"Valorisation of starch-based plastic materials by pyrolysis

FIELD OF THE INVENTION

The present invention relates to a process for the disposal and/or treatment of starch-based polymeric materials, as well as for the production of carbonaceous catalysts or substances useful for the chemical industry starting from said polymeric materials, comprising a step of treating said polymeric materials by pyrolysis.

STATE OF ART

The starch-based plastics have a fundamental role in current bioeconomy, above all for the development of new biomaterials capable of conjugating both mechanical and environmental performances. The thermoplastic starch (TPS) is the starch derivative mainly used in this field, industrially obtainable by treating the native starch with plasticizers (ex. glycerol, ethylene glycol) in an extrusion process. TPS is used alone or mixed with other less biodegradable polymers (of fossil or renewable origin) to improve the TPS mechanical properties and, at the same time, to increase biodegradability of the other polymeric counterpart. The TPS mixtures available on the market include aliphatic polyesters (for ex. poly-s-caprolactone PCL and polylactic acid PLA), polyvinyl alcohol (PVA), aromatic-aliphatic copolyesters (for ex. polybutylene adipate terephthalate PBAT) and cellulose derivatives; they represent about 21 % of the global annual production of bioplastics, with an expected production of about 0.5 Mt in 2024 (www.european-bioplastics.org). The applications of starch-based materials include foams and fillers (mainly TPS alone), films for agricultural use, compostable bags for collecting organic and garden waste, and products for shortterm applications such as shopping bags.

The management of the life end of starch-based plastics by composting and anaerobic digestion is recognized as the most adequate disposal strategy both for reducing the amount of waste sent to landfills and the associated environmental impacts, and for producing energy (biogas) and/or soil improvers (compost or digestate). Even if the quaternary recycling (energy recovery) or the biological approaches are among the best strategies for the treatment of the starch-based plastic waste, nor the primary recycling (re-extrusion of starch mixtures to produce similar products), nor the secondary recycling (reduction of sizes of plastics in pellet, flocks or powders through mechanical procedures), nor the tertiary recycling (chemical treatment for the production of small molecules suitable as raw material for the production of chemical and plastic substances) have been demonstrated up to now. Hydrolysis, pyrolysis, hydrocracking and gasification are among the most promising technologies proposed for the chemical recycling of plastics. In particular, the high-temperature thermal cracking (ex. pyrolysis) is capable of producing bio-oils and gaseous intermediates (without chlorine and heavy metals) from a great variety of plastic waste of fossil origin (ex. polyethylene, polypropylene, polystyrene, polyethylene terephthalate, polyamides), which can act as input for petro-refineries. Pyrolysis is particularly effective on polyolefins, since the produced bio-oil can be used as fuel thanks to a high higher heating value (HHV, about 40 MJ kg ^-1 ) similar to diesel and gasoline. The costs for processing pyrolysis and the quite high energy demand however are debated topics in industrial field.

Pyrolysis-sulfonation procedures have been used to produce a wide variety of catalysts containing SO3H from inexpensive carbon sources such as pure carbohydrates (for ex. starch), lignocellulosic biomasses, agricultural and industrial waste; however, this approach has never been applied to plastic waste.

In such context, then, the need is still much felt for developing new strategies for the disposal and valorisation of starch-based plastic materials.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a new process for the disposal, treatment and valorisation of starch-based plastic waste, such as for example after-use starch-based plastic bags (hereinafter called SBP-bags). The process, the present invention relates to, in particular provides a step of treating the above-mentioned polymeric materials by pyrolysis. This is the first time that the pyrolysis process is applied to this type of waste, usually treated by composting.

According to an aspect of the invention, the process devised by the inventors can be applied for the disposal and/or treatment of biodegradable polymeric materials containing thermoplastic starch (constituting the “disperse” step) and a thermoplastic polymer (for example aliphatic-aromatic polyesters) constituting the continuous step, incompatible with the thermoplastic starch.

Advantageously, the process the present invention relates to allows to valorise both the solid residue and the liquid fraction produced through the pyrolysis process, through:

• the production of a new carbonaceous material containing acid sites (SO3H) by sulfonation of the solid residue (char), useful as heterogeneous catalyst. The catalysts containing SO3H groups are characterized by a flexible amorphous carbonaceous structure, functionalized covalently with SO3H groups, having hydrophilic-oxyphilic properties and strong Bronsted acidity. The materials containing starch and polysaccharides are among the best precursors for the production of sulphonated carbons, and the biodegradable plastic bags currently present on the market contain a relevant percentage of TPS to increase the biodegrability and compostability thereof;

• the recovery of chemical substances (dicarboxylic acids and polyols), precious intermediates for chemical industry, by fractionation of the pyrolysis liquids; the currently most used starch- based plastic bags mainly consist of a mixture of TPS and PBAT, potential sources of anhydro-sugars, terephthalic acid and adipic acid and derivatives thereof.

The depolymerization of condensation polymers such as polylactic acid (PLA), PET and polyurethane (Pll) is usually obtained through catalytic hydrolysis or glycolysis, rather than through thermal treatments; in fact, the liquid fractions obtained from pyrolysis of the condensation polymers are often enriched with oxygenated monomers (such as the benzoic acid from PET) which reduce HHV (for ex. 28 MJ kg ^-1 for the pyrolysis liquid from PET), by making these oils not suitable for energy purposes. On the other hand, these monomers can be re-used to synthetize the original polymers or can be exploited as constituent elements in the chemical and polymeric industry, even in a circular economy perspective.

The pyrolytic approach for the chemical recycling of plastic materials, the present invention relates to, is extremely versatile and can be applied in principle to different starch-based mixtures, with the purpose of producing solid acid catalysts from the starch fraction and chemical substances from the condensation polymeric fraction. In the process devised in the present invention, the long-term pyrolysis (15 h) allows to produce more robust catalysts, reusable with respect to the same catalysts obtained with shorter pyrolysis time. As it is evident from the results shown in the experimental section of the present application, the performances of the catalysts produced through the process the invention relates to, applied on SBP-bags result to be comparable to those of the sulfonate catalyst prepared directly by starch (potato starch), by opening the possibility of synthetizing these materials starting from economic waste.

Therefore, the invention relates to: a process for the disposal and/or treatment of starch-based polymeric materials comprising the following step:

(i) subjecting said polymeric materials to a pyrolysis process; a process for the production of carbonaceous catalysts containing acid sites SO3H starting from starch-based polymeric materials comprising the following steps:

(i) subjecting said polymeric materials to a pyrolysis process so as to produce a solid residue (char) and a liquid fraction;

(ii) collecting the solid residue produced by step (i);

(iii) grinding and/or pulverizing said solid residue;

(iv) subjecting said solid residue to a sulfonation process with concentrated H2SO4 SO as to obtain said catalysts;

(v) filtering the catalysts obtained by step (iv) and subjecting them to one or more washes with hot distilled water;

(vi) desiccating said catalysts obtained by step (v); a process for the production and/or recovery of chemical substances starting from starch-based polymeric materials comprising the following steps:

(i) subjecting said polymeric materials to a pyrolysis process so as to produce apart from the solid residue (char) even a liquid fraction;

(ii) collecting the liquid fraction produced by step (i);

(iii) subjecting said liquid fraction to a fractionation process; and a process for the production of carbonaceous catalysts containing SO3H acid sites and for the production and/or recovery of chemical substances starting from starch-based polymeric materials comprising the following steps:

(i) subjecting said polymeric materials to a pyrolysis process so as to produce a solid residue (char) and a liquid fraction;

(ii) collecting the solid residue produced by step (i);

(iii) grinding and/or pulverizing said solid residue;

(iv) subjecting said solid residue to a sulfonation process with concentrated H2SO4 SO as to obtain said catalysts;

(v) filtering the catalysts obtained by step (iv) and subjecting them to one or more washes with hot distilled water;

(vi) desiccating said catalysts obtained by step (v);

(vii) collecting the liquid fraction produced by step (i);

(viii) subjecting said liquid fraction to a fractionation process.

Other advantages and features of the present invention will result evident from the following detailed description.

BRIEF DESCRIPTION OF FIGURES

Figure 1. Diffraction pattern of post-use starch-based bags (designated as SBP-bags) and potato starch (before and after sulfonation).

Figure 2. Activity and recyclability of the catalyst containing SO3H from SBP-bags or from potato starch (10% by weight) in esterification of lauric acid with methanol (10 eq.) (3 h, 80°C).

Figure 3. Chromatograms of a) terephthalic acid self-precipitated from a solution of the pyrolysis liquid in ethyl acetate obtained from SBP-bags; b) pyrolysis liquid from SBP-bags. (identified main peaks: 1. Lactic acid; 2. Adipic acid (AA); 3. Monobutenyl adipate (BAA); 4. Levoglucosan (LG); 5. Sugars (S); 6. Terephthalic acid (TA); 7. Monobutenyl terephthalate (BTA).

Figure 4. General scheme of the valorisation process of SBP-bags through the pyrolysis for the production of catalysts containing SO3H, terephthalic acid, and fractions enriched with levoglucosan and monobutenyl esters of adipic acid and terephthalic acid.

DETAILED DESCRIPTION OF THE INVENTION

GLOSSARY

All scientific and technical terms used in the present document have the same meaning commonly understood by an expert skilled in the art, unless otherwise designated.

Under the term “pyrolysis”, also known as “pyrolytic process” the present invention relates to a process of thermochemical decomposition of organic materials, obtained by applying heat and in complete absence of an oxidizing agent (normally oxygen). Under such anoxic heating conditions (total absence of oxygen) the materials are subjected to splitting of original chemical bonds with formation of simpler molecules. The so provided heat of the pyrolysis process is used to split the chemical bonds through a process defined as “thermally induced homolysis”. Such pyrolysis process can be normally performed in apparatuses known as pyrolyzers.

Under the expression “liquid fraction” produced by the pyrolysis process in the present description the liquid obtained starting from the condensation of the pyrolysis vapours is meant, also known as tar or pyrolysis oil.

The terms “polymeric materials” and “plastic materials” are used as synonyms in the present description and they relate to organic materials having high molecular weight, generally consisting of a mixture of macromolecules with different length.

The term “biodegradable” is used in the present description according to the meaning known in the art to designate all materials which can be decomposed, or degraded, from natural microorganisms such as fungi or bacteria, for example through enzymatic processes. The term “compostable” is used in the present description to identify the materials which, after natural or industrial degradation, transform into compost.

Under “sulfonation process” in the present description an organic reaction is meant with which on an organic compound one or more -SO3H sulfonic groups are introduced, deriving from the sulphuric acid.

As previously mentioned, the purpose of the present invention is to provide a process effective for the disposal and/or valorisation of starch- based plastic materials, and in particular post-consumption polymeric materials conventionally disposed of through composting. Such process is based upon the use of a process for treating the above-mentioned materials by pyrolysis. As clearly highlighted in the experimental section of the present description, the process the invention relates to, can be used advantageously for the production of solid acid catalysts and of chemical substances useful at industrial level respectively starting from the starch fraction (solid fraction) or from the condensation polymeric fraction generated through the pyrolytic process.

A first aspect of the present invention then relates to a process for the disposal and/or treatment of starch-based polymeric materials comprising the following step:

(i) subjecting said polymeric materials to a pyrolysis process.

The present invention also relates to a process for the production of carbonaceous catalysts containing SO3H acid sites starting from starch-based polymeric materials comprising the following steps:

(i) subjecting said polymeric materials to a pyrolysis process so as to produce a solid residue (char) and a liquid fraction;

(ii) collecting the solid residue produced by step (i);

(iii) grinding and/or pulverizing said solid residue;

(iv) subjecting said solid residue to a sulfonation process with concentrated H2SO4 SO as to obtain said catalysts;

(v) filtering the catalysts obtained by step (iv) and subjecting them to one or more washes with hot distilled water; (vi) desiccating said catalysts obtained by step (v).

According to an embodiment of the process the invention relates to, said carbonaceous catalysts are heterogeneous catalysts.

In step (iv) of the process the invention relates to, the sulfonation process can be performed at a temperature equal to 150°C for a duration equal to 15 hours, preferably under nitrogen atmosphere. After sulfonation, the so-obtained suspension can be cooled down at environment temperature and diluted with distilled H2O.

In step (v) of the process, the sulfonation product, that is the carbonaceous catalysts containing SO3H acid sites, could be filtered by using any one of the conventional filtration techniques known in the art. Subsequently, the so-obtained catalysts could be subjected to one or more washing steps with hot distilled water. Said one or more washing steps could be performed for example by using one or more aliquots of distilled water at a temperature equal to or higher than 80°C.

In step (iv) of the above-mentioned process, the catalysts obtained by step (v) could be dried for example at a temperature equal to 70°C, for an overall duration equal to about 48 hours. The abovedescribed process for the production of said carbonaceous catalysts starting from starch-based polymeric materials could optionally include even an additional final step of chemical-physical characterization of the so-produced catalysts, and of determination of their catalytic activity.

As above mentioned, the authors of the present invention have found that the same starch-based polymeric materials used for the production of catalysts according to the previously described process can be further used for the production and/or recovery of substances useful for the chemical industry. Therefore, the present invention further relates to a process for the production and/or recovery of chemical substances starting from starch-based polymeric materials comprising the following steps:

(i) subjecting said polymeric materials to a pyrolysis process so as to produce a solid residue (char) and a liquid fraction;

(ii) collecting the liquid fraction produced by step (i);

(iii) subjecting said liquid fraction to a fractionation process.

In step (ii) of the above-described process, the liquid fraction produced through the pyrolysis process starting from the condensed pyrolysis vapours could be collected in an ice trap by using a suitable solvent. Examples of solvents which can be used for the dissolution of the liquid fraction obtained from the condensation of the pyrolysis vapours include ethyl acetate, acetone, mixtures of ethyl acetate and acetone.

According to an aspect of the present invention, in step (iii) of the above-described process, the fractionation process is a fractionation process with solvent.

The fractionation process of the liquid fraction produced through pyrolysis can be performed by exploiting the different polarity, partition and solubility of the pyrolysis products in water and in the common organic solvents (for example ethyl acetate and cyclohexane). A person skilled in the art, depending upon the composition of the obtained pyrolysis liquid, will have sufficient information in the art to select the organic solvents most suitable for the separation of the chemical substances of interest. Alternatively, the fractionation process of the liquid fraction produced by pyrolysis can be performed by distillation.

According to an embodiment of the invention, the effectiveness of the fractionation process performed in step (iii) of the process for the production of said chemical substances, could be checked by the following steps: collecting an aliquot of said pyrolysis liquid fraction and subjecting it to a silylation process; and/or drying said pyrolysis liquid fraction and/or an aliquot thereof subjected to a silylation process under nitrogen flow.

Therefore, an aspect of the present invention relates to a process according to any one of the previously described embodiments, wherein said step of subjecting said liquid fraction to a fractionation process further comprises the following steps: collecting an aliquot of said pyrolysis liquid fraction and subjecting it to a silylation process; and/or drying said pyrolysis liquid fraction and/or an aliquot thereof subjected to a silylation process under nitrogen flow. Said silylation process could be performed, for example, at a temperature equal to 70°C, for a total duration equal to 30 minutes.

In a preferred embodiment of the present invention, the steps of the processes for the production of carbonaceous catalysts containing SO3H acid sites and for the production and/or recovery of chemical substances starting from starch-based polymeric materials, according to any one of the previously described variants, could be combined in one single process.

Therefore, an aspect of the present invention relates to a process for the production of carbonaceous catalysts containing SO3H acid sites and for the production and/or recovery of chemical substances starting from starch-based polymeric materials comprising the following steps:

(i) subjecting said polymeric materials to a pyrolysis process so as to produce a solid residue (char) and a liquid fraction;

(ii) collecting the solid residue produced by step (i);

(iii) grinding and/or pulverizing said solid residue;

(iv) subjecting said solid residue to a sulfonation process with concentrated H2SO4 SO as to obtain said catalysts;

(v) filtering the catalysts obtained by step (iv) and subjecting them to one or more washes with hot distilled water;

(vi) desiccating said catalysts obtained by step (v);

(vii) collecting the liquid fraction produced by step (i); and

(viii) subjecting said liquid fraction to a fractionation process.

Steps (vii) and (viii) of the above-described process could be performed even before or parallelly with respect to steps (ii)-(vi).

According to an aspect of the present invention, the starch-based polymeric materials usable in any one of the previously described processes, are starch-based biodegradable or compostable polymeric materials. Examples of such biodegradable or compostable polymeric materials include post-use starch-based polymeric materials, such as starch-based plastic waste selected, for example, among packaging materials, disposable materials for the food field, envelopes or bags. In a preferred embodiment of the present invention, said starch-based biodegradable polymeric materials are starch-based plastic bags, preferably starch-based post-use plastic bags (SBP-bags). Under the expression “starch-based” in the present description biodegradable polymeric materials are meant, characterized by a content by weight of starch comprised between 10 and 80% by weight of the material, preferably comprised between 20% and 50% by weight.

The starch is an organic compound belonging to the class of carbohydrates, characterized by a great number of polymerized glucose units joined therebetween by a-glycosidic bond, mainly consisting of amylopectin (for about 80%) and amylose (about 20%). The starch crude formula is (CeH Osjn wherein n is a variable number from about a hundred to few thousands and which designates the residues of monomeric glucose units which are joined therebetween to form the polymers, therefrom the various types of starches existing in nature derivate (ex. rice starch di, maize starch, etc.).

According to an embodiment, the polymeric materials usable in any one of the herein described processes are thermoplastic starch-base materials. Said thermoplastic starch can be obtained, for example, starting from native starch extracted from vegetable materials such as potatoes, rice, corn, tapioca or maize, and/or starting from chemically or physically modified starch. Examples of chemically modified starch include starch thereto acetate groups (acetate starch), hydroxypropylate, adipate, etc., starch subjected to a fluidifying treatment with acids or bases, or still starch treated by enzymatic route have been added.

Said thermoplastic starch for example can be obtained at high temperatures by the addition of plasticizer agents such as sorbitol or glycerine and/or combined with fibres of lignin and/or cellulose with the purpose of improving the chemical-physical properties thereof.

Starch-based polymeric materials suitable to be used in a process according to any one of the herein described embodiments, are materials prepared by mixing the starch with other materials with high molecular content.

According to an aspect of the invention, said starch-based polymeric materials contain at least one thermoplastic polymer, and preferably a thermoplastic polymer incompatible with thermoplastic starch. Said starch-based biodegradable polymeric materials can be obtained, for example, starting from a composition comprising thermoplastic starch and a thermoplastic polymer incompatible with thermoplastic starch, wherein said thermoplastic starch constitutes the dispersed phase and wherein said thermoplastic polymer constitutes the continuous phase of said composition.

Not limiting examples of thermoplastic polymers incompatible with thermoplastic starch which can be used for the production of said starch-based polymeric materials can be selected in the group of polymers comprising: aliphatic polyesters obtained by polycondensation of hydroxy acids having 2 or more carbon atoms or the corresponding lactones or lactides; aliphatic polyesters obtained by polycondensation of diols having 2-10 carbon atoms with aliphatic dicarboxylic acids, aliphatic polycarbonates, cellulose esters, starch esters, carboxymethyl cellulose, alkyl and hydroxyalkyl ethers of cellulose, polysaccharides, vinyl esters, copolyesters such as, for example, aromatic-aliphatic copolyesters, polyesters-amides, polyesters-ethers, polyesters-ethers- amides, polyesters-urea, and polyesters-urethanes, and/or mixtures thereof.

Not limiting examples of aliphatic polyesters obtained by polycondensation of hydroxy acids having 2 or more carbon atoms or the corresponding lactones or lactides, include polycaprolactones, polymers and copolymers obtained starting from the hydroxy-butyric or hydroxy-valeric acid, polyalkylene tartrate, polymers and copolymers of the glycolic acid and lactic acid.

Not limiting examples of aliphatic polyesters obtained by polycondensation of diols having 2-10 carbon atoms with aliphatic dicarboxylic acids include polyalkylene succinate and polyalkylene adipate. Examples of aliphatic polycarbonates can be selected among polyethylene carbonate and polypropylene carbonate, polyesters-carbonates, polyamides-carbonates, starch polyesters- carbonates.

Not limiting examples of cellulose esters include cellulose acetate, cellulose propionate, cellulose butyrate and mixtures thereof. Starch esters can be selected, for example, among starch acetate, propionate and butyrate, and starches esterified with acids containing up to 18 carbon atoms, wherein the starch replacement level is comprised between 0.5 and 3.

Not limiting examples of vinyl esters and copolyesters comprise vinyl esters and copolyesters as such or partially hydrolyzed such as polyvinyl acetate, polyvinyl acetate/polyvinyl alcohol up to 50% of hydrolysis, polyethylene vinyl acetate, polyethylene-acrylic acid or mixtures thereof.

According to an aspect of the invention, said thermoplastic polymer incompatible with thermoplastic starch can be a polyester comprising repeated units deriving from an aliphatic carboxylic acid and/or from a hydroxy acid having more than 2 atoms of carbon and wherein the ratio R between the average viscosimetric molecular weight and the melting index of polyester, measured at 180°C under a load of 5 kg, is higher than 25000.

In a preferred embodiment of the present invention, said thermoplastic polymer is polybutylene adipate terephthalate (PBAT). In particular, according to an aspect of the present invention, the polymeric materials usable in a process according to any one of the previously described variants could be characterized by a PBAT content by weight comprised between 20 and 90%, preferably at least equal to 70% by weight.

An aspect of the present invention preferably relates to a process according to any one of the previously described embodiments, wherein said biodegradable polymeric materials are post-use starch-based plastic bags characterized by a PBAT content by weight equal at least to 70% by weight.

According to an embodiment, the starch-based biodegradable polymeric materials usable in a process according to the present invention, could include at least a plasticizer agent. Tale plasticizer agent for example could be selected among the group consisting of glycerol, sorbitol, polyglycerol esters and glycerol ethers, sorbitol and polyglycerol, 1 ,3-propandiol and pentaerythritol.

The herein described starch-based biodegradable polymeric materials could further include even a polymer chosen among aliphatic polyester, cellulose acetate, ethylene-vinyl alcohol copolymer, ethylene vinyl acetate copolymer and polyvinyl alcohol, in an amount up to 30% with respect to the weight of the above-mentioned materials.

According to an embodiment of the present invention, the SBP-bags usable in any one of the herein described processes can further include TiC>2, CaCCh and/or rutile. The calcium carbonate has the filling role in a wide range of polymeric resins to improve the optical and mechanical properties, the duration, the smoothness and the ink adsorption; rutile is one of the white pigments most used in the plastic industry.

Starch-based polymeric materials usable in any one of the processes the present invention relates to can be materials obtained through a process providing at least a mixing passage of the components constituting said materials by extrusion. By pure way of example, such materials for example could be obtained through a process comprising an extrusion step wherein the water content during the phase of mixing the components of said materials is kept, by degasification, at values comprised between 1 and 5% by weight.

Said starch-based polymeric materials could include even materials obtainable through a process providing at least a step of mixing the components of said materials by extrusion performed in presence of an interface agent.

Interface agents usable per the production of said starch-based polymeric materials by extrusion can be selected among: esters having values of the hydrophilic/lipophilic equilibrium index (HLB) greater than 8 and which are obtained from polyols and mono-or polycarboxylic acids with pK dissociation constants lower than 4.5 (this value relates to the pK of the first carboxylic group in case of polycarboxylic acids); esters having HLB values comprised between 5.5 and 8, obtained from polyols and from mono- or polycarboxylic having less than 12 carbon atoms and with pK values higher than 4.5 (this value relates to the pK of the first carboxylic group in case of polycarboxylic acids); esters having HLB values lower than 5.5, obtained from polyols and fatty acids with 12- 22 atoms of carbon used in amounts between 10% and 40% by weight with respect to the starch; non-ionic surfactants, soluble in water which, when added to starch and thermoplastic polymer, migrate in water for no more than 30% of their concentration once the material including them has been dipped in water for 100 hours at room temperature; reaction products of an aliphatic or aromatic diisocyanate with a polymer containing terminal groups reactive with diisocyanates.

According to an additional embodiment, the starch-based polymeric materials suitable to be used in any one of the processes according to the present invention, are biodegradable polymeric materials consisting of starch dispersed in a copolyester-based matrix, under the form of particles having average sizes smaller than 1 micron. In an embodiment of the invention, said starch-based polymeric materials are polymeric materials as described in the patent application EP0947559B1 , herein incorporated as reference.

According to an aspect of the present invention, a process according to any one of the previously described embodiments could include an additional step, preceding the pyrolysis step, for manufacturing said starch-based polymeric materials, in particular starch-based plastic bags, according to any one of the methods known in the art.

Before being subjected to the pyrolysis process according to any one of the processes the present invention relates to, said polymeric materials could be cut into pieces, for example into pieces having dimensions approximately equal to 1 cm ² .

In step (i) of the process according to any one of the previously described variants, the pyrolysis process will be performed at a temperature comprised between 350 and 450°C, preferably at a temperature equal to 400°C.

Advantageously, said pyrolysis process will have a duration comprised between 10 and 20 hours, preferably it will have a duration equal to 15 hours. Such prolonged duration allows to maximize and optimize the solid fraction (char) with residence time of the solid materials definitely higher than the conventional configurations.

The pyrolysis process could be performed by using any suitable apparatus known to the person skilled in the art, for example within a pyrolyzing plant. According to an aspect of the invention, said pyrolysis process could be performed by arranging the starch-based polymeric materials according to any one of the previously described embodiments inside an apparatus consisting of a sliding sample holder placed in a quartz tube heated and connected to at least one ice trap and to a settling chamber. Preferably, the pyrolysis process will be performed under nitrogen flow.

The present invention further relates to all products, including the carbonaceous catalysts and the chemical products directly obtained through a process according to any one of the embodiments described in the present application. EXAMPLES

Materials and methods

Preparation of chars from SBP-baqs and potato starch.

In a typical procedure, the SBP-bags (4 g, cut into about 1-cm ² -large pieces) or the potato starch (3 g) were subjected to a pyrolysis on a bench scale, by using an apparatus consisting of a sliding sample-holder placed in a quartz tube heated and connected to ice traps and to a settling chamber. The quartz tube was heated by a cylindrical coaxial oven, flushed with N2 (1 .5 L min ^-1 ). The samples were placed in the heated area of the quartz tube and heated for 15 hours at 400°C (set temperature) under N2 flow. The resulting char was collected and ground into powder in a mortar, whereas the pyrolysis liquid was collected in an ice trap and dissolved in ethyl acetate. The yields of char from SBP-bags and potato starch are respectively 10.8 ± 0.2% by weight and 14.8 ± 0.6% by weight.

Preparation of the catalysts from SBP-bags and potato starch.

The chars (about 1 g) were placed in concentrated H2SO4 (100 mL) and heated at 150°C for 15 hours under N2 atmosphere to sulfonate the material. After sulfonation, the suspension was cooled down at room temperature and diluted with distilled H2O (500 mL); then the catalysts were collected by filtration and washed several times with hot distilled H2O (> 80° C, 100 mL each time). The resulting SO3H catalysts were vacuum-dried at 70°C for 48 hours to remove water.

As model reaction the esterification of the dodecanoic (lauric) acid (1.25 mmol, 250 mg) with methanol (12,5 mmol) at 80°C was used, by using 10% by weight of SO3H catalysts (25 mg) with respect to the lauric acid. After 3h, H2O (2 mL) was added, the solution was centrifuged (3000 rpm for 10 min) and the methyl laurate separated as a well distinct layer on top of the solution. The methyl laurate was collected and weighed, an aliquot was taken, diluted and analysed by means of GC-MS to determine the conversion. An aliquot was also analysed by means of 1 H NMR to detect the presence of possible small polyarene domains derived from the catalyst The FW-MeOH solution, containing the SO3H catalyst, was vacuum-dried under N2 at 25°C for 15 h and at 80°C for 24 h; then, the SO3H- catalysts were reused under the above-described experimental conditions with no additional purification.

Fractionation of the pyrolysis liquid and analysis

Once the pyrolysis liquid from SBP-bags was collected in an ice trap and dissolved in ethyl acetate, a white solid was precipitated from the solution. This solid was collected, washed with ethyl acetate and weighed (yield 4.5 ± 0.4% by weight based upon the amount of pyrolyzed material). An aliquot was taken (1-2 mg), silylated for 30 min at 70 °C (with 0.1 mL of ethyl acetate, 0.08 mL of bis (trimethylsilyl) trifluoroacetamide containing 1% of trimethylchlorosilane and 0.04 mL of pyridine) and then analysed by means of GC-MS. Another aliquot (about 10 mg) was taken and analysed by means of 1 H NMR to determine the purity thereof by means of integration of protonic signals with respect to an internal standard. The pyrolysis liquids were dried under N2 to remove the ethyl acetate, weight (yield of 25.4 ± 0.4% by weight and 29 ± 0.6% by weight, respectively from SBP-bags and potato starch) and then analysed by means of GC-MS after silylation.

Example 1

Production di catalysts containing SO3H from SBP-bags

SBP-bags (about 5 g of material cut into 1-cm ² -large pieces) were subjected to a pyrolytic treatment at 400°C for 15 h, followed by sulfonation with concentrated H2SO4 at 150°C for 15 h; the same treatment was applied to the potato starch to produce an analogous sulfonate material already known in literature, the features and catalytic activity thereof have been herein compared to those of the catalysts deriving from the SBP-bags.

The initial carbon content of SBP-bags (54.5% by weight, table 1), higher than that of potato starch (37.5% by weight), reflects the co-presence of polybutylene adipate terephthalate (PBAT) in the herein used SBP-bags; according to the elementary analysis, a PBAT content of 70% in the mixture could be estimated. The yield of char produced after pyrolysis (10.8 ± 0.2% by weight) is comprised between the typical yield of char from fossil plastics and the one herein obtained from the potato starch (14.8 ± 0.6% by weight), in line with the inhibition phenomenon in the formation of the observed char for the co-pyrolysis of plastics and biomasses.

The molar ratio H/C for the char from SBP-bags (0.46, table 1 ) is slightly higher than that of the char from potato starch (0.41); this could involve the formation of smaller polyarenes having a relatively higher number of “peripheral” hydrogen atoms which could be replaced by means of aromatic electrophile replacement with the SO3H group.

Table 1 - Elementary composition (% by weight), H/C ratio and acid density (total and related to the SO3H groups) of SBP-bags and of the starch, and their carbons before and after sulfonation (average ± standard error).

N C H S Ashes H/C ratio Density of Density of total acid -SO ₃ H sites sites (mmol g ¹ ) ^b

(mmol g ^_1 ) ^a SBP-bags 0.210.01 54.5±0.4 6.7±0.07 - 3.8 1.5 Potato starch - 37.5±0.7 6.4±0.1 - - 2.0 Carbon from SBP-bags 0.4±0.04 62.3±0.4 2.4±0.2 - 0.4 0.46 nd Carbon from p

^H otato - 82.810.3 2.810.1 - 0.5 0.41 nd starch Catalyst from SBP- 0.310.01 59.5±0.7 2.110.09 3.010.3 - 0.42 2.610.04 0.810.01 bags Catalyst from potato „ _ _

0.110.02 67.711.6 2.310.1 1.610.04 - 0.41 1.710.02 0.410.01 starch a. the density of total acids relates to the total acid sites (-SO3H, COOH, -OH phenolic groups) determined by titration with NaOH; b. determined by titration with NaOH; nd: not determined

The X ray diffraction (XRD) detected that the carbons from SBP-bags contain TiC>2, CaCCh rutile and a very low amount of amorphous material; the rutile (model of diffraction peaks marked with "R" in Figure 1) is one of the white pigments most used in the plastic industry, whereas the calcium carbonate (model of the diffraction peaks marked with "C" in Figure 1) has the filling role in a wide range of polymeric resins to improve the optical and mechanic properties, the duration, the smoothness and the ink adsorpion. The presence of TiC>2 e CaCCh was confirmed by SEM images wherein the aggregates of submicron/micron particles are clearly visible on an amorphous structure; a distributed wide porosity was further observed (diameter 100 nm), probably associated to the production of specific volatile compounds during pyrolysis. The char from potato starch instead is wholly amorphous without any detectable clear diffraction model (Figure 1).

After sulfonation, the introduction of SO3H groups on the chars from SBP-bags and potato starch was demonstrated both by the elementary analysis (S amount of 3 and 1.6% by weight, respectively; Table 1) and by titration: the density of SO3H sites in both cases below 1 mmol g ^-1 (0.8 and 0.4 mmol g- ¹ , respectively) as shown for a wide variety of sulfonate chars deriving from lignocellulosic or polymeric materials. The SO3H groups are 31 % of the total acid density in the catalysts from SBP- bags and 23% of the total acid density in the catalyst from potato starch, by demonstrating the presence of weaker acid sites (COOH, -OH phenolic groups) on the surface of these structures capable of conferring hydrophilic/oxyphilic properties, increasing the adsorption of hydrophilic molecules and promoting synergic catalytic activities. XRD confirmed that the catalyst from SBP- bags has an amorphous structure and still contains TiO2 rutile, even if in a lower amount with respect to the pre-sulfonation char (TiO2 is soluble in hot concentrated H2SO4 and it was probably leached); the diffraction pattern of CaCOs is no more visible, presumably due to its transformation during the sulfonation treatment. The catalyst from char of potato starch is wholly amorphous, with two large shoulders clearly visible between 15°-30° and 40°-45° already observed for other sulphonated carbons. The SEM images of the catalyst from SBP-bags confirm the presence of an amorphous structure with a certain porosity, whereas the TiC>2 structures are no more visible; the catalyst from potato starch is mainly characterized by smooth amorphous areas with some nanostructures (average sizes of 200 nm) and aggregates of nanoparticles with diameter of 20-30 nm.

The catalysts from SBP-bags and potato starch were tested in the esterification of fatty acids with alcohols, a typical transformation in liquid phase known to be catalyzed by the sulphonated carbons. The reaction was performed on lauric acid and methanol (10 eq.) at 80°C in 3 h; the yields of methyl laurate result to be between 87 and 93% on 7 cycles with the catalysts from SBP-bags and between 81 and 87% with those from potato starch (Figure 2). The excellent reactivity, common to these catalysts, was attributed to swelling or enlargement of the pores in the alcoholic means, which can favour the adsorption of voluminous hydrophobic substrates (like the fatty acids) on the hydrophilic surface of the catalysts. The observed excellent long-term stability and the recyclability seem to exclude the presence of small aromatic polycyclic domains containing SO3H groups which could be leached during the reaction work-up; this is a confirmation that a prolonged pyrolytic treatment (15 h) in the preparation of carbonaceous precursors provides both highly active and robust catalysts.

Example 2

Production of chemical products by the pyrolysis liquid from SBP-baqs

SBP-bags containing a relevant percentage of PBAT (almost 70%), a condensation polymer consisting of terephthalic acid and adipic acid, which potentially can be recovered by depolymerization, were used. During the first 10 minutes of pyrolysis, a white powder (yield 4.5 ± 0.4% by weight based upon the material subjected to pyrolysis) is self- precipitated from the condensed pyrolysis vapours which were collected in ethyl acetate (Figure 3a): this solid revealed to be terephthalic acid (TA), with a purity from H NMR of 96.5%. Even traces (<1%) of an additional compound, provisionally identified as monobutenyl ester of terephthalic acid (BTA), were detected by GC-MS analyses. A significative yield of pyrolysis liquid was obtained: 25,4 ± 0.4% by weight based upon the material subjected to pyrolysis, compared to the yield of pyrolysis liquid from the potato starch is of 29% by weight.

This liquid mainly includes starch pyrolysis products such as levoglucosan (LG) and other sugars/anhydrous sugars (S) (28 and 6%, respectively) and PBAT pyrolysis products such as BTA (28%), the adipic acid (AA, 12,5%), the monobutenyl ester of adipic acid (BAA, 11%) and the terephthalic acid (TA) (5%) (Table 2 and Figure 3b).

Table 2 - Relative distribution of the chemical compounds in the pyrolysis liquid from SBP-bags and after fractionation in FW/EtOAc determined by means of GC-MS after sample silylation.

Compound Relative Relative Relative composition composition of the composition of the before fraction soluble in fraction soluble in fractionation H ₂ O EtOAc

HzO/EtOAc (%) (%)

(%) Benzoic acid (BA) 0.9±0.4 - 0.9

Adipic acid (AA) 12.5±1.4 8.9 12.8 6-(but-3-en-l-iloxy)-6-oxohexanoic acid (BAA) 10.6±0.8 - 17.2 Di(but-3-en-l-il) adipate (DBAA) 1.2±0.7 - 2.5

Levoglucosan (LG) 27.7±1.5 46.4 1.8

Other sugars and anhydrous sugars (S) 5.6±0.5 32.5

Terephthalic acid (TA) 5.4±0.7 - 4.9

4-((but-3-en-l-iloxy)carbonyl)benzoic acid (BTA) 27.9±2.0 - T1 Di(but-3-en-l-il) terephthalate (DBTA) 1.7±0.5 - 4.0

Lactic acid (LA) 4.0±0.4 4.8 1.2

Others (not identified and oligomers) 2.5±0.6 7.4 27.0

After a complete removal of the ethyl acetate, a brownish syrup was recovered (yield of 21% by weight based upon the material subjected to pyrolysis). An excessive separation of such syrup with ethyl acetate and water provided:

• a water-soluble fraction (32% of the pyrolysis liquid, corresponding to a yield of 6.7% by weight based upon the material subjected to pyrolysis) containing LG (the main component with relative abundance 46%), other sugars I anhydrous sugars (32%) and smaller amounts of AA (9%) and lactic acid LA (5%);

• a fraction soluble in ethyl acetate (68% of the pyrolysis liquid, corresponding to a yield of 14.3% by weight based upon the material subjected to pyrolysis) enriched with monobutenyl dicarboxylic acids (BTA with relative abundance of 28% and BAA 17 %) and adipic acid (13%). Smaller amounts of dibutenyl adipate (DBAA, 2,5%) and dibutenyl terephthalate (DBTA, 4%) were also detected.

Therefore, by exploiting the different solubility of the pyrolysis products in ethyl acetate, it was possible to recover highly pure terephthalic acid, a polar fraction enriched with levoglucosan, and a less polar fraction enriched with monobutenyl esters and adipic acid (Figure 4). Both the terephthalic acid and the adipic acid (and the butenylic esters thereof) can be used as drop-in monomers to produce new condensation polymers in the plastics industry, whereas levoglucosan has a high potential as chiral synton in the organic and intermediate synthesis for biodegradable surfactants and pharmaceutical products. Contrary to what shown in literature when PET is subjected to pyrolysis, herein significative amounts of benzoic acid (<1%) were not detected; this piece of data could be a consequence of the PBAT pyrolytic behaviour (data on PBAT pyrolysis are not shown in literature) or of the herein applied specific pyrolysis conditions.