EP0608642A2

EP0608642A2 - Inhibiting calcium carbonate crystal growth

Info

Publication number: EP0608642A2
Application number: EP93310633A
Authority: EP
Inventors: Florence Tournilhac; Mark Hopwood; John Federick Carr
Original assignee: Rhone Poulenc Chimie SA; Rhone Poulenc Chemicals Ltd
Current assignee: Rhodia Ltd
Priority date: 1992-12-31
Filing date: 1993-12-31
Publication date: 1994-08-03
Also published as: GB9227155D0; JP2828890B2; JPH06293897A; EP0608642A3

Abstract

N,N-dicarboxymethyl-2-aminopentane-1,5-dioic acid or a salt thereof is useful as CaCO₃ crystal growth inhibitor, especially in detergent compositions.

Description

The present invention relates to inhibiting calcium carbonate crystal growth, especially in detergent formulations, and during washing operations.
A detergent composition must "soften" the water used for washing. It is therefore necessary to remove or inactivate any calcium and magnesium which may be present in the water in the form of soluble salts. The removal or inactivation of calcium may be effected by complexation in the form of a soluble ion, by ion exchange, or by precipitation. Precipitation must be controlled to prevent incrustation of the laundry or of parts of the washing machine with calcium carbonate.
Phosphonates have been shown to be effective in detergent applications to prevent incrustation. They can act as crystal growth inhibitors which prevent at substoichiometric concentrations the growth of insoluble calcium and magnesium compounds. However, these compounds can contribute to eutrophication.
Other organic compounds have been proposed for replacing phosphonates, particularly water-soluble polymers such as polyacrylic acids, polyacrylates, and acrylicmaleic copolymers and tertiary amines such as, for example, the sodium salt of ethylenediamine tetraacetic acid. However, the use of organic polymers for inhibiting CaCO₃ crystal growth does not give complete satisfaction. Also, such organic compounds are not biodegradable and consequently pollute any waterways into which they may be discharged.
It is known that certain N-substituted derivatives of dicarboxylic alpha amino acids in which the N substituents are formed by lower or higher acyl groups or by lower or higher alkyl groups, can be used in sequestrating and/or dispersing compositions. Such compositions have the advantage of comprising a derivative of a natural product which is biodegradable to the extent of 85%-90%.
GB 1 439 518 relates to sequestrating compositions including, as essential active constituent, N,N-dicarboxymethyl-2-aminopentane dioic acid. This specification mentions the use of the said compound for its sequestrating power in detergent compositions.
There remains a need for biodegradable compositions which effectively inhibit CaCO₃ crystal growth in detergent applications and formulations.
The present invention provides a method for inhibiting or preventing CaCO₃ crystal growth in a medium in which such growth may occur which comprises incorporating in said medium an effective amount of N,N-dicarboxymethyl-2-aminopentane-1,5-dioic acid or a salt thereof as the main or only CaCO₃ crystal growth inhibitor.
While the aforesaid British specification describes the use of this type of compound to reduce hardness of water by complexing calcium, it does not disclose the addition of N,N-dicarboxymethyl-2-aminopentane-1,5-dioic acid detergent compositions to inhibit CaCO₃ crystal growth.
In a preferred aspect, this invention provides a CaCO₃ crystal growth inhibitor composition comprising N,N-dicarboxymethyl-2-aminopentane-1,5-dioic acid or a water-soluble salt thereof, and detergent compositions containing the same.
By "detergent composition" is meant any detergent for washing laundry, dishwasher detergents, or any other washing product for household, industrial or institutional use.
The N,N-dicarboxymethyl-2-aminopentane-1,5-dioic acid can be prepared according to a process disclosed in USP 2 500 019 or GB 1 439 518.
Alkali metal salts, particularly sodium salts, potassium salts or ammonium salts, can be used as water-soluble salts of N,N-dicarboxymethyl-2-aminopentane-1,5-dioic acid.
The use of this inhibiting system in detergent compositions involves the use of substoichiometric levels of N,N-dicarboxymethyl-2-aminopentane-1,5-dioic acid or a water-soluble salt thereof, which acts to inhibit CaCO₃ crystal growth. As used herein, a substoichiometric level of an amino-dicarboxylic acid means a level which is below that required for equimolar complexation of calcium ions.
More particularly, the present invention provides the use in detergent compositions of N,N-dicarboxymethyl-2-aminopentane-1,5-dioic acid, or a water-soluble salt thereof with a monovalent cation, in a concentration of from about 0.1 percent to about 15 percent of N,N-dicarboxymethyl-2-aminopentane-1,5-dioic acid by weight. A preferred range is about 0.1 to about 7 percent by weight, more preferably from about 0.3 percent to about 5 percent by weight.
In addition to the CaCO₃ crystal growth inhibitor of the present invention, such detergent compositions may contain at least one surfactant in a cleaning effective amount. The surfactant content is preferably from 1 to 20%, and more preferably from about 2 to 15%.
Suitable such surfactants include:

(i) anionic surfactants of the type comprising alkali metal soaps (alkali metal salts of C₈-C₂₄ fatty acids), alkali metal sulfonates (C₈-C₁₃ fatty alkylbenzenesulfonates and C₁₂-C₁₆ alkylsulfonates), oxyethylenated and sulfated C₆-C₁₆ fatty alcohols, oxyethylenated and sulfated C₈-C₁₃ alkylphenols, alkali metal sulfosuccinates (e.g. C₁₂-C₁₆ alkylsulfosuccinates), and the like,
(ii) nonionic surfactants of the type comprising polyoxyethylenated C₆-C₁₂ alkylphenols, oxyethylenated C₈-C₂₂ aliphatic alcohols, ethylene oxide/propylene oxide block copolymers and optionally polyoxyethylenated carboxylic amides,
(iii) amphoteric surfactants of the alkyldimethylbetaine type, and
(iv) cationic surfactants of the type comprising alkyltrimethylammonium chlorides or bromides and alkyldimethylethylammonium chlorides or bromides.

Various other constituents may also be incorporated into the detergent composition, such as:

(1) builders e.g.:
- (i) phosphates in an amount of at least 25% of the total weight of the formulation,
- (ii) zeolites in an amount of up to about 40% of the total weight of the formulation,
- (iii) sodium carbonate in an amount of up to about 80% of the total weight of the formulation,
- (iv) nitrilotriacetic acid in an amount of up to about 10% of the total weight of the formulation,
- (v) citric acid or tartaric acid in an amount of up to about 20% of the total weight of the formulation,
- (vi) polyaspartate salts or polyimide polymers as disclosed in EP 511 037, and
- (vii) particulate detergent builders based on an alkali metal silicate sorbed on to a particulate inert support substrate as disclosed in the EP 488 868 or spherical cogranulates based on a hydrated alkali metal silicate and an alkali metal carbonate, the alkali metal silicate being sorbed on the alkali metal carbonate with a molar ratio SiO₂/M₂O (M = alkali metal) from 1.6 to 4, the carbonate being present in an amount from 5 to 55% by weight based on the total weight of the silicate and the carbonate, and the weight proportion of the water associated with the silicate and carbonate (solids content), is at least 33/100 and preferably 36/100.
The total amount of "builder" is preferably about 0.2% to 80%, preferably 20% to 45%, of the total weight of the detergent composition,
(2) bleaching agents, e.g. a perborate, percarbonate, chloroisocyanurate or N,N,N',N'-tetraacetylethylenediamine (TAED) in an amount of up to 30% of the total weight of the detergent composition,
(3) anti-redeposition agents, e.g. carboxymethyl cellulose or methyl cellulose in an amount up to about 5% of the total weight of the detergent composition, and
(4) fillers, e.g. sodium sulfate for pulverulent detergents in an amount up to 50% of the total weight of the detergent composition.

Various additives can optionally be added to the detergent composition described above in order to obtain detergent or cleaning products in powder or liquid form.
The detergent compositions may be prepared by a process which yields a dry, free-flowing granular mixture, for example by agglomeration or spray-drying. However, the compositions of the invention are not limited to such forms, and may also be formulated in other dry forms, such as tablets or beads, or may be formulated as pastes, gels or liquids. Examples of suitable formulations are given below.
The invention includes within its scope a method for inhibiting calcium carbonate crystal growth in a washing bath which involves incorporating a composition as described above in the bath. By "washing bath" is meant an aqueous solution of detergent used for washing, e.g. an aqueous solution present in a washing machine during the wash cycles.
The following Examples illustrate the invention.

EXAMPLE I

A detergent composition was prepared by mixing:

Ingredient		Proportion
Surfactants:	Linear alkylbenzenesulphonate	30-80
	Ethoxylated lauric acid	1-20
Builder:	Zeolite	24
	Sodium carbonate, anhydrous	10
	Sodium silicate	1-5
Bleach:	Sodium perborate	15
	T.A.E.D.	2
Additive:	N,N-dicarboxymethyl-2-aminopentane-1,5-dioic acid, tetra-sodium salt	3
Enzymes:	Alcalase	0.15
	Savinase	0.15
Processing aid:	Sodium sulphate, anhydrous	q.s.p. 100

To assess the effectiveness of this composition in inhibiting CaCO₃ crystal growth, the constant composition technique is used at low constant supersaturation. This technique is advantageous as it makes it possible to keep constant the chemical composition of the solution by stoichiometric additions of reactants.
The crystal growth experiments are made in a 100 ml cell. The temperature is maintained at 35°C. Stable supersaturated solutions of calcium carbonate are prepared. The tested inhibitor is added as a concentrated solution of alkaline potassium salt. Addition of seed crystal is made with a seed slurry of calcium carbonate. The pH is brought to 8.55 by adding potassium hydroxide. The addition of seed crystal results in an onset of CaCO₃ crystal growth and a lowering of the pH of the solution, which is immediately restored to its preset value by simultaneous addition of the two titrant solutions. The rate of crystallisation is calculated from the volume of titrant solution added (M/l.s. = moles of CaCO₃ precipitated per litre of solution per second).
The kinetic results shown in the following Table I were obtained with a lower concentration of additive (250 ppm) than usual with polymer (500 ppm). They prove the great activity of the tested compound in inhibiting CaCO₃ crystal growth. TABLE I

V(CaCO₃) (M/l.s.)

without additive >10⁻⁴

N,N-Dicarboxymethyl-2-aminopentane-1,5-dioic acid 2. 10⁻⁷
This table shows the good properties of N,N-dicarboxymethyl-2-aminopentane-1,5-dioic acid as a CaCO₃ crystal growth inhibitor. This amino polycarboxylic can thus be used as a direct replacement for ethylenediaminetetraacetic acid. Furthermore, since this amino-polycarboxylic acid is a derivative of a natural product and is 100% biodegradable, it is more environmentally acceptable than ethylenediaminetetraacetic acid.

EXAMPLE II

Formulation of a dishwasher detergent composition containing N,N-dicarboxymethyl-2-aminopentane-1,5-dioic acid.

Table II below gives the composition of two dishwasher detergents A and B, B incorporating the new CaCO₃ crystal growth inhibitor and A being a control detergent without this compound but including citrate.

TABLE II

	A	B
Cogranulate	56	56
Sodium Citrate 2H₂O	25
Colloid 245 G ^R	3	3
N,N-dicarboxymethyl-2-aminopentane-1,5-dioic acid		25
Enzyme	1	1
Sodium Perborate Monohydrate	11	11
T.A.E.D.	2	2
Surfactant	2	2

(Cogranulate compositions: carbonate/silicate ratio: 70/30; water content (by weight) 18.6; non bulk density g/cm³: 0.9; median diameter 1.00 mm;)

The mixtures were prepared by dry mixing in a Lödige ^Rmixer. All the powders were incorporated, and then mixed for approximately 5 minutes. The surfactant was then slowly introduced into the mixture via a dropping funnel. The detergent obtained was fluid and did not aggregate into lumps.

EXAMPLE III

This Example shows the antifilming capacity of the dishwasher detergent compositions of Example II.
Apart from the actual washing, namely, the removal of soiling deposited on cooking or feeding utensils, the appearance of glasses is definitely the feature of which the user is most aware. The quality of the rinse and of the drying are thus predominant. It is customary to use the term filming or spotting to characterise these defects in appearance.
The experiments were carried out in a MIELE D G 560 ^R automatic dishwasher possessing a short program at 65°C with a final hot rinse and drying. The total duration of the cycle was approximately 50 minutes. No rinsing product used. The concentration of the tested formulation is 3g/l.
A sequence of 10 consecutive washing/drying runs was then performed on 2 glass slabs each measuring 20 cm x 20 cm. Initially, the glassware was clean and free from defects. The washing are performed by using a water having a high hardness of about 300 ppm CaCO₃.
The appearance of the glassware was measured using a GARDNER ^R spectrometer, superposing a black slab on the glass slab to be measured. In this manner, the increase in opacity of the bloom was monitored by the parameter L measured in the GARDNER ^R spectrometer. The higher the value of L, the more substantial the bloom.
Table III reports the results: TABLE III

Detergent Formulation A B

L (Filming) 7,4 5,6
Thus the detergent in accordance with the invention (B) gives superior results to the comparison detergent.

Claims

A method for inhibiting or preventing CaCO₃ crystal growth in a medium in which such growth may occur which comprises incorporating in said medium an effective amount of N,N-dicarboxymethyl-2-aminopentane-1,5-dioic acid or a salt thereof.
A method according to claim 1 in which the said medium is a washing bath.
A method according to claim 1 in which the said medium is a detergent in concentrated or diluted form.
A method according to any one of the preceding claims in which the said acid is used in the form of its tetra sodium salt.
A method according to any one of the preceding claims in which the said acid or salt thereof is present in the medium in a concentration of from 0.1 to 15 percent by weight.
A method according to claim 5, in which the said concentration is 0.3 to 5 percent by weight.
Use as a CaCO₃ crystal growth inhibiting composition of N,N-dicarboxymethyl-2-aminopentane-1,5-dioic acid or a salt thereof.
Use according to claim 7 in a detergent composition.
Use according to claim 8 of a substoichiometric amount of the said acid or salt thereof.
A detergent composition comprising, as a CaCO₃ crystal growth inhibitor, N,N-dicarboxymethyl-2-aminopentane-1,5-dioic acid or a salt thereof.
A composition according to claim 10 comprising 0.1 to 15 percent, preferably 0.3 to 5 percent, by weight of the said acid or salt thereof.