WO2025061231A1 - Method for recovering phosphorus from phosphorous-containing organic waste materials - Google Patents

Abstract

The invention relates to a method for recovering phosphorus from a phosphorus-containing organic waste material, the method comprising the steps of: (a) providing a phosphorus-containing starting material, the phosphorus-containing starting material being the phosphorus-containing organic waste material or having been obtained from the phosphorus-containing organic waste material; (b) thermally treating the phosphorus-containing starting material at a temperature of 950°C or higher to obtain a phosphorus-containing product gas; and (c) bringing the phosphorus-containing product gas into contact with an aqueous solution containing copper(II) ions in order to separate phosphorus from the phosphorus-containing product gas.

Description

Description

Process for the extraction of phosphorus from phosphorus-containing organic waste materials

[0001] The invention relates to a process for the recovery of phosphorus from phosphorus-containing organic waste materials.

[0002] According to the new regulations for sewage sludge utilization adopted in 2017 [1], phosphorus recovery from sewage sludge with a phosphorus content above 2% by mass is required from 2029. This can be achieved either by direct phosphorus recovery or by thermal pretreatment, such as co- or mono-incineration, with subsequent phosphorus recovery or by material recycling of the sewage sludge ash using the phosphorus content.

[0003] By 2032, the number of sewage treatment plants subject to mandatory recovery will increase, as from 2032, soil-based recycling will only be possible for sewage treatment plants with a capacity of less than 50,000 population equivalents. If phosphorus is recovered directly from sewage sludge, the phosphorus content in the sewage sludge must be reduced to below 2% by mass. If the sewage sludge contains more than 4% by mass of phosphorus, it is sufficient to reduce the phosphorus content by 50% by mass. If the sewage sludge is incinerated and sewage sludge ash is used, 80% by mass of the phosphorus contained in the ash must be recovered.

[0004] In 2021, a large portion, i.e., over 75%, of the sewage sludge generated was subjected to thermal treatment, primarily through incineration. By 2032 at the latest, the agricultural use of sewage sludge will often no longer be possible, so this sewage sludge must be subjected to another form of treatment. Currently, no data are available in Germany on further treatment options for the sewage sludge ash or mixed ash generated during thermal treatment. [0005] In principle, many processes for phosphorus recovery from sewage sludge have been described in the literature. These can be divided into sewage sludge processes and sewage sludge ash processes with regard to the feedstock, thermochemical and non-thermochemical processes with regard to the process control, and fertilizer-producing and non-fertilizer-producing processes with regard to the products.

[0006] Direct sewage sludge utilization is preferable to sewage sludge incineration and the subsequent recovery of phosphorus from the ash because, on the one hand, the incineration process step is eliminated and, on the other hand, parallel use of other valuable materials such as the carbon bound in the sewage sludge is possible. Furthermore, thermochemical processes are superior to non-thermochemical processes in that they simultaneously sanitize and remove pathogens. Furthermore, for example, reducing processes can produce synthesis gas consisting of carbon monoxide and hydrogen, or pyrolysis can produce additional oil-like intermediates, thus enabling material rather than thermal utilization of the carbon. This is associated with the minimization of CCh emissions. Pyrolysis produces both pyrolysis gas, i.e. synthesis gas and light hydrocarbons, and a liquid by-product. Synthesis gas is understood to be a gas mixture containing carbon monoxide and hydrogen as its main components.

[0007] Compared to fertilizer-producing processes, non-fertilizer-producing processes offer the possibility of recovering phosphorus either in the form of elemental (white) phosphorus or in the form of phosphoric acid. These substances are higher-value products, as they open up additional recycling routes. Furthermore, the phosphorus must be separated from the heavy metals contained in the sewage sludge, which can be achieved, for example, by selective conversion into the gas phase.

[0008] EP 3 305 724 A1 discloses a process for removing phosphorus from organic substrate material. Here, the feedstocks are first Pyrolysis takes place at temperatures between 400 °C and 800 °C, and volatile carbon compounds are removed, which leads to an increased concentration of phosphorus in the coke residue. Phosphate is then extracted from the coke, for example, using acids, alkalis, or other extraction agents. A disadvantage of this process is that the phosphorus is largely not separated from the heavy metals contained in the feedstock, resulting in only low-quality products contaminated with heavy metals. Furthermore, while the recycling of the coke is considered, the utilization of the resulting pyrolysis products, such as pyrolysis oil and pyrolysis gas, is not.

[0009] EP 2 640 531 A2 and US 2013/272944 A1 disclose a process for the treatment of organic waste materials such as sewage sludge, sewage sludge ash, and animal meal. In this process, the feedstock is mixed with chlorine-containing additives, which form more volatile chlorides with the metals contained, in particular, in the sewage sludge ash, so that the feedstock can be depleted of heavy metals in an oxidation step (0.85 < < 1.6). The feedstock, depleted of heavy metals, is then thermally treated in an inductively heated reactor with a graphite bed at 1300 °C to 1600 °C under reducing conditions, so that elemental phosphorus is formed, which can be removed with the product gas. The phosphorus is then separated by quenching. The disadvantage of this process is that the carbon content of the feedstock is only thermally utilized due to the oxidative removal of heavy metals.

[0010] DE 10 2020 001 989 A1 discloses a process in which over 80% of the phosphorus contained in sewage sludge can be recovered in the form of phosphorus pentoxide in a rotary kiln under exposure to carbon and silicon dioxide at temperatures above 1250°C and a residence time of over 20 minutes. It is described that the phosphorus, initially released at least partially in elemental form, is reoxidized with oxygen. The resulting phosphorus pentoxide is then converted to phosphoric acid in a "hydrator." No information is provided on the fate of the exhaust gas not converted in the hydrator. [0011] In view of this state of the art, a process for the recycling of sewage sludge is desirable in which not only phosphorus is recovered but also other chemical elements such as carbon or hydrogen contained in the sewage sludge can be utilized.

[0012] The object of the invention is to eliminate the disadvantages of the prior art. In particular, it is intended to provide a process for the recovery of phosphorus from phosphorus-containing organic waste materials, in particular from sewage sludge, which enables the thermochemical recovery of phosphorus with co-utilization of carbon contained in the phosphorus-containing organic waste materials.

[0013] This object is achieved by the features of claim 1. Expedient embodiments of the inventions emerge from the features of the subclaims.

[0014] According to the invention, a process for recovering phosphorus from a phosphorus-containing organic waste material is provided. The process comprises the steps:

(a) providing a phosphorus-containing feedstock, wherein the phosphorus-containing feedstock is the phosphorus-containing organic waste material or is obtained from the phosphorus-containing organic waste material;

(b) thermally treating the phosphorus-containing feedstock at a temperature of 950 °C or higher to obtain a phosphorus-containing product gas; and

(c) contacting the phosphorus-containing product gas with an aqueous solution containing copper(II) ions to separate phosphorus from the phosphorus-containing product gas. [0015] The term "phosphorus-containing organic waste" can refer to a phosphorus-containing material that contains organic components and/or inorganic components. The phosphorus-containing organic waste also contains carbon. The carbon can be present in elemental form and in chemically bound form. The phosphorus-containing organic waste can be, for example, sewage sludge, sludge coke, sewage sludge ash, dry sludge, biomass, bone meal, or animal meal. The phosphorus-containing organic waste is preferably sewage sludge. The process according to the invention is thus particularly suitable for recovering phosphorus from sewage sludge.

[0016] It is not absolutely necessary for the phosphorus-containing organic waste to be subjected directly to the thermal treatment provided for in step (b). Rather, it can be provided that the phosphorus-containing organic waste is subjected to pretreatment before step (b), whereby the phosphorus-containing feedstock is obtained. Alternatively, the phosphorus-containing organic waste can be used as phosphorus-containing feedstock without pretreatment. The phosphorus-containing feedstock is preferably solid or a mixture of solid and liquid. In particular, it can be provided that the feedstock is solid or a sludge at ambient temperature and atmospheric pressure. It can be provided that step (a) comprises a preparation of the phosphorus-containing organic waste. The preparation can be, for example, a comminution of the phosphorus-containing organic waste. The preparation can be carried out before the pretreatment.

[0017] The pretreatment may include predrying the phosphorus-containing organic waste. For example, the sewage sludge may be subjected to predrying, thereby obtaining predried sewage sludge. The predrying may, for example, take place at a temperature of 50 to 200°C.

[0018] The pretreatment may alternatively or additionally to predrying comprise pyrolysis of the phosphorus-containing organic waste. For example, the sewage sludge is subjected to pyrolysis, whereby sewage sludge coke is obtained. The pyrolysis is preferably carried out at a temperature of 300 °C to 900 °C, more preferably at a temperature of 300 °C to 700 °C and particularly preferably from 400 °C to 600 °C. The pyrolysis temperature and the holding time depend on the phosphorus-containing organic waste material used. The holding time is also dependent in particular on the amount of phosphorus-containing organic waste material to be pyrolyzed. In one example, at a pyrolysis temperature of 500 °C, a holding time of 5 h can be selected for 1 kg of phosphorus-containing organic waste material. It can be provided that the holding time is between 5 min and 10 h. It can be provided that the volatile pyrolysis products obtained during pyrolysis are put to use. For example, synthesis gas components produced during pyrolysis can be put to use.

[0019] It may be provided that the phosphorus-containing organic waste is subjected to pre-drying and subsequent pyrolysis. For example, sewage sludge can be pre-dried and subsequently subjected to pyrolysis.

[0020] By means of pretreatment, in particular by means of pyrolysis, moisture and volatile decomposition products are separated from the phosphorus-containing organic waste. The phosphorus remains in the solid pyrolysis residue. Hydrocarbon-containing components can be condensed from the gaseous and/or vaporous pyrolysis products and further recycled. Whether pretreatment is carried out depends on the phosphorus-containing organic waste material. In contrast to pyrolysis, volatile decomposition products are not separated or are only separated to a limited extent during predrying.

[0021] According to the invention, a thermal treatment of the phosphorus-containing feedstock in step (b) is carried out at a temperature of 950°C or higher. Preferably, the thermal treatment is carried out at a temperature of 980°C or higher, more preferably 1030°C or higher, even more preferably 1200°C or higher, and particularly preferably 1250°C or higher. For example, the thermal treatment can be carried out at a temperature in a range from 950°C to 1550 °C, preferably in a range from 980 °C to 1550 °C, more preferably in a range from 1050 °C to 1450 °C, even more preferably in a range from 1150 °C to 1350 °C and particularly preferably in a range from 1250 °C to 1350 °C. The inventors have found that phosphorus contained in the phosphorus-containing feedstock passes into the gas atmosphere above a temperature of 950 °C. The temperature at which phosphorus contained in the phosphorus-containing feedstock passes into the gas phase depends on the type of phosphorus-containing feedstock. For example, depending on the composition of the sewage sludge, it can be 980 °C or 1030 °C. For energy reasons, it is preferred that the thermal treatment be carried out at a temperature of 1250 °C or above this temperature. The specific temperature at which the thermal treatment is carried out depends on the type of phosphorus-containing feedstock, in particular its components and their proportions in the phosphorus-containing feedstock. The following considerations apply: From 1050 °C, a significant release of phosphorus is detected. However, sufficiently high release rates with regard to particle residence times and a sufficiently high total release of phosphorus are only achieved from 1250 °C. Higher temperatures do not currently represent a disadvantage with regard to phosphorus release. However, they can entail energy-related disadvantages, such as a reduction in the overall efficiency of the thermal treatment.

[0022] The thermal treatment is preferably carried out at a pressure in a range of 0.9 bar to 50 bar absolute pressure. The thermal treatment can be carried out at ambient pressure. The ambient pressure can be 1.013 bar. In one embodiment, the thermal treatment is carried out at a pressure of 10 to 40 bar, more preferably 20 to 30 bar, and most preferably 25 bar.

[0023] The duration of the thermal treatment depends on the phosphorus-containing feedstock, in particular its components and their proportions, the temperature and the amount of the phosphorus-containing feedstock. This duration includes the residence of the phosphorus-containing feedstock at temperatures above 950 °C and may include holding times at temperatures above 950 °C. The thermal treatment may be carried out for a period of 5 seconds to 5 hours. The duration of the thermal treatment may correspond to the residence time of the phosphorus-containing feedstock in the reactor intended for the thermal treatment.

[0024] The thermal treatment in step (b) can be carried out in a reaction chamber. It can be provided that reducing conditions develop in the reaction chamber during the thermal treatment in step (b). It is not absolutely necessary for the reducing conditions to already exist in the reaction chamber at the beginning of the thermal treatment in step (b). Rather, it may be sufficient for the reducing conditions to develop during the thermal treatment in step (b).

[0025] The creation of reducing conditions in step (b) of the process according to the invention can ensure or improve the release of phosphorus from the phosphorus-containing feedstock. It enables the co-utilization of carbon contained in the phosphorus-containing organic waste. The reducing conditions that develop in the reaction chamber ensure that carbon compounds contained in the phosphorus-containing organic waste are not oxidized or are only oxidized by components that also originate from the phosphorus-containing organic waste. The process according to the invention can therefore use a phosphorus-containing organic waste, such as sewage sludge, to thermochemically recover phosphorus with co-utilization of the carbon contained in the waste. Heavy metals contained in the phosphorus-containing organic waste can also be separated. The process according to the invention can provide a phosphorus-containing solution and a phosphorus-containing precipitate, which can be converted into phosphoric acid by regeneration. The phosphoric acid can then be converted into elemental phosphorus. [0026] According to the invention, it can thus be provided that the thermal treatment is carried out under reducing conditions. The reducing conditions ensure that the thermal treatment in the reaction chamber takes place under non-oxidizing conditions. If reducing conditions are provided, the reducing conditions can arise during the execution of step (b). It is therefore not absolutely necessary to add one or more reducing gases to the gas atmosphere in the reaction chamber.

[0027] To create the reducing conditions, a carrier gas and/or a reaction gas may be introduced into the reaction chamber. However, the introduction of only the carrier gas, i.e., no reaction gas, is only advantageous if the phosphorus-containing feedstock contains carbon or if foreign carbon is added to it.

[0028] The carrier gas may consist of one or more of the following gases: nitrogen, argon, helium or a mixture of two or more of these gases.

[0029] The reaction gas may consist of one or more of the following gases: oxygen, water vapor, hydrogen, carbon dioxide, carbon monoxide, or a mixture of two or more of these gases. The use of the reaction gas is intended to create reducing conditions in the reaction chamber during the thermal treatment. The reaction gas may consist, for example, of hydrogen and/or carbon monoxide. In one embodiment, the reaction gas is hydrogen or contains hydrogen. In another embodiment, the reaction gas is water vapor and oxygen.

[0030] Preferably, the reaction space contains a mixture of carbon monoxide and hydrogen. Typically, carbon monoxide is produced together with hydrogen in step (b) during the thermal treatment of the phosphorus-containing feedstock by reaction of the phosphorus-containing feedstock itself with the reaction gas. In this case, carbon monoxide from the phosphorus-containing feedstock will pass into the gas phase without carbon monoxide being used as a reaction gas. gas or component of the reaction gas is used. In this case, hydrogen from the phosphorus-containing feedstock will also pass into the gas phase without hydrogen being used as a reaction gas or component of the reaction gas. It is therefore not necessary in most cases to provide carbon monoxide and/or hydrogen as a reaction gas in step (b). To create reducing conditions in step (b), one embodiment can thus provide a reaction gas consisting of oxygen, water vapor, carbon dioxide, or a mixture of two or more of these gases. Carbon monoxide and/or hydrogen can then pass into the gas atmosphere in the reaction space in step (b) with the formation of reducing conditions. The reaction gas should be provided in a substoichiometric ratio, i.e. the ratio of the amount of oxygen in the reaction gas to the amount of oxygen that would be required for complete combustion of the carbon and hydrogen contained in the phosphorus-containing feedstock. A substoichiometric ratio exists, for example, when the air ratio lambda is less than 1.

[0031] It can thus be provided that the reaction gas is supplied to the reaction chamber in a substoichiometric molar ratio. A substoichiometric molar ratio exists when the molar amount of oxygen in the reaction gas is less than the molar amount of oxygen required for complete combustion of the carbon and hydrogen contained in the phosphorus-containing feedstock. The molar ratio can, for example, be less than 0.5, preferably less than 0.3, and particularly preferably less than 0.1. The molar ratio is 0 when the reaction gas contains no oxygen.

[0032] The gas atmosphere that forms in the reaction chamber during the thermal treatment in step (b) should therefore not contain any oxygen. The gas atmosphere that forms in the reaction chamber is a reducing gas or reducing gas mixture. This reducing gas or reducing gas mixture is generated either by supplying the reaction gas or during the thermal treatment by reacting the reaction gas with the phosphorus-containing feedstock. and/or with the foreign carbon. In these cases, the gas atmosphere formed in step (b) provides reducing conditions.

[0033] If, for example, oxygen is introduced into the reaction chamber as a reaction gas or as part of it, it will be completely consumed in the reaction chamber due to the substoichiometric ratio. Complete consumption of the oxygen is necessary for reducing conditions to develop in the reaction chamber. The same applies to water vapor.

[0034] It can be provided that a mixture of a carrier gas and a reaction gas is fed into the reaction chamber.

[0035] It can be provided that the carbon of the phosphorus-containing feedstock reacts with the reaction gas. In some cases, the carbon is oxidized to CO and CO2 with the oxygen contained in the reaction gas. CO and CO2 can then react further.

[0036] Preferably, only a reaction gas, but no carrier gas, is fed into the reaction chamber. This is advantageous in order to be able to recycle carbon contained in the phosphorus-containing feedstock and which enters the gas atmosphere during the thermal treatment in step (b). However, it is also possible to use a mixture of nitrogen and hydrogen, with a mixture of nitrogen and at most 20 vol.% hydrogen, for example a mixture of nitrogen and 5 vol.% hydrogen, in each case based on the volume of the gas mixture, being preferred. A mixture of nitrogen and hydrogen can, for example, be used to carry out the process according to the invention on a laboratory scale.

[0037] The thermal treatment of the phosphorus-containing feedstock causes the phosphorus contained in the phosphorus-containing feedstock to transition into the gas phase. In this way, the phosphorus-containing product gas is obtained. This transition begins, according to the inventors' findings, at 950 °C. The inventors have further found that phosphorus contained in the phosphorus-containing feedstock in the gas phase in the form of elemental phosphorus. In addition to phosphorus that has passed from the phosphorus-containing feedstock into the product gas, the phosphorus-containing product gas contains all or some of the components of the carrier gas fed into the reaction chamber and/or the reaction gas fed into the reaction chamber. It may contain further components that originate from the phosphorus-containing feedstock and pass into the gas atmosphere during the thermal treatment. For example, the product gas may contain one or more of the following compounds: carbon monoxide (CO), hydrogen (FE), water vapor (FEO), carbon dioxide (CO2) and methane (CEE). The product gas may contain one or more other gases in low concentrations: EES, COS, NEE, ethane, ethene, ethyne, although this list is not exhaustive. A low concentration is understood to mean a concentration of the gas(es) of less than 1 vol.%, based on the volume of the product gas.

[0038] The thermal treatment can be carried out in the reaction chamber of a reactor. The phosphorus-containing feedstock is introduced into the reaction chamber of the reactor. Furthermore, if provided, the carrier gas and/or the reaction gas are fed into the reaction chamber. During the thermal treatment, reducing conditions can develop. The reactor can be a furnace, for example, a furnace with a vertical reaction tube. This furnace can be electrically heated, e.g., via resistance heating elements or, preferably, via a thermal plasma. The process according to the invention enables solid gasification of the phosphorus-containing feedstock. The solid gasification is preferably allothermal. This can be achieved by coupling electrical energy, e.g., via resistance heating elements or plasma. If pretreatment of the phosphorus-containing organic waste by pyrolysis is provided, the pyrolysis and the thermal treatment provided in step (b) can be carried out in separate reactors, which can be located, for example, at different locations, or in a single reactor.

[0039] During the pyrolysis of the phosphorus-containing organic waste, a solid pyrolysis residue is obtained, which according to the invention can be used as a phosphorus-containing feedstock can be used. This solid pyrolysis residue may contain carbon. An example of a phosphorus-containing organic waste material that contains carbon is sewage sludge. Alternatively or additionally, carbon, also referred to as extraneous carbon, can be added to it, either in elemental form or in the form of another carbon-containing compound. An example of a phosphorus-containing organic waste material that does not contain carbon is bone meal. By adding extraneous carbon, an optimal phosphorus/carbon ratio can be set in the phosphorus-containing feedstock. The extraneous carbon can, for example, originate from a carbon-containing, preferably carbon-rich, waste product. The carbon-rich waste product used for this purpose can, for example, be a carbon-containing plastic or a mixture of such plastics. It can be provided that the carbon-rich waste product does not contain any phosphorus. Due to the reducing effect of the carbon contained in the phosphorus-containing feedstock, the extraneous carbon added thereto and/or the reducing conditions formed in the reaction chamber on the one hand and the high temperatures in step (b) on the other hand, the phosphorus contained in the feedstock can be released in the form of elemental phosphorus, phosphorus oxides and/or phosphanes.

[0040] Step (c) of the process according to the invention provides for contacting the phosphorus-containing product gas with an aqueous solution containing copper(II) ions to separate phosphorus from the phosphorus-containing product gas. For this purpose, it can be provided that the phosphorus-containing product gas obtained in step (b) is introduced into the solution containing copper(II) ions. The aqueous solution containing copper(II) ions is preferably a 0.01 M to saturated solution, more preferably a 0.05 M to saturated solution, and particularly preferably a 0.1 M to saturated solution. For example, the aqueous solution containing copper(II) ions can be a 0.1 M, a 0.2 M, a 0.25 M, a 0.5 M, or a 1.2 M solution. In one embodiment, the aqueous solution containing copper(II) ions is a 0.05 M to 0.3 M solution. The saturation concentration for CuSO4*5H2O is approximately 1.4 M at room temperature. It has been shown that the higher the concentration of The higher the concentration of copper(II) ions in the aqueous solution, the higher the separation of phosphorus from the phosphorus-containing product gas.

[0041] By separating phosphorus from the phosphorus-containing product gas, a phosphorus-depleted product gas is obtained. The phosphorus-depleted product gas is also referred to below as depleted product gas.

[0042] The aqueous solution containing copper(II) ions can be provided in a scrubber. The phosphorus-containing product gas is preferably fed to the scrubber at a temperature above the sublimation temperature of phosphorus pentoxide. For this purpose, the phosphorus-containing product gas can be fed to the scrubber via a product gas line having a temperature above the sublimation temperature of phosphorus pentoxide. For this purpose, the product gas line can be heated. Thus, a product gas line heated above the sublimation temperature of phosphorus pentoxide can be provided, through which the phosphorus-containing product gas is fed into the scrubber. The sublimation temperature of phosphorus pentoxide is 362°C at an ambient pressure of 1.013 bar. If the phosphorus-containing product gas is fed to the scrubber at a pressure of 1.013 bar, it is preferably fed to the scrubber at a temperature above 362°C. The scrubber can be a washing bottle or a container with a spray device for the aqueous solution containing copper(II) ions. Multiple scrubbers can be provided. Each scrubber can have a stirring device.

[0043] The aqueous solution containing copper(II) ions can be, for example, an aqueous copper(II) sulfate solution or an aqueous copper(II) chloride solution, with an aqueous copper(II) sulfate solution being preferred. The inventors have achieved particularly high phosphorus recovery with a 0.1 M and a 0.2 M copper(II) sulfate solution. In one embodiment, the copper(II) sulfate solution is a 0.05 M to 0.3 M solution. [0044] By bringing the phosphorus-containing product gas into contact with the aqueous solution containing copper(II) ions, the phosphorus from the phosphorus-containing product gas passes into the aqueous solution containing copper(II) ions, thereby obtaining a phosphorus-containing solution. One or more copper-phosphorus compounds can be formed. The copper-phosphorus compound(s) formed can form a non-water-soluble solid. Alternatively or additionally, one or more phosphorus-oxygen compound(s) can be formed. The phosphorus-oxygen compound(s) formed are preferably water-soluble. A copper-phosphorus compound can be a copper phosphide, for example copper(I) phosphide (CuaP). The inventors assume that copper(I) phosphide (CuaP) is formed. However, it cannot be ruled out that copper(II) phosphide (CU3P2) as well as a mixture of copper(I) phosphide and copper(II) phosphide, and/or copper (hydrogen)phosphate(s) are also formed. A phosphorus-oxygen compound can be phosphoric acid, a phosphoric acid salt, phosphonic acid, a phosphonic acid salt, or a mixture of two or more of these compounds. The inventors have detected ^PCL3 ' in the aqueous solution containing copper(II) ions after it has been brought into contact with the phosphorus-containing product gas. However, it cannot be ruled out that phosphonic acid (H3PO3) is also formed, which is oxidized by atmospheric oxygen. The phosphorus-oxygen compound is preferably phosphoric acid.

[0045] Thus, the phosphorus species contained in the phosphorus-containing product gas can form phosphoric acid and/or a copper phosphide-containing precipitate with the copper(II) ions when the phosphorus-containing product gas is introduced into the aqueous solution containing copper(II) ions. Other gas components contained in the phosphorus-containing product gas, such as CO, EE, CO2 and/or CEL, can pass through the aqueous solution containing copper(II) ions without further reaction. They can then be used for material purposes, e.g., chemical synthesis, or for energy recovery. If the product gas contains H2O, this can remain in the aqueous solution containing copper(II) ions. The other gas components contained in the phosphorus-containing product gas are components that (i) come from the phosphorus-containing feedstock, (ii) from the added foreign carbon or the added carbonaceous, preferably carbon-rich waste product or (iii) from the supplied carrier gas and/or reaction gas.

[0046] The phosphorus-containing product gas can be brought into contact with the aqueous solution containing copper(II) ions at a temperature below the evaporation temperature of the aqueous solution containing copper(II) ions, for example at ambient temperature or room temperature. Room temperature is understood to mean, in particular, a temperature of 10 to 30°C. The phosphorus-containing product gas can be brought into contact with the aqueous solution containing copper(II) ions at an absolute pressure of at least 0.9 bar and less than 50 bar. In one embodiment, the thermal treatment can be carried out at ambient pressure. The ambient pressure can be 1.013 bar.

[0047] The process according to the invention can thus comprise a step (d) which provides for the separation of phosphorus from the phosphorus-containing solution obtained in step (c) and/or the optionally formed phosphorus-containing precipitate. For this purpose, the process according to the invention can comprise the separation of one or more phosphorus-containing compounds. Copper-phosphorus compounds which are obtained as solids when the phosphorus-containing product gas is introduced into the aqueous solution containing copper(II) ions can be separated from the phosphorus-containing solution by a solid-liquid separation process, for example filtration or centrifugation. For example, copper phosphide can be separated by filtration or centrifugation. The separated copper-phosphorus compound(s) can then be converted to elemental phosphorus and/or phosphoric acid, for example by acidification with an inorganic acid such as sulfuric acid and subsequent oxidation using oxygen such as atmospheric oxygen. The air can be supplied by air injection. The phosphorus-containing solution and phosphorus-containing precipitate, both of which can be obtained in step (c), contain, for example, Cu^P, H3PO4, and CuSO4. If the solution is acidified with H2SO4 and subsequently oxidized with air, the 13P is oxidized to Cu3(PO4)2. Thus, a mixture of copper ions, Sulfate ions and phosphate ions are present. If CuSC is separated by ion exchange or another separation process, an aqueous solution containing only H3PO4 is obtained.

[0048] The oxidation of the CU3P can occur from the precipitate if no filtration is carried out. Thus, it can be provided that either (i) the precipitate is filtered to separate it and the precipitate is processed separately, or (ii) no filtration is carried out and the suspension of precipitate and solution is oxidized. In variant (i), it can be provided that the phosphorus species contained in the solution are oxidized by air injection or in another way and then separated, for example by ion exchange. In variant (ii), it can be provided that phosphoric acid formed during the oxidation is separated, for example by ion exchange.

[0049] Phosphoric acid and/or other phosphorus compounds present in the phosphorus-containing solution can be separated from the phosphorus-containing solution by means of a molecular separation process, thereby obtaining a phosphorus-depleted solution. In this way, it is possible to recycle the aqueous solution containing copper(II) ions, for example, the copper sulfate solution.

[0050] Furthermore, it is possible to recover phosphoric acid by introducing oxygen, for example, air, into the phosphorus-containing solution. In this way, not only phosphoric acid but also the aqueous solution containing copper(II) ions, for example, the copper sulfate solution, can be recovered from the solid and dissolved phosphorus compounds. Phosphoric acid and the aqueous solution containing copper(II) ions can be separated by a molecular separation process.

[0051] An example of a molecular separation process is separation by ion exchange. For example, phosphoric acid can be separated by ion exchange. Separation by membrane processes is also possible. [0052] The process according to the invention uses a solution containing copper(II) ions, for example copper sulfate, as a scrubbing medium for separating phosphorus from a product gas formed in a thermochemical process under non-oxidizing conditions. According to the prior art, the phosphorus-containing exhaust gases produced during the thermal treatment are post-combusted or post-oxidized to obtain water-soluble phosphorus species, which are subsequently scrubbed from the exhaust gas. This also results in the oxidation of reaction products such as CO, H2, or gaseous hydrocarbon compounds, which are subsequently no longer available for further utilization. In the separation of elemental phosphorus by quenching, which is also used in the prior art, it cannot be ruled out that a mixture of phosphorus and other condensable components is produced, which subsequently requires complex separation. In addition, condensed but aerosol-like phosphorus may still be present in the gas stream. When separating this mixture, handling the white, toxic, and pyrophoric phosphorus proves difficult. In sewage sludge incineration, which has been practiced up to now, the phosphorus remains in the ash and must then be laboriously removed. In contrast, the process according to the invention selectively removes the phosphorus species from the product gas, allowing not only the utilization of the volatile pyrolysis products obtained previously in the pyrolysis step, but also the utilization of the resulting gas components carbon monoxide and/or hydrogen.

[0053] The process according to the invention enables the recovery of phosphorus and phosphorus-containing compounds from a gas phase. The gas phase can be the product gas obtained in step (b). Using the process according to the invention, phosphorus from phosphorus-containing organic waste materials such as sewage sludge, sewage sludge coke or biomass can be thermally converted into the gas phase (step (b)), separated (step (c)) and thus recovered. At the same time, the material utilization of the carbon contained in the phosphorus-containing feedstock is enabled by at least CO and H2, which are contained in the product gas, passing through the solution containing copper(II) ions, whereby a depleted product gas is obtained and can be further utilized in a subsequent chemical synthesis. For example, the component(s) can be used to synthesize the compounds methanol, methane, ammonia, gasoline, or kerosene. The process according to the invention thus enables carbon recycling.

[0054] The pretreatment of the phosphorus-containing organic waste and the thermal treatment of the phosphorus-containing feedstock according to step (b) can be carried out spatially and/or temporally separately. However, this is not mandatory.

[0055] The invention will be explained in more detail below using exemplary embodiments, which are not intended to limit the invention, with reference to the drawings.

Fig. 1 is a flow diagram of a first embodiment of the process according to the invention; and

Fig. 2 is a flow diagram of a second embodiment of the process according to the invention.

[0056] The first embodiment shown in Fig. 1 illustrates steps (a) to (d) of the process according to the invention, wherein in step (a), a phosphorus-containing feedstock is provided (101) obtained by pre-drying a phosphorus-containing organic waste material, such as sewage sludge. The pre-dried phosphorus-containing organic waste material is not subjected to pyrolysis but is used directly as a phosphorus-containing feedstock. It should be noted that pre-drying is not mandatory.

[0057] The provided phosphorus-containing feedstock is then subjected to a thermal treatment according to step (b) at a temperature of at least 950 °C (102). The thermal treatment takes place in a reaction chamber. In one embodiment of the invention, reducing or non-oxidizing conditions are created in the reaction chamber. To create reducing or non-oxidizing conditions in the reaction chamber, a carrier gas (103) and/or a reaction gas (104) can be supplied to the phosphorus-containing feedstock.

[0058] During the thermal treatment, a gaseous phosphorus-containing product gas is obtained, which is fed to a separation system (106) to carry out step (c). Ash and/or slag are also obtained (105). In the separation system, the phosphorus-containing product gas is brought into contact with an aqueous copper(II) sulfate solution. The phosphorus-containing product gas is scrubbed, whereby phosphorus, for example P2 and P2O5, is separated from the phosphorus-containing product gas to obtain a phosphorus-depleted product gas. One or more components, for example H2, CO, and/or CH4, of the phosphorus-depleted product gas can be subjected to material and/or energy utilization (107). By bringing the aqueous copper(II) sulfate solution into contact with the phosphorus-containing product gas, a phosphorus-containing aqueous copper(II) sulfate solution is obtained (108). A copper phosphide precipitate may form.

[0059] The phosphorus-containing aqueous copper(II) sulfate solution and the phosphorus-containing precipitate can be regenerated according to step (d) (109). For this purpose, the suspension of phosphorus-containing precipitate in phosphorus-containing aqueous copper(II) sulfate solution can be acidified with H2SO4 and subsequently oxidized with air, yielding phosphoric acid. The phosphoric acid can be separated (HO).

[0060] The dashed frame 1 shown in Fig. 1 indicates a process step of the method according to the invention. The narrower dashed frames in Fig. 1 indicate steps (a), (b), (c), and (d). [0061] The second embodiment shown in Fig. 2 corresponds to the first embodiment shown in Fig. 1, except that in step (a) a phosphorus-containing feedstock obtained by pyrolysis of a phosphorus-containing organic waste is provided. The process section shown in Fig. 1 is the second process section 1, which is preceded by a first process section. The first process section is indicated by a dashed frame 2. The narrower dashed frames in Fig. 2 indicate steps (a), (b), (c) and (d).

[0062] In the second embodiment, a phosphorus-containing organic waste material, such as sewage sludge, is provided (201). The provided phosphorus-containing organic waste material is subsequently subjected to preparation by comminution (202). The comminuted phosphorus-containing organic waste material is then subjected to pyrolysis at a temperature of 400 to 600 °C (203), whereby the phosphorus-containing feedstock is obtained. Pyrolysis also produces vaporous pyrolysis products, which are fed to a condensation system (204). The pyrolysis products condensed therein are utilized (205). Uncondensed pyrolysis products, in particular FE, CO, CO2, and CEU, are also obtained therein (206). The uncondensed pyrolysis products are subjected to CO2 removal (207). The remaining uncondensed pyrolysis products can be subjected to material and/or energy utilization (107).

[0063] The phosphorus-containing feedstock obtained during pyrolysis is then subjected to a thermal treatment (102), as already described in connection with the embodiment shown in Fig. 1. This is followed by the steps also described in connection with Fig. 1.

Examples 1 to 3

[0064] For the recovery of phosphorus from sewage sludge, a coke obtained by pyrolysis of sewage sludge was used. This coke is also referred to below as sewage sludge coke. The recovery of phosphorus from sewage sludge coke was carried out using a pilot plant known as GeRiX (Ab- The gasification process is carried out using a gasification system called "gasification equipment for reduction in fixed bed" (abbreviation for "gasification equipment for reduction in fixed bed"). This process quantitatively determines the recovery of phosphorus. The entire process was carried out at a pressure of 1,013 bar.

[0065] To carry out step (b) of the process according to the invention, sewage sludge coke samples, each weighing 2.4 g, were placed in a sample crucible through an opening from below into the reaction chamber of a vertical tube furnace with a ceramic reactor and sealed with a flange system. The process atmosphere was adjusted via mass flow controllers (MFCs) on the periphery of the system. The volume flow for the experiments was 30 l/h STP. The term "STP" describes standard conditions, namely an absolute pressure of 1.01325 bar and a temperature of 0 °C. The sewage sludge coke was treated at a temperature of 1450 °C (heating from room temperature to the final temperature at 5 K/min). For this purpose, the sewage sludge coke was heated from room temperature to a temperature of 1450 °C.

[0066] The product gas exiting the reactor was piped to two gas scrubbers to carry out step (c) of the process according to the invention. This pipe is referred to below as the gas line. The entire gas line downstream of the reactor up to the scrubbers used for phosphorus deposition was heated to over 362°C. The heating was monitored using thermocouples in the gas line to ensure sufficient heating. A temperature of over 362°C is necessary to prevent gaseous phosphorus pentoxide from resubliming. Two glass scrubbers containing CuSO4 solution were installed at the end of the gas line. A product gas containing N2, FE, and small amounts of CO, CEU, and other hydrocarbons, which exited the scrubbers, was piped into the exhaust air. N2 and FE contained in the product gas originate from the carrier gas and reaction gas used in step (b), while at least the carbon and oxygen components of CO, CEU and other hydrocarbons originate from the phosphorus-containing feedstock.

[0067] Before commissioning the plant, a leak test was carried out. To establish reducing conditions in the reaction chamber of the furnace, A mixture of the carrier gas nitrogen and the reaction gas hydrogen, the mixture containing 5 vol.% H2 in N2, was fed into the reaction chamber. The furnace was heated to 1450 °C at a heating rate of 5 K/min, and the stirring device of the CuSO4 wash bottles of the deposition system was switched on. After completion of the inventive process and cooling of the system, the sample crucible was removed from the furnace, the residue was weighed to obtain m residue, and the residual phosphorus content was determined using optical emission spectroscopy with inductively coupled plasma and electrothermal evaporation (ETV-ICP-OES) and, comparatively, using X-ray fluorescence analysis.

[0068] Using the known analysis results of the sewage sludge coke used and the initial weight mCoke, the phosphorus release Pprice can be determined according to equation (1),

In equation (1)

P is the mass fraction of released phosphorus relative to the mass of phosphorus contained in the sewage sludge coke used; mCoke is the mass of sewage sludge coke used according to the initial weight;

PKoks the mass fraction of phosphorus in the mass of the used

Sewage sludge coke mcoke; mresidue is the mass of residue remaining from the sewage sludge coke after step (b) has been carried out, as measured by the final weighing;

Presidue the mass fraction of phosphorus in the mass of the residue mresidue-

[0069] The deposition was balanced after filtration of the filter cake (step (d) of the process according to the invention) and analysis of the solution and the filter cake according to equation (2).

In equation (2)

P separation is the mass fraction of separated phosphorus based on the mass of phosphorus released from the sewage sludge coke used; mp, filter i is the mass of phosphorus contained in the filter cake of the first wash bottle; mp, filter i is the mass of phosphorus contained in the filter cake of the second wash bottle; mp, solution i is the mass of phosphorus contained in the Cu2SO4 solution of the first wash bottle; mp, solution 2 is the mass of phosphorus contained in the Cu2SO4 solution of the second wash bottle; mp, released is the mass of phosphorus released in step (b), where mp, released ^- P price * P coke * n coke.

[0070] The term "phosphorus release" refers to phosphorus that passes from the sewage sludge coke into the gas atmosphere in the reaction chamber in step (b). The term "phosphorus separation," on the other hand, refers to phosphorus that passes from the product gas into the CuSC solution in step (c) or precipitates from this solution as a copper-phosphorus compound. The phosphorus separation is determined from the mass of phosphorus separated by filtration and the mass of phosphorus present in the solution.

[0071] The feed materials, the test conditions, and the results are now presented for two examples. The investigations were carried out using a sewage sludge coke, designated as Coke 1 or Coke Oil, and a sewage sludge coke, designated as Coke 3 or Coke_03. Coke Oil contained approximately 7.6 mass% phosphorus, and Coke_03 contained approximately 6.5 mass% phosphorus. Coke Oil was produced from a sewage sludge, designated as Sewage Sludge 1 or KS 01. Coke_03 was obtained from a sewage sludge referred to as sewage sludge 3 or KS 03. Table 1 shows analytical data for sewage sludges 1 and 3 and cokes 1 and 3. The term "Ma%" means mass% and refers to the mass of the sewage sludge or coke, respectively. The term "wf" means anhydrous.

Table 1

[0072] In all three examples, the following process conditions were used:

(i) To create reducing conditions in the reaction chamber of the furnace, a volume flow V _total of 30 L/h was used. The gas atmosphere in the At the start of step (b), the reaction chamber contained 5 vol% H2 in N2.

(ii) The two wash bottles each contained 2.6 L of CuSC solution and each had a stirring device. Either a 0.25 M CuSC solution or a 0.1 M CuSC solution was used.

(iii) The furnace was heated at a heating rate (AHR) of 5 K/min to a temperature of 1450 °C. After reaching 1450 °C, the furnace was allowed to cool by switching off the heating to allow the residue to be removed.

[0073] In Examples 1 to 3, a depleted product gas was obtained which, in addition to hydrogen, also contained carbon monoxide. The depleted product gas can be used further, for example, for chemical synthesis.

Example 1

[0074] In Example 1, phosphorus was extracted from coke oil using a 0.1 M Cu2SO4 solution. The initial weight mKoks of coke oil was 2.4030 g, and the final weight mRückstand was 1.2823 g. The phosphorus content of the initial weight PKoks was 7.60 mass%, and the phosphorus content of the final weight PRückstana was 4.24 mass%.

[0075] According to equation (1), a phosphorus release P of ~ 70.2% was determined. According to equation (2), 55.2% of this was separated, namely 35% in the filter cake and 65% in solution.

Example 2

[0076] In Example 2, phosphorus was extracted from coke oil using a 0.25 M Cu2SO4 solution. The initial weight mKoks of coke oil was 2.4050 g, and the final weight mRückstand was 1.2933 g. The phosphorus content of the initial weight PKoks was 7.60 mass%, and the phosphorus content of the final weight PRückstana was 4.23 mass%. [0077] According to equation (1), a phosphorus release P of approximately 70% was determined. According to equation (2), 64.3% of this was separated, namely 45% in the filter cake and 55% in solution. Example 3

[0078] In Example 3, phosphorus was extracted from coke_03 using a 0.25 M Cu2SO4 solution. The initial weight mcoke of coke_01 was 2.4010 g, and the final weight mresidue was 1.4576 g. The phosphorus content of the initial weight Pcoke was 6.51 mass%, and the phosphorus content of the final weight Presidue was 0.83 mass%.

[0079] According to equation (1), a phosphorus release P of ~ 92% was determined. According to equation (2), 84.8% of this was separated, namely 31% in the filter cake and 69% in solution.

Claims

Patent claims 1. A process for recovering phosphorus from a phosphorus-containing organic waste material, the process comprising the steps of: (a) providing a phosphorus-containing feedstock, wherein the phosphorus-containing feedstock is the phosphorus-containing organic waste material or is obtained from the phosphorus-containing organic waste material; (b) thermally treating the phosphorus-containing feedstock at a temperature of 950 °C or higher to obtain a phosphorus-containing product gas; and (c) contacting the phosphorus-containing product gas with an aqueous solution containing copper(II) ions to separate phosphorus from the phosphorus-containing product gas. 2. Process according to claim 1, characterized in that the phosphorus-containing organic waste material is sewage sludge. 3. The method according to claim 1 or claim 2, characterized in that the thermal treatment in step (b) is carried out in a reaction chamber and reducing conditions develop in the reaction chamber during the thermal treatment. 4. A process according to any one of the preceding claims, characterized in that the phosphorus-containing feedstock contains carbon or carbon is added to the phosphorus-containing feedstock. 5. A process according to claim 4, characterized in that carbon is added to the phosphorus-containing feedstock by adding a carbon-containing waste product. 6. The method according to any one of claims 3 to 5, characterized in that a carrier gas and/or a reaction gas are supplied to the reaction space in step (b), wherein - the carrier gas is selected from the group consisting of nitrogen, argon, helium and mixtures of two or more of these gases, and - the reaction gas is selected from the group consisting of oxygen, hydrogen, water vapor, carbon dioxide, carbon monoxide and mixtures of two or more of these gases. 7. A process according to claim 6, characterized in that the reaction gas is oxygen, water vapor or a mixture of oxygen and water vapor. 8. A process according to claim 6 or claim 7, characterized in that the reaction gas is supplied to the reaction chamber in a substoichiometric molar ratio, wherein a substoichiometric molar ratio exists when the molar amount of oxygen in the reaction gas is less than the molar amount of oxygen required for complete combustion of the carbon and hydrogen contained in the phosphorus-containing feedstock. 9. Process according to one of the preceding claims, characterized in that the aqueous solution containing copper(II) ions is an aqueous copper(II) sulfate solution. 10. The method according to claim 9, characterized in that the aqueous copper(II) sulfate solution is a 0.1 M to saturated copper(II) sulfate solution. 11. A process according to any one of the preceding claims, characterized in that step (c) comprises the formation of a copper-phosphorus compound and/or a phosphorus-oxygen compound. 12. Method according to one of the preceding claims, characterized in that the method comprises the step (d) separating one or more phosphorus-containing compounds from the phosphorus-containing solution obtained in step (c). 13. A process according to claim 12, characterized in that at least one of the separated phosphorus-containing compounds is converted to elemental phosphorus or to phosphoric acid. 14. A process according to any one of the preceding claims, characterized in that the phosphorus-containing organic waste provided in step (a) has been subjected to pyrolysis. 15. The process according to any one of the preceding claims, characterized in that in step (c) a phosphorus-depleted product gas is obtained and at least one component of the phosphorus-depleted product gas is used for material or energy purposes.