FR2641268A1 - ZINC OXIDE, ZINC CARBONATE AND BASIC ZINC CARBONATE, METHOD FOR THE PRODUCTION THEREOF AND USE THEREOF - Google Patents

Abstract

Zinc oxide, zinc carbonate and basic zinc carbonate, process for their manufacture and uses of these compounds. The compounds are characterized by a specific surface area of 70-200 m ** 2 / g and a bulk density of 400-700 g / l and are made in a spray dryer in hot gas at temperatures of 450-900 degrees ( s) C. The products are useful as a filler for rubber, in the manufacture of catalysts, as a UV stabilizer in combination with known stabilizers and as an adsorbing and absorbing agent in particular as an absorbing agent for gases in desulphurization installations and in the case of oil drilling.

Description

Zinc oxide, zinc carbonate and zinc carbonate

  their manufacturing process and their use.

  The present invention relates to zinc oxide, zinc carbonate and zinc carbonate

  increased active surface area, their process of

  and their use.

  Zinc oxides and surface active zinc carbonates are increasingly needed as activators or crosslinking agents in the case of

  manufacturing of high quality rubber pastes

  ity. In this case, these compounds not only play the

  role of a crosslinking agent in cooperation with other

  rubber additives such as sulfur, but also constitute active charges and

  concentrators for the most diverse types of rubber

  towards. But these compounds are implemented not only

  in the case of the manufacture of rubber, but also

  in the case of the manufacture of many other

  elastomers and plastics.

  In addition, zinc oxides and carbonates

  active zinc compounds are suitable for the manufacture of

  lysers or also as adsorption and absorption agents, in particular with a view to

  sulfur compounds in desulphurization plants.

  Another example of application is the use of zinc carbonate as a scrubber for

  hydrogen sulphide in oil drilling.

  Is characteristic for the activity of these com-

  posed, the specific surface, which can be detected

  using standardized measuring procedures, such as the

  yielded BET (according to Brunauer, Emmett and Teller) by nitrogen adsorption under vacuum on a heated sample. This method detects the total available area, which consists of the inner surface and the outer surface and is

expressed in m2 / g.

  Commercially active zinc oxides commercially

  currently have a specific area

from 10-50 m2 / g.

  From the state of the art is already known the

  decomposition of zinc carbonate with formation of

  active and superficially pure. In Z. anorg.

  Chem. 64 (1931), Htig and Steiner describe the production of a homogeneous, active zinc oxide at the laboratory stage at 300-550 ° C from zinc carbonate. The product

  appearing at 300 C still contains quantities

  bound carbonic acid. The specific surface of

  these products are not indicated in detail.

  It is further known to obtain zinc oxides or zinc carbonates active from basic zinc carbonates. Basic zinc carbonates are compounds which contain not only zinc oxide, but also zinc carbonate in varying molar ratios, as well as possibly further

  water chemically bound in the form of hydroxide.

  DE-OS-24 04 049 discloses a precipitate

  of basic zinc carbonate, a solution of salt

  of zinc and an alkaline solution being continuously

  such that precipitation in a controlled pH range is possible. The alkaline solution consists of a mixture of NaOH and Na2CO3 in proportions, in

equivalents, from 25:75 to 80:20.

  In addition, it is known to keep the

  precipitation temperature in order to obtain

  most active faces possible. It operates in general between 800C and 800C. Temperatures below 40 C can lead to poor filtration capacity and insufficient growth of the filter cake. of the

  temperatures above 80 C certainly favor the

  see filtration, but lead to a decrease in

active properties.

  It is furthermore known that, especially for a useful

  in rubber systems, the impurity content of heavy metals in zinc oxide

  should be kept as low as possible (a few ppm).

  The zinc salt solutions used must therefore

  to be purified. In addition, after the precipitation of zinc carbonate or basic zinc carbonate, the filter cake must be thoroughly washed with pure water in order to lower the content of heavy metals and salts.

  soluble in water below the maximum values

communicable.

  The most serious disadvantage of the known processes

  of the state of the art lies in the operation of se-

  This is because, in this case, the precipitated zinc salt must be heated for prolonged periods at elevated temperatures. This results in high product temperatures in which the solids particles sinter and agglomerate, which substantially reduces their surface area. The properties of zinc oxides and commercially available zinc carbonates are therefore by no means perfectly satisfactory. A growth

  additional active area is desirable.

  The subject of the present invention is the manufacture

  of zinc oxide, zinc carbonate and basic zinc carbonate, the specific surface area of which was

  increased and to propose a process for their manufacture.

  Surprisingly, it has been found that one obtains from zinc carbonate or carbonate of

  basic zinc precipitated and sufficiently pure, in

  determined by the use of a spray dryer.

  high potency, new zinc compounds,

  which are very different in terms of their

  properties, of classic products. With the aid of the process according to the invention, the specific surface area can be increased with respect to commercially available products of 200 to 300%. The new compounds have, in addition to an increased outer surface, also an increased internal surface area. Their apparent density is comparable to commercially available products, but can also be higher, so that advantages arise when

  of manufacture and implementation.

  Despite their increased surface, these products

  have lower levels of impurities-

  qu'accrues. The object of the present invention is active zinc oxide, zinc carbonate and basic zinc carbonate having a specific surface area of

  700-200 m2 / g and an apparent density of 400-700 g / l.

  Preferably, compounds of

  active zinc with a surface area of 90-

  m2 / g, in particular of 100-130 mZ / g and with a

apparent density of 400-600 g / l.

  According to a preferred embodiment, a zinc oxide containing about

  2% by weight of Mg. The additive causes in this case a certain

  tain enlargement of the network and is thus linked to another

  increasing the surface of the active compound.

  The object of the present invention is furthermore a process for manufacturing zinc oxide, active zinc carbonate and basic zinc carbonate and mixtures thereof, according to which zinc carbonate or carbonate is precipitated. basic zinc by mixing an aqueous solution of at least one alkali carbonate, an alkali metal hydroxide or mixtures thereof and a zinc salt solution, and drying or calcining an aqueous suspension in a spray dryer in a hot gas, whose temperature when entering the spray dryer is between 450 C and

900 C.

  In a particular embodiment of the process according to the invention for the production of active zinc oxide, an aqueous suspension of zinc carbonate or precipitated basic zinc carbonate is used and the inlet temperature of the hot gas is between 800 C and 900. The residence time of the product is set at 2 to 60 seconds in a temperature range of 250 ° C. to 450 ° C. and preferably from 300 ° C. to 350 ° C. In a particularly preferred embodiment, the residence time in the range above-mentioned temperature is 5 to 15 seconds. Most of the time, a time

  preferred stay is 10 seconds.

  In another preferred embodiment of the process according to the invention for the production of active zinc carbonate or of active basic zinc carbonate, an aqueous suspension of zinc carbonate or precipitated zinc carbonate is used, the temperature of admission then raises to 450 C to 650 C and in the case of carbonate

  of zinc, a hot gas containing CO2 is used.

  The residence time of the product is set for a temperature range of 150 ° C. to 300 ° C. and preferably of

   C at 280 C, at 2 to 60 seconds. A residence time

  Especially preferred for the temperature range indicated above is 5 to 15 seconds. A residence time of

seconds is the most preferable.

  According to a preferred embodiment, the hot gas is blown in the same direction as the aqueous suspension in the dryer. The solids content

  of the suspension amounts to 20 to 50% by weight.

  The suspension is sprayed according to the invention using a spray disc

  rotating, which is arranged in the head of a column of se-

  stationary chage. The diameter of the disc is usually

  between 500 and 150 mm, the rotation speed being

  between 8000 and 15000 revolutions / minute. It is advantageous

  gious to operate with a disc of 215mm in diameter and a

  rotation speed from 10000 to 12000 rpm.

  Spacing of the spray disc from the side

  the inside of the drying column is dimensioned

  avoid sticking the wet product to the wall

of the column.

  The ratio of the gas to the slurry is set so that the product load of the hot gas stream in the dryer is 10 to 100 g / m3. A product charge of the hot gas flow in the dryer of 30 to 50 g / m3 is

particularly preferred.

  The indicated residence times correspond to values determined by calculation for these time intervals necessary for the product in order to arrive from the

  spray disc in the dryer until a

  separation system, wherein the still hot exit gas is separated from the dry product. The residence time can thus be modified according to the amount of hot gas introduced, the volume of the drying column and the distance between the drying column and the device.

of seperation.

  Preferred zinc salt solutions are aqueous solutions of ZnSO4 or ZnCn2 separately or in admixture. A molar ratio of ZnSO 4 to ZnCl 2 of 1: 2

  in this case is particularly favorable.

  In the case of carbonate precipitation

  zinc, the zinc salt solution and the

  aqueous mixture of alkali hydroxide / alkali carbonate under strict pH control, are simultaneously dosed in a reactor, in which previously heated water

  is previously paid. The addition is carried out

  that the pH value moves in the neutral or slightly alkaline range. A pH range of 7 to 9 is

  preferably used according to the invention.

  Attention is also drawn to the fact

  precipitation is carried out within a time range

  a temperature of 40 ° C. to 80 ° C., preferably 60 ° C. to 80 ° C.

  For precipitation, we use solutions

  zinc salt with a zinc content of 10 to 180 g / l.

  During precipitation, the concentration of zinc salt

  is 0 to 70 g / l, preferably 0 to 50 g / l.

  In view of the precipitation of zinc carbonate

  alkaline hydroxide / carbon dioxide mixture is used

  alkali with a molar ratio of alkali hydroxide: alkali carbonate of 50:50 to 80:20. A ratio of 60:40

  is preferably used according to the invention. accordance

  according to the invention, the alkaline hydroxide and the carbonate

  Preferred alkalis are sodium or potassium salts.

  The sodium salt is preferably used.

  The precipitate obtained is filtered continuously on a filter in the form of a strip and washed until no

  impurity can no longer be removed from the solid matter.

  The washed precipitate is suspended and converted into a homogeneous product that can be pumped. The freshly homogenized suspension is then brought for

  drying in a spray dryer.

  For the implementation of the manufacturing method according to the invention, the installation is preferably used.

  shown schematically in Figure 1. The masterpiece

  braid of this installation is a drying column 1, consisting of a cylindrical upper part 2 and

  part of a conical bottom 3. The introduction of the precipi-

  of zinc salt in suspension and the introduction of the hot gas 9 is via the top 4

of the column.

  In a dough hopper 5, is first placed a homogeneous suspension which can be pumped from the zinc salt precipitate and which is directed, via a conveyor 20, onto a spraying disc 6, which is arranged in the center of the top 4 of the column and rotates at high speed. Due to the high mechanical and chemical stress during the drying process, this disc is made of a particular material, preferably titanium. On the top side of the disc

  are formed drive ribs oriented

  then the center towards the periphery of the disk, which guide the deposited wet product to the outside and allow a uniform and oriented exit of the homogeneous product from the surface of the disc. After its release, the wet product

  is sprayed uniformly under the action of the cen-

  trifuge. Depending on the rotational speed of the spray disc

  6 and the solids content of the initial product, the pulverized product is divided into particles of size from 1 to 50 em. In addition, the surface of the disc

  6 is inclined radially outwards.

  in such a way as to cause a spraying direction

downward direction.

  The hot gas 9, heated in a burner 8 at the respective operating temperature, is introduced into the drying column 1 in the center of the top 4 of the column via an annular channel 10 near the spray disc 6 , so that the

  hot gas 9 runs through the drying column 1 spiral.

  The opening of the annular channel 10 is disposed above the spraying disc 6 so that the hot gas 9, entering the drying column 1, reaches the wet product immediately after the exit of the latter from the spraying disc. 6. The wet sprayed product is thus dried immediately after the exit of the spray discs 6, so that a bonding of the product 17 to the inner side of the drying column is avoided in

a large extent.

  The cold due to the evaporation of the liquid makes

  the product temperature of the active zinc compound is lowered

  in the spiral-shaped hot gas stream 11 is substantially below the temperature of the hot gas, with drying and / or complete calcination being

  obtained because of the small particle size.

  Due to the low residence time of the product 17 in the drying column 1, zinc compounds with improved active properties are obtained. Agglomeration of the active compound is avoided to a large extent. In the case of a constant supply of gas

  the temperature of the product is essentially

  fluencee by the amount of water delivered with the suspension

per unit of time.

  The particle size of the final product 17 may to some extent also be influenced by the temperature as well as the rate of admission of the product.

flow of hot gas.

  The dried product 17 is evacuated continuously

  joint with the hot gas slightly cooled by

  through the lower part 3.

  The product-hot gas mixture is separated in a cyclone separator 13, the product 17 then reaches

  through a sieve 13 at the racking. The last

  residues of solids are separated by

  mediator of a dust collector 14 disposed downstream. Then,

  the hot exhaust 18 is exhausted through the

  a fan 16, possibly after

  recycled wet separation in the process.

  The compounds according to the invention can also

  be produced in an installation including the pulp dryer

  verification operates according to the principle against the current. In this case, the introduction of the pulverized product is carried out

  in the opposite direction to the hot gas flow, the heating time

  day of the product sprayed in the dryer being determined by the amount of hot gas. The product outlet of the particles descending against the flow of hot gas is effected by means of a collector in the bottom of the drying column, while the solid particles rising in the flow of hot gas are removed. together with the hot gas via the top of the column and are separated from each other in

  a cyclone separator arranged downstream or in a

  siéreur. In addition, there is the possibility of manufacturing

  compounds according to the invention in a drying plant.

  ge operating on the reverse currents principle.

  In such installations, the residence time of the product sprayed in the dryer is also adjusted to a value causing firstly a drying and / or a complete calcination and secondly the properties

  of the final product manufactured being maintained.

  According to the invention, it is used for

  generation of the hot gas, preferably atmospheric air

  which is possibly purified before it warms up.

  For the production of active zinc carbonate, we use

  preferably a hot gas enriched with CO2. For reasons

  economic sounds, a closed hot gas circuit is in

this case is desirable.

  The present invention furthermore relates to the use

  The use of compounds produced according to the invention as active fillers for rubber, in the case of the production of catalysts, as adsorbents and absorbents, in particular as adsorbents for gases in desulfurization and in the case of oil drilling as well as UV stabilizers in combination with known stabilizers. The compounds manufactured according to the invention are remarkable in comparison with active compounds manufactured

  conventionally, by a surprising specific surface

  large for the same or greater apparent density.

  In view of the precision of the process according to the invention and the advantageous properties of the new compounds

  zinc actives, the following examples will be explained.

  The properties of the products are recorded in the tables

1 to 3.

  A. Manufacture of zinc oxide compounds with increased surface area. (see Table 1)

Example 1

  It is used as an initial solution. an industrially produced zinc salt solution that contains zinc sulphate and zinc chloride

in a molar ratio of 1: 2.

  The zinc content is 150-160 g / l, the pH is between 4 and 4.5. As impurities, this solution contains in small amounts sodium chloride and sodium sulphate as well as impurities

  heavy metals in an amount of 1 ppm and below.

  For alkalization, a solution consisting of a mixture of sodium hydroxide and

  sodium carbonate in a molar ratio of 60:40.

  Both solutions are dosed in a reactor in which water is present. The calculated concentration of zinc salt during precipitation is between

0 and 50 g / l.

  The reactor consists of an agitator tank equipped with an indirect heating and cooling device. The addition of the two solutions is carried out so as to maintain a pH of 7-9. Due to the low alkali excess, no zinc loss occurs. The basic zinc carbonate precipitated at 60 ° C. is filtered continuously on a filtering strip and washed vigorously. The filter cake is again introduced into a stirring tank with hot water at 60 (4 parts of water for a portion of filter cake). It is then again filtered on a filtering belt with intensive washing and, after mixing,

  sprayed through a reservoir into the colon

  Do not spray high power.

  Direct drying in a flow of hot air of 800-900 C causes, by sudden evaporation of the water, a moderate drying, because the temperature of the product is established

then between 320 and 340 C.

  The residence time in this temperature range

  ture is about 10 seconds. Simultaneously, there is obtained, by spraying, a significant separation

particles.

  The resulting zinc oxide is precipitated according to

  known processes and is bagged.

  The product obtained has a specific surface

  of about 125 m 2 / g with an apparent density of about 450 g / l. The sieve residue of a larger size

  at 45 Km is less than 0.1%.

26 4 1268

Example 2

  The implementation is carried out according to Example 1 with the difference that the precipitation takes place at 90 ° C. The ZnO obtained has a specific surface area of approximately 85 m 2 / g. The reduction of the specific surface is probably due to the precipitation temperature more

higher than in Example 1.

  Example 3 (Comparative Example) The basic zinc carbonate is precipitated according to Example 1. The filter cake is decarboxylated after washing in a laboratory oven for 20 minutes

at 340 C.

  The specific surface is then 45 m / g.

  The example clearly shows that, in the case of calci-

  classic nation, the specific surface area

obtained is much lower.

  Example 4 (Comparative Example) Basic zinc carbonate is precipitated. according to

  Example 1. The filter cake obtained is decarboxyl

  after intensive washing in a laboratory oven

for 20 minutes at 600 C.

  There is still a reduction in the area

  specific to values of the order of 15 mL / g.

  B. Manufacture of basic zinc carbonates with increased surface area. (see Table 2)

Example 5

  The operation is carried out according to Example 1, except that the spray dryer is operated at 190 ° C. The final product is an active basic zinc carbonate. The calcination loss is about 24%, the zinc oxide content about 76%. The

  specific surface is of the order of 100 m2g.

Example 6

* The implementation is carried out according to Example 5 except that the precipitation temperature is OC. The specific surface of the manufactured product

is 75 m2 / g.

Example 7

  The implementation is carried out according to Example 5! with the exception that in the alkaline solution used, the proportion of caustic soda liquor is increased,

  the molar ratio of NaOH to Na2CO is 80:20.

  The specificity of the manufactured product

is 90 m2 / g.

  Example 8 (Comparative Example) The precipitation is carried out according to Example 5 at 60 ° C. The filter cake is dried after intensive washing in a laboratory oven for 20 minutes.

at 190 C.

  The result of the experiment shows that by increasing the duration of drying and according to the type of drying (method with stirring), the specific surface area with respect to the product manufactured according to Example 5 decreases.

  about 60% at values of the order of 40 m2 / g.

  The high specific surface area of the product

  Brick according to the invention according to Example 1 is evidenced by the measurement of the oil index according to DIN 35199. In Table 3, the results of measurement of commercially active zinc oxide are shown opposite.

  available and active zinc oxide according to the invention.

  Table 1 Active Zinc Oxide Example Molar Ratio Temperature Residence Time Analysis Product NaOH: Na2CO3 Precipitation Calcination Calcination Sufe Apparent Density Specific ZnO oC oC Minutes Seconds m2 / g g / l 32 pm%

  1 60: 40 60 340 - 10 126 + 5 440 0.05 94.9

  2 60 40 90 340 - 10 85 5 570 0.15 96.4

  3 60: 40 60 340 20 - 45 1 460 0.5 96.2

  4 60: 40 60 600 20 - 15 1 450 0.5 98

(1) = sieve residue in% above

  Above 32 pm hi 0% 0% Co Table 2 Active Zinc Carbonate Molar Ratio Temperature Residence Time Product Analysis Example NaOH: Na2CO3 Precipitation Drying Drying Surface Related Density SR (1) Specific ZnO C C Minutes Seconds m2 / g g / 1 32 pm%

  60: 40 60 190 - 10 100 + 2 590 0.15 75.8

  6 60 to 40 90 190 - 10 75 + 5 500 0.2 75.2 H

ow

  7 80: 20 60 190 - 10 90 + 5 500 0.2 74.9

  8 60: 40 60 190 20 - 46 + 4 550 0.8 74.5

(1) = sieve residue in% above

above 32 pm.

this

Table 3

  Product Surface area Oil index (BET method) DIN standard 53199 m2 / g

,,,,,,,

Active zinc oxide 39 54

produced by the trader

this) Zinc oxide according to 126 106

Example 1

o '

Claims (18)

R E V E N D I C A T IONS   1. Zinc oxide, zinc carbonate and car-   active basic zinc ketone, characterized by a specific surface area of 70-200 m2 / g and an apparent density 400-700 g / l.   2. Compounds according to claim 1, characterized   with a specific surface area of 90-150 m2 / g and a densi- apparent weight of 400-600 g / l.   3. Compounds according to claim 2, characterized   with a specific surface area of 100-130 m2 / g.   4. Process for producing compounds according to one   any of claims 1-3 and mixtures thereof.   ci, according to which zinc carbonate or basic zinc carbonate is precipitated by mixing a solution   aqueous solution of at least one alkali carbonate, a hydroxide   cured or mixtures thereof and a zinc salt solution, characterized in that an aqueous suspension of the precipitate is dried in a spray dryer in   a hot gas, whose temperature at the entrance to the   Spray chute is between 450 C and 900 C.   5. Process according to claim 4 for the production of active zinc oxide, characterized in that an aqueous suspension of precipitated zinc carbonate or of basic zinc carbonate is used and in that the temperature   the hot gas inlet is between 800 and 900 C.   6. Process according to claim 4 for manufacturing active zinc carbonate or active basic zinc carbonate or mixtures thereof, characterized in that an aqueous suspension of zinc carbonate is used.   or basic zinc carbonate precipitates, in that the temperature   the inlet temperature of the hot gas is between 450 and 650 ° C and that in the case of zinc carbonate is used a hot gas containing CO2.   7. Method according to claim 5, characterized in that the residence time of the product in a temperature range of 250 to 400 ° C and preferably 300 to 350 ° C from 2 to 60 seconds.   8. Method according to claim 6, characterized in that the residence time of the product in a temperature range of 150 to 300 C and preferably from 180 to 220 C from 2 to 60 seconds.   9. Process according to any one of the claims   7 and 8, characterized in that the residence time amounts to   from 5 to 15 seconds and preferably to 10 seconds.   10. Process according to any one of the claims   4 to 9, characterized in that the aqueous suspension   contains from 20 to 50% by weight of solids.   11. Process according to any one of the claims   4 to 10, characterized in that the hot gas is blown   in the same direction as the aqueous suspension in the fall.   12. Process according to any one of the claims   4 to 11, characterized in that the ratio of gas to sus-   The pension is set so that the product loading of the hot gas stream in the dryer is from 10 to 100 g / m3. 13. The method of claim 12, characterized in that the product loading in the gas stream   The temperature in the dryer is 30 to 50 g / m3.   14. Process according to any one of the claims   4 to 13, characterized in that the spray of the sus-   pension is effected by means of a rotating spray disk, which is arranged in the head of a column of stationary drying.   15. The method of claim 14, characterized in that the spraying is performed at a rotational speed of the spraying disc of 8000 to 15000 revolutions /   minute, the diameter of which is 500-150 mm.   16. Process according to any one of the claims   2 to 8, characterized in that the hot gas is blown at   countercurrent of the aqueous suspension in the dryer.   17. Compounds according to any one of the claims   1 to 3, characterized by a magnesium content Viron 2% by weight.   18. Use of compounds according to any one of   claims to 3 and 17, as a load for   rubber, in the manufacture of catalysts, as   UV stabilizers in combination with stabilizers   known as an adsorbent and absorbent agent, in particular as an adsorbent for gases in desulphurization plants and in the case of oil drilling.