RU2778318C2 - Method for purification of wastewater - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to the field of treatment of wastewater of an industrial process of propylene oxide production. Treatment of wastewater is carried out by catalytic wet oxidation, in which a flow containing wastewater is supplied to a reactor, the flow containing wastewater is treated by oxidation in the presence of oxygen and a catalyst containing porous carbon balls doped with metal nanoparticles. At least part of the treated flow is transferred to a separator, where the treated flow is separated into a gas flow and a liquid flow, and part of the liquid flow is recirculated to the reactor.

EFFECT: invention allows for the development of a simple and effective method for purification under milder conditions with reduction in chemical oxygen demand (COD) in absolute and percentage terms.

10 cl, 2 tbl, 1 dwg

Description

Technical field

The present invention relates to a process for treating wastewater from industrial processes that may contain hydrocarbons and salts, in particular for treating wastewater from an industrial process for producing propylene oxide.

State of the art

The treatment or treatment of wastewater generated during industrial processes and containing at least hydrocarbons and salts (organic and/or inorganic) is usually a relatively expensive procedure. Currently, environmental legislation imposes stringent requirements on the treatment of wastewater from industrial processes, especially when treated wastewater is to be released into the environment. Accordingly, the choice of industrial wastewater treatment method is associated with practical, environmental and economic considerations.

Processes for the production of propylene oxide (PO) generate wastewater streams that pose particular problems with regard to treatment. Propylene oxide can be obtained by direct oxidation of propylene with air or oxygen. Since such direct oxidation usually gives low yields of PO, PO is most often produced with the help of a chemical intermediate, which often consists of an organic or inorganic peroxide.

One industrial process for the production of propylene oxide, which generates a relatively large amount of wastewater, is the production of styrene monomer/propylene oxide (SM/PO). In general, SM/PO manufacturing processes include the following steps: (i) reacting ethylbenzene with oxygen or air to form ethylbenzene hydroperoxide, (ii) reacting the thus obtained ethylbenzene hydroperoxide with propene in the presence of an epoxidation catalyst to form propylene oxide, and 1-phenylethanol, and (iii) converting 1-phenylethanol to styrene by dehydration using a suitable dehydration catalyst. The last step is to produce water. In addition to this reaction water, organic by-products are formed such as aliphatic and aromatic hydrocarbons, aldehydes, ketones, alcohols, phenols and organic acids. By-products are separated from the main products either by separation methods such as distillation or absorption or, in the case of organic acids, by neutralization with an alkaline aqueous solution such as an aqueous solution of sodium (bi)carbonate and/or sodium hydroxide. In addition, additional water is introduced with air in step (i) and enters as steam in step (iii) of the above process, and the reaction water generated in step (iii) also appears. These streams also become part of the factory wastewater stream.

Wastewater from a SM/PO plant typically contains a total of 1.0 to 3.5% by weight of non-salt organic compounds and 3.0 to 6.0% by weight of organic salts. These effluents may additionally contain up to and including 3.0% by weight of sodium carbonate and sodium bicarbonate, and/or traces of sodium hydroxide, depending on the alkaline solution used in the neutralization of the organic acids.

The output of wastewater from an SM/PO plant can be tens of thousands of kg/h and cannot be discharged without additional treatment. However, as already mentioned above, the choice of a suitable cleaning treatment is limited by a number of practical, environmental and economic considerations.

Another phenyl hydroperoxide that can be used in the manufacture of propylene oxide is cumene hydroperoxide (2-hydroperoxypropan-2-ylbenzene), which is usually prepared by reacting cumene ((1-methylethyl)benzene)) with oxygen or air. Cumene hydroperoxide reacts with propylene in the presence of an epoxidation catalyst to form PO and cumyl alcohol (2-phenylpropan-2-ol). Cumyl alcohol, also called dimethylphenylcarbinol (DMPC), is usually converted to cumene by hydrogenolysis with a heterogeneous catalyst and hydrogen. The cumene can then be reused in the process.

Wastewater generated in such processes may contain oxygenated compounds having phenolic hydroxyl groups or carbonyl groups. Typical contaminants may include ketones such as acetone, ethyl methyl ketone and diethyl ketone, aldehydes such as formaldehyde, acetaldehyde and propionaldehyde, ethers, aromatic and non-aromatic alcohols such as phenols and methanol, chlorinated compounds such as dichloropropane, and organic sodium salts, such as sodium acetate, sodium formate, sodium benzoate, sodium propionate and sodium oxalate.

Treatment of wastewater streams from the propylene oxide manufacturing process presents particular challenges because such streams often have a higher chemical oxygen demand (COD) than wastewater streams from other chemical processes. For example, typical initial COD values for wastewater streams from the production of propylene oxide range from 80,000 to 125,000 mg/L. Therefore, treatment methods for such wastewater streams must provide a significant reduction in COD, both in absolute terms and in percentage terms.

A typical purification process used in industrial processes to treat wastewater streams from the production of propylene oxide involves liquid phase oxidation with air or oxygen at high temperatures and pressures (the so-called wet air oxidation (WAO) process).

Moist air oxidation is a well-known process stream treatment technology pioneered by F.D. Zimmerman in the 1930s. This technology uses the oxidation of aqueous phase process streams with oxygen-containing gas at elevated temperatures and pressures to oxidize inorganic contaminants and convert organic contaminants to carbon dioxide, water and biodegradable short chain organic compounds.

Moist air oxidation is typically carried out to treat propylene oxide production wastewater streams at temperatures above 300° C. and pressures above 200 bar (20 MPa). However, since the waste from these wet air oxidation processes still has a significant COD, industrial processes for treating wastewater streams from the production of propylene oxide often require subsequent additional treatment steps.

For example, such technologies may use a two-stage process, where the first stage involves the oxidation of the liquid phase with air or oxygen at high temperatures and pressures (the so-called wet air oxidation (WAO) process), and the second stage includes biochemical processing.

In some purification processes, there may be additional optional steps, such as treatment with activated carbon prior to biochemical treatment. For example, US Pat. No. 4,066,538 A describes a process for treating wastewater having a relatively high chemical oxygen demand (COD) due to organic material that is predominantly water soluble. Said process includes treatment with activated carbon followed by a biochemical treatment step.

Repsol presented (CHISA 2002, Praha, Czech Republic, August 25-29, 2002) a method for treating industrial wastewater from the production of propylene oxide/styrene monomer, in which the wastewater, after being oxidized with moist air, is subjected to a two-stage treatment with activated carbon, in which a homogeneous mixture powdered activated carbon and biological solids result in synergistic wastewater treatment. It was stated that the moist air oxidation treatment was carried out at 295° C., 95 bar (9.5 MPa) for 1.5 hours using compressed oxygen gas as the oxidizer.

However, multi-stage processes involving moist air oxidation and biochemical treatments are expensive and have other disadvantages, including equipment reliability issues, corrosion, fouling, and downtime periods due to extreme operating conditions that must be used during humid air oxidation, and these processes can generate other waste streams such as spent activated carbon. Accordingly, various alternative methods have been proposed over the years for treating wastewater streams from propylene oxide production processes.

The purification process disclosed in GB No. 2262052 A involves freeze concentration combined with salt removal, whereby the waste water is separated into at least twice concentrated waste, salt crystals and a substantially pure aqueous product. However, the economic performance of the freeze-concentration process is not satisfactory, and at present the capital investment required to implement the freeze-concentration process is still at least 10% of the total investment required for the SM/PO plant.

WO 99/67003 A1 discloses a process for treating wastewater streams containing at least hydrocarbons and salts to produce a pure aqueous product, a concentrated salt product and a hydrocarbon-rich product, which includes the following steps:

(a) feeding wastewater from above into the first distillation column in stages ranging from 0.05*n to 0.15*n, where n represents the total number of theoretical stages of the first distillation column and has a value in the range from 20 to 40;

(b) taking off a vapor stream from above in stages ranging from 0.55*n to 0.75*n and feeding this vapor stream to the bottom of a second distillation column having m theoretical stages, where m has a value in the range from 3 to 10 ;

(c) withdrawing the pure aqueous product as tops from the second distillation column and withdrawing the bottom stream from the second distillation column, which is fed back to the first distillation column below the overhead vapor stream in step (b) at stages ranging from 0.60* n to 0.85*n;

(d) withdrawing the concentrated salt product as the bottoms of the first distillation column; and

(e) withdrawing the hydrocarbon stream as the tops of the first distillation column. The process according to WO 99/67003 A1 is reported to require 10-50% less investment than freeze concentration processes as disclosed in GB 2262052 A while still achieving good purification.

US Pat. No. 5,993,673 A describes a process for purifying an aqueous purge stream from the production of propylene oxide/styrene monomer containing organic acids, peroxide materials and ethylbenzene, comprising contacting the purge stream with a particulate iron-promoted alumina catalyst in conditions effective to decompose peroxide materials, and recovering a peroxide-reduced treated stream. After that, the stream treated according to the method of US 5993673 A can be purified from ethylbenzene, and then subjected to effective biological treatment.

WO 01/00534 A1 discloses an improved process for treating waste water containing organic pollutants, comprising as a step (a) a freeze concentration process as described in GB 2262052 A followed by (b) treating the resulting aqueous stream with reverse osmosis, resulting in a purified water stream in the form of a filtrate and a stream of relatively contaminated water in the form of a concentrate. However, such a method may present potential difficulties in dealing with solids, as the rotating equipment may be susceptible to contamination.

WO 01/32561 A1 discloses an industrial process for the production of propylene oxide, comprising the following steps:

(a) multi-stage evaporative treatment of waste water, which results in the formation of a vaporous upper fraction and a liquid lower fraction containing non-volatile pollutants; and

(b) condensing at least a portion of the vapor overhead into a liquid stream that is subjected to a stripping treatment, resulting in an overhead stream containing volatile organic wastes and a liquid bottom stream comprising purified water.

The purified water produced by the process according to WO 01/32561 A1 is pure enough to be reused in an industrial process, for example as cooling water, but it can also be subjected to a subsequent biological treatment that produces a stream of pure water, which may be clean enough to be discharged into surface waters.

However, the process according to WO 01/32561 A1 requires the evaporation of a very high fraction of water, which requires a lot of energy and the use of distillation columns with high throughput.

WO 2006/104222 A1 describes a method for treating wastewater containing an oxygenate compound having a phenol hydroxyl group or a carbonyl group, comprising the step of adding an alkaline agent to wastewater containing an oxygenate compound having a phenolic hydroxyl group or a carbonyl group to adjust the pH of the wastewater to 10 or more; and a discharge separating step in which an oxygen-containing compound having a phenolic hydroxyl group or a carbonyl group is concentrated by distilling off the waste water to which an alkaline agent has been added.

WO 2009/138530 A describes a process for converting wastewater streams from propylene oxide and styrene co-production processes, comprising acidifying the wastewater stream with an inorganic acid to pH less than 4.5, separating the two resulting phases at temperatures above 40°C; washing the organic phase obtained in the previous step with an aqueous solution with excess acid and separating the two phases obtained.

However, the process described in WO 2009/138530 A has a number of difficulties, including potential corrosion problems, acid handling and consumption, management of organics dissolved in the aqueous phase, and potential ester formation with organic alcohols.

Despite a large body of research on the treatment of wastewater streams from propylene oxide production processes, there is still a need to develop simpler and more cost-effective wastewater treatment processes that do not pose equipment reliability issues and that produce clean water streams that can be released into the environment. In particular, it is desirable to treat wastewater streams from propylene oxide manufacturing processes under milder conditions and with a preferable reduction in COD, both in absolute and percentage terms.

The essence of the invention

Surprisingly, it has been found that the wastewater treatment process of the present invention can provide one or more of the above desired improvements, which method comprises treating the wastewater with catalytic wet oxidation in combination with recirculating a portion of the liquid stream to the reactor after the oxidative treatment in said reactor and after the separation processed stream to liquid stream and gas stream.

Accordingly, the present invention relates to a process for treating wastewater from an industrial process for producing propylene oxide, which includes treating wastewater with catalytic wet oxidation, comprising:

feeding into the reactor a stream containing waste water;

oxidative treatment of a stream containing wastewater in the presence of oxygen and a catalyst, resulting in a treated stream;

transferring at least a portion of the treated stream to a separator, where the treated stream is separated into a gas stream and a liquid stream; and

recirculation of a portion of the liquid stream to the reactor.

Brief description of graphic materials

On FIG. 1 illustrates an embodiment of the wastewater treatment method of the present invention.

Detailed description of the invention

The wastewater to be treated according to the present invention may be obtained from any propylene oxide production process. However, in a preferred embodiment of the present invention, wastewater is generated from the co-production of propylene oxide and styrene. Until now, such wastewater streams have been very difficult to treat due to their very high COD.

As described above, wet oxidation processes are known in the art and involve the oxidation of water-soluble or suspended components using oxygen as the oxidant. In cases where air is used as the source of oxygen, this process is called the wet air oxidation (WAO) process.

In wet air oxidation systems, rotating equipment is typically used to raise the feed stream and air (or oxygen) to the required operating pressure. Heat exchangers are typically used to extract energy from the reactor effluent, and the recovered energy is used to preheat the feed/air mixture entering the reactor. Since the oxidation reactions are exothermic, enough energy can be released in the reactor after startup to allow the wet oxidation system to operate without any additional heat input.

As described above, non-catalytic wet oxidation processes for treating wastewater from propylene oxide manufacturing processes are not only expensive, but have other disadvantages, including equipment reliability issues, corrosion, fouling, and downtime due to extreme operating conditions. that have to be used.

However, it has surprisingly been found that the catalytic wet oxidation process of the present invention can be successfully carried out under less extreme operating conditions, even for wastewater streams having a very high initial COD.

The oxidation treatment step in the present process may be carried out at a temperature in the range of 120 to 350° C. and at a pressure in the range of 1 to 30 MPa. However, it may preferably be convenient to carry out the oxidative treatment step of the process of the present invention at a temperature in the range of 120 to 300° C. and a pressure in the range of 2 to 20 MPa. Preferably, said oxidative treatment step can be carried out at a temperature in the range of 150 to 280°C, more preferably in the range of 180 to 240°C and a pressure in the range of 2 to 15 MPa, more preferably in the range of 2 to 12 MPa, most preferably in the range of 2 to 8 MPa. For the purposes of this specification, pressure is expressed as "gauge pressure".

The method of the present invention may be carried out in a continuous manner.

In the present process, a stream containing wastewater from an industrial propylene oxide production process is fed into a reactor. In a preferred embodiment of the invention, the subsequent oxidative treatment step of this method is carried out in such a way that the wastewater stream achieves a preferable reduction in COD, both in absolute and percentage terms, without the need for any pre-treatment of the wastewater before implementing the method of the present invention.

In the oxidative treatment step of the present process, a wastewater containing stream is subjected to an oxidative treatment in the presence of oxygen and a catalyst. In addition, in addition to supplying the reactor with a stream containing waste water, a gas stream containing oxygen and optionally an inert gas can be supplied to the reactor. Said gas stream may be fed into the reactor separately or may be fed into the reactor after mixing with the waste water stream. Said inert gas may be any inert gas such as nitrogen.

The amount of oxygen in the above gas stream containing oxygen and optionally an inert gas may range from 1 to 100% by volume, more preferably from 10 to 100% by volume, more preferably from 20 to 100% by volume, more preferably 25 to 100% by volume, more preferably 25 to 95% by volume, more preferably 40 to 85% by volume, most preferably 50 to 75% by volume. In the latter case, the gas stream may contain one or more inert gases, including, for example, nitrogen, in an amount which, together with the amount of oxygen, is up to and including 100% by volume.

The aforementioned gas stream containing oxygen and optionally an inert gas may be a gas stream consisting of air.

In addition, the aforementioned gas stream containing oxygen and possibly an inert gas may be a gas stream consisting of a combination of air and an additional amount of one or more inert gases, including, for example, nitrogen. The specified "additional amount of one or more inert gases" does not include the amount of inert gases present in the air. In the latter case, the oxygen concentration is lower than in air, i.e. below 21 vol.%. In particular, the amount of oxygen in said gas stream may range from 1% to less than 21% by volume, more preferably from 1% to 20% by volume. In the latter case, the gas stream contains one or more inert gases, including, for example, nitrogen, in an amount which, together with the amount of oxygen, is up to and including 100% by volume.

Preferably, the aforementioned gas stream containing oxygen and optionally an inert gas is a gas stream in which the oxygen concentration is higher than air, i.e. higher than 21% by volume. Said gas stream may be a gas stream in which the amount of oxygen is in the range from more than 21 to 100% by volume, preferably from 25 to 100% by volume, preferably from 25 to 95% by volume, preferably from 40 to 85 vol%, most preferably 50 to 75 vol%. In the latter case, the gas stream may contain one or more inert gases, including, for example, nitrogen, in an amount which, together with the amount of oxygen, is up to and including 100% by volume.

The amount of catalyst in the reactor may be appropriately selected depending on the initial COD value of the wastewater to be treated and the degree of COD reduction desired after treatment has been applied. However, the catalyst is generally used in an amount (in grams) per feed rate of the wastewater-containing stream (in liters per hour) in the range of 10 to 300 g/(l/h), more preferably 25 to 250 g /(l/h), more preferably 35 to 200 g/(l/h), more preferably 45 to 150 g/(l/h), most preferably 50 to 125 g/(l/h) .

Further, according to the present method, at least a part of the treated stream, which is formed in the oxidation treatment step, is sent to a separator, where the treated stream is separated into a gas stream and a liquid stream. Before transferring the treated stream to the separator, said stream may be cooled, for example by means of a heat exchanger.

Finally, in the present process, a portion of the above separated liquid stream is returned to the reactor. The relative proportion of the portion of the liquid stream that is returned to the reactor can vary within wide limits. Preferably, 1 to 99% of the liquid stream separated in the separator is returned to the reactor. More preferably, said relative proportion is in the range of 5 to 95%, more preferably 15 to 95%, more preferably 20 to 95%, most preferably 25 to 95%. Said relative proportion of the portion of the liquid stream that is recycled to the reactor is preferably at least 1%, more preferably at least 2%, more preferably at least 5%, more preferably at least 10%, more preferably at least 15%, more preferably at least 20%, most preferably at least 25%. In addition, said relative proportion of the portion of the liquid stream that is recycled to the reactor is preferably at most 99%, more preferably at most 98%, more preferably at most 97%, more preferably at most 96%, most preferably at most greater than 95%.

Optionally, in addition to recirculating part of the liquid stream separated by the separator, part of the gas stream separated by the separator may also be returned to the reactor. Preferably, however, only a portion of said liquid stream is returned to the reactor.

Depending on the initial COD of the wastewater stream and the intended subsequent use of the wastewater stream, optional post-treatment steps may be performed in some embodiments of the present invention. However, for many applications, the high COD reductions achieved with the method of the present invention are sufficient to avoid the need for additional post-processing steps.

After use in the process of the present invention, the spent catalyst can be regenerated and used in subsequent cycles, depending on the residual catalytic activity of the catalyst after the individual cycles.

As mentioned above, the present wastewater treatment method can be conveniently integrated with the SM/PO process.

The wastewater treatment method of the present invention is illustrated in FIG. 1. In the process illustrated in Figure 1, a stream containing industrial process effluent for the production of propylene oxide is fed via feed line 1 to reactor 3. Reactor 3 contains a catalyst and has a downflow configuration. Alternatively, reactor 3 may be in an upflow configuration. In addition, a gas stream containing oxygen and nitrogen is separately supplied to the reactor 3 via line 2. An electric heater (not shown) is used to heat the reactor 3. Alternatively, before entering the reactor 3, the waste water stream and the gas stream can be combined and heated using a heat exchanger (not shown). In the reactor 3, the waste water is subjected to an oxidative treatment in the presence of oxygen and a catalyst. The resulting treated stream leaves the reactor 3 via line 4 and is optionally cooled by a heat exchanger (not shown). Then, optionally, the cooled treated stream is sent to a liquid/gas separator 5, in which said stream is separated into a gas stream and a liquid stream. The gas stream leaves separator 5 via line 6 and may be cooled and sent to a furnace or other processing system (not shown). The liquid stream leaves the separator 5 via line 7. Said liquid stream is divided into 2 substreams. One of these substreams is removed through product line 8. The stream in product line 8 may be further refined, depending on the final COD specifications it must meet. The other substream is directed through the recirculation line 9 to the supply line 1 and combines with the wastewater stream and then returns to the reactor 3.

The oxidative treatment step of the process of the present invention is carried out in the presence of a catalyst. Preferably, the reactor to which the stream containing wastewater is fed contains said catalyst. Said catalyst may be any catalyst suitable for oxidizing wastewater with moist air in the presence of oxygen.

A suitable catalyst that can be used in the oxidative treatment step of the process of the present invention is a catalyst comprising porous carbon beads doped with metal nanoparticles. Such a catalyst for use in the process of the present invention may contain one or more metals incorporated into polymer beads. One or more metals may, for example, be incorporated into the beads during the polymerization step.

The term "bead" as used herein may refer to a particle or a nanoparticle. The particle or nanoparticle size is the same as described herein or as indicated by the context.

Preferably, the metal is selected from one or more of the following metals: aluminum, iron, nickel, copper, silver, cobalt, molybdenum, gold and platinum. More preferably, the metal is selected from one or more of the following metals: iron, nickel, copper and cobalt. Most preferably, the metal is selected from one or more of the following metals: nickel, copper and cobalt. Copper is a particularly preferred catalyst metal.

In some embodiments, a combination of metals or their salts can easily be included in the beads. Examples of preferred combinations include, but are not limited to, iron and copper, copper and nickel, and nickel and iron.

Examples of metal salts that can be used to incorporate metals into polymer beads include, but are not limited to, aluminum nitrate, iron chloride, iron nitrate, nickel nitrate, copper chloride, copper nitrate, silver nitrate, cobalt nitrate, molybdenum nitrate, gold chloride , platinum chloride, or any combination thereof.

The above catalyst that can be used in the process of the present invention can generally be obtained by slurry polymerization methods known in the art. For example, A. Sharma et al. , Chem. Eng. sci. 65 (2010) 3591-3601, R. Saraswat et al. , Chem. Eng. J. 197 (2012) 250-260, US 2013/0319946 A1, P. Khare et al. J. Colloid. interface sci. 418 (2014) 216-224 and US 2015/005626 A1 describe the preparation of various porous carbon spheres doped with metal nanoparticles.

The porous carbon beads doped with metal nanoparticles that can be used as a catalyst in the oxidation treatment step of the process of the present invention can generally be prepared by a process comprising: - (i) preparing a mixture of one or more aromatic alcohol monomers and/or non-aromatic monomers, a solvent, a polymerization catalyst, a cross-linking agent, a suspension stabilizing agent, and one or more metal salts under conditions suitable for preparing polymer beads doped with one or more metals or their salts; and (ii) carbonizing, activating and then reducing the polymer beads obtained in step (i) to obtain porous carbon beads doped with metal nanoparticles.

Aromatic alcohol monomers that can be successfully used in step (i) may be selected from one or more of the following compounds: phenol, vinyl benzyl alcohol, cresol and butylphenol. A particularly preferred aromatic alcohol monomer is phenol.

A preferred non-aromatic monomer that can be successfully used in step (i), alone or in combination with one or more aromatic alcohol monomers or other non-aromatic monomers, is methyl methacrylate (MMA).

The choice of a solvent that can be used in the preparation of the above catalyst is not limited, and it can be any organic solvent or solvent that is suitable for the monomers used for the synthesis of polymer beads. Examples of solvents that can be successfully used include, but are not limited to, formaldehyde, acetaldehyde, paraldehyde, and glyoxal, or any combination thereof.

The polymerization catalyst may be an alkaline catalyst and in particular amine catalysts. Examples of polymerization catalysts that can be successfully used include, but are not limited to, triethylamine (TEA), sodium hydroxide, barium hydroxide, dimethylamine, which can be used alone or in combination with other catalysts.

Crosslinkers that can be successfully used in step (i) include hexamethylenetetramine (also known as HMTA or hexamine), triethylenediamine and sulfuric acid, or any combination thereof.

Suspension stabilizing agents that can be successfully used in step (i) can be selected from one or more of the following compounds: polyvinyl alcohol (PVA), gum arabic (GAP) powder and polyvinylpyrrolidone. However, other suspension stabilizing agents may also be used and the list given here should not be considered limiting.

The order of adding and mixing components in step (i) is not limited. The components to be used in step (i) may be added together at the same time to form a total reaction mixture for said step. Alternatively, one or more of the components to be used in step (i) may be prepared as separate mixtures and then added together to form an overall reaction mixture.

For example, one convenient non-limiting method for preparing the above catalyst that can be used in the process of the present invention involves heating the monomers, solvent, and polymerization catalyst to form a heated mixture. In some embodiments, the monomers, solvent, and polymerization catalyst can be stirred at room temperature (eg, 20-30° C.) until the mixture is homogeneous. The mixture can then be heated to a temperature of about 100°C. The mixture can be heated at any rate including, but not limited to, 1, 2, 3, 4, or 5°C/min. After the mixture is heated, the heated mixture can be brought into contact with a solvent to form a first mixture. In some embodiments, the solvent is water. In some embodiments, the first mixture is stirred for about or at least 10, 20, 30, 40, 50, or 60 minutes. The first mixture can then be brought into contact with a crosslinking agent. Contact of the first mixture with a crosslinking agent results in a crosslinked mixture. In some embodiments, after contacting the first mixture with the crosslinking agent, the mixture is heated. In some embodiments, the mixture is heated until the temperature reaches about 70, 80, 90, 100, or 110°C. The temperature can be increased, for example, at a rate of about 1, 2, 3, 4 or 5°C/min until the desired temperature is reached. The crosslinked mixture can then be contacted with a slurry stabilizer to form a second mixture. In some embodiments, the suspension stabilizing agent and the crosslinked mixture can be mixed for about or at least 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, or 60 minutes. Then, to obtain a third mixture, the second mixture can be brought into contact with one or more metals or their salts. In some embodiments, the third mixture may then be heated. After heating the third mixture, it is cooled to obtain a composition containing polymer beads. When more than one metal is to be included in the beads, these metals may be added sequentially or simultaneously. For example, in some embodiments where multiple metals are to be included in the beads, the metals may be added at different times, at intervals of, for example, about or at least 1, 2, 3, 4, 5, 6, 7, 8 , 9 or 10 minutes. In some embodiments, when multiple metals are to be included in the beads, the metals may be added at intervals of about 1 to 10, 1 to 9, 1 to 8, 1 to 7, 1 to 6, 1 to 5 , 1 to 4, 1 to 3, or 1 to 2 minutes. In some embodiments, when multiple metals are to be included in the beads, the metals may be added at intervals of about 2 to 10, 2 to 9, 2 to 8, 2 to 7, 2 to 6, 2 to 5 , 2 to 4 or 2 to 3 minutes. In some embodiments, when multiple metals are to be included in the beads, the metals may be added at intervals of about 3 to 10, 3 to 9, 3 to 8, 3 to 7, 3 to 6, 3 to 5 , 3 to 4 minutes, In some embodiments, when multiple metals are to be included in the beads, the metals may be added at intervals of about 4 to 10, 4 to 9, 4 to 8, 4 to 7, 4 up to 6 or 4 to 5 minutes. In some embodiments, when multiple metals are to be included in the beads, the metals may be added at intervals of about 5 to 10, 5 to 9, 5 to 8, 5 to 7, or 5 to 6 minutes.

In embodiments where multiple metals are to be included in the beads, the metals may be added in different ratios to each other. In some embodiments, the first metal (or salt thereof) is introduced in a ratio of 3:1, 1:1, or 1:3 relative to the second metal (or salt thereof). Other ratios can also be used to control the final amount of each metal to be included in the polymer beads.

After adding one or more metals or their salts, the reaction mixture can continue to heat. In some embodiments, the mixture is agitated. In some implementations, the stirring rate is kept constant. Without being bound by any theory, the stirring speed is kept constant to avoid solidification of the beads. A mixture containing one or more metals or their salts can be heated, for example, for about or at least 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10 hours. In some embodiments, the mixture is heated for about 1 to 10, 1 to 9, 1 to 8, 1 to 7, 1 to 6, 1 to 5, 1 to 4, 1 to 3, or 1 to 2 hours. In some embodiments, after heating, the mixture is allowed to cool. Cooling can be accelerated by keeping the mixture in a cooling bath, or the reaction mixture is cooled by exposing it or the reaction vessel to ambient temperature.

In some embodiments, polymer beads containing one or more metals or their salts are separated. The beads can be separated once the reaction mixture reaches room temperature. Any separation method may be used. In some embodiments, separating the polymer beads includes filtering them. In some embodiments, the method also includes fractionating the polymer beads to obtain a composition containing polymer beads of substantially the same diameter. Balloon size fractionation allows you to group them according to a specific size or range of sizes. You can use any method of fractionation, such as, but not limited to, the use of sieves. The separated beads may also be washed with various solutions such as, but not limited to, water, alcohol, acetone, and the like. In some embodiments, the beads are washed with water, methanol, or acetone, or any combination thereof. In some embodiments, the detergent alcohol is ethanol, methanol, isopropanol, or any combination thereof.

In step (ii), the polymer beads formed in step (i) are carbonized, for example in a ceramic boat, at a sufficient temperature and for a sufficient period of time. In some embodiments, the beads are carbonized at a temperature in the range of 900 to 1100°C, for example at a temperature of about 900, 1000, 1050, or 1100°C. In some embodiments, the beads are carbonized for about 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, or 120 minutes. In some embodiments, the pellets are carbonized under N ₂ atmosphere. Other inert gases may also be used. In some embodiments, prior to carbonization, the beads are preheated from room temperature to carbonization temperature at a heating rate of about 1, 2, 3, 4, or 5°C/min.

After carbonization, the balls can be activated. The activation of the beads can be done in the same oven used to carbonize the beads, but this is not required. In some embodiments, the carbonized beads are steam activated. In some implementations, the balls can be activated at a temperature in the range from 800 to 1100°C. In some embodiments, the beads can be successfully activated at about 800, 850, 900, 950, 1000, 1050, or 1100°C. In some embodiments, the carbonized beads are activated for about 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, or 120 minutes. In some embodiments, the beads are carbonized at about 850°C and activated at about 1000°C.

The activated beads can then be subjected to hydrogen reduction. Regeneration of the beads can be done in an oven similar to the one used for the carbonization and activation of the beads. The activated beads are reduced at 350° C. for 3 hours, thereby converting the metal oxides in the beads into a metallic state.

Porous carbon balls doped with metal nanoparticles, which are obtained by the methods described in this document, can have a variety of sizes. However, it is preferred that the beads have a relatively uniform size distribution. If necessary, the beads can be processed, for example by grinding or filtering, to reduce their size.

Preferably, the beads that can be used as a catalyst in the oxidation treatment step of the process of the present invention have diameters in the range of 0.1 to 0.8 mm, more preferably in the range of 0.2 to 0.8 mm. The diameter of the beads can be successfully selected using sieves.

It is particularly preferred that the balls have an average diameter in the range of 0.3 to 0.5 mm, and most preferably about 0.5 mm.

As stated above, the polymer beads are doped with one or more metals selected from aluminum, iron, nickel, copper, silver, cobalt, molybdenum, gold and platinum, or salt(s) thereof. In embodiments in which the polymer beads are doped with two of the aforementioned metals or their salts, the ratio of the two metals or their salts is preferably about 1:1, 1:2, 1:3, or 1:4.

The porous carbon beads doped with metal nanoparticles described above are particularly effective as a catalyst in wastewater treatment processes generated from the commercial propylene oxide production process. Accordingly, in the process of the present invention, the wastewater generated from the commercial propylene oxide production process is preferably subjected to a catalytic wet oxidation treatment in the presence of a catalyst comprising porous carbon beads doped with metal nanoparticles.

However, the aforementioned catalyst comprising porous carbon beads doped with metal nanoparticles may further contain carbon nanofibers.

Therefore, the aforementioned catalyst can be obtained by a method including steps (i) and (ii) as described above, which method can further include a third step, step (iii), of treating porous carbon beads doped with metal nanoparticles by chemical vapor deposition. phase (CVD) in the presence of a carbon source, to obtain porous carbon balls doped with metal nanoparticles containing carbon nanofibers.

The above carbon source may be selected from acetylene, benzene, xylene and toluene.

Methods for incorporating carbon nanofibers into porous carbon spheres doped with metal nanoparticles are known in the art. For example, in the works of P. Khare et al. Chem. Eng. J. 229 (2013) 72-81 and N. Talreja et al. J. Water Process. Eng. 3 (2014) 34-45 describes methods for growing carbon nanofibers on porous carbon beads.

A typical CVD plant may consist of a tubular nickel alloy reactor (ID=30 mm, L=0.8 m) placed horizontally in an electric furnace equipped with a temperature controller and programmer. A perforated stainless steel (SS) boat inserted into the reactor can hold approximately 20 g of beads that have been pre-carbonized, activated and reduced with H ₂ . Gaseous acetylene at a flow rate of 50 sccm (cm ³ /min at standard temperature and pressure) is passed through a tubular reactor for CVD and growth of carbon nanofibers (CNF) on activated carbon beads. The included metal nanoparticles inside the carbon beads act as a CVD catalyst. CVD can be carried out at 350° C. for 30 minutes in the presence of acetylene to grow numerous carbon structures in the form of carbon nanofibers (CNF) on the beads at a pressure of 0.1-0.15 MPa.

Thus, the above catalyst can be obtained by a method including steps (i), (ii) and (iii) as described above, which method can further include a fourth step, step (iv), introducing an oxidant into the porous carbon beads doped with metal nanoparticles containing carbon nanofibers obtained in step (iii).

Preferably, said oxidizing agent is a salt of a strong base and a weak acid. Potassium and ammonium salts of a strong base and a weak acid are particularly preferred as oxidizing agents. More preferably, said oxidizing agent is selected from one or more of the following salts: KMnO ₄ , K ₂ S ₂ O ₈ and (NH ₄ )2S ₂ O ₈ .

The general procedure for carrying out step (iv) may include mixing the porous carbon balls obtained in step (iii) doped with metal nanoparticles containing carbon nanofibers with aqueous solutions containing an oxidizing agent at a temperature in the range from 40 to 60 ° C for 4 to 12 hours.

The oxidizing agent for use in step (iv) can be successfully used in water.

After mixing, the catalyst can be filtered and dried before use.

Examples

1) Preparation of oxidation treatment catalyst

Polymer beads doped with copper nanoparticles were obtained by suspension polymerization. The polymerization reaction was carried out in a 2-liter three-necked glass vessel placed over a heating jacket and equipped with a reflux condenser, a thermometer and a continuous stirrer.

A detailed description of the equipment that can be used for the polymerization reaction can be found in Chem. Eng. sci. 3591 (2010). In addition, in FIG. 3 US Patent No. 2015/0056260 A1 illustrates an example of a device that can be successfully used to prepare carbon beads doped with metal nanoparticles by suspension polymerization.

Prepared a solution of phenol (50 g) as a monomer, formaldehyde (63 ml) as a solvent and triethylamine (TEA) (1.5 ml) as a polymerization catalyst. After that, the mixture of phenol, formaldehyde and TEA was stirred (370-410 rpm) at room temperature (about 30°C) for 8 hours to obtain a homogeneous solution.

After 8 hours, the reaction mixture was mixed with 200 ml of water. After another 30 minutes, 3.5 g of hexamethylenetetramine (HMTA) was added as a crosslinking agent, and the reaction mixture was simultaneously heated at a rate of 3°C/min until the temperature reached 100°C. Approximately 45 minutes after the addition of HMTA, 3.5 g of PVA (95% hydrolyzed polyvinyl alcohol, average molecular weight 95,000) was added as a suspension stabilizer.

After 25-30 minutes, 4 g of copper nitrate (Cu(NO ₃ ) ₂ .3H ₂ O) was added. After 30 minutes, the reaction was stopped by turning off the heater. The reaction mixture was then allowed to cool to room temperature.

After cooling, the reaction mixture was filtered to separate the solid beads from the residual liquid. The beads were then washed 2-3 times with water, methanol and acetone, then dried at room temperature for 12 hours. Then the formed polymer beads doped with copper nanoparticles were sieved and a yield of approximately 50 g was obtained.

These polymer beads doped with copper nanoparticles, obtained by the method described in Example 1, were carbonized at 900°C for 2 hours in the presence of nitrogen, and then activated at 900°C for 1 hour in the presence of steam at a pressure of 0.1- 0.15 MPa, to form porous activated carbon beads doped with copper oxide. After that, the porous activated carbon beads doped with copper oxide were reduced at 350°C for 2 hours in the presence of hydrogen at a flow rate of 150 sccm (cm ³ /min at standard temperature and pressure) and a pressure of 0.1-0.15 MPa, for the formation of porous carbon balls doped with copper nanoparticles.

Then, these porous carbon beads doped with copper nanoparticles were subjected to chemical vapor deposition (CVD) at 350° C. for 30 minutes in the presence of acetylene at a flow rate of 100 sccm (cm ³ /min at standard temperature and pressure) to grow on balls numerous carbon structures in the form of carbon nanofibers (CNF) at a pressure of 0.1-0.15 MPa.

These porous carbon beads doped with copper nanoparticles with grown nanofibers were additionally treated with an oxidizing agent by impregnating them with KMnO ₄ by mixing them with an aqueous solution of KMnO ₄ at 55°C. The KMnO ₄ salt solution was prepared separately by mixing 0.8 g of freshly prepared salt with 15 ml of water at room temperature. Approximately 0.3 g of the beads from Example 3 were mixed in a beaker with 15 ml of an aqueous solution of KMnO ₄ . The introduction of the oxidizer into the beads was carried out at 55°C for 8 hours. The balls with the introduced potassium salt were dried in vacuum at 55°С for 30 min.

2) Oxidation treatment experiments

Catalyst beads prepared as described in Section 1 above) were used in Experiments 1-6, in which a wastewater stream from a styrene/propylene oxide (SM/PO) industrial production process was treated. Said experiments included wet oxidative treatment of wastewater in the presence of said catalyst beads.

In these experiments, a wastewater stream was fed into a reactor having a downflow configuration, the reactor containing the aforementioned catalyst beads. The catalyst was used in an amount (in grams) per feed rate of said wastewater stream (in liters per hour) of 100 g/(l/h) for Experiments 1-3 and 6 and 75 g/(l/h)) for Experiments 4- 5.

The reactor was a vertical tubular reactor which contained catalyst beads placed on glass wool. The reactor was a nickel alloy reactor (commercially available under the trade name "Inconel") (diameter 73 mm, height 210 mm, wall thickness 7 mm) equipped with an electric heater and a thermocouple. To maintain the reaction temperature, a PID temperature controller (PID=proportional-integral-derivative controller) was used. A manometer was used to control the pressure at the inlet to the reactor.

In order to pressurize the reactor before starting the liquid flow (feeding the sewage flow), the reactor was separately supplied with a gas flow containing oxygen and nitrogen. Said gas stream was obtained by combining a stream of pure oxygen with an air stream. The combined gas stream contained a mixture of air and (pure) oxygen, with a total pressure of 27 bar, consisting of 15 bar air and 12 bar (pure) oxygen.

Immediately after starting the liquid flow, the pressure in the reactor was maintained by supplying pure oxygen. This flow of pure oxygen had a rate of 1 sccm (cm ³ /min at standard temperature and pressure).

The reactor pressure was 27 bar and the reactor temperature is shown in Table 1 below. In the reactor, the waste water was subjected to an oxidative treatment in the presence of oxygen and catalyst beads. The resulting treated stream leaving the reactor was cooled using a heat exchanger (cooler). The cooled treated stream was then sent to a liquid/gas separator which included a tee in the outlet line where said stream was separated into a gas stream and a liquid stream. The liquid stream leaving the separator was divided into 2 substreams. Then one of these substreams from the recirculation line (hereinafter "the recirculation stream") was combined with the wastewater stream and returned to the reactor. Another substream (hereinafter "stream without recirculation") was discharged through the product line. The pressure in the reactor system, including the cooler, was controlled by an outlet pressure regulator for the gas stream exiting the liquid/gas separator.

The experiments were carried out in a continuous mode. After the start of the experiment, the COD (chemical oxygen demand) of the liquid flow leaving the separator began to decrease. Each experiment lasted 5 hours. After the completion of the experiment and before starting a new experiment, the reactor and the corresponding tubes were washed with water to remove all kinds of deposits and residues.

Table 1 below provides further details of the experiments and wastewater treatment results in relation to COD reduction. Two series of experiments were carried out. In Experiments 1-3, the effluent had a relatively low initial COD, while in Experiments 4-6, the effluent had a relatively high initial COD.

Table 2 below shows the typical characteristics of the wastewater generated during the industrial production of SM/PO, which produces propylene oxide (PO).

table 2

Characteristic unit of measurement Values Initial COD mg/l 80000-125000 Sum of organic sodium salts (formate, acetate, propionate, benzoate) mg/l 35000-42000 propylene glycol mg/l 4000-9000 Phenol mg/l 1500 Aromatic oxygenates (mainly C8/C9) mg/l 3000-3500 Density kg / m ³ 1030-1050 pH ~ 10 Na+ to Na2CO3H/HCO3 mg/l 8500-10000

In Experiments 4-6 (see Table 1), the initial COD is in the range of 80000-125000 for the initial COD indicated in Table 2. The wastewater treated in Experiments 1-3 (see Table 1) was also the wastewater obtained in an industrial SM/PO manufacturing process, but said effluent was first diluted with water, resulting in a lower initial COD value.

As can be seen, for all of these Experiments 1-6, the COD in the effluent is advantageously significantly reduced by recirculating a portion of the treated and separated liquid stream to the reactor. In addition, Experiments 1-3 show that the wastewater COD decreases further as the recycled portion increases. In addition, in particular, Experiments 4-6 show that by using the wastewater treatment method of the present invention, the relatively high COD that is typical of wastewater from the SM/PO process can be successfully reduced by even 97-99% (when recycled parts of only 33%). The foregoing demonstrates the surprising effectiveness of the method of the present invention.

Claims (15)

1. A method for treating wastewater containing hydrocarbons and organic and/or inorganic salts generated in an industrial process for the production of propylene oxide, including treatment of wastewater by catalytic wet oxidation, which includes: feeding into the reactor a stream containing waste water; oxidative treatment of a stream containing wastewater in the presence of oxygen and a catalyst comprising porous carbon balls doped with metal nanoparticles, which results in a processed stream; transferring at least a portion of the treated stream to a separator, where the treated stream is separated into a gas stream and a liquid stream; and recirculation of a portion of the liquid stream to the reactor. 2. The method according to claim 1, characterized in that the oxidation treatment step is carried out at a temperature in the range from 120 to 300°C, preferably from 150 to 280°C and at a pressure in the range from 2 to 20 MPa, preferably from 2 up to 12 MPa. 3. The method according to p. 1 or 2, characterized in that it is carried out in a continuous mode. 4. Process according to any one of the preceding claims, characterized in that the reactor is fed with a gas stream containing oxygen and optionally an inert gas. 5. The method according to p. 4, characterized in that the amount of oxygen in the gas stream containing oxygen and, optionally, an inert gas, is in the range from 1 to 100 vol.%, preferably from 10 to 100 vol.%, more preferably , from 20 to 100% by volume, most preferably from 25 to 100% by volume. 6. The method according to claim 4 or 5, characterized in that the gas stream containing oxygen and optionally an inert gas is a gas stream consisting of air, or a gas stream consisting of a combination of air and an additional amount of one or more inert gases. 7. The method according to claim 4 or 5, characterized in that the gas stream containing oxygen and optionally an inert gas is a gas stream in which the oxygen concentration is higher than in air, preferably is a gas stream in which the amount of oxygen is in the range from 25 to 100 vol.%. 8. The method according to any of the preceding claims, characterized in that the catalyst is used in an amount (in grams) per feed rate of the flow containing waste water (in liters per hour) in the range from 10 to 300 g/(l/h), preferably , from 25 to 250 g/(l/h). 9. Process according to any one of the preceding claims, characterized in that from 1 to 99%, preferably from 5 to 95%, more preferably from 20 to 95% of the liquid stream separated by the separator is returned to the reactor. 10. Process according to any one of the preceding claims, characterized in that the initial COD (chemical oxygen demand) values for the wastewater streams generated during the production of propylene oxide are in the range of 80,000 to 125,000 mg/l.

Images