CA2145636A1

CA2145636A1 - Process for producing sorbents based on smectites and cellulose-containing materials with a low bulk weight

Info

Publication number: CA2145636A1
Application number: CA002145636A
Authority: CA
Inventors: Reinhard Hahn; Otto Haubensak; Max Eisgruber
Original assignee: Individual
Current assignee: Sued Chemie AG
Priority date: 1993-08-12
Filing date: 1994-08-10
Publication date: 1995-02-23
Also published as: JPH08502421A; DE4327159A1; WO1995005072A1; KR950703274A; EP0663793A1; DE59401534D1; ATE147225T1; EP0663793B1

Abstract

A process for producing sorbents based on smectites and cellulose-containing materials with a low bulk weight and high absorbency is described; the process is characterized in that a moist mixture of smectite and crushed cellulose-containing primary raw material is treated with intimate shearing action and with subsequent extrusion and is then dried and granulated.

Description

21g5636 E. PH~N ~ S 4~ r-D
TEXT TRANSLATI~N

TRANSLATION FRO~I GER~IAN

Patent Attorneys Cert. Eng. R. Splanemann Cert. Chem. Dr. B. Reitzner Cert. Eng. K. Baronetzky FirmaAugust 10, 1994 Sud-Chemie AG
Lenbachplatz 6 80333 MunichOur reference: 4465-X-16.538 PATENT APPLICATION

Process for producing sorbents based on smectites and cellulose-containing materials with a low bulk weight SPEC~CATION

The invention relates to a process for producing sorbents based on smectites and cellulose-containing materials with a low bulk weight. These sorbents are suitable for absorbing any liquids; however they are especially suitable as litter for pets, therefore the following details relates in particular to this application.

Keeping pets in a largely urbanized environment is increasingly associated with the use of litter. Litter is designed to absorb the fluids excreted by the animals and thus to inhibit or prevent the development of odors as much as possible. Furthermore it is designed to remove moisture from semisolid, moist animal excrement and discharges in order to thus reduce the dcvelopment of odors. Good litter moreover has the property of absorbing the discharged or extracted fluids with the formation of a compact lulllp which can be removed easily ancl economically. Optimum animal litter thus has a high absorptivity.

Products which can be found on the mar~et are on the one hand organic substances, such as straw, sawdust, wood shavings, bark, porous plastic beads, shredded paper, cellulose fibers, agricultural wastes, polyacrylates, etc: these are used alone or in mixtures with inorganic materials. The disadvantage of organic litters is often unsatisfactory lump formation or their consistency as well as their tendency to bacterial decomposition, especially in interaction with moisture.

On the other hand, litters which bind odor and moisture, especially for small animals, with a cellulose-containing material are known from DE-A-3 ~16 225, in which the cellulose-containing material as a wet substance is mixed at least with one capillary-capable, small grain material with a grain size < 0.5 mm in a weight ratio of 90:10 to 20:~0. Preferably the wet mass formed in the treatment of sewage from paper production (recovered paper stock) with a moisture content from 50 to 60% by weight is used as the cellulose-containing material. For example, bentonite which in the untreated state has a moisture content of roughly 30% by weight can be used as the capillary-capable material. However pumice stone dust with a moisture content of at most 30% by weight is preferred. The mixture can be compacted, tabletted, or pelletized. However it has been ascertained that these treatment methods are not adequate to obtain a litter with satisfactory lump formation.

Furthermore, an animal litter as well as a process for its production are known from DE-A-4 101 243 in which a cellulose material is mixed with weighting material, thickeners, and/or binders as well as water, is dehydrated, crushed and dried. For example, wood, wood products, residues from wood processing and straw can be used as the cellulose material. For example, silicic acid, silicate materials, zeolites, bentonite, and polyacrylates can be used as thickeners .

21~5636 Sorbents based on clays and clay minerals containing minerals from the smectite group which are burned at temperat-lres of more than 650C to achieve a high pore volume are known from DE_B-37 28 8812 and DE-C-38 25 905. Orgallic substances such as sawdust, bark, rice hulls, and the like can be added as the porosity-enhancing a~ent. These porosity-enhancillg agents are however burned up during heating and no longer remain in the product. The material obtained after burning is no longer capable of swelling.

US-A-4 607 594 relates to a granulated sorbent which is suitable as litter. The mixture contains absorbing particles (for example, cellulose-containing materi~l or clay) and inert absorptive grains, for example, volcanic rock, which have been treated with a neutralization agent (carbonate). This is s dry mixture; no shearing forces are used in its production.

US-A-4 591 598 and 4 657 881 relate to a sorbent, containing clay mineral particles (preferably smectite particles) which are bonded using organic binders, such as soluble polysaccharides. For example, cellulose esters such as CMC are mentioned. These cellulose derivatives however are not a cellose-containing primary raw material.

US-A-5 188 064 relates to a process for improvement of the sorption capacity of a smectite clay capable of swelling with a particle size of at least 95% < 200 microns, this clay being mixed with a particulate cellulose-containing material with a particle size of least 95~o < 2000 microns. The weight ratio between the cellose-containing material and smectite is roughly 0.05 to 3:1. The components can be mixed with one another either dry or wet. The mixture obtained after the drying process is extremely dusty. The cellulose component is not bound into the product so that the material tends to adhere strongly to the fur and paws of animals.
This mixture cannot be used as litter. The mixture obtained according to the wet process has a higher density and lower sorption capacity compared to a mixture kneaded wet.

The problem of the invention was to make available a process for producing sorbents based on smectites with low bulk weight in which a considerable portion of cellulose-containing materials can be used without adversely affecting the capacity to form lumps in contact with aqueous liquids.

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The invention thus relates to a process for prodllcing a sorbent based on smectites and cellulose-containing primary raw materials; the process is characterized by the fact that a moist mixt~lre of smectite and cr-lslled cellulose-containing primaly r~w material is treated with in~imate shearing action and with subsequent extrusion and is dried and granulated In assessing the advantages of the process according to the invention, the following can be assumed:

A bentonite granulate which is produced from a high quality smectite (i.e., with a montmorillonite content of at least 60% by weight), is characterized by the followin properties:

- ability to form lumps when used with aqueous liquids, - high water and liquid absorption capacity (2 120~o by weight), - high bulk weight (850-1000 g/l).

The advantage of the process according to the invention now consists in producing a granulate using smectites such as bentonite, and lightweight cellulose-containing primary raw materials, which, in addition to the aforementioned advantages of the granulate consisting only of bentonite, has a low bulk weight (400-800, preferably 550-700 g/l). Moreover, the water absorption capacity can be increased by using the cellulose-containing primary raw materials.

Cellulose-containing primary raw materials according to the invention are defined as crushed wood material or other reduced cellulose-containing material of plant origin, for example of annuals or parts thereof such as straw, grass, husks, chaff, crushed peanut shells, corn and sunflower stalks, as well as long fiber materials such as cotton and cotton waste, flax. China grass, hemp and jute. However, the long fiber materials are less preferred since the fibers must be shortened in the production of the mixture.

Cellulose-containing prim~ry raw materials include chemically untreated cellulose such as sulfite or sulfate cellulose, or rcgenerated cellulose as well as reprocessed scrap paper.

The resulting dried granulate is solid and has a water absorption capacity of morc than 100%, preferably more than 1 20~c. One method of determining the w ater absorption capacity is indicated below, as are a method for determining the water content of the smectite used as the initial material and of the cellulose-containing primary raw material, also a method for determining the water content of the granulate.

The smectite and the cellulose-containing primary raw material are mixed preferably by intensive shearing with a power consumption from 2 to 10, preferably from 3 to 6 kWh/ton of mixture. The smectite portion is preferably on the outside of the granulates.

A shearing device (for example, a Bedeschi mixture or brick molding machine from Haendle) is used for mixing.

Preferably the ratio between the smectite and cellulose-containing primary raw material (relative to the given dry mass) is set to 3.6 to 12.1, especially to 4.2 to 6.8:1.

Preferably an earth al~ali or alkali bentonite which in the mine-moist state usually has a moisture content of roughly 30% is used as the smectite. The smectite can also be pre-dried, especially if the cellulose-containing primary raw material has a high moisture content.

Drying of the sorbent tal~es place preferably by exposing the material to be dried to not more than 150C, preferably not more than 120C. During drying at higher temperatures, the sorption capacity of the smectite can be reduced.

The dried sorbent is preterably granulated to a grain size from roughly 0.1 to 10 mm, preferably from roughlv I to 5 mm.

The subject matter of thc invention is furthermol-e a sorbent wllich can be obtained using the process described above, in the form of a granulate which contains the smectite and cruslled cellulose-containin~ primary raw material, in which the watel content of the granulate is not more than 15% b~ weight.

Preferably the sorbent contains 60 to 90, especially 6~ to 84Yo by weight smectite, 5 to 25, especially 10 to 20~o by weight cellulose-containing primary raw material (each relative to dly substance) and 5 to 15, especially 6 to 12~o by weight free water.

The sorbent according to the invention preferably has a bulk weight from 400 to ~00 g/l, especially *om 550 to 700 g/l, and water absorption of roughly 100 - 200~37o, especially from I 10 to 150%.

The sorbent according to the invention can furthermore be extended with known sorbents, for example organic sorbents. Furthermore the sorbent can contain white pigments, disinfectants, and/or animal acceptors.

The subject matter of the invention is furthermore the use of the aforementioned sorbent as a packing material, as an absorbent for liquids (for example bodily fluids, oil, liquid chemicals) and as a litter for pets, especially as cat litter.

The water content of the smectite used according to the invention is determined as follows:

10 g of smectite are accurately weighed in a flat dish to 0.01 g and at 105C heated up to constant weight (at least 2 hours). Subsequently the specimen is cooled in an desiccator to room temperature and weighed:

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EVALUATION:

initi~l wgt - final wgt x 100 = waler cont~nt (~).
initial wgt The water content of the sorbent according to the invention is determined in the same manner as the water content of the smectite. Heating talces place at 105C up to constant weight.
The water content of the cellulose-containing material is determined in the corresponding manner (drying at 105C up to constant weight).

The water absorption capacity of the sorbent according to the invention is determined using the method from Westinghouse (no. 17-A) (compare Industrial Minerals, Aug. 1992, p. 57).
In this case the sorbent dried to a residual water content of 6~ by weight is weighed in a conical vessel of fine wire gauze (clear mesh width 0.25 mm = 60 mesh, diameter 7 cm, height 7.6 cm) (initially weighed portion E = 20 g). Subsequently the total weight (wire gauze + initially weighed portion E = E, in grams) is determined. The filled gauze is suspended for 20 minutes in a water-filled glass dish such that the sorbent is completely immersed. After 20 minutes the wire gauze is removed from the water and allowed to drip for 20 minutes. Directly afterwards the weight of the vessel with the contents is determined (E2 in grams). The evaluation is done as follows:

E2 - El Water absorption in percent = x lO0 E

The water penetration test is run as follows:

Water is added to a levelled and uncompacted bed of the grainy sorbent in a glass dish (diameter 140 mm, height 75 mm, fill height 50 mm) from a 50 ml burette and the penetration depth is observed. In doing so the outlet of the burette is placed at a height of 3 - - ` 2145636 to 4 cm over the middle of the bed, whereupoll 60 ml of tap water are allowed to run out within 55 to 60 seconds. After waiting 3 minutes it is chec};ed on the bottom of the dish whether water has run through; that water has run thro-lgh is indicated by coloration of the grainy material on the bottom of the dish. The evaluation is done a~s follo~vs:

- coloration on the bottom of the dish not visible: test passed;
- coloration on the bottom of the dish visible: test not passed.

The bulk weight is ascertained as follows:

A 500 ml graduated cylinder is first weighed empty. A powder funnel with an opening of roughly 15 cm and an outlet opening of roughly 3 cm is seated on it and filled with the sorbent granulate within roughly 5 seconds. Afterwards the powder funnel is removed from the graduated cylinder such that the granulate located in it forms a projecting cone. The latter is scraped off using a wide spatula along the surface edge of the graduated cylinder.
Adhering grains or dust are removed from the outside of the filled graduated cylinder and it is reweighed. The bulk weight is computed as follows:

Bulk weight (g/l) = 2 x net weight (g/S00 ml) Lump formation can be quantitatively determined as follows:

- Firmness I (relatively firm) - Lump consists of a homogeneous mass without visible and perceptible ~rains - Lump fractures into smaller fractions upon light pressure - Lump is moist.

21 ~5636 - Firmness 2 (soft, mushy) - Lump consists of a sticky mass - Lump buckles when removed and crumbles upon light pressure - Lump is wet - Firmness 3 (crumbly-wet) - Lump consists of only lightly adhering, crumbly mass - Lump crumbles when removed or into smaller fractions upon light pressure - Lump is wet The invention is explained by the following example in a non-restrictive manner.

EXAMPLE 1 (COMPARISON) 320 g of mine-moist Bavarian calcium bentonite are prekneaded in a Werner-Pfleiderer mixer for 1 minute while a small amount of distilled water is added. Power consumption is 2 kWh/ton. The purpose of prekneading is to homogenize the bentonite and to convert it into a plastic, easily kneadable mass. The ideal water content is according to experience adjusted by adding an amount of water such that a "smacking" noise is generated during kneading and the raw bentonite is similar to plasticine. This is generally the case at a water content from 30 to 35% by weight. Afterwards kneading is continued for another 5 minutes; the plasticine-like state is obtained by adding water as necessary. The kneaded bentonite is crushed into pieces roughly I to 1.5 cm in size, placed in a porcelain dish and dried in a recirculation drying oven for 1 to 2 hours at 80 to 85C to a water content of 4 to 8% by weight. This can be recognized by the fact that the pieces are still colored somewhat dark inside. The granulate fraction between I and 5 mm is screened out, the propoltion of the fraction from 2 to S mm being more than roughly 80~o and the proportion of the fraction from 1 to 2 mm being roughly 20~o.

Water content: 6.3% by weight Bul~ weight: 992 g/l Water absorption capacity: 114%
Water penetration test: passed Lump firrnness: relatively f rm ( I ) EXA~IPLE 2 320 g of mine-moist Bavarian calcium bentonite (water content roughly 30 to 35~o by weight) are added to 5% by weight of sawdust (relative to dry substance) with a grain size of < I mm and a water content of 31%. Then kneading is done as in example I with an energyconsumption of 3 kWh/ton. The kneaded mixture is dried and granulated (particle size roughly 1 - 5 mm - grain size distribution: 80% = 2 to 5 mm; 20~o = I to 2 mm). The granulate has the following properties:

Water content: 5.9% by weight Bulk weight: 775 g/l Water absorption: 126%
Water penetration test: passed Lump firmness: relatively firm (1) 21~5636 E~A~IPLE 3 The procedure of example 2 is repeated with the difference that 10~ sawd~lst is l;neaded in.
The granulate (grain size distribution: 80~c = 2 to 5 mm; 20% = I to 2 mm) has the follo~ving properties:

Water content: 6.35'o by weight Bulk weight: 659 g/l Water absorption: 1 375rO
Water penetration test: passed Lump firmness: relatively firm (I) EXA~IPLE 4 The procedure of example 2 is repeated with the difference that 15% b~ weight sawdust is kneaded in. The granulate (grain size distribution: 80~o = 2 to 5 mm; 20~o = I to 2 mm) has the follo~ving properties:

Water content: 5.4Yo by weight Bulk weight: 573 g/l Water absorption: 145'~o Water penetration test: passed Lump firmness: relatively firm (1) ~ 11 21~S63~

EXAM~LE ~

The proced~lre of example 2 is repeated with the difference that 25% by ~ei~ht sawdust is kneaded in. The grranulate (~rain size distribution: 80~ = 2 to 5 mm; 20~k = I to 2 mm) has the following quantities has the following properties [sic]:

Water content: 6.1% by wei(Jht Bull; weight: 406 g/l Water absorption: 185%
Water penetration test: passed Lump firmness: soft, mushy (2) EXA;I~IPLE 6 The procedure of example 2 is repeated with the difference that 10% chopped straw is kneaded in at a power consumption of 5 kWh/ton. The granulate (grain size distribution:
80% = 2 to 5 mm; 209~o = I to 2 mm) has the following properties: ~' Water content: 6.8% by weight Bulk wei~ht: 674 g/l Water absorption: 134%
- Water penetration test: passed Lump firrnness: relatively firm (I ) E~A ~IPLE 7 (CO~JPA RISO~ ) The procedure of example 2 is repeated with the difference than 42'7c paper resid~le is kneaded in. The paper residue is residues from the paper industry with a solid content of roughly 51'~o and roughly 22% lime as well as 10% }~aolin. The granulate ~grain size distribution: 80% = 2 to 5 mm; 20~o = 1 to 2 Mm) has the followin~ properties:

Water content: 5.3"o by weight Bulk weight: 670 g/l Water absorption: 1 02~o Water penetration test: did not pass Lump firmness: crumbly-wet (3) (cannot be removed compactly) EXAMPLE 8 (COI~IP~RISO~) According to the procedure of example C of US-A-5 188 064 the followving lests were run:

(a) D~ing process 800 g of sodium bentonite with a water content of 7.8% by weight, a bulk weight of 960 g/l and a particle size range from 2.0 to 5.0 mrn were mixed dry in a plastic bag with 200 g of soft wood fibers (Lignocel F9, co,-nmercial product from ~. Rettenmaier & Soehne GmbH & Co., Ellwanoen) with a water content of 12.8qo by weight, a bulk weight of 150 g/l and a particle size range from 1.2 to 0.5 mm. The water content of the mixture was 8.9'ic by weight.
The mixture was extremely dusty so that the material tends to adhere strongly to the fur and paws of animals.

21~5~3 'et process 1000 g of the dry mixture (a) were mixed with 500 g of water in ~n Eirich-mixer. Af[er adding water (roughly 1~ seconds) and a stirring timc of one minute round granulates were formed with a diameter of rouohly 2 to 4 mm wjhich easil~ adhered to one another. Clearly larger wet lumps however also appeared in isolation in the mixture. The mixture clearly heated up as it was stirred and exhibited a water content (after a short waiting period until it wasdry) of 40.5qc by weight. The moist granulates were dried in a recircu}ation drying oven at 75C. After cooling, the fraction from 2.0 to 0.5 mm was screened out. The screening residue ( > 2 mm) was crushed with a jaw crusher, and the screened fraction from 2.0 to 5.0 mm was added to the first screened fraction. The material had a water content of 0.8% by weight, a bulk weight of 511 g/liter and water absorption of 573%. The material passed the water penetration test and had sufficient lump strength (1).

(c) Kneading process (accord~ng to tl~e invention) 1000 g of the dry mixture (a) were mixed with 500 g of tap water. The mixture was kneaded in a kneader from Werner and Pfleiderer for 5 minutes.
The moist mixture (water content 45.0% by weight after a short waiting time - until it is dry) heated up somewhat during kneading. The moist material was reduced after drying in a recirculation drying oven at 75C with a ~aw crusher and screened out to a grain size range from 2.0 to 0.5 mm.

The material had a moisture content of 9.6% by weight, a bulk weight of 482 g/liter and water absorption of 624S~o. It passed the water penetration test.
Lump strength was adequate (1).

The product according to the invention therefore had a lower bulk weight and higher water absorption than the comparison product (b) although based on kneading compaction could be expected. The higher water absorption of products (b) and (c) compared to the products according to examples 1 through 7 is caused by the sodium bentonite used as the initial product having higher water absorption than calcium bentonite.

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Claims

1. Process for producing sorbents based on smectites and cellulose-containing materials with low bulk weight, characterized in that a moist mixture of the smectite and crushed cellulose-containing primary raw material is treated with intimate shearing action and with subsequent extrusion and is then dried and granulated.

2. Process according to claim 1, wherein chopped wood material or another cellulose-containing material of plant origin is used as the cellulose-containing primary raw material.

3. Process according to claim 1 or 2, wherein the smectite at a power consumption from 2 to 10, preferably 3 to 6 kWh/ton of mixture and the cellulose-containing material are mixed with one another by intensive shearing.

4. Process according to one of claims 1 through 3, wherein a cellulose-containing primary raw material with a water content from 10 to 40, preferably from 20 to 30% by weight is used.

5. Process according to one of claims 1 through 4, wherein the ratio of smectite and cellulose-containing primary raw material, relative to the respective dry mass, is set to 3.6 to 12.1, preferably to 4.2 to 6.8:1.

6. Process according to one of claims 1 through 5, wherein an earth alkali or alkali bentonite is used as the smectite.

7. Process according to one of claims 1 through 6, wherein the dried sorbent is granulated to a grain size of roughly 0.1 to 10 mm, preferably of roughly 1 to 5 mm, more than roughly 70% by weight of the granulate having a particle size from 2 to 5 mm and less than roughly 30% by weight of the granulate having a particle size from 1 to 2 mm.

8. Sorbent which can be obtained according to the process according to one of claims 1 through 7 and which contains a smectite and crushed cellulose-containing primary raw material in the form of a granulate, the water content of the granulate being no more than 15% by weight.

9. Sorbent according to claim 8, wherein the cellulose-containing primary raw material represents a chopped wood material or other cellulose-containing material of plant origin.

10. Sorbent according to claim 8 or 9, wherein it contains 60 to 90, preferably 68 to 84% by weight of smectite, 5 to 25, preferably 10 to 20% by weight of a cellulose-containing primary raw material (each relative to dry substance) and 5 to 15, preferably 6 to 12% by weight, free water.

11. Sorbent according to one of claims 8 through 10, wherein it has a bulk weight of roughly 400 - 800 g/l, preferably of roughly 550 - 700 g/l and water absorption of roughly 100 - 200 %, especially of roughly 110 - 150%.

12. Sorbent according to one of claims 8 through 11, wherein it is extended with known sorbents, for example, with organic sorbents.

13. Sorbent according to one of claims 8 through 12, wherein it contains white pigments, disinfectants and/or animal acceptors.

14. Use of the sorbent according to one of claims 8 through 13 as packing material, as absorbents for liquids and as litter for domestic pets, especially as cat litter.