EP3259309A1

EP3259309A1 - Method for producing secondary polyols and their use

Info

Publication number: EP3259309A1
Application number: EP15834632.0A
Authority: EP
Inventors: Jaroslav PETRUJ; Silvestr FIGALLA
Original assignee: Brno University of Technology
Current assignee: Brno University of Technology
Priority date: 2014-12-22
Filing date: 2015-12-18
Publication date: 2017-12-27
Also published as: WO2016101938A1; CZ2014945A3; CZ305739B6

Abstract

The method for producing secondary polyols by means of recycling secondary raw materials containing waste PIR foams, lies in mixing ground waste polyisocyanurate (PIR) foams with polyester based polymers and subjected to controlled glycerolysis in microwave field where it undergoes mixed catalytic depolymerization and secondary polyol is formed in the form of homogeneous liquid product. Mixed catalytic depolymerization is carried out in two phases and with alkali metal carboxylate based catalyzer having the chainlength C6-C20, preferably C6-C12, and/or with organic guanidine and amidine superbases and their mixtures present in glycerol, at concentrations 0,1 up to 1,0 mol.l-1. In the first phase polyester is depolymerized in alcoholysis agent - glycerol and in the second phase PIR foams are depolymerized in the mix of residual agent and oligoesters and polyols formed in the first stage. The reaction mixture subjected to mixed catalytic depolymerization contains 15 to 30 wt. % of waste PIR foams having the isocyanurate index higher than 2, 20 to 40 wt. % of polyesters, preferably waste polyethyleneterephtalat.es, and 40 to 60 wt. % of glycerol. Secondary polyols can be used to prepare new polyisocyanurate foams in the mixture of virgin (primary) and recycled (secondary) polyol. The content of secondary polyol in the mixture of virgin (primary) and recycled (secondary) polyol ranges within 5 - 25 wt. %.

Description

Method for Producing Secondary Polyols and Their Use

Field of the invention

The invention concerns the method for producing secondary polyols via recycling waste polyisocyanurate (PIR) foams and their use.

Backround of the invention

Currently the trend in building industry oriented at energy saving buildings heads towards massive development of production and utilization of polyisocyanurate (PIR) thermoinsulating foams. PIR foams practically replaced polyurethane (PUR) foams, which had been used earlier, as they have better thermoinsulating properties and fire resistance. Waste produced during the production and mainly after the service life of PIR foam poses serious problem for both, the environment and the production itself, apart from the economic waste caused by the disposal of valuable PIR polymers.

High chemical resistance of those materials makes the economical recycling by methods applied for PUR foams, such as simple hydrolysis, amtnorysis or alcoholysis, impossible. The recycling methods are carried out in a way to receive the liquid - polyol, further applied in the production of similar materials. Thus, appropriate chemical and physical properties of prepared materials are required. The preparation of such polyols is described in the patent files such as: US4159972 A, US4316992 A, KR20040024064 A, JPH7126343.

Part of polyester polyols used currently in the production of PIR and PUR foams are received by similar recycling methods, mainly by the alcoholysis of waste polyesters, pofyethyleneterephta!ate (PET) from bottles and its production waste. These methods are described in patent files: US4439550 A, US4048104 A, US4506090A, EP2565226A1, US4701477A, US4469824, US4559370, JPS59105015. The drawback of the chemolysis processes is huge process energy, which can be effectively reduced applying the microwave heating to the reaction mixture, as was published in e.g.: WO2009024102 A2, Chutima A., Prompoom P., EnergyProcedia 9, 428 - 434, 2011; PingaleN.D., ShuklaS.R.,Eur. Polym. J., 45, 2695-2700, 2009.

While recycling of waste polyesters and PET bottles as well as waste PUR foams by the methods described above is quite known, recycling of waste PIR foams due to high chemical resistance of the material was not feasible so far. Some progressive possibilities regarding the recycling of waste PIR foams were implied in published document .The possibilities of recycling waste solid PU foams produced in KingSpan CZ", S. Figalla, VUT Brno, 2011, in which the methods and trends of recycling solid polyurethane materials are evaluated emphasizing solid PU foams applied as thermoinsulating materials in building industry. In the second part of this document the evaluation of the usability of glycerol as alcohotyzing agent in the process of polyol recovery combined with the microwave heating of reaction mixture is made. These possibilities of recycling were further elaborated in the following document„The optimization of microwave gfycerolysis of crosslinked solid PU foam to be re-used in the production process", S. Figalla, VUT Brno, 2013, the published form summarizes the possibilities of chemical recycling of polyurethane and polyisocyanurate insulating foams and the methods of preparation of polyols from alcoholyzates, also applying the microwave heating. However, in both published documents just the summary of results of theoretical works and experiments is given, indicating only further possible industrial utilization.

The task of submitted invention is final solution of industrial recycling of waste PIR foams, as well as further application of secondary polyols received from this process. Summary of the invention

The method for producing secondary polyols is solved by recycling secondary raw materials containing waste polyisocyanurate (PIR) foams, i.e. waste coming from the production of PIR foams and PIR foams after their life span. Ground waste PIR foams are first mixed with polyester based polymers and subjected to controlled glycerolysis in microwave field where they undergo mixed catalytic depolymerization. During subsequent reactions of alcoholyzation and transesterification secondary polyol is formed in the form of homogeneous liquid product, as stated in submitted invention. Polyester based polymers are meant mainly waste polyethyteneterephtalate (PET) from e.g. used PET bottles as they are broadly accessible, and also other polyesters, such as poJybutylenetherephtalate (PBT), polytrimethytenetereprrtalate (PTT) etc. Controlled glycerolysis means the process of depolymerization of polymer mixture under predetermined conditions i.e. the contents of particular components in the mixture, the reaction temperature and time.

The principle of invention lies in processing the mixed catalytic depolymerization with alkali metal carboxylate based catalyzer having the chainlength C6-C20. preferably C₆-C₁₂, and/or with organic guanidine and amidine superbases and their mixtures present in glycerol, at concentrations 0,1 up to 1,0 mol.f¹. The catalyzers solved in glycerol can possibly be alkali metal carboxylate based salts, e.g. potassium 2-ethyihexanoate, potassium decanoate etc., in amounts 0,10 up to 0,40 %mol. Organic superbase can be e.g. tetramethykjuanidine (TMG), triazabicyclodecene etc., in amounts 0,20 up to 0,50 %mol. Mixed catalytic depolymerization proceeds in two stages, in the first stage the depolymerization of polyester takes place in alcoholyzing agent - glycerol and in the second stage the depolymerization of PIR foams proceeds in the mixture of residual agent and oligoesters and polyols formed in the first stage. The reaction mixture subjected to mixed catalytic depolymerization contains 15 to 30 wt % of waste PIR foams having the isocyanurate index higher than 2, turner 20 to 40 wt % of polyesters, preferably waste potyethyleneterephtalates, and 40 to 60 wt % of glycerol.

This reaction mixture can possibly contain also side admixtures and impurities in amounts up to 10 wt %. This is the case that the polyester component contains for example waste ground PET from bottles with residual parts of PVC and paper labels.

The principle of invention lies also in carrying out the mixed catalytic depolymerization at temperatures from 180 up to 300 °C, preferably 200 to 270 °C, applying microwave heating to the reactive mixture from microwave generator at working frequency 0,8 to 3 GHz for the time period max. 1 hour, depending on the generator power.

Within working frequencies of microwave generators the frequencies such as 0,915 GHz or industrially most often used 2,45 GHz come into question.

The principle of invention lies also in depriving the product of mixed catalytic depolymerization from eventual coarse mechanical impurities by filtration, centrifugation or decantation prior to its cooling.

The principle of invention lies also in utilization of secondary polyols produced by the method introduced in this patent application. The mixture of virgin (primary) and recycled (secondary) polyol is used for the preparation of new polyisocyanurate foams. The content of secondary polyol in this mixture ranges within 5 - 25 wt %. tower addition would lead to insufficient valuation of recycled polyols, higher addition could in some cases negatively affect the quality of produced PIR foams.

As for the production method itself, it is the method utilizing the glycerolysis of the mixture of secondary raw materials in the microwave field, where the main components are linear polyester and waste polyisocyanurate thermoinsulating foams (PIR). The utilization of microwave heating brings about substantial shortening of reaction time, which significantly contributes to the improvement of economic balance of the process. For successful preparation of secondary 'polyol based on the depolymerization of tightly cross-linked polyisocyanurate the catalyzer from the group of alkali metal carboxytates having the chainlength mentioned above or from the group of organic superbases is required. The glycerolysis, i.e. the alcoholysis with glycerol was selected due to excellent physical-chemical properties of glycerol, mainly due to high ability to absorb microwave field and high boiling point, which enables non-pressure operation at temperatures required for the preparation of polyol.

For the production of secondary polyols according to the invention mixed depolymerization of polyesters together with polyisocyanurates by glycerol is used, usually at the temperatures from 200 up to 270 °C. The depolymerization of just polyisocyanurate polymers does not give utilizable products, mainly due to their high viscosity. Increasing the ratio of decomposition agent - multifunction alcohol to PIR in order to decrease the product viscosity increases significantly the hydroxyl equivalent of alcohotysate prepared in such way, which worsens its production applicability. Utilizing another component in reaction mixture - linear polyester, which exhibits considerably lower resistance to decomposition agent at similar reaction mechanism, the depolymerization of PIR materials can be achieved even without high agent surplus.

During the depolymerization by glycerol almost all formed molecules are terminated by hydroxyl groups, thus the product can be used as polyol for the preparation of polyurethane and isocyanurate foams modified by polyurethane. The liquid product of mixed depolymerization also exhibits much higher diversity of reaction species and does not crystalize rapidly in a way one-species alcoholysates of polyesters or poryurethanes often do. Hence it can be stored for a long time period even at low temperatures. Higher viscosity of reaction products is caused by large molecules crossllnked by isocyanurate cycles, which are resistant to the depolymerization conditions. However, their presence at tiie preparation of PIR materials containing secondary polyol is necessary. These molecules terminated by polyfunctions! hydroxyl group cause the branching of polymer resulting in increasing its chemical and thermal stability.

From tightly crosslinked PIR materials, alkali metal carboxylates having the chainlength Ce-Ci2 show the highest activity during the depolymerization. They also work as compatibility agents or surfactants for the polymer of low polarity and polar molecules of glycerol during initial phase of depolymerization. The start of reaction is accelerated and formed reaction mixture is stabilized during the storage. Potassium salts are preferably used due to simultaneous catalytic activity in the process of isocyanates trimerisation, the main process in polyisocyanurate polymers preparation. Hence the presence of depolymerization catalyzer in prepared secondary polyol does not affect the production process of PIR materials. Another group of catalyzers exhibiting strong activity in the depolymerization process are organic guanidine and amidine superbases. The successful depolymerization of PIR polymers with alkali metal hydroxides, presented by other authors, faces the problem of residual hydroxides in the depolymerization products, as they can disrupt the materials prepared from such alcoholyzates in long-term prospects. It is the application of organic superbases that circumvents the problem, due to covatent bond of these catalyzers in the polymer structure preventing their mobility. During the process part of organic superbases are decomposed to carboxyl salts due to the reaction with carbon dioxide liberated during the depolymerization. Small amount of C0₂ is always liberated due to thermally induced decarboxylation reactions, proceeding at small rate simultaneously with transesterification. The application of glycerol as depolymerization agent combined with microwave heating of reaction mixture provides an advantage due to very strong absorption of electromagnetic radiation by glycerol in industrially utilized microwave range of 2,45 GHz. This strong interaction makes the reaction time required to reach the equilibrium of depolymerization product much shorter and significantly eaves the energy. Furthermore, glycerol being renewable non-toxic raw material provides considerable environmental advantages, compared to glycols frequently used in glycolysis of potyurethanes and polyesters. The microwave heating of mixture is chosen due to its very low thermal conductivity, which is caused by considerable volume of ground foam material of low density. These foam materials with their microporous nature have considerable outer surface and are capable of entirely absorbing liquid decomposing agent in amounts strongly exceeding optimal ratio agent - polymer. Thus the agent cannot function as heat transfer medium. The microwave heating generating the heat within entire reaction mixture volume is a chemical-engineering solution facilitating the economical depolymerization of PIR foam materials.

Considering the application of secondary polyols according to this invention, we have surprisingly discovered, that new pofyisocyanurate foams, produced from the mixture of virgin (primary) and secondary polyol exhibit narrower distribution and total size of cells followed by better mechanical properties of prepared foams. At the same time the thermal insulating properties of foams are preserved.

Detailed Description of Preferred Embodiments

In all following examples the reaction mixture is formed by hard thermal insulation pofyisocyanurate foam with the isocyanurate index value of 2.5, consisting of modified MDI and polyester polyol. The polyester component is formed by secondary ground bottle polyethyleneterephtalate. The reaction environment is anhydrous glycerol with the purity of 99 %.

EXAMPLE 1

PIR foam was ground to particles smaller than 2 mm in diameter and compounded with dear, colorless PET with floccuie diameter smaller than 4 mm, after which the mixture was subjected to mixed catalytic depolymerization in the microwave field, during which secondary polyol in the form of homogeneous liquid product was formed by alcoholysis and transesterification reactions. The reaction mixture, which was subjected to mixed catalytic depotymerization, contained 20 wL % waste PIR foams, 30 wt. % waste polyethyleneterephthalate and 50 wt. % glycerol.

Glycerol in this example contained 0.35 mol % 2-ethyl sodium-hexanoate (total chain length C₈). Mixed catalytic depotymerization proceeded in two phases, at first polyester was depolymerized in alcoholysis agent - glycerol, followed by the depotymerization of PIR foams in the mixture of remaining agent and oligoesters and polyols formed in the first phase.

30 g of reaction mixture were heated by the microwave generator with working frequency of 2.45 GHz and continuously stirred (1000 rev.min^-1). Complete depotymerization was reached at 250°C after 360 s at absorbed heating power of 125 W. The product was a secondary polyol in the form of clear viscous liquid with the following properties:

EXAMPLE 2

PIR foam was ground to particles smaller than 2 mm and compounded with clear colorless PET with floccule diameter smaller than 4 mm, after which this mixture was subjected to controlled glycerolysis by mixed catalyttcal depotymerization in microwave field, in the same way as in example 1. The reaction mixture in this example consisted of 23 wt % waste PIR foams, 27 wt % waste polyethyleneterepthalate and also 50 wt % glycerol. As in example 1, glycerol contained 0.35 mol % 2-ethyl sodium hexanoate.

Similarly, 30 g of reaction mixture were heated by microwave generator with working frequency of 2.45 GHz and continuous stirred (1000 rev.min^-1). The product was secondary polyol in the form of clear viscous liquid with the following properties:

EXAMPLE 3

The method for producing secondary polyols according to the third example of invention procedure was carried out in the same way as in example 1 with the exception that glycerol contained 0.4 mo)% organic superbase tetramethylguanidine (TMG). The product in this case was secondary polyol in the form of viscous liquid with the following properties: EXAMPLE 4

The method for producing secondary polyols according to the fourth invention example was carried out in the same way as in example 1 with the exception that the reaction mixture, which was subjected to mixed cata!ytical depolymerization, consisted of 20 wt. % waste PIR foams, 30 wt. % waste fraction from recycled PET bottles, composed of colour mix PET particles with traces of PVC and paper labels with 97,2 % total PET amount and with the maximum floccule diameter smaller than 8 mm and also 50 wt % glycerol.

As in example 1, glycerol contained 0.35 mol% 2-ethyl sodium hexanoate, and 30 g of reaction mixture were heated by microwave generator with working frequency of 2.45 GHz and continuously stirred (1000 rev.min^-1). Complete depolymerization was reached after 360 s at absorbed heating power of 125 W.

The deporymerization product was filtered at 150 *C through glass filter with the pore size d<10 pm and secondary polyol was gained as a product, free from mechanical impurities, in the form of viscous liquid with the following properties

EXAMPLE 5

Secondary polyol produced according to example 1 replaced 5, 10 and 15 wt. % of virgin polyol in the manufacturing of heat-insulating PIR foam with identical composition as PIR material used in the process of manufacturing secondary polyol. The properties of foam prepared in such way were compared to those of standard foam without this polyol addition.

The utilization of secondary polyol in the blend with virgin (primary) polyol to manufacture new PIR foam and the properties of PIR foam produced from this blend depending on the addition amount are presented in Table 1.

Table 1. Properties of PIR foams with secondary poiyois according to example 1

Claims

P AT E N T C L AI M S

1. The method for producing secondary polyols by recycling secondary raw materials containing waste polyisocyanurate (PIR) foams, where ground waste PIR foams are first compounded with polymers based on polyesters and then this mixture is subjected to controlled gfycerolysis in microwave field by mixed catalytic depolymerization, and secondary polyols are formed in the form of homogeneous liquid product, characterized by the fact that mixed catalytic depolymerization proceeding in two phases in the presence of catalyzers based on alkali metal carboxylate with the chainlength C₆-C₂₀, preferably C₆-C₁₂ and/or organic guanidine and amide superbases including their mixtures present in glycerol in the concentration 0.1 up to 1.0 mot.r¹ when in the first phase polyester is depolymerized in alcohofysis agent - glycerol and in second phase PIR foams are depolymerized in the mixture of remaining agent and oligoesters and polyols produced in the first phase, wherein the reaction mixture subjected to mixed catalytic depolymerization contains 15 to 30 wt. % waste PIR foams with the isocyanurate index higher than 2, and 20 to 40 wt. % polyesters, preferably waste poryethyleneterephthalate, and 40 to 60 wt % glycerol.

2. The method for producing secondary polyols according to claim 1, characterized by the fact that the reaction mixture contains further maximum 10 wt. % of eventual side admixtures and impurities.

3. The method for producing secondary polyols according to at least one of the previous claims, characterized by the fact that mixed catalytic depolymerization being carried out in the temperature range from 180 to 300°C, preferably 200 to 270°C, and the reaction mixture being heated by microwave generator with working frequency of 0.8 to 3 GHz for maximum time of 1 hour, depending on the power of used microwave generator.

4. The method for producing secondary polyols according to at least one of precedent claims, characterized by the fact that the product of mixed catalytic depolymerization being filtered decanted or centrifuged from eventual coarse mechanical impurities prior to its cooling.

5 .. The use of secondary polyols, produced by the method according to claim 1 to produce new polyisocyanurate foams, in blend of virgin (primary) and recycled (secondary) polyol, characterized by the fact that the addition of secondary polyol in the mixture of virgin (primary) and recycled (secondary) polyol being in the range from 5 to 25 wt. %.