WO2020174456A1

WO2020174456A1 - Method for the removal and recycling of bromide from aqueous streams to produce brominated oils

Info

Publication number: WO2020174456A1
Application number: PCT/IL2019/050216
Authority: WO
Inventors: Mohamad Masarwa; Elizabeta SHANDALOV
Original assignee: Bromine Compounds Ltd.
Priority date: 2019-02-26
Filing date: 2019-02-26
Publication date: 2020-09-03

Abstract

The invention relates to a process for the removal of bromide from aqueous solutions to produce brominated oils, comprising: combining in a reaction vessel bromide-containing aqueous solution and one or more unsaturated compounds selected from the group consisting of unsaturated fatty acids, esters of unsaturated fatty acids and mixtures thereof; oxidizing the bromide in an acidic environment to generate elemental bromine, wherein the bromine adds to the carbon- carbon double bonds of said unsaturated compound(s); and separating the reaction mixture to bromide-depleted aqueous phase and brominated oily phase.

Description

Method for the removal and recycling of bromide from aqueous streams to produce brominated oils

The present invention relates to addition of bromine to carbon-carbon double bonds of oils, to produce brominated vegetable oils. Elemental bromine is supplied to the reaction through in-situ oxidation of bromide ions from waste solutions. The invention therefore pursues a twofold goal: an efficient method for the preparation of brominated vegetable oils and selective separation of bromide from mixed-halide (i.e., bromide + chloride) waste solutions.

Brominated vegetable oils are dense liquids which have been used by the beverage industry to enable the incorporation of citrus oil flavoring agent into soft drinks. Absent the brominated vegetable oil, the creation of stable emulsion in citrus-flavored soft drink is difficult to achieve. A blend of citrus oil flavoring agent and the brominated oil with a suitable specific density is prepared, to enable the formation of a stable emulsion. Brominated vegetable oils could also be used by other industries. For example, coal- fired power plants use bromine to minimize the emission of elemental mercury through the flue gases released to the atmosphere. A bromine-containing additive is useful on account of its ability to oxidize Hg⁽⁰> . Therefore, brominated vegetable oils added to the coal combustion process could serve as bromine source in coal-fired power plants.

Brominated vegetable oils are produced by reacting the vegetable oil with elemental bromine, usually in the presence of a diluent. Bromine adds to the carbon-carbon double bonds in the unsaturated components of the oil. It was reported in US 3,240,794 that the use of water as a sole diluent in the bromination reaction results in the formation of viscous pasty reaction mixture. The product is not easily separable from the pasty reaction mass. To overcome this problem, it was suggested in US 3,240,794 to carry out the bromination reaction of the oil in the presence of water and an organic diluent (e.g., a solvent such as hexane or petroleum ether) .

We have now found that addition of elemental bromine to oils proceeds effectively even in the absence of an organic diluent, in a reaction mixture consisting of an unsaturated oil and bromide-containing aqueous phase, upon generation of the elemental bromine in-situ by oxidation of the bromide. The resultant elemental bromine adds to the carbon-carbon double bonds of the oil, creating a manageable reaction mixture. At the end of the reaction, the oily and aqueous phases are readily separable.

Accordingly, the invention is primarily directed to a process for the removal of bromide from aqueous solution to produce brominated oils. The process of the invention comprises:

combining in a reaction vessel bromide-containing aqueous solution and one or more unsaturated compounds selected from the group consisting of unsaturated fatty acids, esters of unsaturated fatty acids (e.g., glycerol esters) and mixtures thereof (e.g., vegetable oils);

oxidizing the bromide in an acidic environment to generate elemental bromine, wherein the bromine adds to the carbon- carbon double bonds of said unsaturated compound(s); and separating the reaction mixture to bromide-depleted aqueous phase and brominated oily phase.

The reaction mixture is devoid of an organic solvent/diluent ; the organic phase consists solely of the oily starting material and the progressively formed brominated material. As shown below, the oxidation of bromide is conducted in a controllable manner, by gradually adding an oxidant to the reaction vessel under stirring, such that the addition reaction of the resultant bromine to the oil takes place rather quickly, before a significant build-up of bromine concentration occurs in the aqueous phase.

For example, the process involves intermittently adding the oxidant, wherein the addition of the oxidant is interrupted and resumed according to the amount of bromine in the reaction mixture. Owing to the characteristic color of molecular bromine, the progress of the reaction is easily tracked, as explained further below.

Regarding the bromide-containing aqueous solution, as noted above, feed solutions which fit well to the process consist of a mixed halide-containing aqueous waste stream. Removal of bromide from mixed halide-containing aqueous solution is difficult to achieve, because conventional separation methods (i.e., techniques involving ion exchange resins or solvent extraction) do not always show good selectivity towards bromide against chloride and the sharpness of separation may not be satisfactory. For example, in US 9, 963,359, a large number of ion exchange resins were tested to determine their ability to separate bromide from bromide/chloride solutions, but only few demonstrated good efficiency. A different approach towards removal of bromide from bromide/chloride solutions based on solvent extraction is described in US 9,850,129, where tertiary amine extractants were shown to selectively extract bromide from the aqueous phase over chloride and sulfate; bromide was eventually recovered as the calcium bromide salt. But in general, the efficiency of ion exchange resins and extractants-based separation techniques decreases with increasing chloride/bromide ratio in the mixed halide waste solution. The process of the invention benefits from the fact that bromide separation does not depend on the concentration of chloride and other competing anions (e.g., sulfate) in the solution, because only the in-situ generated bromine would add to the unsaturated oily compound and be removed from the solution.

Mixed halide aqueous waste streams that can be used according to the invention generally contain up to 10 wt% Bn, typically up to 5 wt% Bry e.g., from 0.05 to 3.0 wt% Bn, (more specifically, from 0.15 to 1.5 wt% Bn) ; and up to 10 wt% Cly typically up to 5 wt% Cly e.g., from 0.05 to 3.0 wt% Cly

(more specifically, from 0.15 to 1.5 wt% Cl-) . Such aqueous waste streams are generated in industrial plants where brominated chemicals are manufactured. Another example worth mentioning is the flue gas desulfurization (FGD) wastewater produced in coal-fired power plants employing the FGD process. In such power plants, the flue gas flows through a suitable gas-liquid contactor and contacts therein with calcium-containing slurry (e.g., limestone) . Sulfur dioxide present in the flue gas is absorbed in the slurry and transforms into sulfur trioxide which in turn reacts with the calcium compound in a suitable reaction vessel to form gypsum. The following is an exemplary composition of waste aqueous solution generated by a typical WFGD process: 0.1-1 wt% Ca²⁺, 0.05-1.4 wt% Mg²⁺, 0.1-1.5 wt% Na⁺, 0.05-3.0 wt% Bry

0.2-3.0 wt% Cly 0.1-0.4 wt% SO₄ ^2- and 0.005-0.2wt% NCby with specific gravity of about 1.04 g/cm³. Fine chemicals production plants and paper production plants using brominated compounds also generate waste streams treatable by the present invention. It should be borne in mind that in view of strict regulatory requirement, bromide-containing wastewater in some locations can be discarded only if the level of bromide is reduced to below 100 ppm. Thus, the present invention offers an elegant method of recycling bromine in coal-fired power plants, where mixed-halide wastewater is treated to produce brominated oils that can be put to use in the coal burning process as a bromine additive.

The oxidation of bromide (Br^_) to bromine takes place in an acidic environment (at alkaline pH, elemental bromine converts into bromate and therefore will not be available for the addition reaction to the oil) . Hence, nearly neutral, alkaline or even slightly acidic bromide-containing wastewater would require pH adjustment to the strong acidic range. The acidic environment is created by addition of an acid to the bromide-containing aqueous solution, e.g., a strong mineral acid, either monoprotic (for example, hydrogen chloride) or polyprotic acid (e.g., sulfuric acid) . The pH of the aqueous phase is adjusted to the range below 4, e.g., below 3, preferably from 1 to 2.

The use of hydrochloric acid is generally preferred, because the presence of chloride has no negative effect on the efficiency of the process. Another factor that may influence the choice of the mineral acid that is needed to create the acidic environment is the presence of calcium ions in wastewater. When the wastewater contains calcium ions (see for example the case of FGD wastewater) , the likelihood of precipitation of water insoluble calcium sulfate should be taken into consideration. Hydrochloric acid would then be favored over sulfuric acid.

Acid-assisted bromide oxidation to molecular bromine could be achieved using various oxidizing agents such as hypochlorite, hydrogen peroxide and bromate. All these oxidizers convert bromide to bromine in acidic environment in a simple and safe manner. Bubbling chlorine gas through the bromide-containing solution will lead to generation of molecular bromine, but delivering a reactant in a gaseous stream may be less convenient; hence hypochlorite is generally more preferred.

Hypochlorite salts (e.g., sodium hypochlorite, calcium hypochlorite) are available in an aqueous form (sodium hypochlorite; for example, up to 10 wt% sodium hypochlorite solution can be used) or solid forms (calcium hypochlorite; for example, powder, pellets, tablets) . The chemical equations of the relevant reactions are shown below (hypochlorite can directly oxidize bromide to bromine in an acidic environment to suppress bromate formation; elemental chlorine is also formed, which in turn oxidizes bromide to bromine) :

NaClO + 2Br- + 2H⁺ ® Br₂ + NaCl + H₂0

2H⁺ + CIO- + Cl- <® Cl₂ + H2O Cl₂ + 2Br- ® Br₂ + 2C1

It is preferred to use the oxidizer in an excess over the amount dictated by stoichiometry, e.g., about 10 to 50% molar excess. Experimental work conducted in support of this invention indicates that about 30% molar excess would generally suffice to achieve complete bromide oxidation across characteristic bromide concentration ranges existing in mixed-halide wastewater (e.g., wastewater with 0.15 to 1.4 wt% bromide) .

Another useful oxidant is hydrogen peroxide, which is manufactured and sold in aqueous form; low concentration grades (e.g., 5%) and industrial strength grades, typically

>30%, e.g., 35%, 50 and 70%, can be used:

H2O2 + 2H⁺ + 2Br- ® Br₂ + 2H₂0 Bromate can also be considered as a potential oxidizer for in-situ bromine generation, but it should be borne in mind that its presence in wastewater is strongly objected. However, from the viewpoint of liberating molecular bromine from bromide-containing solutions (e.g., other than wastewater streams), to allow the addition of bromine to unsaturated oils, bromate is comparable to other oxidizers and in some cases may offer certain advantages, bearing in mind its availability in a solid form and its contributing of a bromine atom to the brominated oil product:

Br0₃ + 5Br + 6H⁺ ® 3Br₂ + 3H₂0

Turning now to the vegetable oil, for example, sesame, olive, soybean, cottonseed, corn, peanut, linseed oil or mixture thereof may be used, to name a few examples. Oleic acid, linoleic acid or linolenic acid-rich oils, that is, oils in which the total concentration of mono/polyunsaturated fatty acids in the oils is >65%, e.g., >75 or >80%, such as corn, olive, soybean and linseed oil, are especially useful from the viewpoint of efficient bromine removal from wastewater and formation of high-content bromine carriers for use as additives to combat Hg⁽⁰> emission as set out above. Another example is hempseed oil which consists chiefly of linoleic acid, a-linoleic acid and oleic acid and may be considered as a candidate for this purpose.

One convenient way of carrying out the reaction is by charging a reaction vessel with an aqueous bromide solution (e.g., a mixed halide-containing wastewater), adjusting the pH of the solution with the aid of a mineral acid to the range below 3, (e.g., hydrochloric acid to reach l<pH<2), introducing the oil starting material to the reaction vessel, and gradually feeding the oxidant to produce bromine (e.g., preferably intermittently, namely, by portion wise addition; or by continuously feeding the oxidant at a slow rate) .

The proposed order of reactants addition offers several benefits. It should be borne in mind that bromine exhibits low solubility in water. The presence of the oil in the reaction vessel before the addition of the oxidizer solution has been started minimizes the escape of bromine vapors from the system. Owing to the intermittent addition of the oxidizer solution, it is possible to manage the reaction efficiently, enabling in-situ generated bromine to be consumed quite quickly by the oil, before build-up of excessive concentration of bromine occurs due to oxidation of bromide in the aqueous phase.

That is, with the aid of the intermittently added oxidizing agent, the progress of the two chemical reactions (bromide oxidation and bromine addition to the oil) is nicely coordinated. The pair of reactions are illustrated by the chemical equations depicted below (for the case in which oxidation of bromide is by sodium hypochlorite, and the bromine adds to oleic-acid rich oil) :

The intermittent addition of the oxidizing agent can be conducted as follows. The aqueous solution of the oxidizing agent is added portion wise with stirring. Upon addition of a small volume of the oxidizing agent solution, the reaction mixture acquires an orange-red color owing to the formation of elemental bromine in the aqueous phase. The characteristic color disappears as the addition reaction of elemental bromine to the carbon-carbon double bonds occurs. The addition of the oxidizing agent resumes once the reaction mixture has regained its original colorless-yellowish hue; then the next portion of oxidizer solution is delivered to the reaction mixture.

On a laboratory scale, color changes in the reaction mixture are readily visible. On a larger (industrial) scale production, the aqueous solution of the oxidizing agent could be fed to the reactor using a pump designed to respond to measurements of color intensity in the reaction mixture or measurements of online analyzer for bromide/bromine. That is, the operation of the pump is halted and resumed once the intensity of the color or bromine/bromide concentrations rises above, or drops below, predetermined thresholds, respectively .

The process of the invention is carried out under vigorous stirring to effectively mix and increase the interface between the organic and aqueous phases, at a temperature in the range from 20°C to 70°C. High temperature may have an undesired effect on the escape of bromine vapors, but operating at temperatures in the middle of the proposed range, say, from 35°C to 45°C, has been shown to achieve good balance between acceleration of the rate of bromine addition to the oil on the one hand, and minimization of escaping bromine vapors on the other hand. For example, working in the range from 35°C to 45°C, e.g., around 40°C. The weight ratio bromide : oil is preferably in the range from 1:1.5 to 1:2.5; the time of the bromination reaction decreases with increasing concentration of the oil in the reaction medium. In general, bromine addition to the oil can be completed within not more than two-three hours. The reaction mixture is readily separable into organic (lower) and aqueous (upper) phases. The bromide-depleted aqueous phase can be discarded after conventional treatment (reduction of residual oxidants by bisulfite) .

The organic phase consisting of the highly dense brominated oil is collected. The product is washed with water. Analysis based on decomposition by oxygen bomb and argentometric titration of bromide indicate that it is possible to achieve high degree of bromination of the oil, i.e., more than 80% of the oil is brominated.

Examples

Bromide and chloride concentrations in the aqueous phase were determined by direct potentiometric titration using silver electrode and 0.1M AgNCb titrant solution after adding 2N HN0₃.

Low concentrations of Bromide (<100 ppm) were determined by Ion Chromatography Dionex IC-ICS2100 fitted with an automatic pump and autosampler. An anion column IonPac AS9-HC (Dionex, P/N 051786) (250 x 4 mm) protected by a guard column IonPac

AG9-HC (Dionex, P/N 01517014) (50 x 4 mm) was used.

pH measurements - pH of the solutions was measured using Mettler Toledo 1120 pH meter with Mettler Toledo pH electrode of type HA405-DXK-S8/425.

Example 1

Addition of in-situ prepared bromine

to double bonds of corn oil

A multi-necked round bottomed flask fitted with a mechanical stirrer, a dropping funnel and thermometer was charged with 500 g of aqueous waste solution which contained 1.4% and 1.3% by weight bromide and chloride ions, respectively. The pH of the as-received aqueous waste solution was 8.5. The pH was adjusted to the acidic range (pH~1.0) by addition of 20 g of 20 wt% hydrochloric acid solution.

17.5 g of vegetable oil (corn oil) was introduced into the flask under stirring, such that the weight ratio bromide : oil was 1:2.5. The temperature of the reaction was kept at 40°C .

Next, 10 wt% sodium hypochlorite solution was slowly fed to the reaction vessel through the dropping funnel over a period of seventy minutes. The total amount of hypochlorite solution added was 45 g. The dropping funnel was fitted with a tube that was immersed in the reaction mixture, to introduce the hypochlorite solution beneath the surface of the liquid in the vessel. The reaction mixture acquired orange-red color on addition of the oxidizer, marking the formation of elemental bromine. The gradual disappearance of the orange-red color indicated that addition of bromine to the carbon-carbon double bonds has occurred. The portion wise addition of the hypochlorite solution continued until no color change was observed in the solution, i.e., no orange-red color was created, indicating that all bromide ions were oxidized by the hypochlorite to bromine, which in turn was consumed by the addition reaction.

After the feed of the hypochlorite solution was completed, the reaction mixture was kept under stirring for additional thirty minutes and was then separated into aqueous and oily phase. The aqueous phase is treated with bisulfite. Oxidant and bromate concentration after the bisulfite treatment are each below the detection limit of <10 ppb .

The analysis of the aqueous phase before and after the bromination reaction is tabulated in Table 1:

Table 1

The organic phase consisting of the brominated oil is collected, washed twice with water and characterized by decomposition by oxygen bomb and argentometric titration of bromide. The analyses indicate that 80-85% of the oil was brominated .

It is seen that the invention enables selective bromide removal from mixed halide (bromide/chloride) aqueous stream with production of brominated oils.

Example 2

Addition of in-situ prepared bromine

to double bonds of soybean oil

The procedure according to Example 1 was repeated, using soybean oil in place of corn oil . The analysis of the aqueous phase before and after the bromination reaction is tabulated in Table 2 :

Table 2

Claims

1) A process comprising:

combining in a reaction vessel bromide-containing aqueous solution and one or more unsaturated compounds selected from the group consisting of unsaturated fatty acids, esters of unsaturated fatty acids and mixtures thereof;

2) A process according to claim 1, wherein the reaction mixture is devoid of an organic solvent or diluent.

3) A process according to claim 1 or 2, wherein the bromide- containing aqueous solution is a mixed halide-containing wastewater stream.

4) A process according to anyone of claims 1 to 3, comprising gradually feeding an oxidant to the reaction vessel under vigorous stirring to oxidize bromide to bromine, such that the addition reaction of the bromine to the unsaturated compound (s) takes place before build-up of bromine concentration occurs in the aqueous phase.

5) A process according to claim 4, comprising intermittently feeding the oxidant to the reaction vessel.

6) A process according to claim 5, wherein the feeding of the oxidant is interrupted and resumed according to the amount of bromine in the reaction mixture. 7) A process according to any one of the preceding claims, wherein bromide oxidation is achieved with the aid of hypochlorite .

8) A process according to anyone of the preceding claims, wherein the unsaturated compound is one or more vegetable oils .

9) A process according to claim 8, wherein the vegetable oil is selected from the group consisting of corn and soybean oils, or a mixture thereof.