Depolymerization process

Abstract

Depolymerization process of a polymer belonging to the family of polyamides or polycarbonates or polyurethanes or polyesters with the exception of polyethylene terephthalate; said depolymerization process being characterized in that said polymer, an ionic liquid consisting of (2-hydroxyethyl)trimethylammonium argininate [Cho][Arg] and methanol are mixed together at a temperature ranging from -50 to 70°C.

Description

[0001] DEPOLYMERIZATION PROCESS

[0002] CROSS-REFERENCE TO RELATED APPLICATIONS

[0003] This Patent Appl ication claims priority from Italian Patent Application No . 102023000014904 filed on July 17 , 2023 , the entire disclosure of which is incorporated herein by reference .

[0004] FIELD OF THE ART

[0005] The present invention relates to a depolymerization process of polymers belonging to the family of polyamides or polycarbonates or polyesters excluding polyethylene terephthalate , and to the preparation of a speci fic ionic liquid necessary for the same depolymeri zation process .

[0006] STATE OF THE ART

[0007] To date , the disposal of plastic waste constitutes one of the main problems , i f not the main problem, from an environmental point of view .

[0008] In fact , plastic is currently the main material used in packaging and, as a result , ever greater quantities thereof accumulate every year, which necessarily constitute a signi ficant environmental risk i f they are not subj ected to ef fective disposal and / or recycling processes .

[0009] In this respect , it should be considered that while plastic was made to ensure the integrity of long-lasting products , it has long since constituted the raw material for most of the products defined as "disposable" .

[0010] As may be immediately apparent , the disposal and / or recycling solutions involving the treatment of plastic waste , in order to be socially attractive , must be economically viable as well as technically ef ficient .

[0011] Generally, polymeric materials can be disposed of by means of both chemical recycling or by means of mechanical recycling .

[0012] While chemical recycling allows the polymer to be restored to the monomer state to be also subsequently reused for the production of a new polymer also for food use , mechanical recycling produces products of lower quality but , at the same time , is far cheaper . For example, generally the products resulting from mechanical recycling may not be used for the food industry, except for mineral water and soft drinks containers according to special modes .

[0013] One of the forms of chemical recycling relates to depolymeri zation by means of glycolysis . Glycolysis is a type of chemical recycling method which converts the polymer to monomer through a succession of chemical reactions . With respect to other recycling methods , the most obvious advantage of glycolysis is that the monomer may be repolymeri zed into new material s under relatively mild reaction and low-volatile solvent conditions .

[0014] In recent years , depolymeri zation processes by glycolysis have been implemented using ionic liquids ( IL ) as catalysts . Ionic liquids are organic salts with a low melting point and are considered a safer alternative than traditional organic solvents due to their low vapour pressure and nonflammability . Naturally occurring aliphatic cation ionic liquids , such as ( 2-hydroxyethyl ) trimethylammonium, also known as cholinium, have drawn great interest .

[0015] To date , the processes developed for depolymeri zation by means of ionic choline liquids provide pressure and temperature conditions such as to make them unattractive when applied on an industrial scale .

[0016] The need was therefore felt to provide a depolymeri zation process with choline ionic liquid, the technical features of which were such as to make it more industrially attractive than the processes of the prior art .

[0017] AIM AND SUMMARY OF THE INVENTION

[0018] The inventors of the present invention have implemented a process capable of satis fying the above need .

[0019] The aim of the present invention is a depolymeri zation process , the essential features of which are reported in the independent claim 1 , and the secondary and auxiliary features of which are reported in the dependent claims 2 - 7 .

[0020] A further obj ect of the present invention is a process for preparing the ionic liquid useful for the depolymeri zation process according to the present invention, the essential features of which are reported in the independent claim 8 , and the secondary and auxiliary features of which are reported in the dependent claims 9 and 10 .

[0021] A further obj ect of the present invention is an ionic liquid consisting of ( 2 -hydroxyethyl ) trimethylammonium argininate [ Cho ] [Arg] made according to the present invention .

[0022] DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

[0023] Below are example embodiments merely for illustrative , non-limiting purposes , with the aid of the attached figure , which is an NMR spectrum of a depolymeri zation product obtained with the procedure of one of the examples shown .

[0024] Choline argininate [ Cho ] [Arg] ionic liquid synthesis 0 . 70 grams of 1-arginine powder at the highest available purity were introduced into a 20 ml vial and a suitably si zed magnetic stirrer .

[0025] 1 ml of an aqueous solution of 2 -hydroxy-N, N- trimethylethanammonium (ChoOH) was added to the vial drop by drop. The amount of added ChoOH represents a number of moles equal to that of 1-arginine. In addition, 7 ml of MilliQ water were also added to the vial. At this point, a constant 350 rpm rotation was set on the magnetic stirrer, while the vial was maintained at a temperature of 30°C by means of a thermostat bath. These conditions were maintained for a time interval of 48h.

[0026] Adding the ChoOH aqueous solution directly to the 1- Arginine powder is necessary to prevent the acid-base equilibrium of the guanidine group of the amino acid from forming, which would make the neutralization reaction between the acid proton of the carboxylic group of the amino acid and the hydroxyl group of the choline hydroxide more difficult .

[0027] It was verified that if this addition is carried out drop by drop or in a single solution, on an aqueous solution of 1-arginine, maintaining an equal number of moles between 1-arginine and choline hydroxide in both solutions, the [Cho] [Arg] yield decreased significantly from 100% to about 30%. Subsequently, the contents of the vial were transferred to a 50 ml volume flask.

[0028] At this point, the water was removed by means of a rotavapor (pressure values of approx. 35-30 mbars) , keeping the water bath first at 30°C and then, after approx. 40% water removal, at 40°C. The inventors believe that the step of removing water from the reaction matrix must be a timeconsuming process which requires great care. From the above, a compound, exceeding from zero to 3.5% by mass, was obtained .

[0029] Depolymerization examples [Cho] [Arg] offers unique structural, electromagnetic and chemical features. These synergistically contribute to determining the conditions necessary for the depolymerization process presented herein. In particular, the conformational freedom of the ion pair allows it to assume conformations which are useful in establishing highly site-specific interactions when interfaced with polymer molecules in which the acyl functional group is linked to one (polyesters, polyamides, polycarbonates) or more (polyurethanes) electronegative atoms. In fact, this group is fundamental in the structure of these polymers and the electrical properties of the ionic liquid, which are mainly divided into two polar regions, one located in the methyl groups of the choline characterized by an excess of positive charge (5q > 0) and the other in the guanidine group of the amino acid characterized by a prevalence of negative charge (5q < 0) , chemically activate the reaction centres. This results in the lysis of the acyl bond at the expense of the polymer's ester or amide bonds. The last feature concerns the possibility of [Cho] [Arg] managing to enter in solution in alcoholic solvents, such as methanol and generate a nucleophilic environment therein. This phenomenon is the result of an acid-base reaction between the protic solvent (donor) and the guanidine group (acceptor) of the ion pair. All these factors result in a transient catalytic matrix (TCM) in the reaction environment.

[0030] Essentially, the occurrence of point interactions between the [Cho] [Arg] pair and the carbonyl functions of the acyl groups of the polymer molecules allow the nucleophilic attack on the carbons of the carbonyl group by the methoxide ions it has produced within the matrix. Thus, on the one hand, [Cho] [Arg] activates the carbon atoms of the carbonyl groups of the polymer, and on the other hand produces the CH3CA ion responsible for the lysis of the acyl bond. Furthermore, ChAr also facilitates the removal of the polymer's first rather cluttered exiting groups. For these reasons, the ion pair molecule is capable of performing a bi-molecular bi-catalyzed reconversion (rBMBc) on the polymer molecules. The biological origin of the two constituent molecules of the ionic liquid justifies the use of the suffix bio, while the catalytic aspect is the result of the sum of the highly site-specific interactions between the carbonyl functional groups of the polymer molecule and the ionic liquid and the concomitant production of nucleophiles (in this case methoxides) , which are indispensable to the depolymerization process. This latter aspect makes the process analogous to what occurs in biological chemistry by enzymes, proteins able to perform highly specific chemical reactions, considerably lowering the energy costs required to carry out the reactions. In fact, it is no coincidence that the depolymerization process already occurs at ambient temperature and pressure, typical physical features found in the biological chemistry of enzymes .

[0031] Based on the above, the inventors claim that the effectiveness of the process is to be extended to all the polymers of the polyester family with the exception of PET, polyamides, polycarbonates and polyurethanes.

[0032] General description of the depolymerization process

[0033] The following general description summarizes the necessary steps for depolymerization according to the present invention and applies to polymers of the family of polyamides , polycarbonates , polyurethanes and polyesters , excluding PET . The post-consumer plastic product based on polymer material is preferably shredded by means of a professional mill . The ionic liquid is added to the shredded polymer material and amalgamation is carried out by means of , for example , vibration, rotation, ultrasound, propellers , etc . The amalgamation is conducted at a temperature comprised between 0 ° C and 40 ° C and for a duration no less than sixty minutes . During this amalgamation step, the interactions responsible for the chemical activation of the carbonyl carbon of the acyclic groups in the polymer chain are carried out .

[0034] To the mixture of [ Cho ] [Arg] and polymer, in continuous and persistent amalgamation, a certain volume of methanol is added drop by drop or in a single solution . The volume of methanol added is determined by a theoretical starting ratio which is equal to the number of acyclic bonds present in the polymer molecule . The amalgamation process lasts for the required duration . An alcoholic solution (preferably methanol ) of sodium methoxide can be added to said mixture consisting of methanol , [ Cho ] [Arg] and polymer .

[0035] Below are examples of the process according to the present invention performed on the polymer PLA.

[0036] PLA depolymeri zation

[0037] An example of depolymeri zation carried out in the laboratory is hereinafter reported .

[0038] As may be immediately apparent to a person skilled in the art , the example reported below aims to demonstrate the depolymeri zation ef fectiveness of ( 2- hydroxyethyl ) trimethylammonium argininate according to the process of the invention . In this respect , the reported yields are not to be regarded as particularly significant as they may be improved by a cyclic repetition of the process or by industrial adjustments falling outside the features defined in the claims.

[0039] EXAMPLE 1

[0040] A 50 ml reaction flask was filled with 1.0052 grams of PLA deriving from a disposable beaker which was cut into small pieces and 0.9155 grams of choline argininate ionic liquid. The ratio of moles of ionic liquid to moles of repetitive units (UR) of PLA was approximately 0.24.

[0041] The contents of the reaction flask were amalgamated for one hour by means of rotating the reactor with a rotavapor. Once the rotation with rotavapor was stopped, 0.1 ml of methanol was added by means of a micro-pipette. This addition occurred in a single solution and was repeated every hour for eight hours. After the additions, the solution had an ionic liquid concentration of 4.1 M and was left to amalgamate by means of the action of the rotavapor for a period of 13.5 hours.

[0042] Following each successive addition of methanol, the solution is amalgamated by means of the action of the rotavapor .

[0043] Subsequently, 0.2 ml of methanol was added every hour for 12 hours and the ionic liquid concentration decreased to 1.0 M.

[0044] Subsequently, 0.4 ml of methanol was added every hour for 6 hours .

[0045] Subsequently, 20 ml of methanol was added, bringing the ionic liquid concentration to 0.125 M.

[0046] Up to this point, all the operations were performed at a temperature of 20°C and a pressure of 1 atm. After the above-mentioned addition of methanol, the reactor was moved to a thermostatically controlled bath at 30°C, in which amalgamation was achieved by means of the action of a Teflon-coated stirbar.

[0047] After 24 hours under these conditions, an additional 20 ml of methanol was added, thus reaching an ionic liquid concentration of 0.071M. The reaction was left stirring for a further 48 hours.

[0048] Although the complete dissolution of PLA was verified, it was not possible to extract the methyl-lactates (PLA monomers) produced through hydrolysis. In fact, it was not possible to isolate lactic acid by acidifying the solution (with 0.1 M HC1) , as lactic acid is miscible with water at temperatures above 6°C.

[0049] EXAMPLE 2

[0050] A 50 ml reaction flask was filled with 0.9978 grams of PLA deriving from a disposable beaker which was cut into small pieces and 0.998 grams of choline argininate ionic liquid. The ratio of moles of ionic liquid to moles of repetitive units (UR) of PLA was approximately 0.26.

[0051] The contents of the reaction flask were amalgamated for one hour by means of the action of the rotavapor.

[0052] Subsequently, 26.4 ml of methanol was added, obtaining an ionic liquid concentration of 0.136 M.

[0053] Up to this point, all the operations were performed at a temperature of 20°C and a pressure of 1 atm.

[0054] After the above-mentioned addition of methanol, the reactor was moved to a thermostatically controlled bath at 30°C, in which amalgamation was achieved by means of the action of a Teflon-coated stirbar.

[0055] The reactor was left in the bath at 30°C and under stirring for 36 hours. At the end of 36 hours, no more macroscopic pieces of PLA are visible.

[0056] Next, methanol was extracted from the depolymerization matrix by means of rotavapor. When the extraction was complete, a weight of 0.3211 grams more than the theoretical weight calculated on the basis of the methyl-lactate produced alone was measured. It was assumed that the extra mass is due to the methanol not yet been extracted. The amount of methyl lactate was too low to be recovered. This experiment therefore served to demonstrate how depolymerization also occurs, and indeed in a shorter time, when methanol is added in a single solution.

[0057] EXAMPLE 3

[0058] A 50 ml reaction flask was filled with 16.6177 grams of PLA deriving from a disposable beaker which was cut into small pieces and 4.1657 grams of choline argininate ionic liquid. The ratio of moles of ionic liquid to moles of repetitive units (UR) of PLA was approximately 0.065.

[0059] The contents of the reaction flask were amalgamated for one hour by means of the action of the rotavapor.

[0060] Subsequently, 150 ml of methanol was added, obtaining an ionic liquid concentration of 0.100 M.

[0061] Up to this point, all the operations were performed at a temperature of 20°C and a pressure of 1 atm.

[0062] After the above-described addition of methanol, the system was moved to a thermostatically controlled bath at 30°C and amalgamation was produced through Teflon-coated stirbar. After 72 hours of amalgamation under the conditions reported above, the depolymerization matrix was cloudy but without the presence of macroscopic pieces of PLA. The depolymerization process was stopped and the matrix was filtered. Dust and hairs are collected on what was retained and the excess methanol is extracted from the depolymerization matrix by means of a rotavapor. Although it was not possible to recover the theoretical 22 ml of methyl lactate, a fair amount was extracted and an NMR analysis was performed thereon, which produced the spectrum shown in the attached figure.

[0063] Furthermore, a 1 ml sample of methyl lactate yielded 1.0922 grams, thus confirming the density data which can be found in the literature. This example showed that the depolymerization process according to the present invention is quantitative and catalytic.

[0064] COMPARATIVE EXAMPLE

[0065] A 50 ml reaction flask was filled with 1.0061 grams of PLA deriving from a disposable beaker which was cut into small pieces and 0.9531 grams of choline argininate ionic liquid. The ratio of moles of ionic liquid to moles of repetitive units (UR) of PLA was approximately 0.25.

[0066] 0.1 ml of milliQ water was added to the solution by means of a micro-pipette. This addition occurred in a single solution and was repeated every hour for eleven hours.

[0067] The solution formed had an ionic liquid concentration of 3.124 M and was left to amalgamate with rotavapor for 13 hours .

[0068] Subsequently, additions of 0.2 ml of milliQ water were performed every hour for eleven hours, resulting in an ionic liquid concentration of 0.982 M.

[0069] No appreciable change was observed on the PLA pieces without, therefore, any depolymerization process occurring.

[0070] COMPARATIVE EXAMPLES

[0071] For comparative purposes, three comparative examples were made in which [Cho] [Arg] was replaced with [Cho] [Gly] , [Cho] [Pro] and L-Arginine, respectively.

[0072] - Example with [Cho] [Gly]

[0073] In this example, 4.0893 g of [Cho] [Gly] and 16.6041 g of PLA were used.

[0074] The time and temperature conditions of depolymerization example 3 according to the above invention were repeated and the amount of methanol added in a single solution was 150 ml .

[0075] [Cho] [Gly] was synthesised in the laboratory using the same synthesis procedure as in the case of choline argininate and described above. The reagents used are all Merck- certified.

[0076] At the end of the depolymerization procedure, the recovered non-depolymerized PLA was found to weigh (16.6112) g and thus 0.043% more (within the weighing error of the scale) than the PLA initially used.

[0077] It is clear from the above that the use of the ionic liquid consisting of [Cho] [Gly] does not produce any depolymerization .

[0078] - Example with [Cho] [Pro]

[0079] In this example, 4.1004 g of [Cho] [Pro] and 16.5470 g of PLA were used.

[0080] The time and temperature conditions of depolymerization example (3) according to the above invention were repeated and the amount of methanol added in a single solution was 150 ml.

[0081] [Cho] [Pro] was synthesised in laboratory using the same synthesis procedure as in the case of choline argininate and described above. The reagents used are all Merck-certified.

[0082] At the end of the depolymerization procedure, the recovered non-depolymerized PLA was found to weigh 16.5601 g and thus 0.079% more (within the weighing error of the scale) than the PLA initially used.

[0083] It is clear from the above that the use of the ionic liquid consisting of [Cho] [Pro] does not produce any depolymerization .

[0084] - Example with L-Arginine

[0085] In this example, 4,003 g of L-Arginine and 16.4157 g of PLA were used.

[0086] The time and temperature conditions of depolymerization example (3) according to the above invention were repeated and the amount of methanol added in a single solution was 150 ml.

[0087] At the end of the depolymerization procedure, the recovered non-depolymerized PLA weighed 16.4217 g.

[0088] It is clear from the above that the use of L-Arginine (Merck-certified) does not produce any depolymerization.

[0089] From the above description, it appears that only the use of ionic liquid [Cho] [Arg] is able to obtain PLA depolymerization under ambient temperature and pressure conditions. Such a result offers important production and environmental advantages.

[0090] In this respect, it is important to underline how the use of the ionic liquid [Cho] [Arg] according to the present invention is capable of achieving depolymerization of the polymers under ambient pressure and temperature conditions. Such a feature offers important production and environmental advantages .

[0091] The inventors considered that the above reported procedure may be effective at any temperature that keeps the reagents in their liquid state. For this reason, it was considered that in the temperature range from -50 to 70 ° C, the above reported depolymeri zation procedure can take place .

[0092] Conducting depolymeri zation at a higher temperature than indicated could lead to a number of problems such as degradation of the ( 2 -hydroxyethyl ) trimethylammonium argininate or evaporation of the solvent ( CH3OH) .

[0093] Furthermore , as may be obvious to a person skilled in the art , the use of a higher temperature than indicated necessarily leads to productivity problems i f the process of the invention is applied on an industrial scale .

[0094] The inventors of the present invention considered the optimal temperature range to be between 20 and 40 ° C .

[0095] Furthermore , the inventors of the present invention believe that the ratio of polymer to ionic liquid may be unbalanced with respect to both the polymer and the ionic liquid without af fecting the ef fectiveness of the depolymeri zation .

[0096] Finally, it is important to note that the proces s of the present invention, when applied to products in which the polymer is combined with other materials , succeeds in achieving the depolymeri zation of the polymer while leaving the other components constituting the material available .

[0097] In this regard, the following is an example of depolymeri zation of PLA and food film ( PVC ) carried out in the laboratory .

[0098] - Example of depolymeri zation of plastic PLA pieces covered on one side with a food-grade film ( PVC-Carrefour )

[0099] A 250 ml volume flask was loaded with a composite plastic sample consisting of PLA pieces of a cup with a mass of 1.3274 g on which a thin food-grade film (PVC-Carrefour) with a mass of 0.1005 g and 0.5802 g of ionic liquid consisting of ( 2-hydroxyethyl ) trimethylammonium argininate ( [Cho] [Arg] ) was adhered. After a 45-minute amalgamation period conducted at 30°C between the ionic liquid and the composite sample, carried out with the aid of the rotor of a rotavapor, 20 ml of methanol was added by inserting a stirbar into the matrix and moving the flask into an oil bath thermostated to 30°C, and the stirbar was rotated at 250 rpm for the next 24 hours.

[0100] The depolymerization reaction was then stopped when the PLA pieces were no longer visible to the naked eye. The food film samples were then withdrawn with tweezers and washed with methanol. They were then dried under a fume hood at room temperature.

[0101] All the methanol and methyl lactate was then extracted from the reaction matrix by means of rotavapor.

[0102] Once dry, the pieces of food film were weighed, returning a mass value of 0.1012 grams.

[0103] It can therefore be concluded that the depolymerization of the PLA pieces was successful.

Claims

C L A I M S1. A depolymerization process of a polymer by using a ionic liquid comprising choline; said polymer belonging to the family of polyamides or polycarbonates or polyurethanes or polyesters with the exception of PET; said depolymerisation process being characterized in that PET, a ionic liquid consisting of ( 2-hydroxyethyl ) trimethylammonium argininate [Cho] [Arg] and methanol are mixed together at a temperature ranging from -50 to 70°C.

2. The process according claim 1, characterized in that the weight ratio between the polymer and the ionic liquid ranges from 10 to 0.05.

3. The process according to claim 1 or 2, characterized in that it comprises (a) a first mixing step, during which the polymer is mixed with the ionic liquid consisting of (2- hydroxyethyl ) trimethylammonium argininate [Cho] [Arg] at a temperature ranging from 20 to 70°C, and (b) a depolymerization step, during which the mixture obtained from said mixing step is added to ROH alcohol and stirred at a temperature ranging from -50 to 70°C.

4. The process according to one of the preceding claims, characterized in that methoxide of an alkali metal is added together with methanol.

5. The process according to one of the preceding claims, characterized in that said methanol is added to the mixture drop by drop.

6. The process according to one of the preceding claims, characterized in that said depolymerization step comprises the repetition of a methanol adding operation and of a mixing operation one after the other.

7. The process according to one of the preceding claims,characterized in that said polymer is polylactic acid or nylon .

8. A ionic liquid preparation process useful for the depolymerization process according to one of the preceding claims; said ionic liquid preparation process being characterised in that it comprises an addition step, during which a choline aqueous solution is added to 1-arginine powder ; and a subsequent mixing step, during which the mixture made in the addition step is stirred for a time interval ranging from 12 hours to 72 hours; said addition step and said mixing step being carried out at a temperature ranging from 15 to 45 °C; the mole ratio between said choline and said 1-arginine being between 0.5 and 2.1.

9. The ionic liquid preparation process according to claim 8, characterised in that said choline aqueous solution is added drop by drop to said arginine powder.

10. The ionic liquid preparation process according to claim 8 or 9, characterized in that it comprises a water removal step following said mixing step; said water removal step taking place at a temperature that is equal to or smaller than 40°C.

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