Cleaning compositions for solid surfaces – auxiliary compositions – Cleaning compositions or processes of preparing – Solid – shaped macroscopic article or structure
Reissue Patent
1999-06-22
2002-12-31
Ogden, Necholus (Department: 1751)
Cleaning compositions for solid surfaces, auxiliary compositions
Cleaning compositions or processes of preparing
Solid, shaped macroscopic article or structure
C510S444000, C510S457000, C510S536000
Reissue Patent
active
RE037949
ABSTRACT:
The present invention relates to detergent particles, a process for their production and a composition containing them. More particularly the present invention relates to a process for the production of detergent particles having a high level of anionic surfactant which involves in situ neutralisation of an acid precursor of the anionic surfactant and drying of the surfactant thereby produced and to the particles thereby obtained.
Detergent-active compounds conventionally employed in detergent compositions include anionic surfactants e.g. linear alkylbenzene sulphonates (LAS), linear alkyl ether sulphate (LES) and primary alkyl sulphates (PAS), and nonionic surfactants e.g. alcohol ethoxylates. To improve detergency performance it is desirable to provide a high level of detergent-active material in the powder.
Often, the maximum level of active that may be incorporated is limited by process requirements. Detergent compositions having a high bulk density are typically prepared by a process involving mixing or granulation of components of the composition and/or a base powder obtained for example from a spray-drying process and provide significant consumer benefits as compared to compositions of lower bulk density. It is known to incorporate detergent active compounds into such compositions in liquid form. However as it is necessary to control the ratios of liquids to solids in order to form detergent granules the maximum level of detergent active material which may be incorporated in this manner is limited. It is also known to incorporate anionic surfactant e.g. PAS in detergent compositions by means of a solid adjunct, that is, a particle comprising the surfactant and other components of the composition e.g. sodium carbonate and builder. Hitherto, the level of anionic surfactant present in such adjuncts has been limited due to the need to provide good flow properties and reduce the tendency to agglomerate. It is also known to incorporate anionic surfactants by the in-situ neutralisation of an acid precursor of the surfactant.
EP-A-506 184 (Unilever) discloses a process for the continuous dry neutralisation of liquid acid precursor of anionic surfactant. Detergent particles having an active detergent content of 30 to 40% by weight may be prepared by this process.
EP 572 957 discloses a process for producing a powdery anionic surfactant by feeding an aqueous slurry of the surfactant containing 60 to 80% solids into an evaporator, forming a film of the surfactant on the reactor wall and scraping it from the wall whilst drying and concentrating the slurry. The production of particles comprising anionic surfactant by in-situ neutralisation is not disclosed.
However, sufficient water must be present in the slurry to ensure that the slurry be pumpable. A large proportion of this water is necessarily removed in producing the powdery surfactant which requires energy and increases residence time. Thus, the energy required in the process and the throughput of the process are adversely effected where the slurry has a high water content. Moreover, a powder having a high water content may interact unfavourably with water sensitive components in fully formulated detergent compositions, e.g. bleach, thus providing poor stability and storage difficulties.
We have found that by feeding a liquid acid precursor of a anionic surfactant and neutralising agent to a drying zone and forming the anionic surfactant in-situ in the drying zone the above disadvantages may be ameliorated.
Accordingly a first aspect of the invention provides a process for the production of detergent particles comprising at least 50% and preferably 65% by weight of an anionic surfactant and not more than 20% and preferably not more than 15% by weight of water which comprises contacting a pumpable precursor acid of an anionic surfactant with a pumpable aqueous neutralising agent in a drying zone to produce an anionic surfactant the total water content being in excess of 10% by weight and preferably in excess of 20% by weight, heating the surfactant to a temperature in excess of 130° C. and preferably in excess of 140° C. in the said drying zone to reduce the water content to not more than 20% and preferably not more than 15% by weight, and subsequently cooling the surfactant to form detergent particles.
The heat of neutralisation evolved in the drying zone reduces the requirement for external heating of the drying zone and is advantageous over processes in which surfactant paste is employed as a feedstock.
Moreover, it is a particular advantage of the present invention that the precursor acid may be fed to the drying zone in liquid form rather than as an aqueous solution and the neutralising agent may be concentrated. The total amount of water introduced into the drying zone may be reduced significantly as compared to processes in which a surfactant paste is employed. Such pastes may require at least 30% by weight of water in order to be pumpable.
The present process may be operated as a single step process (ie. the detergent particles are obtained directly from a precursor acid feedstock) rather than as a two step process involving production of the surfactant and subsequent formation and drying of a paste to form the detergent particles. This is advantageous as the need to produce a surfactant paste, which can present technical difficulties, is avoided as is the need for transport and storage of the paste.
The precursor acid for example PAS acid, is suitably fed to the drying zone in the liquid phase. As the precursor acid may be thermally unstable, the neutralisation preferably occurs sufficiently rapidly and substantially completely such that thermal decomposition of the acid due to the elevated temperature is minimised and desirably avoided.
The precursor acid is suitably fed into the drying zone at a temperature of 40° to 60° C. to ensure it is in the liquid form but without encouraging thermal decomposition. The neutralising agent may be fed into the drying zone at any desired temperature but 50° to 70° C. is preferred to facilitate neutralisation rather than acid decomposition.
In order to effect removal of water, the walls of the drying zone are suitably at a temperature of at least 100° C., preferably at least 130° C. and especially at least 140° C.
Suitably the neutralising agent is introduced as an aqueous solution or slurry. Conventional neutralising agents may be employed including alkali metal hydroxides for example sodium hydroxide and alkali metal carbonates, for example sodium carbonate.
Suitably the neutralising agent is present in an amount of 25 to 55% and preferably a 30 to 50% by weight of the aqueous solution or slurry. A high concentration of the neutralising agent may give unwanted crystallisation and a low concentration is undesirable due to the large proportion of water.
The concentration of the neutralising agent solution or slurry may be varied in order to control the water content in the drying zone. Thus, optimum viscosity characteristics may be attained whereby the material in the drying zone remains transportable/pumpable.
A stoichiometric excess of neutralising agent with respect to the acid precursor may be employed. The excess neutralising agent combines the acid, for example sulphuric acid which may be produced if part of the precursor acid thermally decomposes.
Desirably the drying zone is under a slight vacuum to facilitate the removal of water and volatiles. The vacuum may be from 100 Torr up to atmospheric pressure as this provides significant process flexibility. However, a vacuum in excess of 500 Torr up to atmospheric has the advantage of reducing capital investment whilst providing vacuum operation.
We have found that improved control of residence time and particle size may be secured, disadvantageous thermal decomposition of the acid may be reduced or avoided and process throughput may be increased by agitating the material in the drying and/or cooling zone.
Accordingly a second aspect of the invention provides a process for the production of detergent particles comprising at leas
Emery William Derek
Metcalfe Kenneth
Tollington Peter James
Lever & Brothers Company, division of Conopco, Inc.
Mitelman Rimma
Ogden Necholus
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