GB2425128A

GB2425128A - Granular detergent and process of making granular detergent

Info

Publication number: GB2425128A
Application number: GB0507275A
Authority: GB
Inventors: John George Chambers; Stephen Thomas Keningley; Philip Ronald Moore; Geraint Paul Roberts
Original assignee: Unilever PLC
Current assignee: Unilever PLC
Priority date: 2005-04-11
Filing date: 2005-04-11
Publication date: 2006-10-18
Anticipated expiration: 2025-04-11
Also published as: GB2425128B; GB0507275D0

Abstract

A process for drying a surfactant to form a granule having 50 to 90 wt% non soap anionic surfactant and 5 to 25% hydrated inorganic hydratable salts, comprises <SL> <LI>(i) mixing an aqueous surfactant blend (I) containing from 20 to 50 wt% water and one or more inorganic hydratable salts (II) to form a mixture having a maximum viscosity of 100 Pa.s, at a shear rate of 20 s<-1> and a temperature of 80{C, where the ratio of I:II is greater than 1:1 and less than 10:1, <LI>(ii) drying the mixture by applying heat to produce an intermediate material with a total water content of 4 to 15 wt%. <LI>(iii) processing this intermediate material to form a free flowing granular detergent component. </SL> Use of the inorganic hydratable salt reduces the heat needed for the drying step. Also disclosed is a free flowing granular detergent material.

Description

DRYING SURFACTANT PASTE

TECHNICAL FIELD

This invention relates to drying surfactant paste, particularly to drying a hygroscopic surfactant such as an alpha olef in sulphonate.

BACKGROUND AND PRIOR ART

Surfactants, like alpha olef in sulphonate (AOS), are ***S I I manufactured as an aqueous paste with about 40% active surfactant. For some detergent applications, it is desirable to drive off the water to form a solid material.

This solid material may then be milled or otherwise S.' granulated to enable it to be dry mixed with other detergent S.." ingredients. This problem is only present for non-soap detergents. When making soap detergents active levels of nearly 90% can be achieved without there being any problem in achieving the necessary drying.

There are two problems associated with the production of such dried material. The first problem is that the energy used to dry the surfactant sufficiently for it to be millable is considerable. This is because as the paste loses water it takes proportionately more and more energy to drive off the remaining water. This problem becomes worse if the process is being operated in a very humid climate where the drying air is already at a high humidity and requires additional heating to get it sufficiently dry to be able to pick up the water. This could be overcome by use of

C

vacuum drying and/or by reducing the throughput of the drying equipment. These are costly solutions that may not

be acceptable.

The second problem that remains even if the above alternative drying techniques are employed is that the solid produced has a tendency to reabsorb moisture vapour from the air, leaving it sticky and difficult to mill, especially if it cannot be processes immediately. Many processes cannot be fed with hot surfactant so if the drying process *, has been modified to use high temperature this is: : particularly disadvantageous. * *

**. .*a * Sodium pyrophosphate and similar salts have been used as ** ingredients in detergent formations. EPO 349 199 teaches *S* S that the reversion of tripolyphosphate to pyrophosphate and "is.' orthophosphate is to be avoided so far as possible, thus reducing the levels of orthophosphate and pyrophosphate to less than 3%.

US 4 186 114 discloses a granular detergent composition comprising 18 wt% AOS and 15 wt % sodium pyrophosphate. The composition is spray dried and contains other ingredients than these two.

International application (PCT/EP2004/0l1462) is concerned with a process for manufacturing a detergent granule comprising blending a paste of anionic surfactant with a dehydrating agent. This process must not dry the materials by more than 5 wt%. As such, it should not be regarded as a drying process.

GB2308128 describes a detergent composition in paste form comprising an anionic surfactant in an amount of 5 to 40% by weight of the composition and a hydratable builder salt in an amount of more than 5% by weight of the composition wherein the level of the builder salt exceeds that of the anionic surfactant and the paste has a viscosity of 7 to 700Pa.s at a shear rate of ls. Suitably any hydratable salt may be employed although it is preferred if the hydratable builder salt is selected from builders such as polyphosphates orthophosphates, 2 tripolyphosphates, phosphates, tetraphosphates, pyrophosphates, carbonates and bicarbonates and the alkaline metal and ammonium salts of any of the foregoing. In a particularly preferred embodiment, the hydratable salt comprises sodium tripolyphosphate and optionally sodium carbonate. Any conventional anionic surfactant may be employed. Suitably the level of hydratable builder salt exceeds the level of surfactant in the composition but is preferably less than 5:1, more preferably 1.1 to 2.5:1 builder salt to surfactant on a weight basis.

StThIMARY OF THE INVENTION According to the present invention there is provided a free flowing granular detergent component comprising, to 90 wt% of, at least one, non-soap surfactant, 2 to 30 wt% water, and to 25 wt% inorganic hydratable salts, the inorganic hydratable salts being capable of forming inorganic hydrates at temperatures greater than 45 C where the water content of the hydrated salt is at least 25% by weight based on the weight of the unhydrated salt provided that when the inorganic hydratable salt is admixed with the at least one non soap surfactant at a temperature in excess of 75 C, preferably 85 to 90 C, the degree of hydration of the inorganic hydratable salt is less than 5% of its maximum degree of hydration.

Preferably the detergent material is made by a physical drying process where the feedstock is comprised of a mixture of component I and component II wherein the ratio of I: II lies in the range 1:1 to 20:1 and the viscosity of the feedstock at 80 C is less than 100 Pa.s at a shear rate of -1 S...

20 s the components being: *5*S * * S...

Component I: a surfactant system containing at least 50% *.

non-soap anionic surfactant and at least 15% water where this system has a maximum viscosity of 100 Pa.s at a shear rate of 20 s' and 80 C, and Component II: one or more inorganic hydratable salts.

The non-soap anionic surfactant may comprise a surfactant paste containing 15 to 30 wt% water and at least one surfactant selected from the group comprising PAS, SLES and AOS.

The inorganic hydratable salt preferably comprises anhydrous sodium pyrophosphate as this provides a particularly cost effective solution to the problem of improving drying efficiency, especially where phosphate containing compositions are desired.

Soap may be present in the feedstock at a level of less than wt%, preferably less than 20 wt% and most preferably less than 10 wt% based on the total weight of the feedstock. The soap may provide the advantage of structuring of the component or composition.

Also according to the invention there is provided a process for the drying of a surfactant to form a granule having from 50 to 90 wt% non soap anionic surfactant and 5 to 25% hydrated inorganic hydratable salts, the process comprising S.'.

the steps of: (i) mixing an aqueous surfactant blend (I) containing from 20 to 50 wt% water and one or more inorganic hydratable salts (II) to form a mixture having a maximum viscosity of 100 Pa.s, at a shear rate of 5 and a temperature of 80 C, where the ratio of 1:11 is greater than 2:1 and less than 20:1, (ii) drying the mixture by applying heat to produce an intermediate material with a total water content of 5 to 15 wt%, (iii) processing this intermediate material to form a granular detergent component.

Advantageously the hydratable salts are able to form inorganic hydrates which are stable at greater than 45 C and where the total water content of the hydrated hydratable salt at 45 C, is at least 25 wt% of the weight of the unhydrated salt. Most advantageously the initial water content of the mixture is 10 to 30%.

The surfactants suitable for use in the process may comprise a major part of anionic surfactant, preferably AOS, PAS, LAS, SLES, or mixtures of these, with nonionic, cationic and/or amphoteric surfactants; excluding soaps.

S

A process wherein step (iii) is carried out by cooling, milling and granulating with an appropriate liquid binder; * * ** such as water, aqueous polymer solutions, or PEG, cooling is preferred. In this case, the most suitable hydratable salt S...

is sodium pyrophosphate.

The level of component I used in the process is preferably 60-90 wt%, most preferably 70-90 wt% of the product of step (iii) . If present soap may be in the feedstock at a level of less than 25 wt% of the total surfactant (s) Incorporation of a hydratable salt at a temperature above its hydration temperature produces a pumpable paste, which can be fed into a drier and allows for the evaporative load on the dryer to be reduced. For the purposes of this invention, a pumpable paste is one having a viscosity of at most 100 Pa.s. The salt hydrates on cooling after the dryer giving chemical dehydration and salt crystal structuring to the product. This reduces the drying load at lower relative humidity (RH) or moisture content. I.e. the moisture that is most difficult or costly to remove.

This process allows the dryer to operate more efficiently and gives a product that is suitable for milling or subsequent post processing at higher total moisture contents than could be achieved without the use of inclusion of the inorganic hydratable salt.

The Inorganic Hydratable Salt * * I *I * * The inorganic hydratable salt can absorb water such that, when fully hydrated, at least 25% of its weight is water and it has an equilibrium relative humidity at 25 C of less than *.

60%. In this way, it can absorb significant amounts of moisture but keeps the moisture locked away' so that it does not readily evaporate and create powder flow problems.

It is also preferable that it is stable with respect to moisture loss up to 50 C. This means that the water bound in the hydrated salt remains in a stable state up to 50 C.

Sodium carbonate decahydrate heated up to 40 C dissolves in its own water of crystallisation and results in sodium carbonate solution, this then is not stable with respect to moisture loss.

Suitable hydratable salts are few in number. It has been found that magnesium sulphate; sodium pyrophosphate, sodium acetate and mixtures thereof have suitable characteristics to function as dehydrating agents in the context of the present invention, Of these, sodium pyrophosphate is preferred due to its high efficacy and compatibility with built detergent systems (magnesium salts being regarded as undesirable components of normal detergent systems) Swelling cellulosics absorb water only at an unacceptably high RH. Therefore, they are not suitable.

Table 1 gives a list of hydratable salts and other water absorbing agents or common detergent ingredients and demonstrates why they are suitable (pass) or unsuitable (fail) as hydratable salts for use in the present invention. * a

*.**a.

Table 1

___________________ * a.....

Material Hydrate % Water Dehydration Minimum Pass *...

in RH of or *.,,..

level Temp.

hydrate hydrate Fail C) **.e ____________________ a a...

Magnesium 7H20 51 >100 43 Pass. :: Sulphate ____________ ________ Sodium Acetate 3 H2o 40 55 32 Pass Sodium 10 H20 40 76 52 Pass Pyrophosphate _____________ _________ Sodium Carbonate H20 14 - - Fail 63 34 93 H20 Fail Sodium Sulphate 10 H20 56 32 93 Fail Sodium 12 H20 57 75 88 Fail Orthophosphate Disodium 12 H20 60 35 - Fail Hydrogen orthophosphate 2 H20 20 - - Fail Sodium 6 1-120 23 >100 52 Fail Tripolyphosphate _____________ _________ _____________ Tn-sodium 2 1-120 12 - 52 Fail Citrate _____________ I __________ ________ The invention will now be further described with reference to the following non-limiting examples:

Example 1

parts of AOS paste, (80% surfactant, ca 20% water) was mixed with 10 parts of anhydrous Sodium Pyrophosphate at 80 C. The viscosity of the mixture at this temperature was measured to be 43 Pa.s @ 20 s_i. * I.

The mixture was then oven dried at 120 C to a target total water content of 8.0 wt%. The actual measured moisture * S S.....

content was 7.6% and the measured hardness value was *5SS 3.08 N/mm2. This intermediate material was then cooled to * S.* ambient temperature and milled to form a powder. s.... * S..

S S *5 *

Finally, the powder was granulated, using a 90/10 ratio of powder to water, in a high shear granulator.

Finished formulation: AOS (surfactant) = 81 Sodium pyrophosphate = 11 Total water content = 8 - 10 - Comparative Example 2 This comparative example used Sodium Sulphate as the electrolyte. This hydratable salt falls outside the scope of claim 1 because it loses its water on heating to 45 C

(see table 1)

parts of AOS paste (80% surfactant, ca 20% water) was mixed with 10 parts of anhydrous Sodium Sulphate at 80 C. * S S

This mixture was oven dried at 120 C to a target total water: : *S....

S

content of 8.0 wt%. The actual measured moisture content was 6.7%. Hardness value 2.48 N/mm2. *. .s * S * SS

The intermediate material obtained was then cooled to S...

ambient temperature. An attempt was made to mill the cooled material, but it was too soft to mill.

AOS (surfactant) = 81 Sodium sulphate = 11 Total water content = 8 Comparative Example 3 100 parts of AOS paste, (80% surfactant, ca 20% water) was oven dried at 120 C to a target total water content of 8.0 wt%. The actual measured total water content was 7.6%.

The Hardness value was measured to be 2.36 N/mm2.

- 11 - This intermediate material was then cooled to ambient temperature and an attempt made to mill to form a powder.

The product was too soft to mill.

AOS (surfactarit) = 92 Total water content = 8 * * * ** * * * * * * * S * S. * S... * * * *.. * S * S. *

Claims

- 12 - CLAIMS

1. A free flowing granular detergent material comprising, 50 to 90 wt% of, at least one, non-soap surfactant, 2 to 30 wt% water, and to 25 wt% inorganic hydratable salts, the inorganic hydratable salts being capable of forming inorganic hydrates at temperatures greater than 45 C where the water content of the hydrated salt is at least 25% by weight based on the weight of the unhydrated salt *Ias.* provided that when the inorganic hydratable salt is admixed with the at least one non soap surfactant at a temperature in excess of 75 C, preferably 85 to 90 C, the degree of hydration of the inorganic hydratable salt is less than 5% of its maximum degree of S....' hydration.

2. A detergent material according to claim 1 made by a physical drying process where the feedstock is comprised of a mixture of component I and component II wherein the ratio of 1:11 lies in the range 2:1 to 20:1 and the viscosity of the feedstock at 80 C is less than Pa.s at a shear rate of 20 s1 the components being: Component I: a surfactant system containing at least 50% non-soap anionic surfactant and at least 15% water where this system has a maximum viscosity of 100 Pa.s at a shear rate of 20 s_i and 80 C) - 13 - Component II: one or more inorganic hydratable salts.

3. A detergent material according to claim 1, wherein the non-soap anionic surfactant comprises a surfactant paste containing 15 to 30 wt% water and at least one surfactant selected from the group comprising PAS, SLES and AOS.

4. A detergent material according to claim 1, wherein the inorganic hydratable salt comprises anhydrous sodium: , pyrophosphate.

5. A detergent material according to claim 1, wherein soap is present in the feedstock at a level of less than 25 s.. * *5*

wt%, preferably less than 20 wt% and most preferably S...

less than 10 wt% based on the total weight of the * S..

feedstock. ** :

6. A process for the drying of a surfactant to form a granule having from 50 to 90 wt% non soap anionic surfactant and 5 to 25% hydrated inorganic hydratable salts, the process comprising the steps of: (i) mixing an aqueous surfactant blend (I) containing from 20 to 50 wt% water and one or more inorganic hydratable salts (II) to form a mixture having a maximum viscosity of 100 Pa.s, at a shear rate of 20 s and a temperature of 80 C, where the ratio of 1:11 is greater than 1:1 and less than 10:1, - 14 - (ii) drying the mixture by applying heat to produce an intermediate material with a total water content of 4 to 15 wt%.

(iii) processing this intermediate material to form a free flowing granular detergent component.

7. A process according to claim 6 in which the hydratable salts are able to form inorganic hydrates which are stable at greater than 45 C and where the total water content of the hydrated hydratable salt at 45 C, is at *, * least 25 wt% of the weight of the unhydrated salt. :

8. A process according to claim 6 in which the initial water content of the mixture is 10 to 30%. *

9. A process according to claim 6 in which the surfactants 1I: * 0*I comprise a major part of anionic surfactant, preferably. : AOS, PAS, LAS, SLES, or mixtures of these, with nonionic, cationic and/or amphoteric surfactants; excluding soaps.

10. A process according to claim 6 in which step (iii) is carried out by cooling, milling and granulating with an appropriate liquid binder; such as water, aqueous polymer solutions, or PEG.

11. A process according to claim 6 in which the hydratable salt is sodium pyrophosphate.

12. A process according to claim 6 in which the level of component I is 60-90 wt%, preferably 70-90 wt% of the product of step (iii) - 15 -

13. A process according Lo claim 6 in which soap is present in the feedstock at a level of less than 25 wt% of the total surfactant (s) I. S S. * * ,$ *.S.* * . *..,I. * *.. * S **,-

S *.e. I Is,

S p