Process for the purification of an aqueous effluent

Abstract

The present invention relates to a process for the purification of an aqueous effluent (A) generated in the manufacture of hydrogen peroxide by the anthraquinone method, comprising the steps of a) adding to the aqueous effluent (A) an acid (C) and an organic solvent (B) to obtain a mixed medium (D); b) decanting the mixed medium (D) obtained in step a) to obtain 2 phases (E, F), wherein the aqueous phase (E) has a TOC content lower than the aqueous effluent (A) and the liquid organic phase (F) has a TOC content higher than the aqueous effluent (A); and c) entering the aqueous phase (E) obtained in step b) into a coalescer (4) to separate the aqueous phase (E) in 2 new phases, a first fluid (G) with a TOC content lower than the aqueous phase, and a second fluid (H) with a TOC content higher than the aqueous phase. Further, the present invention relates to an apparatus for the purification of an aqueous effluent generated in the manufacture of hydrogen peroxide by the anthraquinone method. Further, the present invention relates to the use of the inventive process in the manufacture of hydrogen peroxide by the anthraquinone method; and to a process for the manufacture of hydrogen peroxide and for the purification of an aqueous effluent (A) generated in said manufacture of hydrogen peroxide.

Description

[0001] Process for the purification of an aqueous effluent

[0002] TECHNICAL FIELD

[0003] The present invention relates to the field of hydrogen peroxide manufacture by the anthraquinone method, in particular to the purification of effluents generated in this method, and to an apparatus for performing the purification.

[0004] TECHNICAL BACKGROUND

[0005] Hydrogen peroxide is one of the most important inorganic chemicals to be produced worldwide. Its industrial applications include textile, pulp and paper bleaching, organic synthesis (propylene oxide), the manufacture of inorganic chemicals and detergents, environmental and other applications.

[0006] Synthesis of hydrogen peroxide is predominantly achieved by using the large scale Riedl-Pfleiderer process, also called anthraquinone (loop) process or AO (auto-oxidation) process. The process is a cyclic process taking an organic anthraquinone dissolved in solvent and circulating this “Working Solution” (WS) mix around the plant.

[0007] The first step of the AO process is the chemical reduction of the anthraquinone derivatives present in the organic working solution using hydrogen gas and a catalyst. The mixture of organic solvents, hydroquinone and quinone species is then separated from the catalyst and the hydroquinone species are oxidized using oxygen, air or oxy gen-enriched air thus regenerating the quinone(s) with simultaneous formation of hydrogen peroxide.

[0008] Hydrogen peroxide is then typically extracted in an extraction column with water and recovered in the form of a crude aqueous hydrogen peroxide solution, and the working solution is returned to the hydrogenator to complete the loop. Typically, a mixed solvent is used as Working Solution to allow for good solubility of both the reduced and the oxidized form of anthraquinone. During the cyclic process, part of anthraquinone becomes broken and accumulates in the WS.

[0009] Improved modifications of the hydrogen peroxide autoxidation process are disclosed for instance in WO 2023 / 117360 Al and WO 2024 / 132319 Al. The AO process to produce hydrogen peroxide generates some alkali metal containing aqueous effluent that also contains some Total Organic Carbon (TOC), e.g. due to broken anthraquinone. In a certain embodiment of the process the chemistry of the anthraquinone process organic working solution is kept in good working order by performing some aqueous washes of the organic solution. Such washing steps can generate both alkali and acid aqueous effluents. Typically, these effluents are discharged to a biological wastewater treatment plant (BWWTP).

[0010] In particular the alkali effluent can contain significant quantities of Total Organic Carbon (TOC) which will need to be reduced in concentration before discharge out of the production facility in order to meet permit limits. The TOC reduction is typically achieved by a biological wastewater treatment plant (BWWTP). The size of such a biological treatment plant is proportionally bigger if the TOC concentration in the effluent is higher. Accordingly, if the TOC concentration in the effluent is low, the efficacy of a given BWWTP is improved since the BWWTP can handle more effluent.

[0011] In general, is desirable to keep the size of the BWWTP low. As such, in order to reduce Capex (Capital Expenditure) and Opex (Operational Expenditure), it is advantageous to be able to reduce the TOC concentration in the effluent stream before sending it to the BWWTP. This effect is not sufficiently achieved by the methods of the prior art. Thus, there remains the need to provide a process which reduces TOC and COD within an aqueous effluent generated in the manufacture of hydrogen peroxide by the anthraquinone method to reduce Capex and Opex of a biological treatment plant.

[0012] In addition, it is desirable to reduce the chemical oxygen demand (COD). COD is a critical parameter in effluent treatment that measures the total amount of oxygen required to chemically oxidize carbon compounds present in water. The COD value is typically expressed in milligrams of oxygen per liter of water (mg / L) and is commonly used to assess the overall quality of wastewater. During biological treatment of the effluent, carbon contained in the effluent is converted to carbon dioxide. This is important because the treated effluent eventually discharged into a river should not contain high amounts of forms of carbon that will absorb oxygen from the water. In other words, high COD levels indicate a large amount of oxidizable material, which could potentially deplete oxygen in natural water bodies, harming aquatic life. CN 108275846 A discloses a method for treating anthraquinone wastewater comprises adjusting the pH of the wastewater to acidic, adding inorganic / organic salts of Fe2+as active ingredients, and performing an oxidation reaction to simultaneously remove nitrite and TOC in the wastewater. BRPI0904942 A2 discloses a process of physicochemical treatment of caustic residues arising from auto-oxidative processes of hydrogen peroxide production, wherein in a first step, the emulsion obtained by the process is broken down by dosing the caustic residue with H2SO4, followed by decantation or flotation of the oil. No organic solvent is added in this process.

[0013] SUMMARY OF THE INVENTION

[0014] The present invention relates to the pretreatment of an alkali containing effluent to reduce the Total Organic Content (TOC) concentration within the effluent before said effluent is sent for biological treatment. Further, the present invention relates to an apparatus useful for this pretreatment. Further, the present invention relates to the use of the inventive process in the manufacture of hydrogen peroxide by the anthraquinone method; and to a process for the manufacture of hydrogen peroxide and for the purification of an aqueous effluent generated in said manufacture of hydrogen peroxide.

[0015] The inventive process is a process for the purification of an aqueous effluent (A) generated in the manufacture of hydrogen peroxide by the anthraquinone method, comprising the steps of: (a) Adding to the aqueous effluent (A) an acid (C) and an organic solvent (B) to obtain a mixed medium (D), (b) Decanting the mixed medium (D) obtained in step a) to obtain 2 phases (E, F), wherein the aqueous phase (E) has a TOC content lower than the aqueous effluent (A) and the liquid organic phase (F) has a TOC content higher than the aqueous effluent (A), and (c) Entering the aqueous phase (E) obtained in step b) into a coalescer (4) to separate the aqueous phase (E) in 2 new phases, a first fluid (G) with a TOC content lower than the aqueous phase, and a second fluid (H) with a TOC content higher than the aqueous phase.

[0016] The inventive apparatus is an apparatus for the purification of an aqueous effluent generated in the manufacture of hydrogen peroxide by the anthraquinone method, comprising: (i) a holding tank (1) configured to store an aqueous effluent (A); (ii) at least one device (2) configured to add an acid (C) and an organic solvent (B) to the aqueous effluent (A) to obtain a mixed medium (D); (iii) a settling tank (3) configured to store the mixed medium (D) and to allow for phase separation and configured to decant the mixed medium (D) to obtain 2 phases , namely a floating organic phase (F) and an aqueous phase of an acid effluent (E) comprising traces of organics in the form of organic droplets; and (iv) a coalescer (4) configured to coalesce the organic droplets of the phase (E) and to separate it (i.e. phase (E)) into an aqueous first fluid (G) and a floating organic second fluid (H) comprising coalesced organic droplets. Preferably, the apparatus further comprises (v) a first collection tank (5) configured to store aqueous effluents (G, I); (vi) optionally, a device configered to add base to the aqueous first fluid (G) to prepare an alkalized first fluid (I); (vii) optionally, a pump (6) configured to pump the aqueous first fluids (G, I) around the first collection tank (5) and / or to pump the alkalized first fluid (I) to a biological waste water treatment unit (BWWTP); (viii) optionally, a second collection tank

[0017] (7) configured to store the organic effluents (F, H); and (ix) optionally, a pump

[0018] (8) configured to pump the organic effluents (F, H) from the second collection tank (7) to a facility to dispose of the waste organic material.

[0019] The present inventors have surprisingly found that the removal of TOC from the effluent can be significantly improved by adding both an acid and an organic solvent before decantation. The solubility of the TOC within the aqueous effluent can be reduced by acidifying the effluent. Once acidified roughly 40% by weight of the TOC can be removed by decantation. Once this has been done the remaining effluent can be sent for biological treatment in a biological treatment plant that is 40% smaller in size (% by volume) because of the pretreatment. The removal of TOC can be further improved using a coalescer.

[0020] This invention is a useful tool to reduce the TOC in the effluent and thus to reduce the potential size of any biological unit designed to treat the effluent.

[0021] DETAILED DESCRIPTION OF THE INVENTION

[0022] Before the method of the invention will be described in detail, it is to be understood that this invention is not limited to specific method conditions described herein, since such conditions may, of course, vary.

[0023] It is also to be understood that the terminology used herein is not intended to be limiting, since the scope of the present invention will be limited only by the appended claims. As used herein, the singular forms "a", "an", and "the" include both singular and plural referents unless the context clearly dictates otherwise. By way of example, "a compound" means one compound or more than one compound.

[0024] The terms "containing", "contains" and "contained of' as used herein are synonymous with "including", "includes" or " comprising", "comprises", and are inclusive or open-ended and do not exclude additional, non-recited members, elements or method steps. It will be appreciated that the terms “containing”, “contains”, "comprising", "comprises" and "comprised of as used herein comprise the terms "consisting of', "consists" and "consists of.

[0025] Throughout this application, the term "about" is used to indicate that a value includes the standard deviation of error for the device or method being employed to determine the value.

[0026] As used herein, the term “average” refers to number average unless indicated otherwise.

[0027] As used herein, the terms “% by weight”, “wt.-%”, “weight percentage”, or “percentage by weight” are used interchangeably. The same applies to the terms “% by volume”, “vol.- %”, “vol. percentage”, or “percentage by volume”, or “% by mol”, “mol- %”, “mol percentage”, or “percentage by mol”.

[0028] The recitation of numerical ranges by endpoints includes all integer numbers and, where appropriate, fractions subsumed within that range (e.g. 1 to 5 can include 1, 2, 3, 4 when referring to, for example, a number of elements, and can also include 1.5, 2, 2.75 and 3.80, when referring to, for example, measurements). The recitation of end points also includes the end point values themselves (e.g. from 1.0 to 5.0 includes both 1.0 and 5.0). Any numerical range recited herein is intended to include all sub-ranges subsumed therein.

[0029] All references cited in the present specification are hereby incorporated by reference in their entirety. In particular, the teachings of all references herein specifically referred to are incorporated by reference.

[0030] Unless otherwise defined, all terms used in disclosing the invention, including technical and scientific terms, have the meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. By means of further guidance, term definitions are included to better appreciate the teaching of the present invention. In the following passages, different alternatives, embodiments and variants of the invention are defined in more detail. Each alternative and embodiment so defined may be combined with any other alternative and embodiment, and this for each variant unless clearly indicated to the contrary or clearly incompatible when the value range of a same parameter is disjoined. In particular, any feature indicated as being preferred or advantageous may be combined with any other feature or features indicated as being preferred or advantageous.

[0031] Furthermore, the particular features, structures or characteristics described in present description may be combined in any suitable manner, as would be apparent to a person skilled in the art from this disclosure, in one or more embodiments. Furthermore, while some embodiments described herein include some but not other features included in other embodiments, combinations of features of different embodiments are meant to be within the scope of the invention, and from different embodiments, as would be understood by those in the art.

[0032] Should the disclosure of any patents, patent applications, and publications which are incorporated herein by reference conflict with the description of the present application to the extent that it may render a term unclear, the present description shall take precedence.

[0033] Definitions and Methods of Measurement

[0034] The term “aqueous effluent” in the context of the present inventions refers to the water-based waste stream that is produced after the extraction of hydrogen peroxide from the working solution.

[0035] The term “coalescer” refers to a device used to promote the merging of small droplets of liquid into larger ones, typically in an emulsion, to facilitate phase separation. Accordingly, the term “coalesced organic droplets” refers to organic liquid droplets resulting from the combination of smaller organic droplets through the action of a coalescer or equivalent means.

[0036] The terms “floating organic phase” and “floating organic fluid” refer to the organic liquid layer that separates from and resides above an aqueous phase due to density differences. A “biological wastewater treatment unit” (BWWTP) is a system that uses microorganisms, primarily bacteria, to break down and remove organic matter, nutrients, and contaminants from wastewater.

[0037] The COD (Chemical Oxygen Demand) is a parameter expressing the total amount of oxygen required to chemically oxidize organic and inorganic compounds, particularly organic matter, present in water. It is expressed in milligrams of oxygen per liter (mg / L) or ppm (parts per million). Chemical oxygen demand (COD) is the amount of a strong oxidising agent per liter of effluent needed to oxidise the organic compounds in the effluent, expressed as the equivalent amount of oxygen per liter. The effluent samples are heated in the presence of sulphuric acid, potassium dichromate (oxidiser), silver sulphate (oxidation catalyst) and mercuric sulphate (chloride complexing agent). The concentration of green Cr3+ions, formed by the reduction of dichromate, is then determined photometrically.

[0038] The TOC (Total Organic Carbon) is a parameter expressing the amount of carbon found in organic compounds present in water. It is expressed in milligrams of carbon per liter (mg / L) or ppm (parts per million). TOC is determined as the mathematical difference between the total carbon (TC) and the total inorganic carbon (TIC). In a TOC-analyser, the TC is determined by catalytic combustion, whereas the total inorganic carbon is determined by acidification. In both cases, the released CO2 is quantified with an infrared detector. Suitable TOC-analyser are commercially available and known to the skilled person.

[0039] Figures

[0040] Figure 1 shows an overview of the inventive method and apparatus.

[0041] Figure 2 shows the results from an experiment evaluating the effect of pH on TOC removal in a combined stream consisting of 1 part alkaline reversion effluent and 2 parts acidic effluent.

[0042] The inventive process

[0043] The present invention provides a process for the purification of an aqueous effluent generated in the manufacture of hydrogen peroxide by the anthraquinone method, comprising the steps of: a) Adding to the aqueous effluent (A) an acid (C) and an organic solvent (B) to obtain a mixed medium (D), b) Decanting the mixed medium (D) obtained in step a) to obtain 2 phases (E, F), wherein the aqueous phase (E) has a TOC content lower than the aqueous effluent (A) and the liquid organic phase (F) has a TOC content higher than the aqueous effluent (A), and c) Entering the aqueous phase (E) obtained in step b) into a coalescer (4) to separate the aqueous phase (E) in 2 new phases, a first fluid (G) with a TOC content lower than the aqueous phase, and a second fluid (H) with a TOC content higher than the aqueous phase.

[0044] Further, the present invention provides an apparatus for the purification of an aqueous effluent generated in the manufacture of hydrogen peroxide by the anthraquinone method, comprising: i) a holding tank (1) configured to store an aqueous effluent (A); ii) at least one device (2) configured to add an acid (C) and an organic solvent (B) to the aqueous effluent (A) to obtain a mixed medium (D), preferably, the device (2) is a pump; iii) a settling tank (3) configured to store the mixed medium (D) and to allow for phase separation and configured to decant the mixed medium (D) to obtain 2 phases, namely a floating organic phase (F) and an aqueous phase of an acid effluent (E) comprising traces of organics in the form of organic droplets; and iv) a coalescer (4) configured to coalesce the organic droplets of the phase (E) and to separate it into an aqueous first fluid (G) and a floating organic second fluid (H) comprising coalesced organic droplets.

[0045] Preferably, the apparatus further comprises: v) a first collection tank (5) configured to store aqueous effluents (G, I); vi) optionally, a device configered to add base to the aqueous first fluid (G) to prepare an alkalized first fluid (I); vii) optionally, a pump (6) configured to pump the aqueous first fluids (G, I) around the first collection tank (5) and / or to pump the alkalized first fluid (I) to a biological waste water treatment unit (BWWTP); viii) optionally, a second collection tank (7) configured to store the organic effluents (F, H); and ix) optionally, a pump (8) configured to pump the organic effluents (F, H) from the second collection tank (7) to a facility to dispose of the waste organic material.

[0046] The inventive apparatus is preferably used to perform the inventive process. The inventive process and apparatus are illustrated in Figure 1 :

[0047] An alkali aqueous effluent, A, coming from the hydrogen peroxide plant, is pumped into a holding tank, 1. Alkali effluent from tank 1 is pumped with pump 2 into tank 3. To the stream leaving tank 1 is added solvent (B) and acid (C). The acid that is added should be a strong mineral acid such as nitric acid, sulfuric acid, hydrochloric acid, phosphoric acid.

[0048] The effect of adding the solvent and the acid to the alkali solution is to turn the solution into two phases, an aqueous phase of acid effluent (E) and an organic phase (F) in the form of small droplets.

[0049] The combined solution of the alkali effluent, solvent and acid (mixed medium (D) then enters settling tank 3.

[0050] Settling tank 3 is designed so that the entering solution enters at roughly the midpoint in the tank where there is an interface of floating organic solution (F) on the remaining aqueous solution (E) below.

[0051] The floating organic solution (F) is removed from tank 3 by decantation into the organic effluent collection tank 7.

[0052] The aqueous solution (E) from the bottom of tank 3 is passed through a coalescer, 4, in order to remove remaining traces of separated organic. After the coalescer, 4, the separated organics that float to the top of the coalescer (second fluid (H)) are separated and sent to tank 7 for disposal. The remaining aqueous solution (first fluid (G)) flows from the coalescer, 4, to the collection tank 5. In order to adjust the pH of the first fluid (G) in preparation for the BWWTP, some alkali solution is readded to the solution in tank 5 via a first line to obtain an alkalized first fluid (I). The solution in tank 5 is pumped around tank 5 using pump 6 in order to make a homogeneous solution before pumping the alkalized first fluid (I) via a second line to the BWWTP using pump 6.

[0053] Waste organic (W) from tank 7 is pumped using pump 8 to a facility to dispose of the waste organic material (W).

[0054] Preferably, the aqueous effluent (A) is an alkaline effluent, preferably having a pH of from 10 to 12. Preferably, the mixed medium obtained in step a) has a pH of from 2 to 6.

[0055] Preferably, the organic solvent (B) is added in step a) in an amount of 0 - 5 mL per 1 L of aqueous effluent (A), more preferably 0 - 2 mL per 1 L of aqueous effluent (A), more preferably 0.5 to 1.5 mL per 1 L of aqueous effluent (A). This corresponds to around 0.1 to 0.5 kg / volume of effluent obtained in the production of one ton of hydrogen peroxide. Preferably, the duration of step b) is from 1 to 36 hours, preferably 6 to 36 hours, more preferably 6 to 24 hours, i.e. the mixed medium (D) is stored, e.g. in a tank, for 1-36 hours to allow for phase separation before decantation.

[0056] Preferably, the acid (C) is at least one strong mineral acid, in particular selected from HNO3, H2SO4, H3PO4, HC1 and mixtures thereof, more preferably HNO3, H2SO4, and mixtures thereof.

[0057] The 2 phases obtained in step b) are, on one side, an aqueous phase (E) having a TOC content lower than the aqueous effluent, and, on the other side, a liquid organic phase (F) having a TOC content higher than the aqueous effluent, which is optionally disposed of as a waste (W). Waste W can for instance be burned.

[0058] Within the alkaline effluent there are organic species which have formed alkaline organic salts. These alkaline organic salts are highly soluble due to the polarity of the alkaline species which is, in turn, highly soluble in water. For this reason, high concentrations of soluble TOC, 1000 to 10000 ppm, can be measured.

[0059] If acid is added to the alkaline solution, then a proportion of the alkaline organic salts are converted to organic acids which are far less soluble in the aqueous solution. When adding a mineral acid, some of the alkaline cations which are attached to the organic molecules are replaced by a proton. The displaced alkaline cation, such as sodium, forms a mineral salt which remains in solution. Such salts can be nitrates, sulfates, phosphates, chlorides.

[0060] It has been found that by simply adding a mineral acid to the alkali effluent, as in BRPI0904942 A2, that two separate layers of organic will form. A floating light layer will form on top of the tank and a denser tarry heavy layer forms at the bottom of the separation tank. The aqueous phase will be sandwiched between these two organic layers. Removing the tarry heavy layer at the bottom of the tank is complicated and thus, it would be desirable to avoid formation of this layer. It has been found that by adding a small amount of organic solvent into the alkaline effluent stream (this can be done just before, simultaneously with or shortly after the addition of the acid) that it is possible to avoid the heavy tarry layer of organic and instead achieve a single layer of floating organic.

[0061] It is possible to remove the floating organic by decantation and by doing so reduce the TOC concentration remaining in the effluent before it is sent to the BWWTP. There remains no heavy tarry layer at the bottom of the separation tank which cannot be removed by decantation, and which increases TOC amount of the obtained effluent.

[0062] Preferably, the aqueous effluent (A) contains aromatic impurities, such as unsubstituted or Ci-Cio alkyl-substituted phthalic acids or salts thereof, and mixtures thereof. More preferably, the aromatic impurities are chosen from sodium or potassium salts of phthalic acid, tert-amylphthalic acid, secamylphthalic acid, and mixtures thereof. Typical examples of impurities are biodegradable impurities, such as phthalic Acid, tert-amylphthalic acid, secamylphthalic acid, and other molecules coming from the breakdown of the Quinone and solvent molecules used to make the hydrogen peroxide.

[0063] Preferably, the organic solvent (B) comprises a mixture of (i) a non-polar aromatic solvent, such as a non-polar aromatic alkyl solvent, preferably a nonpolar aromatic (C9 to Cl l)alkyl solvent, more preferably a non-polar aromatic (ClO)alkyl solvent, and (ii) a polar solvent, such as an alcoholic solvent or an acetate. Preferred examples of alcoholic solvent are mono alcoholic solvents, more preferably a Ci-Cio dialkyl carbinol, more preferably diisobutylcarbinol (DBC). A preferred example of an acetate is ortho methyl cyclohexane acetate. Preferred is a mixture of (i) a non-polar aromatic alkyl solvent and (ii) an alcoholic solvent or acetate, more preferably an alcoholic solvent, in particular a mono alcoholic solvent. More preferred is a mixture of (i) a non-polar aromatic (C9 to Cl l)alkyl solvent and (ii) Ci-Cio dialkyl carbinol. More preferred is a mixture of (i) a non-polar aromatic (ClO)alkyl solvent and (ii) diisobutylcarbinol (DBC). The concentration of the non-polar solvent in the mixture of the nonpolar aromatic solvent (i) and the polar solvent (ii) could be 1 - 99 % by volume. In other words, the non-polar aromatic solvent (i) and the polar solvent (ii) can be used in a ratio of from 1 :99 - 99: 1 by volume, more preferably in a ratio of from 5:95 - 95:5 by volume, more preferably in a ratio of from 10:90 - 90: 10 by volume, more preferably in a ratio of from 20:80 - 80:20 by volume.

[0064] It is possible that the solvent (B) used in the inventive process is at least in small quantities identical to the impurities contained in effluent (A). However, according to the inventive process, additional solvent (B) is added in step a). To improve waste removal efficiency of the overall process (i.e. the overall process of manufacture of hydrogen peroxide and decomposition of waste effluents), and to reduce the amount of chemicals that need to be purchased, it is preferred to use solvents recovered from the manufacturing process.

[0065] Preferably, the organic solvent (B) is an organic solvent (Bl) recovered from the manufacture of hydrogen peroxide by the anthraquinone method.

[0066] Preferably, the anthraquinone process comprises the successive steps of hydrogenating a working solution, oxidizing the hydrogenated working solution and extracting hydrogen peroxide from the oxidized working solution, and wherein the aqueous effluent (A) originates from performing aqueous washes of the working solution.

[0067] Preferably, the anthraquinone process makes use of a non-polar solvent, a polar solvent, and an anthraquinone compound, and wherein the organic solvent (Bl) is a mixture containing the non-polar solvent, the polar solvent and degradation products of the anthraquinone.

[0068] Thus, the overall process is a process of manufacturing hydrogen peroxide by the anthraquinone method and purifying an aqueous effluent generated in the manufacture. In other words, the invention further relates to a process for the manufacture of hydrogen peroxide and for the purification of an aqueous effluent (A) generated in said manufacture of hydrogen peroxide, said process comprising: manufacturing hydrogen peroxide by an anthraquinone method, and purifying the aqueous effluent (A) by the inventive process as described above. The overall process preferably comprises the following steps: al) preparing a working solution, typically an organic working solution, preferably by dissolving an anthraquinone compound in a solvent, more preferably by dissolving an anthraquinone compound in a mixture of a non-polar solvent and a polar solvent, bl) hydrogenating the working solution, e.g. chemically reducing the anthraquinone derivatives present in the working solution using hydrogen gas and a catalyst, cl) optionally, separating the mixture of organic solvents, hydroquinone and quinone species from the catalyst, dl) oxidizing the hydrogenated working solution, e.g. oxidizing the hydroquinone species using oxygen, air or oxy gen-enriched air thus regenerating the quinone(s) with simultaneous formation of hydrogen peroxide, el) extracting hydrogen peroxide from the oxidized working solution, e.g. in an extraction column with water, fl) optionally, recovering hydrogen peroxide in the form of a crude aqueous hydrogen peroxide solution, gl) optionally, returning the working solution to the hydrogenator, hl) obtaining an aqueous effluent (A) by performing aqueous washes of the working solution, il) adding to the aqueous effluent (A) an acid (C) and an organic solvent (B) to obtain a mixed medium (D), preferably, the organic solvent (B) is an organic solvent (Bl) recovered from the manufacture of hydrogen peroxide in steps al) to gl), more preferably, the organic solvent (Bl) is a mixture containing the non-polar solvent used in step al), the polar solvent used in step al) and degradation products of the anthraquinone, j 1) decanting the mixed medium (D) obtained in step il) to obtain 2 phases (E, F), and kl) entering the aqueous phase (E) obtained in step j 1) into a coalescer (4) to separate the aqueous phase (E) in 2 new phases, a first fluid (G) with a TOC content lower than the aqueous phase, and a second fluid (H) with a TOC content higher than the aqueous phase.

[0069] More preferably, the overall process comprises in addition the following step:

[0070] 11) disposing the second fluid (H) as a waste (W). Waste W can for instance be burned.

[0071] More preferably, the overall process comprises in addition the following steps: ml) increasing the pH of the first fluid (G) to a value from 4 to 6, by adding an alkaline solution to the first fluid (G) to obtain an alkalized first fluid (I), and nl) transferring the alkalized first fluid (I) to a biological wastewater treatment unit (BWWTP).

[0072] Typically, the organic species in the effluent (A) comprises around 80 wt.-% TOC, the rest being all the other connected atoms. COD (Chemical Oxygen Demand) is the amount of oxygen needed to convert the convertible TOC to CO2. The COD can be estimated as follows: In theory, if all the TOC was convertible to CO2 in the process, then COD = 44 g / mol / 12 g / mol [(molecular weight CO2) / (molecular weight carbon)] = 3.6 times the amount of TOC (in mol). But in reality, not all the TOC is convertible to CO2, so on average the COD value will be around 2.5 times the TOC concentration (in mol) by experience.

[0073] The inventive process can remove around 40 wt.-% of the TOC / COD. In the biological treatment system, typically 86 wt.-% COD reduction with respect to the COD value of the effluent sent to the BWWTP is achieved. This efficacy of the BWWTP is irrespective of the pre-treatment (acid cracking or no acid cracking in advance). Thus, the COD removal in the BWWTP can be calculated as follows:

[0074] • No acid cracking: COD removal of 86 wt.-%, relative to the COD of the initial effluent (A)

[0075] • With acid cracking according to the invention: COD removal = COD removal before BWWTP + COD removal in BWWTP = 40 wt.-% + (0.6*86 wt.-%) = 91.6 wt.-%, relative to the COD of the initial effluent (A)

[0076] Thus, the total COD removed is increased with the acid cracking system in operation. The high efficiency of TOC / COD removal by the inventive process is obtained inter alia by step c): c) Entering the aqueous phase (E) obtained in step b) into a coalescer (4) to separate the aqueous phase (E) in 2 new phases, a first fluid (G) with a TOC content lower than the aqueous phase, and a second fluid (H) with a TOC content higher than the aqueous phase.

[0077] Preferably, the inventive process further comprises the following step: d) Disposing the second fluid (H) as a waste (W). Waste W can for instance be burned.

[0078] Step c) allows for a more complete separation of impurities from the aqueous phase. In particular, if the organic phase in step b) comprises rather small droplets, it may be difficult to achieve a complete phase separation by decantation in step b).

[0079] More preferably, in addition to steps c) and d), the inventive process further comprises the following steps: e) Increasing the pH of the first fluid (G) to a value from 4 to 6, by adding an alkaline solution to the first fluid (G) to obtain an alkalized first fluid (I), and f) transferring the alkalized first fluid (I) to a biological wastewater treatment unit (BWWTP).

[0080] After acid cracking (step a)), the mixed medium (D) preferably has a pH of from 2 to 6. A pH of 2 is often too aggressive for biological treatment. Thus, it is preferable to increase the pH in step e) to a value from 4 to 6, more preferably 4 to 5, more preferably 4 to 4.5, before sending the solution to the BWWTP.

[0081] EXAMPLES

[0082] In the following, the inventive process will be described in more detail by way of non-limiting examples. Example 1

[0083] Test procedure

[0084] Effluents obtained from an AO process to produce hydrogen by the anthraquinone method were used for this trial. In particular, the organic working solution is treated by performing some aqueous washes of the organic solution, generate both alkali and acid aqueous effluents. Two types of samples were evaluated. The initial range of the pH of the alkali effluent from CE5855 / 1 in the tests was + / - 10.7 to 11.2.

[0085] • CE-5855 / 1 alkaline reversion effluent (i.e., alkaline wash centrifuge)

[0086] • A combined stream consisting of 1 part CE-5855 / 1 and 2 parts P-5864 acidic effluent (i.e., alkaline wash centrifuge plus acid wash effluent)

[0087] The concentration of TOC in the CE5855 / 1 is higher than S5864, but on the other hand, the S5864 effluent is acid. Test were done on CE5855 / 1 alone and then CE5855 / 1 + S5864 to see which gave the best result. All of the trials were carried out with 300 mL of samples contained in 500 mL separatory funnels. The pH of the samples was adjusted using sulfuric acid. The range of the pH after the acid was added was 1.3 to 2.95.

[0088] In the general procedure, the concentration of the solvent added was 0.45 ml / 300 ml sample of effluent. In additional experiments, we varied the concentration of solvent to investigate the influence of solvent concentration. The organic solvent used was a mixture of Solvesso 150 (naphtha solvent) and DBC (Diisobutylcarbinol) in a ratio of from 1 :4 to 4: 1 (in the following: “Solvent G + DBC”).

[0089] After lowering the pH of effluent samples with sulfuric acid, we allowed the samples to separate overnight and analysed the aqueous portion for total organic carbon (TOC) and chemical oxygen demand (COD). We also made visual notes and photographed the solution, as sometimes 3 phases were formed.

[0090] For both the CE-5855 / 1 sample and the combined stream, we evaluated the effect of pH level on TOC and COD removal (see Table 1).

[0091] For both the CE-5855 / 1 sample and the combined stream, we evaluated the effect of adding solvent (Solvent G + DBC) to the mixture during the low pH stage. We accomplished this by adding a dose of solvent to the separatory funnel, hand-shaking the funnel for 60 seconds, and then allowing the phases to separate overnight (see Table 1).

[0092] We measured the amount of acid required to achieve the low pH target, and also measured the corresponding base required to bring the pH back to neutral. We did this both before separation of the organic phase from the sample and also following separation of the organic phase (see Table 2).

[0093] Results

[0094] CE-5855 / 1

[0095] Influence of pH (acid addition without solvent addition)

[0096] For the CE-5855 sample, we achieved TOC reductions of 44 to 52 wt.-%, with the best (52 wt.-%) removal at the lowest pH (Samples la to 4a).

[0097] We achieved 36 to 44 wt.-% reductions in COD when the pH of the sample was reduced. The best reduction in COD also came at the lowest pH level (Samples la to 4a).

[0098] Values for TOC reductions and COD reductions (in wt.-%) are given relative to the TOC value and COD value, respectively, present in the initial sample (effluent A).

[0099] Influence of solvent concentration

[0100] Following the acid cracking step, we added 3 different dose levels of solvent to 300 mL of the CE-5855 sample:

[0101] • At a solvent dose level of 15 mL (30 times more than target) we achieved a 70 wt.-% reduction in TOC and a 55 wt.-% reduction in COD (Sample 2a). The “target” concentration of solvent is as low as possible and was found to be in the range of 0 - 0.6 mL per 300 mL of sample, preferably 0.45 mL per 300 mL of sample. This corresponds to 0 - 2 mL per 1 L of acidified effluent, preferably 1.5 mL per 1 L of acidified effluent.

[0102] • At a solvent dose level of 1.0 mL (twice the target) we achieved 56 wt.-% reduction in TOC, compared with 47 wt.-% reduction without the addition of the solvent (Sample 4a). At a solvent dose level of 0.45 mL, we achieved 42 wt.-% reduction in TOC, compared to 44 wt.-% reduction without the addition of solvent (Sample 3a). We estimated this to be the dose level (0.45 mL / 300 mL effluent).

[0103] Maybe the most significant observation during the evaluation of the solvent addition was the complete absence of an organic phase at the bottom of the separatory flask.

[0104] Without the addition of solvent, when the pH of the CE-5855 sample is lowered, three phases are formed, including a red oil-like phase that sinks to the bottom of the container. The 3rd oil-like phase is not present with the addition of the solvent, but rather appears to be combined with the top layer organics.

[0105] Combined Stream (CE 5855 / 1 + P-5864, 1:2 ratio)

[0106] Influence of pH

[0107] For the combined stream sample, we achieved 11 - 70 wt.-% reductions in TOC after acidic addition (Sample 1c to 10c).

[0108] In 10 experiments with the combined stream, the average TOC reaction removed was 43 wt.-% when the pH of the combined stream was adjusted to levels between 1.3 and 2.5. If we eliminate the lowest result (18 wt.-% removed) and the highest result (70 wt.-% removed), the average of the remaining 8 experiments remains at 43 wt.-% TOC removed.

[0109] Fig. 2 shows the dependency of aromatic TOC in the sample on the pH value.

[0110] Influence of solvent concentration

[0111] We also evaluated the effect of adding solvent to the combined stream sample at 2 levels. Following the acid cracking step, we added 2 different dose levels of solvent to 300 mL of the combined stream sample.

[0112] • At a solvent dose level twice that of target (1.0 mL per 300 mL of sample), the TOC fraction that was removed increased to 40 wt.-%, versus 16 wt.-% when no solvent was added. The COD fraction removed increased to 25 wt.- % versus 6 wt.-% when no solvent was added (Sample 4c).

[0113] At a solvent dose level at target (0.45 mL per 300 mL of sample), the TOC fraction remove increased to 32 wt.-% versus 29 wt.-% when no solvent was added in one experiment at pH 2.5. COD measurements show 34 wt.-% fraction removed versus 31 wt.-% when no solvent was added. (Sample 3c). In another experiment at pH 2.05 the difference was more significant, with 64 wt.-% of the TOC removed with solvent versus 44 wt.-% without solvent (Sample 5c).

[0114] When experiments with the combined stream were carried out, we did not observe the presence of a red oil-like phase that sinks to the bottom of the funnel. However, in some cases we noted the presence of an opaque residue adhering to the walls of the funnel. pH Adjustment

[0115] Samples of CE-5855 required 1.8 to 2.3 grams of sulfuric acid (96% acid basis) per 300 mL of sample to lower the pH to levels between 1.3 and 2.3.

[0116] For the combined stream samples, the acid required to lower the pH of 300 mL of sample varied between 0.65 and 0.91 grams (96% acid basis). In these experiments, the final pH of the combined stream was 1.74 to 2.1.

[0117] In experiments to re-neutralize the combined stream sample back to pH 7, we required 0.1 - 0.14 grams caustic soda (100% basis) per 100 mL sample.

[0118] The caustic requirements to re-neutralize the CE-5855 back to pH 7 appear to be about the same, with 0.42 - 0.47 grams NaOH required per 300 mL sample.

[0119] Table 1: Results of pH, TOC and COD measurements for samples as received (samples: CE-5855 / 1 (“5855 / 1”), P-5864 (“5864”), mixture of 1 part CE-5855 / 1 and 2 parts P-5864 (“1 to 2 mixture”), after acid addition (sulfuric acid, 96%) and after solvent addition (Solvent G + DBC). The percentage amount of TOC and COD that could be removed in each case is indicated for each sample (“Fraction removed”).

[0120]

[0121]

[0122]

[0123] Table 2: Amount of acid required to achieve the low pH target, and amount of base required to bring the pH back to neutral. The amount of acid added is before separation of the organic phase and the amount of base is added after separation of the organic phase.

[0124]

[0125]

[0126] Example 2 (according to the invention)

[0127] In Example 2, the influence of using a coalescer was investigated.

[0128] In an industrial plant, 164 T / day of an aqueous effluent (A) was generated in a manufacture of hydrogen peroxide by an anthraquinone method. This aqueous effluent (A), which had a pH of 10.7 and an organic content of 1204 ppm (corresponding to 198 kg / day organic compounds), was stored in a holding tank 1.

[0129] Then, the aqueous effluent (A), an organic solvent (B) and an acidic effluent (C) were mixed in a mixer to obtain a mixed medium (D).

[0130] The mixed medium (D) was introduced in a settling tank (3) and decanted to obtain 38.6 kg / day of a floating organic phase (F) and an aqueous phase of an acid effluent (E) comprising traces (160 kg / day, 970 ppm) of organics in the form of organic droplets.

[0131] Then, the acid effluent (E) was introduced in a coalescer (4) where it was separated into an aqueous first fluid (G) containing 723 ppm organics (119 kg / day) and 40.8 kg / day of a floating organic second fluid (H) made of the coalesced organic droplets.

[0132] Therefore, the coalescer allowed for decreasing the organic content of the acid effluent (E) from 160 kg / day down to 119 kg / day, i.e. by about 25%.

[0133] Considering the cumulative effect of the settling tank (3) and of the coalescer (4), the organic content of the aqueous effluent (A) could be reduced from 198 kg / day organics to 119 kg / day, i.e. by about 40%.

[0134] The aqueous first fluid (G) was then collected in a tank (5) and sent to a “biological waste water treatment unit” using a pump (6).

[0135] The organic phase (F) and organic second fluid (H) were collected in a second collection (7), pumped and disposed as a waste (W).

[0136] Consequently, the organics that were separated by the invented process, using the settling tank (3) and the coalescer (4) amount to:

[0137] • 38.6 kg / day of the floating organic phase (F) from the settling tank (3), plus • 40.8 kg / day of the floating organic second fluid (H) separated by the coalescer (4), that is 79.4 kg / day organics, out of which more than 50% were unexpectedly removed thanks to the coalescer (4).

[0138] CONCLUSION

[0139] 1. The organic loading of aqueous effluent can be effectively reduced by combining the alkaline effluent from CE-5855 / 1 and the acidic effluent from P- 5864, lowering the pH to 2, and separating the resultant organic phase. When these streams are combined in a 1 :2 ratio, only 2 phases are observed.

[0140] 2. By lowering the pH of the mixed stream of CE-5855 and P-5864, we can physically separate an organic layer from the aqueous effluent, thereby reducing the TOC and COD by 30 - 40 wt.-%.

[0141] 3. Organic removal from the mixed stream is improved by the addition of solvent. Further, the formation of only 2 phases (see points 4. and 5. below) contributes to an increased separation efficacy.

[0142] 4. When the CE-5855 stream (alone) is acid cracked, 3 phases are formed, a light organic phase, an aqueous phase, and a heavy organic phase.

[0143] 5. Solvent can be added to the acid cracked CE-5855 stream to produce only 2 phases, a light organic phase and an aqueous phase.

[0144] 6. Based on acid requirements of 0.65 - 0.9 grams / 300 mL to achieve pH levels at 2.0, the demand for acid, e.g. H2SO4, can be reduced, which is advantageous from an ecological and economical point of view.

[0145] 7. Based on caustic requirements of 0.1 - 0.14 grams caustic soda / 100 mL effluent), to neutralize to pH 7 following acid cracking, the demand for caustic soda can be reduced, which is advantageous from an ecological and economical point of view.

[0146] 8. A solvent addition (DBC + Solvent G) dose of 0.45 mL / 300 mL appeared to work in these experiments. That means that only a rather low amount of solvent is needed, which is advantageous from an ecological and economical point of view. 9. The removal of organics can be further improved by using a coalescer.

[0147] Summary

[0148] In summary, it has been demonstrated that addition of sulfuric acid in combination with an organic solvent to the combined dark water stream produces a good phase separation with one single low density organic phase being produced. By reducing the pH to 2.0, a 40 wt.-% reduction in TOC can be achieved. The use of a coalescer can significantly improve the removal of organics.

Claims

CLAIMS1. A process for the purification of an aqueous effluent (A) generated in the manufacture of hydrogen peroxide by the anthraquinone method, comprising the steps of: a) Adding to the aqueous effluent (A) an acid (C) and an organic solvent (B) to obtain a mixed medium (D), b) Decanting the mixed medium (D) obtained in step a) to obtain 2 phases (E, F), wherein the aqueous phase (E) has a TOC content lower than the aqueous effluent (A) and the liquid organic phase (F) has a TOC content higher than the aqueous effluent (A), c) Entering the aqueous phase (E) obtained in step b) into a coalescer (4) to separate the aqueous phase (E) in 2 new phases, a first fluid (G) with a TOC content lower than the aqueous phase, and a second fluid (H) with a TOC content higher than the aqueous phase.

2. The process according to claim 1, wherein the aqueous effluent (A) is an alkaline effluent, preferably having a pH of from 10 to 12.

3. The process according to claim 1 or 2, wherein the aqueous effluent (A) contains aromatic impurities, such as unsubstituted or Ci-Cio alkylsubstituted phthalic acids or salts thereof, and mixtures thereof, preferably, wherein the aromatic impurities are chosen from sodium or potassium salts of phthalic acid, tert-amylphthalic acid, sec-amylphthalic acid, and mixtures thereof.

4. The process according to any of claims 1 to 3, wherein the acid (C) is at least one strong mineral acid, in particular selected from HNO3, H2SO4, H3PO4, HC1 and mixtures thereof.

5. The process according to any of claims 1 to 4, wherein the mixed medium (D) obtained in step a) has a pH of from 2 to 6.

6. The process according to any of claims 1 to 5 wherein the organic solvent (B) comprises a mixture of (i) a non-polar aromatic solvent, preferably a non-polar aromatic alkyl solvent, more preferably a non-polar aromatic(C9 to Cl l)alkyl solvent, more preferably a non-polar aromatic (ClO)alkyl solvent, and (ii) a polar solvent, preferably an alcoholic solvent, such as a Ci-Cio dialkyl carbinol, preferably diisobutylcarbinol, or an acetate, such as ortho methyl cyclohexane acetate.

7. The process according to any of claims 1 to 6, wherein the organic solvent (B) is an organic solvent (Bl) recovered from the manufacture of hydrogen peroxide by the anthraquinone method.

8. The process according to claim 7, wherein the anthraquinone process comprises the successive steps of hydrogenating a working solution, oxidizing the hydrogenated working solution and extracting hydrogen peroxide from the oxidized working solution, and wherein the aqueous effluent (A) originates from performing aqueous washes of the working solution.

9. The process according to claim 7 or 8, wherein the anthraquinone process makes use of a non-polar solvent, a polar solvent, and an anthraquinone compound, and wherein the organic solvent (Bl) is a mixture containing the non-polar solvent, the polar solvent and degradation products of the anthraquinone.

10. The process according to any of claims 1 to 9, wherein the organic solvent (B) is added in step a) in an amount 0 - 5 mL per 1 L of aqueous effluent (A), more preferably 0 - 2 mL per 1 L of aqueous effluent (A), more preferably 0.5 to 1.5 mL per 1 L of aqueous effluent (A) .

11. The process according to any of claims 1 to 10, wherein the duration of step b) is from 1 to 36 hours, preferably 6 to 36 hours, more preferably 6 to 24 hours.

12. The process according to any of claims 1 to 11, further comprising the step: d) Disposing the second fluid (H) as a waste (W).

13. The process according to claim 12, further comprising the following steps:e) increasing the pH of the first fluid (G) to a value from 4 to 6, by adding an alkaline solution to the first fluid (G) to obtain an alkalized first fluid (I), and f) transferring the alkalized first fluid (I) to a biological waste water treatment unit (BWWTP).

14. An apparatus for the purification of an aqueous effluent generated in the manufacture of hydrogen peroxide by the anthraquinone method, comprising: i) a holding tank (1) configured to store an aqueous effluent (A); ii) at least one device (2) configured to add an acid (C) and an organic solvent (B) to the aqueous effluent (A) to obtain a mixed medium (D); iii) a settling tank (3) configured to store the mixed medium (D) and to allow for phase separation, and configured to decant the mixed medium (D) to obtain 2 phases, namely a floating organic phase (F) and an aqueous phase of an acid effluent (E) comprising traces of organics in the form of organic droplets; and iv) a coalescer (4) configured to coalesce the organic droplets of the phase (E) and to separate it into an aqueous first fluid (G) and a floating organic second fluid (H) comprising coalesced organic droplets.

15. The apparatus according to claim 14, further comprising: v) a first collection tank (5) configured to store aqueous effluents (G, I); vi) optionally, a device configered to add base to the aqueous first fluid (G) to prepare an alkalized first fluid (I); vii) optionally, a pump (6) configured to pump the aqueous first fluids (G, I) around the first collection tank (5) and / or to pump the alkalized first fluid (I) to a biological waste water treatment unit (BWWTP); viii) optionally, a second collection tank (7) configured to store the organic effluents (F, H); andix) optionally, a pump (8) configured to pump the organic effluents (F, H) from the second collection tank (7) to a facility to dispose of the waste organic material.

16. Use of the process according to any one of the preceding claims in the manufacture of hydrogen peroxide by the anthraquinone method.

17. A process for the manufacture of hydrogen peroxide and for the purification of an aqueous effluent (A) generated in said manufacture of hydrogen peroxide, said process comprising: manufacturing hydrogen peroxide by an anthraquinone method, and purifying the aqueous effluent (A) by the process according to any one of claims 1 to 13.

18. The process according to claim 17, comprising the following steps : al) preparing a working solution, typically an organic working solution, preferably by dissolving an anthraquinone compound in a solvent, more preferably by dissolving an anthraquinone compound in a mixture of a non-polar solvent and a polar solvent, bl) hydrogenating the working solution, e.g. chemically reducing the anthraquinone derivatives present in the working solution using hydrogen gas and a catalyst, cl) optionally, separating the mixture of organic solvents, hydroquinone and quinone species from the catalyst, dl) oxidizing the hydrogenated working solution, e.g. oxidizing the hydroquinone species using oxygen, air or oxy gen-enriched air thus regenerating the quinone(s) with simultaneous formation of hydrogen peroxide, el) extracting hydrogen peroxide from the oxidized working solution, e.g. in an extraction column with water, fl) optionally, recovering hydrogen peroxide in the form of a crude aqueous hydrogen peroxide solution,gl) optionally, returning the working solution to the hydrogenator, hl) obtaining an aqueous effluent (A) by performing aqueous washes of the working solution, il) adding to the aqueous effluent (A) an acid (C) and an organic solvent (B) to obtain a mixed medium (D), preferably, the organic solvent (B) is an organic solvent (Bl) recovered from the manufacture of hydrogen peroxide in steps al) to gl), more preferably, the organic solvent (Bl) is a mixture containing the non-polar solvent used in step al), the polar solvent used in step al) and degradation products of the anthraquinone, j 1) decanting the mixed medium (D) obtained in step il) to obtain 2 phases (E, F), and kl) entering the aqueous phase (E) obtained in step j 1) into a coalescer (4) to separate the aqueous phase (E) in 2 new phases, a first fluid (G) with a TOC content lower than the aqueous phase, and a second fluid (H) with a TOC content higher than the aqueous phase.

19. The process according to claim 18, further comprising the step:11) disposing the second fluid (H) as a waste (W).

20. The process acceding to claim 19, further comprising the following steps: ml) increasing pH of the first fluid (G) to a value from 4 to 6, by adding an alkaline solution to the first fluid (G) to obtain an alkalized first fluid (I), and nl) transferring the alkalized first fluid (I) to a biological wastewater treatment unit (BWWTP).

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