutile t~tanlum diox~de are formed. Subseguently, these seeding crystals are pcptl~ed by the addltlon of furth-r quantitiei of hydrochloric acid, a titanlum dloxlde 801 thu~ being form~d.
ln another proc-~, described on Page~ 302-304 o~ the above-cited publication, an aqueous titanium tetrachlorlde solution i8 U8ed a8 th- ource mat-rial ~n which the deJired seeding cry~tal~ of rutile titanium dioxide are formed by heating and/or partlal neutrallzation. The titanium dioxide 801 thus obtalnea can be used dlr-ctly as the rutilisation seed in the production of the rutile tltanlum d~oxlde. Thls titanium diox~de sol, bow-v-r, contains 5~~guantltleJ of procesJ-integrated chloriae ion~. These chloride ion~ may cau~- corro~ion, more ~peci~ically, pitting ~ r--corro~ion of equipment parts used in the titanium dioxide manufacture. Moreover, the corros~on product~ have an adverce effect on the titan'um dioxide, eQpec'ally on the pigment properties of a rutile titanium dloxide pigment produced using the titanium dioxide ~ol.
Process for the removal of chloride ions from a fine-particle titanium dioxide, -uch fine-particle titanium dioxide freed from chlor$de ions and its use Description 5 The invention relates to a process for the remoYal of chloride ions from a fine-particle titanium d~oxide that was produced using hydrochloric acid, titanium tetrachloride and/or the products of its reaction with water and which contain~ seeding crystals consisting o~ titanium dioxide of the rutile crystal modification, to such fine-particle titanium dioxide freed from chloride ions and obtainable by said process and to its use in various fields of application In this patent application, ~fine-particle titanium dioxide~ is unaerstood to be titanium dioxide of a particle ~ize below that lS which i~ normAl and optically eff-ctive in titanium dioxide plgmentJ~ ~aid titanium dioxide may contain hydroxyl groups and/or water bonded like in a usual product denoted as titanium dioxide hydr~te A ~nown process for producing titanium dioxide consists of ~u~ecting ~ titanyl sulphate solution to a thermal hydrolysis, which result~ in a titanium dioxide hydrate from which titanium __ __ : __r.~l--dlo~ide i~ produced by calc.nation This process is often termed -_ r__~sulphate process~ Titanium ~ioxide of the anata~e crystal form is deve:oped from ~uch titanium dioxide hydrate by ca'cining it at temperatures where there i~ -ot yet an excese'~e par~'cle croh~h and at which the pigmentary properties are maintained To produce titanium dioxide of the rutile crystal form ~hereinafter referred to 08 ~rut$1e titanium dioxide~), one adds, prior to calcination, 20697~5 small amounts of a seed which promotes the transformation of the first formed anatase into the rutile modification ~hereinafter this seed being referred to as ~rutilisation seed~). The rutilisation ~eed is mostly used in the form of a t$tanium dioxide sol containing seeding crystals of rutile titanium dioxide.
Since such seeding erystals consisting of rutile titanium dioxide are preferably formed in solutions which contain only univalent acid radicals, e.g. chloride ions, the proce~ses used to produce the titanium dioxide sol containing seeding cry~tals of rutile titanium dioxide are preferably those in which hydrochloric acid, titanium tetrachloride and/or the products of lts reaction with water are used as the compounds furnishing chloride lons.
According to J. Barksdale, ~Titanium~, 2nd edition, The Ronald Press Company, 1966, Pages 341-345, for instance, such a titanium dioxide ~ol is produced by ~reating with hydrochloric acid an alkali titanate washed free of sulphate. This ac~d treatment decomposes the alkali titanate, whereby seeding crystal~ of rutile t~tanlum diox~de are formed. Subseguently, these seeding crystals are pcptl~ed by the addltlon of furth-r quantitiei of hydrochloric acid, a titanlum dloxlde 801 thu~ being form~d.
ln another proc-~, described on Page~ 302-304 o~ the above-cited publication, an aqueous titanium tetrachlorlde solution i8 U8ed a8 th- ource mat-rial ~n which the deJired seeding cry~tal~ of rutile titanium dioxide are formed by heating and/or partlal neutrallzation. The titanium dioxide 801 thus obtalnea can be used dlr-ctly as the rutilisation seed in the production of the rutile tltanlum d~oxlde. Thls titanium diox~de sol, bow-v-r, contains 5~~guantltleJ of procesJ-integrated chloriae ion~. These chloride ion~ may cau~- corro~ion, more ~peci~ically, pitting ~ r--corro~ion of equipment parts used in the titanium dioxide manufacture. Moreover, the corros~on product~ have an adverce effect on the titan'um dioxide, eQpec'ally on the pigment properties of a rutile titanium dloxide pigment produced using the titanium dioxide ~ol.
2~$~7~
There is a particularly great risk of corrosion as a result of the chloride ions introduced by the titanium dioxide sol into the TiO2 manufacturing process, when the washing liquids obtained in the TiO2 manufacturing process cannot be simply removed for environmental reasons but are returned to the process.
~or the above-stated reasons it is necessary to reduce as far as possible the chloride ion content of the titanium dioxide sol.
Attempts were made, therefore, to wash the titanium dioxide sol free of chloride prior to using it (DE-Cl 39 38 693). But owing to the extremely flne particle size of the seeding crystals, this method is very expensive technically and i8 not customary. In other procedures, as are described in DE-Al- 38 17 909, US-A-2 494 492 und US-A-2 479 637, the fine-particle titanium dioxide contained in the titanium dioxide sol is flocculated by addition of an alkaline reagent and the flocculated fine-particle titanium dioxide is separated from the liquid phase and washed with water.
In this process, the titanium dioxide sol usually contains relatively little TiO2 before being flocculated. Long flltration times are required, and the washing of the flocculated and separatcd fine-particle titanium dioxide is intricate ~nd tlm--consuming. During these washing procedureJ, the flocculated fine-particle titanium dioxide i8 repeotedly slurried with water and filtered again. Crack~ may readlly form ln the fllter cake and permlt TiO2 to penetrate through the filter. It may happen that, during the washlnq procedure, the ~cparated fine-part~cle titanium aioxlde i8 rodi~pcrsed though thls is unaesirable, the flocs being brok-n down.
A new process has therefore been searched for which overcomes the dr~b~rck~ of the known methods while permitting to separate and wash the flocculated flne-particle tltanium dioxide readily and r--rapidly. Surprisingly, this ob~ective ~as found to be achievable by a combir.atlon of certain process steps, thls combination unexpectedly showing additional advantages over the known procedures in other respects.
2~7~5 Accordingly, a new process has been found for the removal of chlor$de ions from a fine-particle titanium dioxide that was produced using hydrochloric acid, titanium tetrachloride and/or the products of its reaction with water and which contains seeding 5 crystals consisting of titanium dioxide of the rutlle crystal form This process comprises a) using a titanium dioxide sol as the source material which has a titanium dioxide content of at least 100 g/litre, calculated as TiO2;
b) mixing said titanium dioxide sol with an aqueoug solution of an alkaline reagent, the fine-particle titanium dioxide being flocculated, under such condition~ that (i) the solution of the alkaline reagent containE this reaqent in a concentration of from 10 per cent by weight to the point of ~aturations (ii) the alkaline reagent is added to the titanium dioxide 801 in such a quantity that the mixture has a pH of between 4 0 and 11 0;
(iii) the titanium dioxlde sol, during the addition of the alkaline reagent, iQ kept at a temperature between 40C
and the boiling point and iJ stirrea ln a vessel, without g-n-rating hlgh ~hear forc-, Juch as to produco in the veJJ-l Js-ntlally only ~ tang-ntial to radlal flow of the ligulds c) ~-paratlng the ~locculat-d fine-particle titanium dioxide by flltr~tion at a temp-rature between 20C and lOO-C7 and hing th- ~-parat-a fln--particle titanium dloxide at a t-~p-ratur- be~w-en 20-C and lOO-C with an aqu-ous solution of ~n l-ctrolyte who~e concentratlon ln the wasb liquid i9 between 0 1 per cent by weight and the point of ~aturation, -_ ~J~oK~o~ive ~ubstances, particularly chloride ion~, being excluded aJ an electrolyte The preferable source material i8 a titanlum dioxide 801 which has a titanium dloxide content of between '00 ana 200 g/litre, preferably between 150 and 170 g/litre, calculnted as TiO2 The preferable alkaline reagent for the i'locculatlon i~ hydroxides and/or carbonates of sodium and/or of pota~sium, and/or ammonia, and~or ~mmonium hvdroxide, and~Gr carbonate~ of the a~o~iu~ on 20~7~
The solution of the alkaline reagent is added to the titanium dioxide sol preferably at a temperature between 60~C and 90C.
The solution of the alkaline reagent is added to the titanium dioxide sol preferably in a quantity to attain a p~ of between 7 and 9 in the mixture.
The flocculated fine-particle titanium dioxide is separated by filtration preferably at a temperature between 60C and 90C.
~he separated fine-particle titanium dioxide is washed also preferably at a temperature between 60C and 90C.
The interaction of all the process parameters claimed i~ essential for achievin~ the ob~ective, which is to obtain a readily filterable and washable fine-particle titanium dioxide with a sufficiently reduced chloride ion content and containing seeding crystal~ of rutile titanium dioxide.
The solution of the alkaline reagent may contain said reagent in a wide variety of concentrations. But in order to prevent the titanlum dioxide from being too much diluted through the addition o~ aaid solution, this solution ~hould contain the alkaline reagent generally ln not too low a concentration. This solution may be even a saturated solution.
Tho temperature, at which the alkaline reagent should be added to the ~itanlum dioxide 801, at which the fine-particle titanium dloxide contained in the titanium dioxide 801 should be flocculated through ~aid addltion, and/or ~t which the flocculated - 2~--1~e-p~rticle tit~nium in the solutions should be filtered, may be ad~u~ted by an external heating and/or by utilization of the heat ~ that i8 generated in the reaction of the added alkaline reagent with the acid in the titanium dioxide sol.
7 ~ ~
In this $nvention, particular attention is paid to stirring while adding the alkaline reagent to the titanium dioxide ~ol The solutions need tO be thoroughly and rap~dly m~xed while avoiding, however, that high she~r i8 applied to the mixture If the ~ixing i~ done too slowly, there i8 a risk of having an excessively high pH in parts of the mixture and/or of having in the mixture zones with considerably different pH values; in both cases there will be _ an unde~irable increa~e in viscosity If excessive shear forces are appl~ed, the flocs formed will be di~integrated again A
satisfactory effect of stirring esQentially depends on the type of stirrer ~n order to homogenizc the mixture, i e homogenizing the concentration witbin the mixture while adding the alkaline reagent, stlrrer~ are su~table which effect in the mixture an essentially tangential to radial flow of the liquid An axial flow of the liquid, however, should be avoided -as far as ever possible Suitablc stlrrers ~re crossed-beam paddle mixers, gate paddle mixers or flat-blade paddle mixers, the two latter types being particularly appropriate Further det~ a~out su~table stirrers are given in ~Ullmanns Enzyklop~die der techniRchen Chemie~, 4th edition, volume 2, 1972, pages 261-262 A particularly favourable embodlment of this invontlon comprises ~tirring th- tit-nlum dioxlde rol during the additlon of the alk~line r--gent wlth a gate paddl~ mixer or a flot-bl~de paddle mix~r.
ln ddlng th- alkaline reagent to the titanlum dloxide 801~ after p~ o~ ~ ha~ been attained, one experiences a marked decline ln the relativ- vl~co~ity of the mixture ~ratio of the vi~cosity of the mlxture at the pH v~lues attainea to the viaco~ity of the titan~um aioxide 801 before the addition of the a~kaline reagent);
3e'~ien the p~ i~ further increased, the rclative vi~coslty es~entially remains at the low lovel reached 2~S97~S
This behaviour is extremely surprising and differs essential'y from the behaviour the titanium dioxide sol shows when not all of the claimed steps are adhered to. In such a case, the relative viscosity markedly increases when pH 4 is exceeded to decrease but insignificantly with further rising pH and the initial value of tbe relati~e viscosity is not reached again.
In the process of this invention, the mixture i9 filtered after ~ the desired p~ has been reached. If the flocculated fine-particle titanium dioxide in the mixture settles prior to the filtration, this titanium dioxide will form a fluffy ~ediment which can be ~tirred up again without problem by one of the stirrers mentioned.
The filtered product is washed to remove the chloride ions adhering to it. The wash liquid u~ed therefor is an eleetrolyte solution: the use of pure water is to be avoided.
1~ As a rule, the electrolyte consists of ~alts of inorganic and/or organic acids or of a buffer mixture. Accordingly, a particularly favourable embodiment of this invention comprises washing the separated f$ne-particle titanium dioxide with an aqueous solution of an electrolyte which consists of one or several ~alt(s) of inorganic and/or organic acids or of a buffer mixture. The electrolyte solution contains, for instance, saltJ of monovalent and~or multivalent ions, specifically salts of alkali metals or of alkalirearth met~ls or of ammonium, more specifically saltJ of sodium or potasniu~ or mixtures thereof. The electrolyte solution must not contain ~ubstances which, on further processing and use of the washcd fine-particle titanium dioxidc, are corroslve toward~ the equ$pment employed.
It i~ particularly advantageous to use chloride-free wash liquids -_o~ cntially neutral reaction and derived from the titan$um dloxide manufacturing process: particularly adv~ntageous f~ltrates are tho~e derived from the post-treatment of titanium dioxidc in the titan~um dioxide manufacture or neutralized filtrates o~tained ~n washing an alkal$ titanate free from sulphate, which ti~anate 206~7~
is meant for the titanium dioxide sol productions the latter filtrates comprise especially sodium sulphate solutions In this way, it is possible profitably to utilize liquids obtained as waste material in the manufacture of titanium dioxide S As a rule, the washing of the flocculated and filtered fine-particle titanium dioxide is to be carried on until the residual chloride ion content in said fine-particle titanium dioxide is not more than 0 1 to 0 5 per cent by weight Cl , related to ~iO2 To this end, a preferable embodiment of this invention continues washing the fine-particle titanium dioxide separated by filtration until the chloride ion content in the wash filtrate has dropped to 0 1 g/litre at most In general~ the mixture obtained from the t$tanium dioxide sol and containing the flocculated fine-particle titanium dioxide has so low a viscosity that it can readily be filtered immediately after the desired p~ range has been ad~usted In a particular embodiment of thi~ invention it may be advisable, however, to dilute the mixture containing the flocculated fine-partlcle t$tanium dioxide prior to filterlng it Dilution, for example, may be with water Sometim-s it i8 advi~able, according to anoth-r embodiment of this invention, to add an organic flocculant, g polyacrylamide, to th- mixture containlng the flocculat-d fin--partlcle titanium dioxid-It wa~ found that flocculating the titanium dioxld- ~ol ln co~pliance wlth thi~ inv-ntion, and filtrating and wa~hing the flocculated flne-particle titanium dioxide do not alter the propertieJ of the J-eding cry~talJ of rutile titanium dioxide n~a~rned in ~aid titanlum dloxide It i~, in particular, the ,rutilizing e~-ct of the Jeed~ng cry~tals o~ rutile titanium dioxide which i8 pre~erved unrestr$ctealy ~he washed product can readily be redi~persed in ~ulphuric acid-containing wnter 20~97~
~he flocculated and neutralized mixture obtained from the titanium dioxide sol, with a titanium dioxide content of 120 to 250 9/
litre, calculated as TiO2, has a viscosity of from 6.B x 10 2 Pa.s to 16.~ x 10-2 Pa.s at 25~C.
The size of the flocs ranges from 10 to 40 microns: the seeding crystals contained in the flocs have a particle size of 0.01 to 0.1 microns (measured on the longest axiQ) and, as a rule, are needle-shaped and have rutile crystal form.
The flocs readily settle and are very easily filtered and washed.
It is not necessary to slurry the fine-particle titanium dioxide prior to washing or between the various washing steps.
The titanium dioxide 801 wbich is the source material in the process of the present invention can be produced by various ways.
One embodiment of the present invention, for example, comprises lS producing the titanium dioxide 801 by reacting a titanium dioxide hydrate suspended in water and produced by hydrolysis of A titanyl sulphate solutlon with an alkali hydroxide solution thus forming alkali titanat-, waJhing free of sulphate the mixture obtained in th- r-action, decomposing with hydrochloric acld the alkali tltanate obtain-d thus forming titanium dlo~lde hydrate, ~nd peptizing this titanium dioxide hydrate by adding a further quantity of hydrochloric acid.
A p~rticularly dvantageous embodiment of this production method con-~ts Or thc following rteps:
25 a) A titanium dloxide hydrate of anatase cry~tal form produced by the hydrolysiJ of a titanyl sulphate Jolution is ~lurried with ~ r ~uch a~ to obtain ~n the ~lurry a concentration of 20 to .-_ r'_~_ 26 per cent by weight TiO2J
b) the titanium dioxide hydrate slurry obtained ls heated to between 60C and 70C.
.
2~6~
c) the heated titanium dioxide hydrate slurry is added, while stirring, to an aqueous sodium hydroxide solution heated to between 90C and 100C in sufficient amount to achieve, after addition, a weight ratio of NaOH to TiO2 of between 1.25 and 1.65 in the mixture:
d) the mixture is heated to the boil and maintained at the boiling point for 120 to 140 minutes:
e) the mixture is then cooled down to between 50C and 60C and is filtered;
f) the filter cake obtained is washed until the So2 content $n the wash filtrate i9 less than 0.05 g/litre;
g) the washed filter cake is slurried in water to obtain a TiO2 content of between 10 and 25 per cent by we~ght: the mixture thus obtained i8 mixed with hydrochloric acid containing 20 to 25 per cent by weight HCl to attain a pH value of 2.8 to 3.1 h) the mixture is heated to between 55C and 65C and kept at this temperature for 30 to 45 minutes, the pH range of between 2.8 and 3.1 being maintained:
il the mixture is peptised at 55 to 65C with hydrochloric acid of 20 to 25 per cent by weight HCl in suff$cient amount to ad~ust a weight ratio of hydrochloric acid, expressed as HCl, added in this stage, to TiO2 of between 0.15:1 and 0,25:1~ and k) the suspenslon obtained i8 heated to the boil within 30 to 40 minute~ and kept at the boiling point for 60 to 90 minutes.
In another advantageous embodiment of the present invention, the titanium dioxide 801 is produced by hydrolysis of a solution of titanium tetrachloride in water and/or by an agueou~ solution of one or several compoundg formed by the reaction of titanium tetrachloride with water.
~~- 34h~n produc~ng the titanium dioxide sol, substances may be added which have defined effects on the particle size and/or the particle sha?e of the seeding crystals of rutile tita~ium dioxide.
20~7~
Among such substances, fine-particle tin dioxide is particularly suitable. An addition of such tin dioxide in the production of the titanium dioxide sol is described in the German patent application P 41 05 345.1.
Accordingly, a particularly advantageous embodiment of the invention consists in using a titanium dioxide 901 in the production of which a fine-particle tin dioxide is used the particle size of wh~ch is between 1 and 10 nm, preferably between 1 and 4 n~, the tin dioxide being added in an amount of between 0.5 and 10 per cent by weight, related to the amount of titaniu~
dioxide contained in the titanium dioxide sol.
According to an advantaqeous method of operation, one may proceed as follows, for example:
a) A titanium dioxide hydrate of anatase crystal form produced by the hydrolysis of a titanyl sulphate solution is slurried with water such as to obtain in the slurry a concentration of 20 to 26 per cent by weight TiO2:
b) the titanlum dioxide hydrate slurry obtained is heated to between 60 and 70cl . 20 c~ the heated titanium dioxide hydrate slurry i~ added, while stlrring, to an aqueous sodlum hydroxide solutlon heated to between 90C and 100C in sufficlent amount to achieve, after ~ddition, a weight ratio of NaOH to ~iO2 of between 1.25 and 1.65 in the mixture~
d) the mixture is he~ted to the boil ~nd maintained at the boiling polnt for 120 to 140 minutes;
e) the mixture i8 then cooled down to between 50C and 60C and is i'lltered;
filter cake obtained is washed until the So2 content in 3gL~ - the wash filtrate is less than 0.05 g/litre:
g) the washed filter cake is slurried in water to obtain a TiO~
content of between 10 and 25 per cent ~y weight; the mixture thus obtained is mixed with hydrochloric acid containing 20 to 25 per cent by welght NCl to attain a pH value of 2.8 to 3.1;
, 20~7~
hl the mixture is heated to between 55C and 65C ~nd kept at this temperature for 30 to 45 minutes, the pH range of between 2.8 and 3.1 being maintained;
i) a colloidal tin dioxide solution is added to the mixtyre, in which tin dioxide solution the tin dioxide has a particle size of between 1 and 10 nm, preferably between 1 and 4 nm;
j) the mixture to which the colloidal tin dioxide solution was added ls peptized at 55C to 65~C with hydrochlor$c acid of 20 to 25 per cent by weight HCl in sufficient amount to adjust a weight ratio of hydrochloric acid, expressed as HCl, added in this stage, to TiO2 of between 0.15:1 and 0.25:1; and k~ the suspension obtained is heated to the boil within 30 to 40 minute~ and kept at the boiling point for 60 to 90 minutes.
The invention also relates to a fine-particle titanium dioxide freed of chloride ions that was produced using hydrochloric acid, tltanium tetrachloride and/or the products of its reaction with water and which contains seeding crystals consistlng of titanium dioxide of the rutile crystal modification and which can be obtalned by a proceQ~ according to this invention. This 20 i'ine-partlcle tltanium dioxlde, according to a proferred embodiment of thi8 invention, i8 tO have a chloride ion content not in exce8~ of 0.5 per cent by welght Cl , related to TiO2, in ~pecial ca~eJ not in excess of 0.1 per cent by weight Cl , related to TiO2.
25 Sald fine-partlcle tltanlum dioxide can be employed in numerous fi-lds of application.
A particularly preferred mode of application consist~ of using the - -_ ~c~pnrt$cle tltanlum dloxlde as the rutll~zatlon ~eed for the manufactur- of rutile titanium dioxide from titanium dioxide r--30 hydrate that wa~ obtained through hydroly~i~ of a titanyl sulphate solution.
2~7~
Further preferable modes of application are its use as a uY
absorber in plastics or paints, as a uV absorber in sunscreen compositions or in other cosmetic articles or as an agent for the generation of special optical effects in paints, such as the so-called ~down flop~ (cf. EP-Al-0 270 472).
The fine-particle titanium dioxide freed from chloride ions according to this invention can be dried before being used, a substance be~ng added optionally, prior to drying, which prevents the formation of hard agglomerates. The titanium dioxide agglomerates formed in drying may be milled and/or tempered. Prior to and/or after drying and/or tempering, the fine-particle titanium dioxide may be post-treated with one or several inorganic and/or organic substances.
The invention ls illustrated in more detail in the following Examples.
ExamPle A tltanium dioxlde 801 was produced in a known way in which, essentlally according to DE-Al-38 17 909, a titanlum dioxide hydrate having anatase crystal structure and having been obtained by the hydrolysis of a titanyl sulphate solution was reacted, at elevated temperature, slurried in water, with a sodium hydroxide solutlon and the product obtalned was ~iltered and washed until the wash filtrate contained less than 0.05 g/l sulphate ions (S0~ d-tectlon by the BaC12 test). The washed product was then 25 slurried with water and mixed with hydrochloric acid up to a pH of 2.8 to 3.1 and heated to 60 at this pH. The resulting product was then pepti~ed by addition of a further amount of hydrochloric acid r~oncentration 25 per cent by wsight) up to a weight ratio of Cl to TiO2 of 0.15:1 and by heating to the boiling point.
~0~7~
In producing the titanium dioxide sol, operation was such that the titanium dioxide sol obtained had a titanium dioxide content of 220 9/1, calculated as ~iO2. 455 ml quantities of this titanium dioxide sol, corresponding to 100 g TiO2, were cbarged into s beakers of 9 cm inner diameter and mixed with various quantities of sodium hydroxide solution of an NaO~ content of 30 per cent by weight in order to attain different p~ values in the range from 4.1 to 8.5. During the addition of the sodium hydroxide solution, which took about 2 minutes, the temperature of the mixture was adjusted to 80C by means of a thermostat and the mixture was stirred by way of a flat-blade paddle mixer, initially at a speed of 350 rpm. The flat-blade paddle mixer was 6.4 cm high and 3.6 cm wide. After a pH of 3-4 was attained, the titanium dioxide sol began to flocculate. When the flocculated state was reached, the viscosity of the mixture dramatically dropped and the stirrer speed had to be reduced to 200 rpm. After the desired p~ was reached, the mixture was stirred for 5 minutes: the stirrer then was stopped and product adhering to the wall was stirred into the suspension by means of a glass rod. Then, without lowering the temperature, the mixture was stirred for another 10 minutes by mean~ of the flat-blade paddle mixer.
SubJequently the mixtures were cooled down to 23C and each mlxture wa8 divlded i~to ten equal portisn8, ach portion thus containlng 10 g TlO2. Each portlon was filtered through a laboratory ~uctlon ilter 17.5 cm diameter) (0.3 bar pressure).
The i'iltet medium was a binder-fre0 glass fibre filter paper of a baJi~ w-lght of 90 q/m in the form of a round filter. The time required from the beginning of flltration up to slight surface . _a,~ UL ltime of filtration) was measured. The mean values were determined from 10 trlals each. (~Slight surface drying~ refers ~o '~ the state at whlch the liquid level has dropped to the level of the 'ilter cake surface).
-20~7~
After the slight surface drying was attained, a wash solution, which was a solution of sodium sulphate in water of a concentration of 2.5 g/l Na2S04 and a temperature of 22C, was passed onto the filter cake and the time was measured that was required for 250 ml and 350 ml of this solution to pass through the filter cake, again until a slight surface drying (wash time) was achieved. The efficiency of the washing was assessed by - determining the chloride lon content in the filtrate at the end of the washing by means of a silver nitrate solution in nitric acid lO medium. The chloride ion content in the filter cake, after 350 ml wash solution having been passed through it, wa6 0.08 per cent by weight Cl , related to TiO2. The particle size of the flocs was between 10 and 40 microns. Particle size was measured on a SALD-llO0 particle size instrument by Shimadzu.
The filtered and washed fine-particle titanium dioxide could be redispersed in sulphuric acid-containing water.
The results shown in Table 1. In this Table, chloride contents smaller than or equal to 0.1 g/l are denoted as ~chloride-free~;
chlorlde contents of more than 0.1 g/l are denoted ~not 20 chlorlde-free~.
Example 2 ~comparatlve example) The tltanlum dloxide 801 was the same sourc- material a8 in Ex~mple 1. In oraer to attain dlfferent pH values, varying ~mounts oi' the sodium hydroxide solutlon usea in Example 1 were added at a 25 ~peea of about 1 ml per mlnute. Addltlon, however, was at amblent temperature while stlrring at 800 rpm by means of a propeller stirrer. The filtration and washing time~ were measured as in Example 1. The results are al80 shown in Table 1.
r--~0~7~5 The comparison of the two examples shows that though it was possible to achieve an absence of chloride ions also in the comparative example, the filtration and washing times were considerably longer than with the process of the $nvention and the filter cake showed cracking while this was not the case with the process of the invention Example 3 The procedure was the same as in Example 1 But the washing solution was a sodium sulphate solution of a concentration of 5 9/1 Na2S04 instead of 2 5 g/l Na2S04 Compared with the use of a solution of 2 5 g/l Na2S04, a further marked shortening of the washing times was achieved, especially with lower pH values ~he results of Example 3 are shown in ~able 2 Example 4 Tho procedure wa~ th- same as ~n Example 1 with the difference that the flocculation of the titanium d~oxide 801 was achieved, in one ln~tance, by addltion of 55 0 ml of an ammonium hydroxide ~olutlon of a concentration of 25 per cent by weight NH3 and, in another in-tance, by addition of 100 ml of a ~odium carbonate ~olution of a concentration of 25 per cent by weight Na2C03 ln both in~tancc~, flocculation took place up to p~ 7 In this Exampl-, too, xcellcnt ~lltration ana washing times were achieved Th- rc~ult~ of Example ~ are shown in ~able 3 . ~ ,,.~,_r--- 17- 2~6~7~
7~ble 1 E~pl~ ~emper-ture Sodium hydroxide pH ~djust~d Filtr tion l~shlng time ~sh solution Of th solution dded time Na2so4 flocculation C ~1 s~e ~in 9/1 250 ~1 350 ~1 8047 5 4.1 7 13~ 20~ 2 5 110 50.0 5.2 5 ~ 14~ 2.5 110 52 0 7.0 3 2.5~ ~ 2.5 8054.5 8 5 2 2~ ~ 2 5 2 2348 5 5 0 250 60~ 94~ 2 5 2351 0 6 D 250 49~ 73~ 2 5 2352.0 7.0 200 71~101~ 2 5 2354.0 9.0 120 51~ 76~ 2 5 5 ~) e~ O ~So.l 9~1) ~) not el~-f,.- (~0.19~1) ~~1ng of the filt r ca'~e ~i~h eont1nu1ng ~uhing ':
2~7~
- lB -T-ble 2 Ex~mple IEmper~-ure Sodium hydroxide pH ~djusted filtr~tion ~shing tire ~ash solution of the solution ~dded time ~254 floecul~tion _ _ C ~1 see min 9/1 250 ~1 350 ml 3 ~0 48 5 S 0 5 5 5~ 8~ S
Sl 0 6 0 ~ 3 5~ 6~ S
52 0 7 0 ~ 2~ 3~ 5 1 0 80 53 0 8 0 3 2~ 3~ 5 ~) tl -~r~ 0 1 9~1) ~) not Cl-- r~o (>0 1 9/1) T~ble 3 E~pl~ Tomper~ture ~lk~lln ph ~dJusted F11tr~tion ~ shlng t h e ~ sh solutlon 1 5 O- tho solut1On ~dd d t1me ~b2S04 flocc41~t~o~
C ml see 1n 9~1 2S0 ~1 3S0 ~1 4 ~0 55 0 ~H3- ol 7 0 4 3.5~ S 5~ 2 5 2 0 ~0 100 ~2C03 7 0 ~ 3~ 5 2 5 tl -fr~ 0 1 9~1) 2~7~
Example S
A titanium dioxide sol was produced as in Example 1 but with a TiO2 content of 160 9/l This titanium dioxide 801 was adjusted to different pH values by addition of a 30 per cent by weight NaOH solution and flocculated in the same way as in Example 1 In the flocculated mixtures, the viscosity was determined as the relative viscosity, i e the ratio of the viscosity of the mixture, at the p~ ad~usted, to the viscosity of the original titanium dioxide 801 which had a pH of about 0 Moreover, the filtrat$on and washing times were determlned as in Example 1 The results are shown in Table 4 ~xample 6 (comparat$ve example) ~he titanium dioxide sol of Example S was used as the source material and the procedure was that of Example 5 with the dli'ference of the Jodlum hydroxide Jolution being 810wly added at ambient temperature ~about 1 ml/mln) a~ in Example 2, whlle Jtirrlng by means of a propell-r mlxer at a rate of BOO rpm The r-sults ar- also shown ln Table 4 Table 4 ~hows that there was no differ-nce between the two example~ in th-lr vlscoaity behaviour up to p~ 4, but then with rl~lng pH thelr behaviour markedly dlffered While, in the proccdure of the comparative example, the relative vl~coffity markedly ~ncrea~ed and remained at a high l-vel up to p~ 11 0, the relative vlJcoJity~ in the proccsJ of the inventlon, warkedly dkopped on reaching the flocculated Jtate and remained at this low level up to pH 11 Accordingly, the process of the invention yielded much shorter times of filtration and waQhing and better washing efficiency than the procedure of the comparative example The proce~s of the invention did not involve any def~ciency in the filter cake as was encountered wlth the procedure of the comparative example 206~7~S
Table 4 Example pH ad- Relative Filtration Washing time ~usted viscosity time (sec) 250 ml 350 ml .
S 3 0 l l 720 redispersion after 50 ml s 4 0 1 4 410 redlspersion after 60 ml ~ 5 0 0 2 220 62~ 9S~
6 0 - 30 35* 49 7 0 0 1 30 16~ 21 8 0 - 40 l9~ 30 9 0 0 1 25 16~ 23 11 0 0 1 40 41~ 68 6 3 0 1 1 960 redispersion after 20 ml~
4 0 1 4 810 redispersion after 80 ml~
S 0 2 8 440 92~ 133~/*~
7 0 3 9 370 S9~ 78 9 0 3 7 300 61~* redispersion~
11 0 2 9 275 65~ 86 ~) Cl~-fre- ~ 0 1 g/l Cl-) ~ ) not Cl~-fr-e ~ ~ 0 1 9/l Cl-) zo ~) Cracklng of th- filter cnke with continuing wn~hlng ~x~mDl- 7 ~ an~um d$oxide ~ol~ with different TiO2 loadings were produced - like in ~xample l A~ in Example l, these titanium dioxide sols were floccul~ted at 80 C by ~d~usting a pH v~lue of 7 0 by means of a sodium hydrox$ae solution of 30 per cent by weight NaOH:
2~6~7~
subsequently, the fine-particle titanium dioxide was filtered like in Example l and washed with 250 ml of a sodium sulphate solution of a concentration of 2.5 g/l Na2SO4. The filtration and washing times determined like Example l are shown in Table 5.
Table 5 ;
TiO2 concentration Piltration time Washing time ;
9/1 sec min lO0 120-360 46-60 140 30-60 15_25 The results of Table 5 show that the filtration and washing times of the product produced according to this invention are rather short alr-ady at a TiO2 content of as little as 100 g/l in the original titanlum dioxide 801, but are becoming markedly shorter still with rising TlO2 content in the original titan~um diox~de 801.
Th- u~e of high TiO2 concentrations in the original titanium dloxide 801 has the advantage of smaller vessels being required and ~maller volumes of waste water being obt~ined.
_ Exluu~Le 8 $ne procedure was like in Example 7 with the difference that, after addition of the sodium hydroxide solution and the resulting flocculation of the titanium dioxide 801, the m~xture was diluted with water to a uniform TiO2 content of 100 g/l prior to filtration. The filtration and washing times determined are shown in ~able 6.
-. :.
2~7~5 Table 6 TiO2 concentration TiO2 concentration Filtration Washing after flocculation prior to filtrat1on time time g/l g/l sec min 140 100 lOS 21 The results of Table 6 indicate that the improved filtr~tion times are less due to the quantity of liguid passed through the iilter during filtration than to the TiO2 content of the slurry during flocculation and that this TiO2 content ha3 al80 a beneficial ffect on th- wa~hing behaviour A great advantage of the process of thi~ invention is the posslbil~ty o~ using, as the sourc- material, tltanium dioxide 8018 as are typical produo-d which need not be dlluted for the ~locculation and or the Jubsequent ~tep~ The proce~s is very ~l-xibl- and can be largely adapted to the requir-ments of each Jitu-tion.
The invention relates to a process for th- removal of chloride ions _ from a fin--part~cle titanium dioxide A titanium dioxide 801 containing at l-ast 100 gJl TiO2 i8 mixed, at a temp-rature between 40C and th- boiling point, with an aqueous alkaline solution up to a pH of between 4 0 ana 11 0 whil- ~tirring without generating high shear, resulting essentially in a tangential to 2~6~7~5 radial flow of the liquid; the fine-particle titanium dioxide is flocculated in this procedure, subsequently it i8 filtered and washed with an aqueous electrolyte solution. The flocculated mixture ha3 a low viscosity, which results in short filtration and washing times and in an improved removal of chloride. The titanium dioxide sol can be produced by reacting titanium dioxide hydrate with alkali, decomposing the titanate formed and peptising, with hydrochloric acid, the mixture washed free of sulphate or by heating and/or partially neutralizing an aqueous ~iC14 solution.
The invention also relates to the fine-particle titanium dioxide freed of chloride ions that is obtainable in the process of this invention and to its use as a rutilisation seed in the production of rutile from titanyl sulphate solutions, as a ~ absorber and for the generation of special optical effects in paints.
,, ,- ~
r--
There is a particularly great risk of corrosion as a result of the chloride ions introduced by the titanium dioxide sol into the TiO2 manufacturing process, when the washing liquids obtained in the TiO2 manufacturing process cannot be simply removed for environmental reasons but are returned to the process.
~or the above-stated reasons it is necessary to reduce as far as possible the chloride ion content of the titanium dioxide sol.
Attempts were made, therefore, to wash the titanium dioxide sol free of chloride prior to using it (DE-Cl 39 38 693). But owing to the extremely flne particle size of the seeding crystals, this method is very expensive technically and i8 not customary. In other procedures, as are described in DE-Al- 38 17 909, US-A-2 494 492 und US-A-2 479 637, the fine-particle titanium dioxide contained in the titanium dioxide sol is flocculated by addition of an alkaline reagent and the flocculated fine-particle titanium dioxide is separated from the liquid phase and washed with water.
In this process, the titanium dioxide sol usually contains relatively little TiO2 before being flocculated. Long flltration times are required, and the washing of the flocculated and separatcd fine-particle titanium dioxide is intricate ~nd tlm--consuming. During these washing procedureJ, the flocculated fine-particle titanium dioxide i8 repeotedly slurried with water and filtered again. Crack~ may readlly form ln the fllter cake and permlt TiO2 to penetrate through the filter. It may happen that, during the washlnq procedure, the ~cparated fine-part~cle titanium aioxlde i8 rodi~pcrsed though thls is unaesirable, the flocs being brok-n down.
A new process has therefore been searched for which overcomes the dr~b~rck~ of the known methods while permitting to separate and wash the flocculated flne-particle tltanium dioxide readily and r--rapidly. Surprisingly, this ob~ective ~as found to be achievable by a combir.atlon of certain process steps, thls combination unexpectedly showing additional advantages over the known procedures in other respects.
2~7~5 Accordingly, a new process has been found for the removal of chlor$de ions from a fine-particle titanium dioxide that was produced using hydrochloric acid, titanium tetrachloride and/or the products of its reaction with water and which contains seeding 5 crystals consisting of titanium dioxide of the rutlle crystal form This process comprises a) using a titanium dioxide sol as the source material which has a titanium dioxide content of at least 100 g/litre, calculated as TiO2;
b) mixing said titanium dioxide sol with an aqueoug solution of an alkaline reagent, the fine-particle titanium dioxide being flocculated, under such condition~ that (i) the solution of the alkaline reagent containE this reaqent in a concentration of from 10 per cent by weight to the point of ~aturations (ii) the alkaline reagent is added to the titanium dioxide 801 in such a quantity that the mixture has a pH of between 4 0 and 11 0;
(iii) the titanium dioxlde sol, during the addition of the alkaline reagent, iQ kept at a temperature between 40C
and the boiling point and iJ stirrea ln a vessel, without g-n-rating hlgh ~hear forc-, Juch as to produco in the veJJ-l Js-ntlally only ~ tang-ntial to radlal flow of the ligulds c) ~-paratlng the ~locculat-d fine-particle titanium dioxide by flltr~tion at a temp-rature between 20C and lOO-C7 and hing th- ~-parat-a fln--particle titanium dloxide at a t-~p-ratur- be~w-en 20-C and lOO-C with an aqu-ous solution of ~n l-ctrolyte who~e concentratlon ln the wasb liquid i9 between 0 1 per cent by weight and the point of ~aturation, -_ ~J~oK~o~ive ~ubstances, particularly chloride ion~, being excluded aJ an electrolyte The preferable source material i8 a titanlum dioxide 801 which has a titanium dloxide content of between '00 ana 200 g/litre, preferably between 150 and 170 g/litre, calculnted as TiO2 The preferable alkaline reagent for the i'locculatlon i~ hydroxides and/or carbonates of sodium and/or of pota~sium, and/or ammonia, and~or ~mmonium hvdroxide, and~Gr carbonate~ of the a~o~iu~ on 20~7~
The solution of the alkaline reagent is added to the titanium dioxide sol preferably at a temperature between 60~C and 90C.
The solution of the alkaline reagent is added to the titanium dioxide sol preferably in a quantity to attain a p~ of between 7 and 9 in the mixture.
The flocculated fine-particle titanium dioxide is separated by filtration preferably at a temperature between 60C and 90C.
~he separated fine-particle titanium dioxide is washed also preferably at a temperature between 60C and 90C.
The interaction of all the process parameters claimed i~ essential for achievin~ the ob~ective, which is to obtain a readily filterable and washable fine-particle titanium dioxide with a sufficiently reduced chloride ion content and containing seeding crystal~ of rutile titanium dioxide.
The solution of the alkaline reagent may contain said reagent in a wide variety of concentrations. But in order to prevent the titanlum dioxide from being too much diluted through the addition o~ aaid solution, this solution ~hould contain the alkaline reagent generally ln not too low a concentration. This solution may be even a saturated solution.
Tho temperature, at which the alkaline reagent should be added to the ~itanlum dioxide 801, at which the fine-particle titanium dloxide contained in the titanium dioxide 801 should be flocculated through ~aid addltion, and/or ~t which the flocculated - 2~--1~e-p~rticle tit~nium in the solutions should be filtered, may be ad~u~ted by an external heating and/or by utilization of the heat ~ that i8 generated in the reaction of the added alkaline reagent with the acid in the titanium dioxide sol.
7 ~ ~
In this $nvention, particular attention is paid to stirring while adding the alkaline reagent to the titanium dioxide ~ol The solutions need tO be thoroughly and rap~dly m~xed while avoiding, however, that high she~r i8 applied to the mixture If the ~ixing i~ done too slowly, there i8 a risk of having an excessively high pH in parts of the mixture and/or of having in the mixture zones with considerably different pH values; in both cases there will be _ an unde~irable increa~e in viscosity If excessive shear forces are appl~ed, the flocs formed will be di~integrated again A
satisfactory effect of stirring esQentially depends on the type of stirrer ~n order to homogenizc the mixture, i e homogenizing the concentration witbin the mixture while adding the alkaline reagent, stlrrer~ are su~table which effect in the mixture an essentially tangential to radial flow of the liquid An axial flow of the liquid, however, should be avoided -as far as ever possible Suitablc stlrrers ~re crossed-beam paddle mixers, gate paddle mixers or flat-blade paddle mixers, the two latter types being particularly appropriate Further det~ a~out su~table stirrers are given in ~Ullmanns Enzyklop~die der techniRchen Chemie~, 4th edition, volume 2, 1972, pages 261-262 A particularly favourable embodlment of this invontlon comprises ~tirring th- tit-nlum dioxlde rol during the additlon of the alk~line r--gent wlth a gate paddl~ mixer or a flot-bl~de paddle mix~r.
ln ddlng th- alkaline reagent to the titanlum dloxide 801~ after p~ o~ ~ ha~ been attained, one experiences a marked decline ln the relativ- vl~co~ity of the mixture ~ratio of the vi~cosity of the mlxture at the pH v~lues attainea to the viaco~ity of the titan~um aioxide 801 before the addition of the a~kaline reagent);
3e'~ien the p~ i~ further increased, the rclative vi~coslty es~entially remains at the low lovel reached 2~S97~S
This behaviour is extremely surprising and differs essential'y from the behaviour the titanium dioxide sol shows when not all of the claimed steps are adhered to. In such a case, the relative viscosity markedly increases when pH 4 is exceeded to decrease but insignificantly with further rising pH and the initial value of tbe relati~e viscosity is not reached again.
In the process of this invention, the mixture i9 filtered after ~ the desired p~ has been reached. If the flocculated fine-particle titanium dioxide in the mixture settles prior to the filtration, this titanium dioxide will form a fluffy ~ediment which can be ~tirred up again without problem by one of the stirrers mentioned.
The filtered product is washed to remove the chloride ions adhering to it. The wash liquid u~ed therefor is an eleetrolyte solution: the use of pure water is to be avoided.
1~ As a rule, the electrolyte consists of ~alts of inorganic and/or organic acids or of a buffer mixture. Accordingly, a particularly favourable embodiment of this invention comprises washing the separated f$ne-particle titanium dioxide with an aqueous solution of an electrolyte which consists of one or several ~alt(s) of inorganic and/or organic acids or of a buffer mixture. The electrolyte solution contains, for instance, saltJ of monovalent and~or multivalent ions, specifically salts of alkali metals or of alkalirearth met~ls or of ammonium, more specifically saltJ of sodium or potasniu~ or mixtures thereof. The electrolyte solution must not contain ~ubstances which, on further processing and use of the washcd fine-particle titanium dioxidc, are corroslve toward~ the equ$pment employed.
It i~ particularly advantageous to use chloride-free wash liquids -_o~ cntially neutral reaction and derived from the titan$um dloxide manufacturing process: particularly adv~ntageous f~ltrates are tho~e derived from the post-treatment of titanium dioxidc in the titan~um dioxide manufacture or neutralized filtrates o~tained ~n washing an alkal$ titanate free from sulphate, which ti~anate 206~7~
is meant for the titanium dioxide sol productions the latter filtrates comprise especially sodium sulphate solutions In this way, it is possible profitably to utilize liquids obtained as waste material in the manufacture of titanium dioxide S As a rule, the washing of the flocculated and filtered fine-particle titanium dioxide is to be carried on until the residual chloride ion content in said fine-particle titanium dioxide is not more than 0 1 to 0 5 per cent by weight Cl , related to ~iO2 To this end, a preferable embodiment of this invention continues washing the fine-particle titanium dioxide separated by filtration until the chloride ion content in the wash filtrate has dropped to 0 1 g/litre at most In general~ the mixture obtained from the t$tanium dioxide sol and containing the flocculated fine-particle titanium dioxide has so low a viscosity that it can readily be filtered immediately after the desired p~ range has been ad~usted In a particular embodiment of thi~ invention it may be advisable, however, to dilute the mixture containing the flocculated fine-partlcle t$tanium dioxide prior to filterlng it Dilution, for example, may be with water Sometim-s it i8 advi~able, according to anoth-r embodiment of this invention, to add an organic flocculant, g polyacrylamide, to th- mixture containlng the flocculat-d fin--partlcle titanium dioxid-It wa~ found that flocculating the titanium dioxld- ~ol ln co~pliance wlth thi~ inv-ntion, and filtrating and wa~hing the flocculated flne-particle titanium dioxide do not alter the propertieJ of the J-eding cry~talJ of rutile titanium dioxide n~a~rned in ~aid titanlum dloxide It i~, in particular, the ,rutilizing e~-ct of the Jeed~ng cry~tals o~ rutile titanium dioxide which i8 pre~erved unrestr$ctealy ~he washed product can readily be redi~persed in ~ulphuric acid-containing wnter 20~97~
~he flocculated and neutralized mixture obtained from the titanium dioxide sol, with a titanium dioxide content of 120 to 250 9/
litre, calculated as TiO2, has a viscosity of from 6.B x 10 2 Pa.s to 16.~ x 10-2 Pa.s at 25~C.
The size of the flocs ranges from 10 to 40 microns: the seeding crystals contained in the flocs have a particle size of 0.01 to 0.1 microns (measured on the longest axiQ) and, as a rule, are needle-shaped and have rutile crystal form.
The flocs readily settle and are very easily filtered and washed.
It is not necessary to slurry the fine-particle titanium dioxide prior to washing or between the various washing steps.
The titanium dioxide 801 wbich is the source material in the process of the present invention can be produced by various ways.
One embodiment of the present invention, for example, comprises lS producing the titanium dioxide 801 by reacting a titanium dioxide hydrate suspended in water and produced by hydrolysis of A titanyl sulphate solutlon with an alkali hydroxide solution thus forming alkali titanat-, waJhing free of sulphate the mixture obtained in th- r-action, decomposing with hydrochloric acld the alkali tltanate obtain-d thus forming titanium dlo~lde hydrate, ~nd peptizing this titanium dioxide hydrate by adding a further quantity of hydrochloric acid.
A p~rticularly dvantageous embodiment of this production method con-~ts Or thc following rteps:
25 a) A titanium dloxide hydrate of anatase cry~tal form produced by the hydrolysiJ of a titanyl sulphate Jolution is ~lurried with ~ r ~uch a~ to obtain ~n the ~lurry a concentration of 20 to .-_ r'_~_ 26 per cent by weight TiO2J
b) the titanium dioxide hydrate slurry obtained ls heated to between 60C and 70C.
.
2~6~
c) the heated titanium dioxide hydrate slurry is added, while stirring, to an aqueous sodium hydroxide solution heated to between 90C and 100C in sufficient amount to achieve, after addition, a weight ratio of NaOH to TiO2 of between 1.25 and 1.65 in the mixture:
d) the mixture is heated to the boil and maintained at the boiling point for 120 to 140 minutes:
e) the mixture is then cooled down to between 50C and 60C and is filtered;
f) the filter cake obtained is washed until the So2 content $n the wash filtrate i9 less than 0.05 g/litre;
g) the washed filter cake is slurried in water to obtain a TiO2 content of between 10 and 25 per cent by we~ght: the mixture thus obtained i8 mixed with hydrochloric acid containing 20 to 25 per cent by weight HCl to attain a pH value of 2.8 to 3.1 h) the mixture is heated to between 55C and 65C and kept at this temperature for 30 to 45 minutes, the pH range of between 2.8 and 3.1 being maintained:
il the mixture is peptised at 55 to 65C with hydrochloric acid of 20 to 25 per cent by weight HCl in suff$cient amount to ad~ust a weight ratio of hydrochloric acid, expressed as HCl, added in this stage, to TiO2 of between 0.15:1 and 0,25:1~ and k) the suspenslon obtained i8 heated to the boil within 30 to 40 minute~ and kept at the boiling point for 60 to 90 minutes.
In another advantageous embodiment of the present invention, the titanium dioxide 801 is produced by hydrolysis of a solution of titanium tetrachloride in water and/or by an agueou~ solution of one or several compoundg formed by the reaction of titanium tetrachloride with water.
~~- 34h~n produc~ng the titanium dioxide sol, substances may be added which have defined effects on the particle size and/or the particle sha?e of the seeding crystals of rutile tita~ium dioxide.
20~7~
Among such substances, fine-particle tin dioxide is particularly suitable. An addition of such tin dioxide in the production of the titanium dioxide sol is described in the German patent application P 41 05 345.1.
Accordingly, a particularly advantageous embodiment of the invention consists in using a titanium dioxide 901 in the production of which a fine-particle tin dioxide is used the particle size of wh~ch is between 1 and 10 nm, preferably between 1 and 4 n~, the tin dioxide being added in an amount of between 0.5 and 10 per cent by weight, related to the amount of titaniu~
dioxide contained in the titanium dioxide sol.
According to an advantaqeous method of operation, one may proceed as follows, for example:
a) A titanium dioxide hydrate of anatase crystal form produced by the hydrolysis of a titanyl sulphate solution is slurried with water such as to obtain in the slurry a concentration of 20 to 26 per cent by weight TiO2:
b) the titanlum dioxide hydrate slurry obtained is heated to between 60 and 70cl . 20 c~ the heated titanium dioxide hydrate slurry i~ added, while stlrring, to an aqueous sodlum hydroxide solutlon heated to between 90C and 100C in sufficlent amount to achieve, after ~ddition, a weight ratio of NaOH to ~iO2 of between 1.25 and 1.65 in the mixture~
d) the mixture is he~ted to the boil ~nd maintained at the boiling polnt for 120 to 140 minutes;
e) the mixture i8 then cooled down to between 50C and 60C and is i'lltered;
filter cake obtained is washed until the So2 content in 3gL~ - the wash filtrate is less than 0.05 g/litre:
g) the washed filter cake is slurried in water to obtain a TiO~
content of between 10 and 25 per cent ~y weight; the mixture thus obtained is mixed with hydrochloric acid containing 20 to 25 per cent by welght NCl to attain a pH value of 2.8 to 3.1;
, 20~7~
hl the mixture is heated to between 55C and 65C ~nd kept at this temperature for 30 to 45 minutes, the pH range of between 2.8 and 3.1 being maintained;
i) a colloidal tin dioxide solution is added to the mixtyre, in which tin dioxide solution the tin dioxide has a particle size of between 1 and 10 nm, preferably between 1 and 4 nm;
j) the mixture to which the colloidal tin dioxide solution was added ls peptized at 55C to 65~C with hydrochlor$c acid of 20 to 25 per cent by weight HCl in sufficient amount to adjust a weight ratio of hydrochloric acid, expressed as HCl, added in this stage, to TiO2 of between 0.15:1 and 0.25:1; and k~ the suspension obtained is heated to the boil within 30 to 40 minute~ and kept at the boiling point for 60 to 90 minutes.
The invention also relates to a fine-particle titanium dioxide freed of chloride ions that was produced using hydrochloric acid, tltanium tetrachloride and/or the products of its reaction with water and which contains seeding crystals consistlng of titanium dioxide of the rutile crystal modification and which can be obtalned by a proceQ~ according to this invention. This 20 i'ine-partlcle tltanium dioxlde, according to a proferred embodiment of thi8 invention, i8 tO have a chloride ion content not in exce8~ of 0.5 per cent by welght Cl , related to TiO2, in ~pecial ca~eJ not in excess of 0.1 per cent by weight Cl , related to TiO2.
25 Sald fine-partlcle tltanlum dioxide can be employed in numerous fi-lds of application.
A particularly preferred mode of application consist~ of using the - -_ ~c~pnrt$cle tltanlum dloxlde as the rutll~zatlon ~eed for the manufactur- of rutile titanium dioxide from titanium dioxide r--30 hydrate that wa~ obtained through hydroly~i~ of a titanyl sulphate solution.
2~7~
Further preferable modes of application are its use as a uY
absorber in plastics or paints, as a uV absorber in sunscreen compositions or in other cosmetic articles or as an agent for the generation of special optical effects in paints, such as the so-called ~down flop~ (cf. EP-Al-0 270 472).
The fine-particle titanium dioxide freed from chloride ions according to this invention can be dried before being used, a substance be~ng added optionally, prior to drying, which prevents the formation of hard agglomerates. The titanium dioxide agglomerates formed in drying may be milled and/or tempered. Prior to and/or after drying and/or tempering, the fine-particle titanium dioxide may be post-treated with one or several inorganic and/or organic substances.
The invention ls illustrated in more detail in the following Examples.
ExamPle A tltanium dioxlde 801 was produced in a known way in which, essentlally according to DE-Al-38 17 909, a titanlum dioxide hydrate having anatase crystal structure and having been obtained by the hydrolysis of a titanyl sulphate solution was reacted, at elevated temperature, slurried in water, with a sodium hydroxide solutlon and the product obtalned was ~iltered and washed until the wash filtrate contained less than 0.05 g/l sulphate ions (S0~ d-tectlon by the BaC12 test). The washed product was then 25 slurried with water and mixed with hydrochloric acid up to a pH of 2.8 to 3.1 and heated to 60 at this pH. The resulting product was then pepti~ed by addition of a further amount of hydrochloric acid r~oncentration 25 per cent by wsight) up to a weight ratio of Cl to TiO2 of 0.15:1 and by heating to the boiling point.
~0~7~
In producing the titanium dioxide sol, operation was such that the titanium dioxide sol obtained had a titanium dioxide content of 220 9/1, calculated as ~iO2. 455 ml quantities of this titanium dioxide sol, corresponding to 100 g TiO2, were cbarged into s beakers of 9 cm inner diameter and mixed with various quantities of sodium hydroxide solution of an NaO~ content of 30 per cent by weight in order to attain different p~ values in the range from 4.1 to 8.5. During the addition of the sodium hydroxide solution, which took about 2 minutes, the temperature of the mixture was adjusted to 80C by means of a thermostat and the mixture was stirred by way of a flat-blade paddle mixer, initially at a speed of 350 rpm. The flat-blade paddle mixer was 6.4 cm high and 3.6 cm wide. After a pH of 3-4 was attained, the titanium dioxide sol began to flocculate. When the flocculated state was reached, the viscosity of the mixture dramatically dropped and the stirrer speed had to be reduced to 200 rpm. After the desired p~ was reached, the mixture was stirred for 5 minutes: the stirrer then was stopped and product adhering to the wall was stirred into the suspension by means of a glass rod. Then, without lowering the temperature, the mixture was stirred for another 10 minutes by mean~ of the flat-blade paddle mixer.
SubJequently the mixtures were cooled down to 23C and each mlxture wa8 divlded i~to ten equal portisn8, ach portion thus containlng 10 g TlO2. Each portlon was filtered through a laboratory ~uctlon ilter 17.5 cm diameter) (0.3 bar pressure).
The i'iltet medium was a binder-fre0 glass fibre filter paper of a baJi~ w-lght of 90 q/m in the form of a round filter. The time required from the beginning of flltration up to slight surface . _a,~ UL ltime of filtration) was measured. The mean values were determined from 10 trlals each. (~Slight surface drying~ refers ~o '~ the state at whlch the liquid level has dropped to the level of the 'ilter cake surface).
-20~7~
After the slight surface drying was attained, a wash solution, which was a solution of sodium sulphate in water of a concentration of 2.5 g/l Na2S04 and a temperature of 22C, was passed onto the filter cake and the time was measured that was required for 250 ml and 350 ml of this solution to pass through the filter cake, again until a slight surface drying (wash time) was achieved. The efficiency of the washing was assessed by - determining the chloride lon content in the filtrate at the end of the washing by means of a silver nitrate solution in nitric acid lO medium. The chloride ion content in the filter cake, after 350 ml wash solution having been passed through it, wa6 0.08 per cent by weight Cl , related to TiO2. The particle size of the flocs was between 10 and 40 microns. Particle size was measured on a SALD-llO0 particle size instrument by Shimadzu.
The filtered and washed fine-particle titanium dioxide could be redispersed in sulphuric acid-containing water.
The results shown in Table 1. In this Table, chloride contents smaller than or equal to 0.1 g/l are denoted as ~chloride-free~;
chlorlde contents of more than 0.1 g/l are denoted ~not 20 chlorlde-free~.
Example 2 ~comparatlve example) The tltanlum dloxide 801 was the same sourc- material a8 in Ex~mple 1. In oraer to attain dlfferent pH values, varying ~mounts oi' the sodium hydroxide solutlon usea in Example 1 were added at a 25 ~peea of about 1 ml per mlnute. Addltlon, however, was at amblent temperature while stlrring at 800 rpm by means of a propeller stirrer. The filtration and washing time~ were measured as in Example 1. The results are al80 shown in Table 1.
r--~0~7~5 The comparison of the two examples shows that though it was possible to achieve an absence of chloride ions also in the comparative example, the filtration and washing times were considerably longer than with the process of the $nvention and the filter cake showed cracking while this was not the case with the process of the invention Example 3 The procedure was the same as in Example 1 But the washing solution was a sodium sulphate solution of a concentration of 5 9/1 Na2S04 instead of 2 5 g/l Na2S04 Compared with the use of a solution of 2 5 g/l Na2S04, a further marked shortening of the washing times was achieved, especially with lower pH values ~he results of Example 3 are shown in ~able 2 Example 4 Tho procedure wa~ th- same as ~n Example 1 with the difference that the flocculation of the titanium d~oxide 801 was achieved, in one ln~tance, by addltion of 55 0 ml of an ammonium hydroxide ~olutlon of a concentration of 25 per cent by weight NH3 and, in another in-tance, by addition of 100 ml of a ~odium carbonate ~olution of a concentration of 25 per cent by weight Na2C03 ln both in~tancc~, flocculation took place up to p~ 7 In this Exampl-, too, xcellcnt ~lltration ana washing times were achieved Th- rc~ult~ of Example ~ are shown in ~able 3 . ~ ,,.~,_r--- 17- 2~6~7~
7~ble 1 E~pl~ ~emper-ture Sodium hydroxide pH ~djust~d Filtr tion l~shlng time ~sh solution Of th solution dded time Na2so4 flocculation C ~1 s~e ~in 9/1 250 ~1 350 ~1 8047 5 4.1 7 13~ 20~ 2 5 110 50.0 5.2 5 ~ 14~ 2.5 110 52 0 7.0 3 2.5~ ~ 2.5 8054.5 8 5 2 2~ ~ 2 5 2 2348 5 5 0 250 60~ 94~ 2 5 2351 0 6 D 250 49~ 73~ 2 5 2352.0 7.0 200 71~101~ 2 5 2354.0 9.0 120 51~ 76~ 2 5 5 ~) e~ O ~So.l 9~1) ~) not el~-f,.- (~0.19~1) ~~1ng of the filt r ca'~e ~i~h eont1nu1ng ~uhing ':
2~7~
- lB -T-ble 2 Ex~mple IEmper~-ure Sodium hydroxide pH ~djusted filtr~tion ~shing tire ~ash solution of the solution ~dded time ~254 floecul~tion _ _ C ~1 see min 9/1 250 ~1 350 ml 3 ~0 48 5 S 0 5 5 5~ 8~ S
Sl 0 6 0 ~ 3 5~ 6~ S
52 0 7 0 ~ 2~ 3~ 5 1 0 80 53 0 8 0 3 2~ 3~ 5 ~) tl -~r~ 0 1 9~1) ~) not Cl-- r~o (>0 1 9/1) T~ble 3 E~pl~ Tomper~ture ~lk~lln ph ~dJusted F11tr~tion ~ shlng t h e ~ sh solutlon 1 5 O- tho solut1On ~dd d t1me ~b2S04 flocc41~t~o~
C ml see 1n 9~1 2S0 ~1 3S0 ~1 4 ~0 55 0 ~H3- ol 7 0 4 3.5~ S 5~ 2 5 2 0 ~0 100 ~2C03 7 0 ~ 3~ 5 2 5 tl -fr~ 0 1 9~1) 2~7~
Example S
A titanium dioxide sol was produced as in Example 1 but with a TiO2 content of 160 9/l This titanium dioxide 801 was adjusted to different pH values by addition of a 30 per cent by weight NaOH solution and flocculated in the same way as in Example 1 In the flocculated mixtures, the viscosity was determined as the relative viscosity, i e the ratio of the viscosity of the mixture, at the p~ ad~usted, to the viscosity of the original titanium dioxide 801 which had a pH of about 0 Moreover, the filtrat$on and washing times were determlned as in Example 1 The results are shown in Table 4 ~xample 6 (comparat$ve example) ~he titanium dioxide sol of Example S was used as the source material and the procedure was that of Example 5 with the dli'ference of the Jodlum hydroxide Jolution being 810wly added at ambient temperature ~about 1 ml/mln) a~ in Example 2, whlle Jtirrlng by means of a propell-r mlxer at a rate of BOO rpm The r-sults ar- also shown ln Table 4 Table 4 ~hows that there was no differ-nce between the two example~ in th-lr vlscoaity behaviour up to p~ 4, but then with rl~lng pH thelr behaviour markedly dlffered While, in the proccdure of the comparative example, the relative vl~coffity markedly ~ncrea~ed and remained at a high l-vel up to p~ 11 0, the relative vlJcoJity~ in the proccsJ of the inventlon, warkedly dkopped on reaching the flocculated Jtate and remained at this low level up to pH 11 Accordingly, the process of the invention yielded much shorter times of filtration and waQhing and better washing efficiency than the procedure of the comparative example The proce~s of the invention did not involve any def~ciency in the filter cake as was encountered wlth the procedure of the comparative example 206~7~S
Table 4 Example pH ad- Relative Filtration Washing time ~usted viscosity time (sec) 250 ml 350 ml .
S 3 0 l l 720 redispersion after 50 ml s 4 0 1 4 410 redlspersion after 60 ml ~ 5 0 0 2 220 62~ 9S~
6 0 - 30 35* 49 7 0 0 1 30 16~ 21 8 0 - 40 l9~ 30 9 0 0 1 25 16~ 23 11 0 0 1 40 41~ 68 6 3 0 1 1 960 redispersion after 20 ml~
4 0 1 4 810 redispersion after 80 ml~
S 0 2 8 440 92~ 133~/*~
7 0 3 9 370 S9~ 78 9 0 3 7 300 61~* redispersion~
11 0 2 9 275 65~ 86 ~) Cl~-fre- ~ 0 1 g/l Cl-) ~ ) not Cl~-fr-e ~ ~ 0 1 9/l Cl-) zo ~) Cracklng of th- filter cnke with continuing wn~hlng ~x~mDl- 7 ~ an~um d$oxide ~ol~ with different TiO2 loadings were produced - like in ~xample l A~ in Example l, these titanium dioxide sols were floccul~ted at 80 C by ~d~usting a pH v~lue of 7 0 by means of a sodium hydrox$ae solution of 30 per cent by weight NaOH:
2~6~7~
subsequently, the fine-particle titanium dioxide was filtered like in Example l and washed with 250 ml of a sodium sulphate solution of a concentration of 2.5 g/l Na2SO4. The filtration and washing times determined like Example l are shown in Table 5.
Table 5 ;
TiO2 concentration Piltration time Washing time ;
9/1 sec min lO0 120-360 46-60 140 30-60 15_25 The results of Table 5 show that the filtration and washing times of the product produced according to this invention are rather short alr-ady at a TiO2 content of as little as 100 g/l in the original titanlum dioxide 801, but are becoming markedly shorter still with rising TlO2 content in the original titan~um diox~de 801.
Th- u~e of high TiO2 concentrations in the original titanium dloxide 801 has the advantage of smaller vessels being required and ~maller volumes of waste water being obt~ined.
_ Exluu~Le 8 $ne procedure was like in Example 7 with the difference that, after addition of the sodium hydroxide solution and the resulting flocculation of the titanium dioxide 801, the m~xture was diluted with water to a uniform TiO2 content of 100 g/l prior to filtration. The filtration and washing times determined are shown in ~able 6.
-. :.
2~7~5 Table 6 TiO2 concentration TiO2 concentration Filtration Washing after flocculation prior to filtrat1on time time g/l g/l sec min 140 100 lOS 21 The results of Table 6 indicate that the improved filtr~tion times are less due to the quantity of liguid passed through the iilter during filtration than to the TiO2 content of the slurry during flocculation and that this TiO2 content ha3 al80 a beneficial ffect on th- wa~hing behaviour A great advantage of the process of thi~ invention is the posslbil~ty o~ using, as the sourc- material, tltanium dioxide 8018 as are typical produo-d which need not be dlluted for the ~locculation and or the Jubsequent ~tep~ The proce~s is very ~l-xibl- and can be largely adapted to the requir-ments of each Jitu-tion.
The invention relates to a process for th- removal of chloride ions _ from a fin--part~cle titanium dioxide A titanium dioxide 801 containing at l-ast 100 gJl TiO2 i8 mixed, at a temp-rature between 40C and th- boiling point, with an aqueous alkaline solution up to a pH of between 4 0 ana 11 0 whil- ~tirring without generating high shear, resulting essentially in a tangential to 2~6~7~5 radial flow of the liquid; the fine-particle titanium dioxide is flocculated in this procedure, subsequently it i8 filtered and washed with an aqueous electrolyte solution. The flocculated mixture ha3 a low viscosity, which results in short filtration and washing times and in an improved removal of chloride. The titanium dioxide sol can be produced by reacting titanium dioxide hydrate with alkali, decomposing the titanate formed and peptising, with hydrochloric acid, the mixture washed free of sulphate or by heating and/or partially neutralizing an aqueous ~iC14 solution.
The invention also relates to the fine-particle titanium dioxide freed of chloride ions that is obtainable in the process of this invention and to its use as a rutilisation seed in the production of rutile from titanyl sulphate solutions, as a ~ absorber and for the generation of special optical effects in paints.
,, ,- ~
r--
Claims (25)
1) Process for the removal of chloride ions from a fine-particle titanium dioxide that was produced using hydrochloric acid, titanium tetrachloride and/or the products of its reaction with water and which contains seeding crystals consisting of titanium dioxide of the rutile crystal modification, comprising a) using a titanium dioxide sol as the source material which has a titanium dioxide content of at least 100 g/litre, calculated as TiO2;
b) mixing said titanium dioxide sol with an aqueous solution of an alkaline reagent, the fine-particle titanium dioxide being flocculated under such conditions that (i) the solution of the alkaline reagent contains this reagent in a concentration of from 10 per cent by weight to the point of saturation;
(ii) the alkaline reagent is added to the titanium dioxide sol in such a quantity that the mixture has a pH of between 4.0 and 11.0;
(iii) the titanium dioxide sol, during the addition of the alkaline reagent, is kept at a temperature between 40°C
and the boiling point and is stirred in a vessel, without generating high shear force, such as to produce in the vessel essentially only a tangential to radial flow of the liquid.
c) separating the flocculated fine-particle titanium dioxide by filtration at a temperature between 20°C and 100°C;
d) washing the separated fine-particle titanium dioxide at a temperature between 20°C and 100°C with an aqueous solution of an electrolyte whose concentration in the wash liquid is between 0.1 per cent by weight and the point of saturation, corrosive substances, particularly chloride ions, being excluded as an electrolyte.
b) mixing said titanium dioxide sol with an aqueous solution of an alkaline reagent, the fine-particle titanium dioxide being flocculated under such conditions that (i) the solution of the alkaline reagent contains this reagent in a concentration of from 10 per cent by weight to the point of saturation;
(ii) the alkaline reagent is added to the titanium dioxide sol in such a quantity that the mixture has a pH of between 4.0 and 11.0;
(iii) the titanium dioxide sol, during the addition of the alkaline reagent, is kept at a temperature between 40°C
and the boiling point and is stirred in a vessel, without generating high shear force, such as to produce in the vessel essentially only a tangential to radial flow of the liquid.
c) separating the flocculated fine-particle titanium dioxide by filtration at a temperature between 20°C and 100°C;
d) washing the separated fine-particle titanium dioxide at a temperature between 20°C and 100°C with an aqueous solution of an electrolyte whose concentration in the wash liquid is between 0.1 per cent by weight and the point of saturation, corrosive substances, particularly chloride ions, being excluded as an electrolyte.
2) Process according to claim 1, wherein a titanium dioxide sol is used as the source material which has a titanium dioxide content of between 100 and 200 g/l, preferably between 150 and 170 g/l, calculated as TiO2.
3) Process according to claim 1 or 2, wherein the alkaline reagent used for the flocculation is hydroxides and/or carbonates of sodium and/or of potassium and/or ammonia and/or ammonium hydroxide and/or carbonates of ammonium.
4) Process according to one or more of claims 1 to 3, wherein the solution of the alkaline reagent is added to the titanium dioxide sol at a temperature between 60°C and 90°C.
5) Process according to one or more of claims 1 to 4, wherein the solution of the alkaline reagent is added to the titanium dioxide sol in a quantity to attain a pH of between 7 and 9 in the mixture.
6) Process according to one or more of claims 1 to 5, wherein the flocculated fine-particle titanium dioxide is separated by filtration at a temperature between 60°C and 90°C.
7) Process according to one or more of claims 1 to 6, wherein the separated fine-particle titanium dioxide is washed at a temperature between 60°C and 90°C.
8) Process according to one or more of claims 1 to 7, wherein the titanium dioxide sol is stirred during the addition of the alkaline reagent by means of a gate paddle mixer or a flat-blade paddle-mixer
9) Process according to one or more of claims 1 to 8, wherein the separated fine-particle titanium dioxide is washed with an aqueous solution of an electrolyte which consists of one or several salts of inorganic and/or organic acids or of a buffer mixture
10) Process according to claim 9, wherein the wash liquids are chloride-free liquids of essentially neutral reaction which are derived from the titanium dioxide manufacturing process
11) Process according to claim 10, wherein the wash liquids used are filtrates derived from the post-treatment of titanium dioxide in the titanium dioxide manufacture or neutralized filtrates obtained in washing an alkali titanate free from sulphate, which titanate is meant for the titanium dioxide sol production
12) Process according to one or more of claims 1 to 11, wherein the fine-particle titanium dioxide separated by filtration is washed until the chloride ion content in the wash filtrate has dropped to 0.1 g/l at most
13) Process according to one or more of claims 1 to 12, wherein the mixture containing the flocculated fine-particle titanium dioxide is diluted prior to being filtered
14) Process according to one or more of claims 1 to 13, wherein an organic flocculant is added, prior to filtration, to the mixture containing the flocculated fine-particle titanium
15) Process according to one or more of claims 1 to 14, wherein the titanium dioxide sol is produced by reacting a titanium dioxide hydrate suspended in water and produced by hydrolysis of a titanyl sulphate solution with an alkali hydroxide solution thus forming alkali titanate, washing free of sulphate the mixture obtained in the reaction, decomposing with hydrochloric acid the alkali titanate obtained thus forming titanium dioxide hydrate, and peptising this titanium dioxide hydrate adding a further quantity-of hydrochloric acid
16) Process according to claim 15, comprising a) slurrying a titanium dioxide hydrate of anatase crystal form produced by the hydrolysis of a titanyl sulphate solution with water such as to obtain in the slurry a concentration of 20 to 26 per cent by weight TiO2;
b) heating the titanium dioxide hydrate slurry obtained to between 60°C and 70°C.
c) adding the heated titanium dioxide hydrate slurry, while stirring it, to an aqueous sodium hydroxide solution heated to between 90°C and 100°C of sufficient amount to achieve, after addition, a weight ratio of NaOH to TiO2 of between 1 25 and 1.65 in the mixture;
d) heating the mixture to the boil and maintaining it at the boiling point for 120 to 140 minutes;
e) then cooling the mixture to between 50°C and 60°C and filtering it;
f) washing the filter cake obtained until the SO?- content in the wash filtrate is less than 0.05 g/litre;
g) slurrying the washed filter cake with water to obtain a TiO2 content of between 10 and 25 per cent by weight, and mixing the mixture thus obtained with hydrochloric acid containing 20 to 25 per cent by weight HCl to attain a pH
value of 2.8 to 3.1;
h) heating the mixture to between 55°C and 65°C and keeping it at this temperature for 30 to 45 minutes, the pH range of 2.8 to 3.1 being maintained;
i) peptising the mixture at 55°C to 65°C with hydrochloric acid of 20 to 25 per cent by weight HCl in sufficient amount to adjust a weight ratio of hydrochloric acid, expressed as HCl, added in this stage, to TiO2 of between 0.15:1 and 0.25:1; and k) heating the suspension obtained to the boil within 30 to 40 minutes and keeping it at the boiling point for 60 to 90 minutes
b) heating the titanium dioxide hydrate slurry obtained to between 60°C and 70°C.
c) adding the heated titanium dioxide hydrate slurry, while stirring it, to an aqueous sodium hydroxide solution heated to between 90°C and 100°C of sufficient amount to achieve, after addition, a weight ratio of NaOH to TiO2 of between 1 25 and 1.65 in the mixture;
d) heating the mixture to the boil and maintaining it at the boiling point for 120 to 140 minutes;
e) then cooling the mixture to between 50°C and 60°C and filtering it;
f) washing the filter cake obtained until the SO?- content in the wash filtrate is less than 0.05 g/litre;
g) slurrying the washed filter cake with water to obtain a TiO2 content of between 10 and 25 per cent by weight, and mixing the mixture thus obtained with hydrochloric acid containing 20 to 25 per cent by weight HCl to attain a pH
value of 2.8 to 3.1;
h) heating the mixture to between 55°C and 65°C and keeping it at this temperature for 30 to 45 minutes, the pH range of 2.8 to 3.1 being maintained;
i) peptising the mixture at 55°C to 65°C with hydrochloric acid of 20 to 25 per cent by weight HCl in sufficient amount to adjust a weight ratio of hydrochloric acid, expressed as HCl, added in this stage, to TiO2 of between 0.15:1 and 0.25:1; and k) heating the suspension obtained to the boil within 30 to 40 minutes and keeping it at the boiling point for 60 to 90 minutes
17) Process according to one or more of claims 1 to 14, wherein the titanium dioxide sol is produced by hydrolysis of a solution of titanium tetrachloride in water and/or of an aqueous solution of one or several compounds formed by the reaction of titanium tetrachloride with water;
18) Process according to one or more of claims 1 to 17, wherein a titanium dioxide sol is used a the source material in the production of which fine-particle tin dioxide is used the particle size of which is between 1 and 10 nm, preferably between 1 and 4 nm, the tin dioxide being used in an amount of between 0.5 and 10 per cent by weight, related to the amount of titanium dioxide content in the titanium dioxide sol.
19) Fine-particle titanium dioxide freed of chloride ions that was produced using hydrochloric acid, titanium tetrachloride and/or the products of its reaction with water and which contains seeding crystals consisting of titanium dioxide of the rutile crystal modification and which is obtained by a process according to any one of claims 1 to 18
20) Fine-particle titanium dioxide according to claim 19, wherein the chloride ion content is not in excess of 0.5 per cent by weight Cl-, related to TiO2
21) Fine-particle titanium dioxide according to claim 20, wherein the chloride ion content is not in excess of 0.1 per cent by weight Cl-, related to TiO2.
22) Use of the fine-particle titanium dioxide of one or more of the claims 19 to 21 as a rutilisation seed for the production of rutile titanium dioxide from titanium dioxide hydrate that was obtained through hydrolysis of a titanyl sulphate solution.
23) Use of the fine-particle titanium dioxide of one or more of the claims 19 to 21 as a UV absorber in plastics or paints.
24) Use of the fine-particle titanium dioxide of one or more of the claims 19 to 21 as a UV absorber in sunscreen compositions or other cosmetic articles.
25) Use of the fine-particle titanium dioxide of one or more of the claims 19 to 21 as an agent for producing special optical effects in paints.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DE4123772A DE4123772A1 (en) | 1991-07-18 | 1991-07-18 | Removal of chloride ions from finely divided titanium di:oxide - by pptn. from titanium di:oxide solution with alkali at elevated temp. with stirring, followed by filtration and washing |
| DEP4123772.2 | 1991-07-18 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2069705A1 true CA2069705A1 (en) | 1993-01-19 |
Family
ID=6436421
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002069705A Abandoned CA2069705A1 (en) | 1991-07-18 | 1992-05-27 | Process for the removal of chloride ions from a fine-particle titanium dioxide, such fine-particle titanium dioxide freed from chloride ions and its use |
Country Status (3)
| Country | Link |
|---|---|
| CA (1) | CA2069705A1 (en) |
| DE (1) | DE4123772A1 (en) |
| NO (1) | NO922840L (en) |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| TWI279254B (en) | 1999-10-29 | 2007-04-21 | Sumitomo Chemical Co | Titanium oxide, and photocatalyst and photocatalyst coating composition using the same |
| DE102004014020A1 (en) * | 2004-03-19 | 2005-10-06 | Eckart Gmbh & Co. Kg | Cosmetic preparation with UV protection and use of effect pigments |
-
1991
- 1991-07-18 DE DE4123772A patent/DE4123772A1/en not_active Withdrawn
-
1992
- 1992-05-27 CA CA002069705A patent/CA2069705A1/en not_active Abandoned
- 1992-07-17 NO NO92922840A patent/NO922840L/en unknown
Also Published As
| Publication number | Publication date |
|---|---|
| NO922840L (en) | 1993-01-19 |
| DE4123772A1 (en) | 1993-01-21 |
| NO922840D0 (en) | 1992-07-17 |
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