GB2128979A - Treatment of oil slicks on seawater - Google Patents

Abstract

The process for disposing of oil slicks on seawater consists in treating the polluted seawater with a liquid dispersing composition and with a nitrogen-containing nutrient for the micro-organisms which are active in oil metabolism. The nutrient is a diguanidinium salt XH.H2N - C(=NH) - NH - R - NH - C (NH) - NH2.HX wherein R is an alkyl radical containing from 2 to 12 carbon atoms and X is a halogen or an acid anion.

Description

SPECIFICATION Process for disposing of oil slicks The present invention relates to a process for disposing of oil slicks on seawater and it relates more particularly to a process for improving the biodegradation of oils polluting seawater. The invention is also concerned with dispersing compositions for treating oil slicks.

Pollution of seawater by oil (crude oil or fractions of crude oil) occasioned by accidents, offshore drilling operations and/or discharge of ballast water or spillage from oil tankers, results in the formation of a continuous film or slick of oil which tends to continuously spread. In open seas, this oily film is undesirable because it constitutes a barrier to the transfer of air and light from the atmosphere into seawater which are indispensable to support marine life. In coast waters, the oily film does damage to the crustacea beds and to the beaches.

One way of dealing with such pollution problems is to use oil dispersing compositions containing surface-active compounds. These compositions are applied on the oil slicks, generally by spraying mans.

They desintegrate the cohesive oily film into small droplets and disperse the droplets into the water column to a depth of several meters under the sea surface. The film is thus broken and there is again a transfer of air and light from the atmosphere. Moreover, fauling of the solid structures and beaches along the coasts is avoided.

The oil droplets which are dispersed under the sea surface are then biodegraded and consumed by micro-organisms which are living in seawater and are active in oil metabolism. This biological degradation is however a relative slow process and is consequently unable to prevent the settling of undegraded oil droplets and the formation of oil deposits on the floor of seas, more particularly where the water is shallow.

An active biodegradation of oil droplets needs the presence of a high amount of micro-organisms at the oil-water interfaces. However, these organisms are present in seawater in limited quantities. In order to stimulate the biodegration, it is therefore necessary to speed up the proliferation of the micro-organisms. To this end, they need not only oxygen and carbon, which are present respectively in water and in polluting oils, but also nitrogen and phosphor. Generally, the concentration in these latter two elements is very low in seawater and consequently the natural biodegradation of oil is a very slow process.

In order to increase the biodegradation rate, it has been proposd to add microbial nutrients to sea water.

Mineral salts, such as ammonium salts,nitrates and phosphates, have been used. But these mineral salts are too water soluble and have practically no affinity for the polluting oil. They are too quickly dissolved and dispersed into seawater and are not maintained at the oil-water interface where their presence is needed.

It has also been suggested to use nitrogen-containing organic nutrients which are oleosoluble, such as condensation products of urea or melamine with aldehydes. However, these organic compounds are also soluble in water. They dissociate from the oil and are dissipated into the aqueous phase. In order to overcome this disadvantage, it has been proposed to modify the solubility in water. For instance, condensation products of urea and an aldehyde containing less than four carbon atoms are first absorbed on an inert carrier and are then rendered lipophilic by coating with a paraffinic or other protective colloid. These treatments require special equipment and they increase the cost of nutrients. Furthermore, the coating may be quickly dissolved if the polluting oil, such as a fresh crude oil, contains aromatic hydrocarbons.

Other techniques have been suggested to reduce the solubility of nutrients in water, but the result is compositions which only float on the water surface. These nutrients will not then promote the development of micro-organisms into the water column under the sea surface where the oil droplets are dispersed.

The difficulties encountered with prior art nutrients have been overcome by the development of new lipophilic nutrients for the micro-organisms which are present in seawater and are active in oil degradation.

These new nutrients achieve a rapid and more complete biodegradation of the oils, at low cost.

It is an object of the present invention to provide a process for disposing of oil slicks on seawater by treating the poluted water with a dispersing composition and with a nitrogen-containing compound which is poorly soluble and is stable in water.

It is another object of the invention to improve the biodegradation rate of the polluting oil by treating the polluted water with a dispersing composition and with a nitrogen-containing compound which increases the development of micro-organisms which are active in oil metabolism.

A further object of the invention is to provide, as nutrient for the micro-organisms, a nitrogen-containing compound which is oleophilic and which exhibits a low toxicity towards aquatic flora and fauna.

It has now been found that unexpected results are obtained in terms of oil-dispersing efficiency and biodegradation by micro-organisms by treating the oil polluted seawater with a dispersing composition and with a nitrogen-containing nutrient for the micro-organisms, said nutrient consisting of a diguanidinium salt having the general formula

wherein R is an alkyl radical containing from 2 to 12 carbon atoms and X is a halogen or an acid anion.

The process of the present invention for disposing of oil slicks on seawater consists essentially in treating the oil slicks with a dipsersing composition and with a diguanidinium salt as hereinabove defined.

The diguanidinium salts are easily prepared by a known method by reacting a diamine salt XH.H2N-R-NH2.HX with cyanamid H2N-Cs N, R and X being as hereinabove mentioned. An amine salt or a mixture of amine salts may be used. The molar ratio between the diamine salt and cyanamid is at least 1: 2.

By way of example, 1 ,6-bisguanidinohexane hydrochloride

is prepared from 1 ,6-diaminohexane and cyanamid. To this end, 1 mole of diamine, which has been previously dried and dissolved in isopropyl alcohol, is introduced into a flask, equiped with a stirrer, a thermometer and an outlet tube linked to a Dan and Stark decanter provided with a water cooler. Then, 3 moles of hydrochloric acid are slowly introduced into the flask. After reaction, water and isopropyl alcohol are removed. Xylene is then added and the mixture is heated under reflux in order to remove any remaining water. When the temperature of the mixture has decreased down to about 80 C, 2 moles of cyanamid are added and the reaction mixture is heated at 1400C for 2 hours.After cooling, the reaction mixture is filtered, washed with alcohol, stirred at 60 C for 30 minutes in the presence of alcohol containing about 1% active carbon and filtered on a millipore filter. After elimination of residual solvent, 1,8bis 1 ,6-bisguanidinohexane chloride is obtained with a yield of 98%.

The nitrogen content of the diguanidinium salts depends upon the specific R and X, but it lies generally in the range of about 15 to about 40%.

Diguanidinium salts where the radical contains 12 or even more carbon atoms may be used. However, taking into account the availability and the price of the diamine,it is more advantageous to prepare diguanidinium salts wherein the radical R contains up to 8 carbon atoms. Moreover, as a function of the selection of the radical R and of X, one can prepare diguanidinium salts which are sufficiently soluble or which can be suspended in most dispersing compositions used to dispose of oil slicks. Diguanidinium salts wherein the radical R contains from 2 to 6 carbon atoms have this characteristic and therefore they may be applied as a solution or a suspension in these dispersing compositions. If the diguanidinium salt is not soluble or cannot be suspended in dispersing compositions, it can be added to the polluted water, either before or after application of the dispersing composition.

In the above given formula, X may be a halogene, more particularly Cl, or an acid anion, such as the radical of sulphuric acid, nitric acid, methyl- or ethylsulphuric acid, alkylbenzenesulphonic acid, acetic acid, lactic acid or similars. For economic reasons, it may be advantageous to prepare disguanidinium salts where X is Cl or the radical of sulphuric acid, nitric acid or acetic acid. The radical X may also be selected in order to obtain diguanidinium salts which are soluble or easily suspended in the usual dispersing compositions. By way of example, diguanidinium salts wherein R is the dodecyl radical are practically insoluble in most dispersing compositions when X is Cl, but are soluble in these compositions when X is the radical of lactic acid.

In order to promote the development of micro-organisms, the diguanidinium salts are advantageously employed in admixture with a phosphorous compound, acting also as a nutrient to supply phosphorous. The phosphorous compound may be an alkaline or alkalino-earth salt of phosphoric ester of fatty alcohol, a salt or an ester of organophosphonic acid or a phosphatide or similar product having a low toxicity towards aquatic flora and fauna. Esters obtained by neutralization of hexamethylene diamine tetra (methylene phosphonic acid) of formula (H2PO3CH2)2 - N(CH2)6N -(CH2PO3H2)2 with an amine, such as monoethanolamine or a fatty amine containing from 12 to 18 carbon atoms, give good results.Phosphatic or phospholipides, more particularly lecithin or kephaline, act at the same time as source of nitrogen and phosphorous, and thus they reinforce the action of the disguanidinium salts.

According to a preferred embodiment of this invention, diguanidinium salts wherein the radical R contains up to 8 carbon atoms are preferably employed. They are used as a solution or a suspension in dispersing compositions containing at least one surface-active compound and at least one solvent exhibiting a low toxicity towards aquatic flora and fauna.

As surface-active compound, it may be cited ethoxylated tall oil, mono- or polyesters of polyhydroxylic alcohols, more particularly the esters of saturated or not saturated aliphatic carboxylic acids containing from 12 to 20 carbon atoms and of alcohols, such as sorbitol, glycerol and polyethyleneglycol. Mixtures of two or more than two of these esters may be used, with the optional addition of other surface-active agents, such as ethoxylated fatty alcohols, alkaline salts of dialkyl sulphosuccinates or condensation products of ethylene oxide or propylene oxide on the above mentioned esters.

The surface-active agents are dissolved in at least one solvent having a low toxicity towards aquatic flora and fauna. The solvent has a double action: it makes easier the handling and the application of the surface-active agents and moreover, due to its affinity, it promotes the penetration of the composition into the oil film. As solvents, it may be cited liquid hydrocarbons containing less than 5%, and preferably less than 3% aromatic compounds. Liquid hydrocarbons having from 5 to 20 carbon atoms, such as paraffinic hydrocarbons containing from 6 to 12 carbon atoms, cycloparaffinic hydrocarbons, by example cyclopen tane and cyclohexane, alkylcycloparaffinic hydrocarbons and naphtenic hydrocarbons are preferably used.

Aliphatic alcohols containing up to 8 carbon atoms, such as ethyl-, propyl- and isopropyl alcohols, and glycols monoethers, more particularly monoalkylethers (where the alkyl radical contains from 1 to 4 carbon atoms) of glycols, such as mono or diethyleneglycol and mono- or di-propyleneglycol are also suitable solvents. The organic solvent may also contain water-in an amount which does not exceed the amount of organic solvent.

The weight ratio of surface-active agents to solvent may vary between wide limits. It is of course desirable to employ compositions which are as concentrated as possible, but the amount of solvent in the composition must be sufficient to dissolve the surface-active agents and nutrients and also allow the application of the composition at low temperatures. It has been found that compositions containing more than about 85% of surface-active agents and nutrients are too viscous at lowlow temperatures. Moreover they do not easily penetrate into the oil slick and they are therefore less active. On the other hand,compositions containing less than about 30% of surface-active agents and nutrients have a low effectiveness.

The amount of dialkylguanidinium salt in the dispersing compositions may vary between relatively wide limits and may be as high as 35% or even more, based on the total weight of composition. This amount depends upon many factors, such as the specific guanidinium salt used and its nitrogen content, the optional presence of other nutrients and the specific solvent used. Compositions containing from about 2 to 20 wt %, and more particularly from about 5 to about 15 wt %, of dialkylguanidinium salt are very effective with respect to the biodegradation of oil droplets dispersed in seawater.

The compositions of the present invention may also contain other components and elements such as magnesium and calcium which are useful for the development of micro-organisms. The compositions contain these elements in the form of organic salts, namely in the form of magnesium or calcium salt of alkylbenzenesulphonic acid. The amount of these additives does not generally exceed about 3 %, based on the total weight of the composition.

The compositions are applied on the oil slicks by using any known method. They may be used after dilution by water. They may be sprayed on the oil slicks from aircrafts or from boats which are provided with suitable spraying means.

Example 1 The following dispersing composition was prepared (parts by weight) 53 diethyleneglycol monobutylether 23 polyethyleneglycol monooleate (mean molecular weight of the glycol: 400) 6,5 sorbitan monolaurate 9,5 water 8 bisguanidinobutane hydrochloride The toxicity of this composition was determined by subjecting the species Artemia salina to increasing doses of the composition to determine the maximum amount of composition which, after 24 hours, will still leave 50% of the tested species alive (test CL 50-24 hours). it was found that the toxicity was 3 500 ppm.

Biodegradation effectiveness is determined by the following method: 200 ppm of the tested composition are added to unsterilized seawater (700 ml) containing topped crude oil (5000ppm). This is left to incubate for 41 days at 25 C, while being stirred by air bubling. The residual oil is then extracted. It was found that the biodegradation effectiveness with the above given composition was 1.8 times higher than with a similar but nutrient-free composition and 1.4 times higher than with a similar composition containing ammonium nitrate instead of bisguanidinobutane hydrochloride.

Example 2 A composition as described in Example 1 was prepared, but by using bisguanidinoethane hydrochloride as diguanidinium salt.

The characteristics of this composition, with respect to toxicity and biodegradation effectiveness, were the same as the characteristics of the composition of Example 1.

Example 3 Thefolowing dispersing composition was prepared (parts by weight): 16.75 sorbitan monooleate 13.50 ethoxylated sorbitan monooleate (about 20 moles of ethylene oxide) 24 sodium salt of di(2-ethylhexyl) sulphosuccinate (a 75% aqueous solution) 11,24 water 12 monoethyleneglycol monobutylether 2.50 diethyleneglycol 15 bisguanidinohexane nitrate 5 monoethanolamine ester of hexamethylenediamine tetra (methylenephosphonic acid).

With this composition, the biodegradation effectiveness was 1.8 times higher than with a similar, but nutrient-free composition.

Example 4 Acomposition as described in Example 3 was prepared, but by using bisguanidinohexane lactate as nitrogen-containing nutrient.

The biodegradation effectiveness was 1.6 times higher than with the nutrient-free composition.

Example 5 Bisguanidinododecane acetate was prepared from 1,4 -diaminododecane acetate and cyanamid.

50 ppm of a mixture containing 65% of this biguanidinium salt and 35% lecithine were added to unsterilized seawater (700 ml) containing topped crude oil. 150 ppm of a commercial dispersing compositior were then added. The mixture was maintained at 25 C for 41 days, while being stirred by air bubling. The.

residual oil was extracted by methylene chloride.

It was found that the biodegradation effectiveness was 1.7 higher than with the nutrient-free dispersing composition.

Claims (11)

1. Process for disposing of oil slicks on seawater characterized in that it consists in treating the polluted seawater with a liquid dispersing composition and with a nitrogen-containing nutrientforthe microorganisms which are active in oil metabolism, said nutrient being a disguanidinium salt having the general formula:

wherein R is an alkyl radical containing from 2 to 12 carbon atoms and X is a halogen or an acid anion.

2. Process according to claim 1, characterized in that R is an alkyl radical containing from 2 to 8 carbon atoms.

3. Process according to claim 2, characterized in that R contains from 2 to 6 carbon atoms.

4. Process according to claim 1, characterized in that X is selected from the group containing Cl and the anions of nitric acid, sulphuric acid, methyl- or ethylsulphuric acid,alkylbenzenesulphonic acid, acetic acid, lactic acid.

5. Process according to claim 1 characterized in that it consists in treating the polluted seawater with a liquid dispersing composition containing at least one surface-active compound, at least one solvent and at least a diguanidinium salt which is at least easily dispersed in said composition.

6. Liquid dispersing composition for the process according to claim 5, characterized in that said composition contains at least one surface-active compound, at least one solvent for said compound and a diguanidinium salt wherein R contains 2-6 carbon atoms.

7. A composition according to claim 6, characterized in containing up to 35% of diguanidinium salt.

8. A composition according to claim 7, characterized in containing 2 - 20% of diguanidinium salt.

9. A composition according to claim 8, characterized in containing 5 - 15% of diguanidinium salt.

10. A composition according to claim 6, characterized in containing also a phosphorous compound acting as a nutrient for the micro-organisms.

11. A composition according to claim 10, characterized in containing from about 30 to about 85 wt % of surface-active compound, diguanidinium salt and phosphorous compound.