WO2008132768A1

WO2008132768A1 - Method for removing organic compounds, in particular hydrocarbons, btex, organic halogenated compounds and mineral oils, from water

Info

Publication number: WO2008132768A1
Application number: PCT/IT2007/000318
Authority: WO
Inventors: Rita Mastromarino
Original assignee: Rita Mastromarino
Priority date: 2007-04-27
Filing date: 2007-04-27
Publication date: 2008-11-06

Abstract

A method for decontaminating aqueous matrices containing organic pollutants such as BTEX, organic halogenated compounds, MTBE, mineral oils and hydrocarbons in general, comprises the steps of introducing a hydrocarbon solvent which is capable of dissolving the pollutants contained in the aqueous matrix arranged in a suitable container, stirring the blend resulting from said aqueous matrix and said hydrocarbon solvent and separating the hydrocarbon phase containing the pollutants from the purified aqueous phase. Said hydrocarbon solvent has a density ranging from 0,5 to 2,0 g/cm3, a solubility ranging from 0 to 1000 mg/l and a boiling temperature ranging from 40 to 300°C. In particular, said solvent is selected from the group consisting of n-decane, 1-decene, 1-octadecene, 1-hexadecene or mixtures thereof. The method according to the present invention allows to extract a wide range of organic contaminants from aqueous matrices by means of a single process and by using a solvent or a solvent mixture.

Description

METHOD FOR REMOVING ORGANIC COMPOUNDS, IN PARTICULAR HYDROCARBONS, BTEX, ORGANIC HALOGENATED COMPOUNDS AND MINERAL OILS, FROM WATER

The present invention relates to a method for decontaminating aqueous matrices polluted by organic compounds and in particular aqueous matrices contaminated by BTEX, halogenated organic compounds, MTBE, mineral oils and hydrocarbons in general.

Aqueous matrices polluted by organic compounds are, for example, groundwaters underlying various industrial plants such as refineries, plastic material manufacturing and/or processing plants, oil mills, etc. or groundwaters underlying commercial plants such as, for example, gas stations. The hydrocarbon compounds produced and/or used in the production, processing and distribution processes in the above-mentioned plants, if they come into contact with the soil, can permeate down to the aquifers thus polluting the water. Particularly dangerous pollutants are for example BTEX (acronym of benzene, toluene, ethylbenzene an xylene), organic halogenated compounds, MTBE

(methyl tert-butyl ether), mineral oils, organic compounds and hydrocarbons in general.

Methods for decontaminating polluted aqueous matrices are already known which in general have a specific and effective action on very limited groups of hydrocarbon pollutants or even on single pollutants. For example, patent US 5,282,974 discloses methods for removing benzene from process waters of the hydrocarbon industry by adding aluminium hydrochloride to water and subsequently separating benzene by solvent extraction. However, it is not specified which solvent can be used for extraction.

Patent US 6,045,696 discloses a process for purifying waste waters containing organic and inorganic sulphurous compounds, mercaptobenzothiazole, benzothiazole and/or derivatives of the last two, wherein waters are treated with an extraction agent which comprises salts of aliphatic amines and aliphatic and/or aromatic hydrocarbons. Kerosene and dodecane are mentioned as examples of aliphatic hydrocarbons which can be used for extraction. Patent JP 61212380 discloses a treatment for waste waters which contain an organic chlorine compound, such as for example dichloroethane and trichloroethylene, with a high-boiling hydrocarbon, such as for example liquid paraffin. The high-boiling hydrocarbon is introduced in a separation container wherein it sorbs the organic chlorine compound. Due to the difference of specific weight in the container two layers are formed: an upper layer containing the high-boiling hydrocarbons and the organic chlorine compounds, and a lower layer of decontaminated water. Decontaminated water is taken away, while the hydrocarbon layer is subjected to fractional distillation thus separating the organic chlorine compound from the high-boiling hydrocarbon which can be reused in the process.

As it is apparent from the analysis of the above-mentioned prior art documents, so far no general methods are known for decontaminating aqueous matrices which are effective with respect to all possible organic pollutants of the industrial waste waters.

Therefore, using decontaminating processes suitably designed and developed in view of specific water pollutants, or groups of pollutants, is essential.

Object of the present invention is thus to provide a method for decontaminating aqueous matrices which allows to effectively treat aqueous matrices polluted by a wide range of pollutants such as BTEX, organic halogenated compounds, MTBE, mineral oils, hydrocarbons and organic compounds in general. Said object is achieved by a process which essentially consists of decontaminating aqueous matrices by means of an extraction by a hydrocarbon solvent which is insoluble in water and particularly suitable to dissolve the above-mentioned pollutants. The main features of said process are specified in the first claim and other features are those specified in the following claims.

The main advantage of the process according to the present invention is the possibility to extract from aqueous matrices a wide range of organic pollutants by means of a single process and by using a single type of solvent. Another advantage provided by the process according to the present invention is the possibility to easily reuse the solvent for subsequent extraction steps of the above- mentioned pollutants from aqueous matrices.

Further advantages and characteristics of the process according to the present invention will be evident to those skilled in the art from the following detailed non- limiting disclosure of some embodiments thereof which are illustrated in the operative examples below. Aqueous matrices containing organic pollutants particularly belonging to the group comprising BTEX₅ organic halogenated compounds, MTBE, mineral oils and hydrocarbons are treated according to the present invention with a process comprising the following operative steps: a) adding to the aqueous matrix the hydrocarbon solvent capable of dissolving the pollutants contained in the aqueous matrix arranged in a ' suitable container, b) subsequently stirring the resulting blend, and c) finally separating the aqueous phase from the overlying hydrocarbon phase containing the above-mentioned hydrocarbon contaminants.

Numerous hydrocarbon solvents were tested for purifying the aqueous matrices containing, for example, BTEX, organic halogenated compounds, MTBE and mineral oils, and some hydrocarbon solvents were surprisingly found to be optimal for extracting any kind of contaminant and do not require to add other adjuvant agents for extraction. Said solvents preferably have a density ranging from 0,5 to 2,0 g/cm³, a solubility in H₂O ranging from 0 to 1000 mg/1 and a boiling temperature ranging from 40 to 300⁰C. In particular, it was found that the most suitable hydrocarbon solvents for the purpose are those belonging to the group consisting of 1-decene, 1-octadecene, 1- hexadecene, n-decane or blends thereof. In a preferred embodiment the used hydrocarbon solvent is n-decane which, as it is evident from the examples below, allows to extract almost all hydrocarbon pollutants which are in the aqueous matrix. Example 1 500 ml of n-decane under stirring at a speed of 200 rpm continuously for 5 minutes were added to 1000 ml of groundwater polluted by BTEX and other organic compounds coming from a production plant of plastic materials. A IKA RCT Basic type heating plate stirrer was used for this step. The obtained blend was subsequently left to decant in a clear glass cylinder for 30 minutes, at the end of which the separation of the aqueous phase from the overlying hydrocarbon phase of the pollutants dissolved in n- decane looked evident and sharp. The aqueous phase obtained after solvent extraction of the contaminants was subjected to analysis and the obtained results are reported in the following Table 1. In the fourth column of the table there is reported the percentage of abatement of the pollutants at the conclusion of the treatment thereof by the process according to the present invention.

Table 1

Example 2

500 ml of n-decane were added to 1000 ml of groundwater containing concentrations of pollutants which are different from Example 1 and were stirred continuously for 5 minutes by the same stirrer as in Example 1. The so-obtained blend was left to decant in a clear glass cylinder for 30 minutes and then the aqueous phase, once it had been separated from the hydrocarbon phase of the pollutants dissolved in n- decane, was subjected to analysis and the obtained results are reported in the following

Table 2. Also in this case the percentage of abatement of the pollutants is very close to the entirety. Table 2

Numerous other experiments have also been carried out with other solvents among the above-listed ones, thus obtaining similar results to those of Examples 1 and 2.

Carrying out the process according to the present invention requires a time which substantially depends on the duration of the mixing step under stirring of the aqueous matrix and the hydrocarbon solvent. Said duration ranges from 1 to 60 minutes, preferably from 1 to 15 minutes. Further, it has been observed that the temperature positively influences the stirring step thus favouring the extraction process of the hydrocarbon. Suitable temperatures for maximizing the efficiency of the stirring step range from 5 to 80°C, preferably from 15 to 35⁰C.

The process according to the present invention may also comprise a step of decanting the blend of the aqueous matrix and the hydrocarbon solvent, in order to favour the step of demixing the aqueous phase from the hydrocarbon phase contained therein.

The step of separation of the hydrocarbon phase containing the contaminants from the aqueous phase may comprise a stage of centrifugation and/or addition of a chemical additive suitable to favour the demixing of the aqueous phase from the hydrocarbon phase. For example, such chemical additive may be NaCl, which, by increasing the ionic strength of water, favours the demixing of the phases.

In a preferred embodiment, after said stage of separation of the hydrocarbon phase, the process according to the present invention comprises a step of separation of the above-mentioned pollutants from the hydrocarbon solvent in order to reuse the latter in a further cycle of treatment of anew aqueous matrix.

The steps of adding the hydrocarbon solvent, stirring, decanting and separating included in the method according to the present invention may be repeated several times in order to reach a still higher purification grade. hi order to increase the purification efficiency the process according to the invention may also be performed as a continuous cycle.

The simplicity of the process according to the invention allows carrying it out either in situ, that is by working directly in the place where the aqueous matrix to be purified is, or ex situ, that is by collecting the aqueous matrix and then treating it in another place.

Further, the method according to the present invention is particularly suitable for purifying groundwaters containing organic pollutants, thus allowing to use said waters for an industrial use or household purposes or even for making them drinkable.

Claims

1. Process for purifying aqueous matrices containing organic pollutants, comprising the steps of: a) introducing a hydrocarbon solvent which is capable of dissolving the pollutants contained in the aqueous matrix arranged in a suitable container, b) stirring the blend resulting from said aqueous matrix and said hydrocarbon solvent, and c) separating the hydrocarbon phase containing the pollutants from the purified aqueous phase, characterized in that said hydrocarbon solvent has a density ranging from 0,5 to 2,0 g/cm³, a solubility ranging from 0 to 1000 mg/1 and a boiling temperature ranging from 40 to 300°C.

2. Process according to the preceding claim, characterized in that said solvent is selected from the group consisting of n-decane, 1-decene, 1-octadecene, 1- hexadecene or mixtures thereof.

3. Process according to one of the preceding claims, characterized in that the duration of the step of stirring the blend formed of the aqueous matrix and the hydrocarbon solvent ranges from 1 to 60 minutes.

4. Process according to the preceding claim, characterized in that the duration of the step of stirring the blend formed of the aqueous matrix and the hydrocarbon solvent ranges from 1 to 15 minutes.

5. Process according to one of the preceding claim, characterized in that said step of stirring the blend formed of the aqueous matrix and the hydrocarbon solvent is carried out at temperatures ranging from 5 to 80°C.

6. Process according to the preceding claim, characterized in that said step of stirring the blend formed of the aqueous matrix and the hydrocarbon solvent is carried out at temperatures ranging from 15 to 35⁰C.

7. Process according to one of the preceding claims, characterized by comprising also a step of decanting the blend formed of the aqueous matrix and the hydrocarbon solvent.

8. Process according to one of the preceding claims, characterized in that said step of separation of the hydrocarbon phase from the aqueous phase comprises a stage of centrifugation.

9. Process according to one of the preceding claims, characterized in that said step of separation of the hydrocarbon phase from the aqueous phase comprises the addition of a chemical additive suitable to favour the demixing of said hydrocarbon solvent from the aqueous matrix.

10. Process according to one of the preceding claims, characterized by comprising a further step of separation of said organic pollutants from said hydrocarbon solvent, after the step of separation of the hydrocarbon phase from the aqueous phase.