WO1999019011A1

WO1999019011A1 - Anti-caking agents

Info

Publication number: WO1999019011A1
Application number: PCT/EP1998/006247
Authority: WO
Inventors: Johannes Adrianus Cornelis Van Ooijen
Original assignee: Verdugt B.V.
Priority date: 1997-10-09
Filing date: 1998-09-30
Publication date: 1999-04-22
Also published as: AU1028799A; GB9721397D0

Abstract

This invention relates to a free-flowing composition comprising hydrated sodium acetate and a magnesium salt which is a carboxylate or a hydroxycarboxylate and a process for making the same. One of the principal advantages of using magnesium salts over silica as an anti-caking agent is that magnesium carboxylates and hydroxycarboxylates are soluble in the same solvents as sodium acetate and in chemical activity they are substantially similar to sodium acetate.

Description

ANTICAKΪNG AGENTS

This invention relates to novel compositions comprising sodium acetate and an anti-caking agent.

It is well known that sodium acetate, especially anhydrous sodium acetate, is highly hygroscopic and that when stored in powder or solid form, it has a high tendency to absorb moisture and thereby caking. This results in the formation of lumpy material which is difficult to handle and/or break up. It is conventional in the industry to use silica and silicate salts as anti-caking agents, though not necessarily for use with sodium acetate. One of the problems with silica is that it is insoluble in water whereas sodium acetate is often used as an aqueous solution. Furthermore, silica is chemically substantially dissimilar to sodium acetate and hence any reactions in which sodium acetate is used even in solid form may suffer from the presence of a substantially alien component such as silica. Prior published US-A-3560380 describes dry concentrate for making hemodialysis solutions comprising as major components dextrose, sodium chloride and sodium acetate along with smaller amounts of the chlorides or acetates of calcium, magnesium and sometimes potassium. The sodium acetate component of the formulation having a moisture content sufficiently low for use in such solutions are said to be conveniently prepared by spray-drying a concentrated sodium acetate solution. This is then combined with ordinary anhydrous grades of the other components to prepare dry hemodialysis concentrates which resist caking and discolouration if protected from external moisture. Thus, the compositions described in this patent not only need the use of sodium acetate which has been spray dried but all the other components have to be anhydrous. Furthermore, this document is silent on which of the components is the cause of caking - it is well known that one of the major ingredients is sodium chloride which is highly prone to caking - and which of the minor components added to the major components reduces caking. The patent states that previously, after a time, the dry concentrates became caked and discolored and underwent other deleterious chemical changes. The patent, identifies a major cause of "these changes" - presumably meaning the recited deleterious chemical changes but not the problem of caking - having been traced to the moisture present in the sodium acetate (col. 1, lines 49-56). Each of the Examples in this US patent contains magnesium acetate, calcium chloride, potassium chloride and dextrose in addition to spray-dried sodium acetate and sodium chloride apart from Example 2 in which potassium chloride is omitted. In Example 1 it is stated that the sodium acetate used had a moisture content of less than 0.2% by weight and that the total moisture content of the concentrate did not exceed 0.75% by weight. This document further states that it was not possible to achieve these limits using commercially available anyhydrous sodium acetate which is said to contain at least 0.5% by weight moisture. Hence the need to spray-dry such sodium acetate prior to use in the dry concentrate. Thus, it does not identify what is responsible for caking of the concentrate and which of the minor components is making the dry concentrate resistant to caking. A more recent US- A 4756838 describes a method of preparing dry dialysate products which are said to be chemically homogeneous granules and which are dry, non-caking, free- flowing and readily soluble systems. The formulations described in the '838 patent are said to comprise an intimate admixture of sodium acetate and sodium chloride and physiologically acceptable salts of magnesium and calcium, for example, magnesium chloride and calcium chloride. The products of the '838 patent contain in addition bicarbonates as an alkalizing agent. Optionally, potassium salts, eg chloride, lactate ions and/or gluconates may also be present. Importantly, the feature of the invention in the '838 patent is the formation of the dry dialysate as chemically homogeneous granules which exist as a "micro homogeneous mixture" of discrete particles of simultaneously formed mixed small crystals or amorphous forms of components. This patent goes on to state that "The low water content, absence of fines and somewhat open, i.e., porous, granular structure mitigates against bulk caking during storage and during the solution process" (col. 1, lines 42-45). Thus, the resistance to caking is attributed not to the chemical components of the formulation but to the specific structure/mesh size of the granules. Moreover, the process of producing these granules comprises (a) intimately mixing by handworking sodium acetate with calcium, magnesium and potassium chlorides as the corresponding hydrated salts in a mortar to form a chemically homogeneous mixture and vacuum drying the same in an oven at about 120°C under static conditions to produce an anhydrous product and (b) crushing the anhydrous product so as to enable it to pass through a 20 mesh US standard screen. There is no mention of the use of any magnesium carboxylate in the '838 patent.

As can be seen, these processes for making sodium acetate cake resistant are complex and capital intensive and need a number of chemicals. In any event, the above patents are specific for formulations comprising sodium acetate and are for hemodialysis use only.

It has now been found that the problem of caking in hydrated sodium acetate can be mitigated by the use of a suitable magnesium salt.

Accordingly, the present invention is a free-flowing composition comprising hydrated sodium acetate and a magnesium salt which is a carboxylate or a hydroxycarboxylate.

The magnesium salt is suitably present in the composition in powder form. In particular, the magnesium salt is preferably, magnesium acetate or magnesium citrate. It is preferable that the magnesium salt is anhydrous although some hydrated forms of magnesium salts can also be effective. The amount of magnesium salt present in the composition to prevent the tendency of sodium acetate to cake is suitably at least 0.05 % by weight with respect to the sodium acetate in the composition, and can be 100% by weight (ie in an amount equivalent to the weight of the sodium acetate therein) since a salt such as e.g. magnesium acetate is itself free flowing. However, the amount of magnesium salt present in the composition with respect to its sodium acetate content is preferably from 0.1-20% by weight and even more preferably from 0.5 to 10% by weight.

The particle size of the hydrated sodium acetate which is to be treated with an anti-caking agent is suitably in the range from 200-1000 microns and the particle size of the magnesium salt present in said composition as the anti-caking agent is suitably from 20-150 microns, preferably from 60-80 microns.

According to a further embodiment, the present invention is a process for making a free-flowing composition comprising hydrated sodium acetate, said process comprising admixing with said composition a magnesium salt which is a carboxylate or a hydroxycarboxylate. One of the principal advantages of magnesium salts over silica as an anti-caking agent is that magnesium salts, especially the carboxylates and hydroxycarboxylates, are soluble in the same solvents as sodium acetate and in chemical activity they are substantially similar to sodium acetate. The present invention is further illustrated with reference to the following

Examples. EXAMPLES:

Magnesium acetate was intimately mixed with sodium acetate trihydrate in a nauta mixer under conditions of ambient temperature and pressure at levels of 0, 2, 4 and 6% by weight with respect to the amount of sodium acetate trihydrate in the mixture. The mixtures were packed in 25 kg polyethylene-lined paper bags and stored under 1000 kg/m² pressure in air. After 6 months storage, the packages were re-opened and the stored mixtures re-examined. It was found that the sodium acetate trihydrate with 0% magnesium acetate (not according to the invention) had become lumpy with severe caking. The mixture containing 2% by weight magnesium acetate formed very small lumps which could be readily broken up. The other two mixtures, which respectively contained 4% and 6% by weight magnesium acetate, remained free flowing.

The above experiments were repeated with mixtures of anhydrous sodium acetate and anhydrous magnesium acetate with similar results.

Claims

Claims:

1. A free-flowing composition comprising hydrated sodium acetate and a magnesium salt which is a carboxylate or a hydroxycarboxylate.

2. A free-flowing composition according to Claim 1 wherein the magnesium salt is present in said composition in powder form.

3. A free-flowing composition according to Claim 1 or 2 wherein the magnesium salt is magnesium acetate or magnesium citrate.

4. A free-flowing composition according to any one of the preceding Claims wherein the magnesium salt is anhydrous.

5. A free-flowing composition according to any one of the preceding Claims wherein the amount of magnesium salt present in said composition with respect to its sodium acetate content is at least 0.05 % by weight.

6. A free-flowing composition according to any one of the preceding Claims wherein the magnesium salt is present in an amount ranging from 0.1-20% by weight of the composition with respect to the sodium acetate content thereof.

7. A free-flowing composition according to any one of the preceding Claims wherein the magnesium salt is present in an amount ranging from 0.5 to 10% by weight of the composition with respect to its sodium acetate content.

8. A free-flowing composition according to any one of the preceding Claims wherein the particle size of the hydrated sodium acetate is in the range from 200- 1000 microns and the particle size of the magnesium salt is in the range from 20- 150 microns.

9. A free-flowing composition according to any one of the preceding Claims wherein the particle size of the magnesium salt in said composition is from 60-80 microns.

10. A process for making a free-flowing composition comprising hydrated sodium acetate, said process comprising intimately mixing with said composition a magnesium salt which is a carboxylate or a hydroxycarboxylate.