GB2120924A - Aqueous formaldehyde solutions - Google Patents

Abstract

Aqueous formaldehyde solutions contain polyacrylamide or methyl vinyl ether/maleic anhydride copolymers as vapour release suppressants. The compositions are particularly of use as silage preservatives preferably mixed with an acid such as sulphuric, formic, acetic, propionic or isobutyric.

Description

SPECIFICATION Aqueous formaldehyde solutions This invention relates to aqueous formaldehyde solutions.

Aqueous formaldehyde solutions are widely used for various preservative applications but their use give rise to objectionable odours and vapour losses. In extreme cases health hazards may result from the release of formaldehyde vapour.

We have found that the release of formaldehyde vapour from such aqueous solutions may be reduced by the addition of certain additives to the solution.

Accordingiy the present invention provides an aqueous solution of formaldehyde containing 0.05 to 2.5% by weight, based on the weight of formaldehyde in the solution, of a water soluble additive selected from polyacrylamide and/or a methyl vinyl ether/maleic anhydride copolymer.

It is well known that various stabilisers may be incorporated into aqueous formaldehyde solutions: such stabilisers generally act as polymerisation inhibitors. Examples of such stabilisers include urea, lower alcohols, in particular methanol, polyvinyl alcohols, glycerol, hydroxy or carboxy alkyl celluloses, gelatin, pectin, carrageenan, polyoxyethylene ethers of higher alcohols, and polyvinyl pyrrolidone. While some of these polymerisation inhibitors exhibit a vapour suppressant effect immediately upon addition to the formaldehyde solution, this effect is lost after storage of the solution for a short time. In most cases the storage time before any vapour suppressant effect is lost is less than 2 hours.

The solutions of the present invention may contain such stabilisers in addition to the additive of the invention.

The additive of the invention preferably has a moiecular weight above 50,000 particularly above 100,000.

The amount of the additive should be within the range 0.05 - 2.5, preferably 0.1 - 2, % by weight of the weight of formaldehyde in the solution.

The aqueous solution preferably contains 5 to 40% by weight of formaldehyde.

It will be appreciated that, when using methyl vinyl ether/maleic an hydride copolymers, the anhydride linkage is liable to cleavage in solution. The additive employed may be the copolymer or the polymeric acid, or a salt or partial ester thereof, resulting from such cleavage.

Aqueous formaldehyde solutions, unless buffered are somewhat acid, generally having a pH within the range 2.5 to 4, as a result of hydrolysis of a small amount of the formaldehyde to formic acid. Typically commercial aqueous formaldehyde solutions, i.e. formalin, contan 0.01 to 0.05, % by weight of formic acid.

The vapour suppressant additives are also effective in highly acid solutions, e.g. those having a pH below 2.

One particular application of highly acidified formaldehyde solutions, in which the additives may usefully be employed, is in ensilement processes. In this application the material being ensiled, e.g. grass, hay, cereals, grains, straw, maize, clover, lucerne, root crops such as sugar beet, including the tops thereof, and/or wastes from animal or fish processing, is treated with a preservative comprising an aqueous formaldehyde solution which contains one or more mineral acids, e.g. mineral acids such as hydrochloride, sulphuric, and/or phosphic acids, as described in GB-A-1276677, GB-A-1401420, and GB-A-1518808, the disclosures of which are hereby incorporated by reference, and/or organic acids, e.g. formic, acetic, propionic, and/or isobutyric acids.

Ensilement processes using aqueous formaldehyde solutions containing no additional acid are also known: the additives of the invention may of course also be used in such processes.

Preferred silage preservatives comprise a mixture of formalin (35 - 40% by weight aqueous solution of formaldehyde - generally stabilised with methanol) and the acid, together with any other stabilisers such as urea, and the additive of the invention, in proportions corresponding to 1 to 9, particularly 1 to 5, volumes of formalin (expressed as a 37% by weight solution of formaldehyde in water) to 1 volume of 5 M acid.

It is not, however, necessary to use 5 M acid: other strength acids can be employed and the volumes used modified accordingly.

The strength of the acid employed is preferably between 1 and 10 M and in particular is above 3 M in order to minimise the volume of the acid/formalin mixture that has to be applied to the material being ensiled.

The silage preservative solution is typically applied at a rate of 2 to 5 litres per tonne (fresh weight) of material being ensiled.

When used in conjunction with formaldehyde containing silage preservatives, the additive of the present invention may be incorporated into the formaldehyde solution during the manufacture of the silage preservative or may be added to the solution just prior to use for ensilement.

The use of the additive of the invention in formaldehyde containing silage preservative compositions may provide a greater preservative effect on the material being ensiled as a result of the reduced formaldehyde vapour losses.

The invention is illustrated by the following examples. In Examples 1 to 5 the formaldehyde vapour emission from the test solution was measured by the following technique.

The test solution is continuously poured at a rate of 17 ml/min down the surface of a vertical glass rod of about 1cm diameter extending co-axiallythrough a vertical glass tube 183 cm long and 2.54cm internal diameter. The glass tube is provided with a sampling port of 0.635 cm internal diameter midway along its lenath to which a 100 ml aas tiaht svrinae is fitted. 1 Minute after commencing flow of the test solution down the tube a 10 ml sample of the vapour in the tube is drawn into the syringe. Further 10 ml samples are drawn into the syringe at 10 second intervals. When 10 samples have been taken, the flow of the test solution is stopped and the 100 ml of gas in the syringe expressed into a chromotropic acid solution to absorb the formaldehyde from the gas in the syringe. The formaldehyde is then assayed spectrophotometrically.

Example 1 Test solutions were made up by adding various amounts of a polyacrylamide ("Superfloc" N-100 Cyanamid of Great Britain Ltd) to an aqueous solution containing 66% by weight of 37% formalin and 15% by weight sulphuric acid (expressed as 100% acid). The results are shown in Table 1.

TABLE 1 Concentration of Concentration of polyacrylamide formaldehyde in Example (% by weight) sampled gas Fgiml S F 1A* 0 0 12.9 1be 0.01 0.04 14.8 1C 0.02 0.08 10.5 1D 0.03 0.12 6.9 1E 0.04 0.16 6.0 1F 0.05 0.20 6.5 1G 0.10 0.41 7.2 * comparative S - based on weight of test solution F - based on weight of formaldehyde in test solution Example 2 Example 1 was repeated using a methyl vinyl ether/maleic anhydride copolymer ("Gantrez" AN-149; GAF Corporation) in place of the polyacrylamide. In this example the test solution were stored for various times before testing. The results are shown in Table 2.

TABLE 2 Concentration ofmethyl vinyl etherlmaleic Concentration of anhydride copolymer Storage time formaldehyde in Example (% by weight) (days) sampled gas Fjxglml) S F 2A* ) 1 11.1 2B* ) 2 13.5 2C* ) 3 11.9 2D* ) 4 11.9 2E* )- 0 0 5 12.5 2F* ) 6 14.9 2G* ) 13 11.1 2H* ) 21 11.0 21 ) 1 4.7 2J ) 0.25 1.02 6 5.5 2K ) 21 4.5 2L ) 1 2.9 2M ) 2 2.7 2N (- 0.3 1.23 3 3.1 20 ) 4 3.2 2P ) 13 2.9 * comparative S based on weight of test solution F based on weight of formaldehyde in test solution.

Example 3 Test solutions were made up from 60 ml (66 g) of 37% formalin, 15 g of an organic acid, and deionised water to give 100 ml of the test solution. 0.3 g of the methyl vinyl ether/maleic anhydride copolymer used in Example 2 were then added.

TABLE 3 Concentration ofmethyl vinyl etherlmaleic anhydride copolymer (% Concentration of by weight of the weight formaldehyde in of formaldehyde in the sampled gas Example Acid test solution) ,ig/m) 3A* formic 0 5.3 3B 1.23 2.5 3C* acetic 0 4.5 3D 1.23 2.2 3E* propionic 0 4.5 3F 1.23 2.0 3G* isobutyric 0 3.6 3H 1.23 2.4 * comparative Example 4 {Comparative) By way of comparison Example 1 was repeated using (a) a partially hydrolysed polyacrylonitrile ("Matexil") and (b) a poly acrylic acid ('Versicol' E 21) in place of the polyacrylamide. The results are shown in Table 4.

TABLE 4 Concentration of additive Concentration of (% by weight) formaldehyde in sampled gas Example Additive S F { giml) 4A none 0 0 12.9 4B Matexil 0.3 1.23 11.2 4C Versicol E 0.1 0.41 13.2 4D Versicol E 0.2 0.82 13.0 4E Versicol E 0.3 1.23 12.3 4F Versicol E 0.5 2.05 10.4 4G Versicol E 1.0 4.10 9.7 S - based on weight of test solution F - based on weight of formaldehyde in test solution.

This example shows that, in a highly acid system, (the pH was about 1) large amounts of polyacrylic acid are required to give any significant vapour suppression.

Example 5 An aqueous formaldehyde solution containing 18% by weight of formaldehyde was made up and the additive materials used in Examples 1 and 2 were added to samples thereof, with the results shown in Table 5.

TABLE 5 Concentration ofadditive Concentration of % by weight formaldehyde in sampled gas Additive S F Fgiml none 0 0 4.0 polyacrylamide 0.03 0.17 0.9 methyl vinyl ether/ maleic anhydride copolymer 0.25 1.4 0.8 S - based on weight of test solution F - based on weight of formaldehyde in test solution.

Even in shuch a non-acidified solution, a large amount, over 5% (based on the weight of formaldehyde) of polyacrylic acid was required to give a similar degree of vapour suppression.

Example 6 In this Example, measurements of atmospheric formaldehyde concentrations were made during ensilement trials at 3 farms, using conventional farming practice employing tractor drawn harvesters which applied the silage preservative to the sward as it was harvested. The silage preservatives employed were those of Examples 2L and 2A, i.e with and without an additive in accordance with the invention; and were applied to the sward at a nominal rate of 5 1 per tonne of sward (fresh weight).

The atmosphere formaldehyde concentration (AFC) measurements we made with a portable instrument incorporating a fuel cell which generates a voltage proportional to the concentration of formaldehyde in the sample aspirated into the instrument.

A large number of measurements were taken of the AFC (a) during filling of the silage preservative tank on the harvester from a supply drum, (b) in the vicinity of the harvester during the harvester operation, and (c) inside the tractor cab during the harvesting operation.

The results for each trial were averaged and a Formaldehyde Index defined as AFC using formulation 2L x 100 AFC using formulation 2A was generated for each average. The formaldehyde indexes are quoted in Table 6.

TABLE 6 Formaldehyde index Farm A Farm B Farm C Filling harvester silage preservative tank 26 - During harvesting (a) around harvester 61 27 66 (b) inside tractor cab 47 26 Example 7 A silage preservative composition was made up as an aqueous solution containing 50% by weight of 37% formalin and 20% by weight sulphuric acid (expressed as 100% acid) To one half of the solution the methyl vinyl ether/maleic an hydride copolymer used in Example 2 was added in an amount corresponding to 1.7% by weight of the formaldehyde in the sample.

The resultant solutions, i.e. with and without the additive, were used to treat, under identical conditions, samples of fresh grass at a rate of 5 ml per kilogram and, at 15 minutes from treatment, i.e. before any significant protein binding had occurred, the grass samples were extracted and analysed for their formaldehyde content. The mean of 5 analyses for each test solution is quoted in Table 7.

TABLE 7 Formaldehyde content of treated grass Test solution parts per million rby weight) no additive 1260 methyl vinyl ether/ maleic anhydride copolymer added 1650 It is seen that the use of the additive of the invention results in a higher amount of formaldehyde retained by the grass.

Claims (9)

1. An aqueous solution of formaldehyde containing 0.05 to 2.5% by weight, based on the weight of formaldehyde in the solution, of a water soluble additive selected from polyacrylamide and/or a methyl vinyl ether/maleic anhydride copolymer.

2. An aqueous solution according to claim 1 wherein said additive has a molecular weight above 50,000.

3. An aqueous solution according to claim 1 or claim 2 containing 0.1 to 2% by weight, based on the weight of formaldehyde in the solution, of said additive.

4. An aqueous solution according to any one of claims 1 to 3 also containing an acid to give a solution of pH below 2.

5. An aqueous solution according to claim 4 comprising an aqueous solution of formaldehyde containing 35 to 40% by weight of formaldehyde in admixture with an aqueous solution of an acid, in proportions corresponding to 1 to 9 volumes of an aqueous formaldehyde solution containing 37% by weight of formaldehyde to 1 volume of 5 M acid.

6. An aqueous solution according to any one of claims 4 and 5 comprising a mixture of an aqueous formaldehyde solution and an aqueous solution of an acid having a strength between 1 and 10 M.

7. An aqueous solution according to any one of claims 4 to 6 wherein the acid is sulphuric acid.

8. An aqueous solution according to any one of claims 1 to 7 substantially as hereinbefore described and with specific reference to the Examples.

9. The use of an aqueous solution according to any one of claims 1 to 8 as an ensilement additive.