Method for depolymerising polyurethane by means of ozonolysis in an aqueous medium

Abstract

The present invention relates to a method for depolymerising polyurethane by means of ozonolysis in an aqueous medium comprising: (a) introducing the polyurethane foam into at least one reactor containing water, producing a suspension of polyurethane foam in water; and (b) injecting ozone inside the reactor, making it bubble under stirring, producing an ozonolysis reaction of the polyurethane foam during which the polyurethane foam is converted into compounds with low molecular weight, lower than 700 Da, in an aqueous solution.

Description

[0001] POLYURETHANE DEPOLYMERIZATION PROCESS BY OZONOLYSIS IN AQUEOUS MEDIUM

[0002] DESCRIPTION

[0003] TECHNICAL SECTOR

[0004] The present invention falls within the field of chemical and environmental technology. In particular, it relates to a novel process for the treatment and recycling of polyurethane waste.

[0005] BACKGROUND OF THE INVENTION

[0006] Polyurethane is a polymer synthesized through the chemical reaction between a polyol and an isocyanate. It is a highly versatile product, being one of the most widely used polymers in humankind. It is particularly used in applications as diverse as insulation, coatings, shoe soles, adhesives, automotive parts, mattresses, sportswear, and more.

[0007] Global polyurethane production is estimated to reach millions of tons annually, which has a significant environmental impact, contributing to the overexploitation of natural carbon sources and global warming. In particular, the byproducts and waste generated during the manufacture of polyurethane foams lack an environmentally sustainable alternative for management, as these materials are difficult to recycle and generally accumulate in landfills and storage areas, only to be ultimately incinerated.

[0008] In turn, current polyurethane recycling processes are based on chemical reactions with a high environmental impact due to greenhouse gas emissions, high consumption of chemical compounds, and the high energy costs associated with these processes.

[0009] In particular, numerous patents have been found in the state of the art relating to various polyurethane recycling techniques. The disclosed techniques can be classified as follows:

[0010] Acidolysis: A chemical technique that uses chemical compounds, such as carboxylic acids, and high temperatures to break long polyurethane chains and recover polyols. This technique has been described in various patents, such as patent applications CN 107286369 and CN 113637222. The disadvantages of this technology are the use of chemical compounds and the high energy requirements required to carry out the process.

[0011] Hydrolysis: This chemical technique decomposes polyurethane using water at high temperatures and alkaline compounds, such as ammonium hydroxide. It has been described in various patents, such as patent US6515036. In turn, patent EP0990674 describes the use of organic solvents, such as polyols or glycols, to carry out a hydroglycolysis reaction. This patent also describes the possibility of eliminating or separating the primary amines formed after the depolymerization of polyurethane, which can be used, after separation and purification, as raw material to synthesize new isocyanates. The problems associated with using this technique are its high economic cost and the need to use chemical agents to carry it out.

[0012] Glycolysis: This technique is based on a chemical degradation process of polyurethane waste using glycolytic agents as degradation compounds in combination with high temperatures (140-220°C). There are numerous patents, such as EP1693409, which employ this technique for the degradation of polyurethane and the recycling of polyols formed during glycolytic processes to form new polyurethane foams. However, these processes require extreme operating conditions, as well as high energy and chemical consumption. They also involve secondary reactions that considerably reduce process efficiency, hindering the formation of new foams and the reuse of the generated polyols.

[0013] Aminolysis: This technique is based on a chemical process for the depolymerization of polyurethane. It consists of a mixture of chemical compounds such as metal hydroxyls and alkanolamines that react at high temperatures to obtain polyols and amines derived from the depolymerization. The technique has been described in patents such as US5274004. One of the major drawbacks of this technique is the increase in free amines, which can modify the physical properties of the new foams synthesized from the polyols obtained during the process.

[0014] There is, therefore, a need to develop new processes capable of managing the large volume of polyurethane waste currently available, which, to date, has lacked adequate management, leading to its disposal and conversion into new functional products.

[0015] DESCRIPTION OF THE INVENTION

[0016] The present invention solves the problems associated with currently used polyurethane recycling techniques through a new process capable of achieving complete depolymerization of polyurethane foams, converting them into low-molecular-weight compounds such as polypropylene, amines, or acids. The process is based on an ozonolysis method that only requires water and ozone. It is also a sustainable process with a low environmental impact, since the water used in the reaction can be separated, purified, and reused in the process itself, and the ozone can be generated on-site using renewable electricity.

[0017] It is, therefore, a first object of the invention, a process for the depolymerization of polyurethane foam characterized in that it comprises: a) introducing the polyurethane foam into at least one reactor in an inert atmosphere (preferably air) containing water, preferably osmotized, inside, giving rise to a suspension of polyurethane foams in water; b) injecting ozone into the reactor, bubbling it, giving rise to an ozonolysis reaction or oxidative attack of the polyurethane foam by means of ozone at a temperature preferably between 10 ° C and 30 ° C, more preferably between 20 and 25 ° C, under stirring at a speed preferably between 300 and 500 rpm, more preferably 350 rpm, ensuring correct homogenization of the suspension;where, during the ozonolysis reaction, ozone reacts with the most reactive oxygen in the urethane bond, destabilizing it and causing the cleavage of the ester bond and, consequently, the decarboxylation of the polyurethane. In this way, an aqueous solution is generated that comprises low molecular weight compounds, understood as compounds with a molecular weight less than 700 daltons (Da) such as, for example, polies (such as polyethylene glycol or polypropylene glycol) or amines derived from the cleavage of isocyanate or carboxylic acids (dihydroxy-3-methylpentanoate, adipic acid, etc.), among others.;

[0018] This process can be carried out either in batches or continuously.

[0019] For the purposes of this patent, polyurethane foam is understood to be the product formed by a catalyzed addition reaction of diisocyanates, polyether or ester, and water, resulting in a cellular polyurethane foam in which all reactants are chemically bonded to form the polymer's polyurethane matrix. In a preferred embodiment of the invention, the process may comprise a prior pretreatment step of the polyurethane foam, which may include its mechanical rupture into fractions of a size that can preferably range between microns and millimeters. More preferably, the polyurethane foam will be a waste that can have different origins, without limiting the object of the invention. Thus, in particular embodiments of the invention, said waste may come from refrigerator or freezer insulation, mattresses, rejects from plastic part manufacturing processes, etc.

[0020] In a particular embodiment of the invention, the process may comprise an additional step for generating the ozone used in the reaction, which may consist of a conventional process for generating ozone from atmospheric air, which is passed through an ozone-generating lamp where, by means of an electrical discharge, the oxygen is converted into ozone. In another alternative embodiment of the invention, the oxygen source for generating ozone may be pure oxygen, instead of atmospheric air, or alternatively, enriched oxygen (with an oxygen concentration greater than 21% by volume), in order to accelerate the reaction.

[0021] Preferably, the electrical energy required for the ozone production process can be generated on-site in a sustainable manner and may consist of electrical energy from renewable sources, such as photovoltaic energy. In a further particular embodiment of the invention, the process may comprise an additional ozone destruction step, such that the gases generated during the process, upon exiting the reactor, are subjected to a conventional process for destroying the ozone contained therein, thereby preventing the release of polluting gases into the atmosphere.

[0022] In turn, in another preferred embodiment of the invention, once the process is complete, the water contained in the reactor can be extracted and subjected to a purification process (preferably by filtration and osmosis), and then reintroduced into the reactor to be reused in a new ozonolysis process. This reduces the consumption of natural resources, which is an additional advantage of the process.

[0023] Another of the process's main advantages is that it allows for the complete recovery of a currently difficult-to-manage waste, polyurethane foam, by converting it completely into low-molecular-weight compounds that are completely soluble in water and contain essential elements for life, such as carbon and nitrogen. The process can thus include a subsequent stage of utilization of these compounds, which can be carried out after a preliminary stage of concentration of the aqueous solution (resulting from the ozonolysis process) and its extraction from the reactor, preferably by reverse osmosis filtration, resulting in two solutions: one composed of a concentrate of organic compounds and the other of osmosis water.The concentrate of organic compounds, in turn, can then be fractionated by distillation, giving rise to two groups of compounds: a) a volatile fraction, composed of unaltered polypropylene, which can then be subjected to a separation and purification stage (preferably, by means of conventional distillation, osmosis and / or filtration systems) to be used subsequently, preferably, as raw material in a new polyurethane foam synthesis process; and b) a non-volatile fraction in an aqueous medium comprising oxidation products such as, for example, amines derived from the cleavage of isocyanate or carboxylic acids (dihydroxy-3-methylpentanoate, adipic acid, etc.), lactones (caprolactone, pantolactone, among others), etc.In a particular embodiment of the invention, this non-volatile fraction may be used as an agricultural fertilizer and / or as a fermentation medium for the growth of organisms and / or microorganisms, such as plants or bacteria, among others, as it is a source of carbon and nitrogen, essential nutrients for life. In a preferred embodiment of the invention, this process can be carried out in situ on agricultural farms.

[0024] Among the technical advantages that the claimed process presents compared to other known methods in the state of the art, the following are worth mentioning: it allows the total conversion of polyurethane foams into low molecular weight compounds, soluble in water and with a high percentage of carbon and nitrogen; it can be carried out using completely sustainable energy, such that the energy cost of the process can be reduced to practically zero; it does not emit greenhouse gases, making it a non-polluting process; it is a rapid process, although the duration of the process may vary depending on the quantity of foams treated, as well as their size, temperature at which the process is carried out, ozone generation, etc.; and it requires low water consumption because, in preferred embodiments of the invention, the water used in the process can be reused in a new ozonolysis process, following a prior purification process.

[0025] In short, it is a green circular economy process that solves the current problems associated with the recycling of polyurethane foams, offering a process with low costs and pollutant emissions, which allows the compounds obtained in the process to be additionally used in different applications such as, for example, as a culture medium for the growth of beneficial bacteria for plants, the recovery of the generated policies for the synthesis of new polyurethane foams, etc.

[0026] BRIEF DESCRIPTION OF THE FIGURES

[0027] Accompanying this description is the following figure (Fig. 1) where, for illustrative and non-limiting purposes, a device is shown to carry out the claimed process, where: (1) Ozone producing machine

[0028] (2) Chemical reactor

[0029] (3) Gas outlet

[0030] (4) Air flowmeter

[0031] (5) Temperature sensor

[0032] (6) Polyurethane foam

[0033] DETAILED DESCRIPTION OF THE INVENTION

[0034] A particular embodiment of the polyurethane foam depolymerization process object of the present invention is described below, which can be carried out in a device as shown in Figure 1.

[0035] As described above, said polyurethane foam depolymerization process is characterized in that it comprises the following steps: a) generating ozone in an ozone-producing machine (1) from atmospheric air, with an oxygen concentration of 21% by volume or, alternatively, from pure oxygen, thus accelerating the reaction. The atmospheric air (or pure oxygen) can be fed to the ozone-producing machine (1) by means of a pump controlled by an air flow meter (4), creating an air flow that can be 60 l / min. In turn, the ozone-producing machine (1) can consist of a dielectric lamp by means of which a high alternating voltage and frequency variations are achieved that cause the pulsed ionization of oxygen, generating ozone with a production that can be 8 mg / h;b) next or simultaneously, the polyurethane foam (6), previously fragmented, is introduced into the reactor (2), where said reactor (2) can be made of a material that can consist of glass, steel, or any other material inert to ozone, and contains inside: a reaction medium consisting of osmotized water, a temperature sensor (5) connected to a controller for regulating the temperature and stirring means connected to a stirring speed controller, such that the polyurethane foam (6) is suspended in the water contained in the reactor (2);c) once the polyurethane foam has been introduced into the reactor (2), the ozone generated in the ozone-producing machine (1) is injected into its interior, bubbling it, giving rise to an oxidative attack reaction of the polyurethane foam by means of ozone at a temperature preferably between 10°C and 30°C, more preferably between 20 and 25°C, under stirring at a speed preferably between 300 and 500 rpm, more preferably 400 rpm, ensuring correct homogenization of the suspension. Preferably, the introduction of ozone into the reactor (2) can be carried out by pulses, until reaching its saturation concentration in water (40 mg / l), which can be kept constant over time.;

[0036] During the process, the ozone that has been bubbled into the water leaves the reactor through a gas outlet duct (3) and, before being emitted into the atmosphere, passes through an ozone destruction trap so that, during the process, only clean air is released into the atmosphere.

[0037] As a result of the process, low molecular weight compounds (less than 700 Da) are generated, derived from the breakage of polyurethane molecules, cumulatively over time. These compounds may consist mainly of polypropylene or amine derivatives from the breakage of isocyanates or carboxylic acids, among others, the concentration of these compounds being variable over time. As described above, after the reaction, the generated compounds can be extracted in aqueous solution through an outlet conduit (not shown in Figure 1), as well as separated from the water, such that the water, once separated and purified, can be fed back to the reactor (2) to be used in a new ozonolysis process and, in turn, the generated compounds can be used, either directly or in subsequent processes, given their high concentration of carbon and nitrogen.

Claims

CLAIMS 1. Process for the depolymerization of polyurethane foam, characterized in that it comprises: a) introducing the polyurethane foam into at least one reactor containing water inside, giving rise to a suspension of polyurethane foam in water; b) injecting ozone into the reactor, bubbling it under stirring, giving rise to an ozonolysis reaction of the polyurethane foam during which the polyurethane foam is converted into low molecular weight compounds, less than 700 Da, in aqueous solution.

2. Process according to claim 1, wherein said process is carried out at a temperature between 10°C and 30°C.

3. Process according to claim 1 or 2, wherein said process is carried out at an agitation speed between 300 and 500 rpm.

4. Process, according to any one of the preceding claims, wherein the low molecular weight compounds consist of polies or amines, as well as any combination thereof.

5. Process, according to any one of the preceding claims, wherein said process comprises a stage prior to stage (a) of pretreatment of the polyurethane foam which comprises its mechanical breaking into fractions of a size that varies between microns and millimeters.

6. Process, according to any one of the preceding claims, wherein said process comprises an additional stage of generating the ozone used in the ozonolysis reaction, from atmospheric air, pure oxygen, or enriched oxygen, understanding enriched as an oxygen concentration greater than 21% by volume.

7. Process, according to claim 6, where the energy required for the ozone generation process consists of electrical energy of renewable origin.

8. Process, according to any one of the preceding claims, wherein during the ozonolysis process gases comprising ozone are generated, which are subjected to an ozone destruction stage prior to their release into the atmosphere.

9. Process, according to any one of the preceding claims, where, once the process is completed, the water contained in the reactor is extracted and subjected to a purification process, and is then reintroduced into the reactor to be reused in a new ozonolysis process.

10. Process according to any one of the preceding claims, wherein said process comprises a subsequent stage of utilization of the low molecular weight compounds obtained in the process, where said utilization stage comprises the extraction of the aqueous solution generated in the process and its concentration, giving rise to two solutions: a first one comprising a concentrate of organic compounds and a second one comprising water.

11. Process according to claim 10, wherein the first solution comprising the concentrated organic compounds is then subjected to a distillation process, resulting in: a) a volatile fraction comprising unaltered compounds; and b) a non-volatile fraction comprising oxidation products in an aqueous medium.

12. Process, according to claim 11, wherein the volatile fraction is then subjected to a separation and purification stage, followed by the use of the policies as raw material in a new polyurethane foam synthesis process.

13. Process, according to claim 11 or 12, wherein the non-volatile fraction is used as an agronomic fertilizer and / or as a fermentation medium for the growth of organisms, microorganisms, or both.

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