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High Lights in Industrialization of Polyurethane Foam Wastes Chemical Recycling: Economical Roots to Polyol Recovery, Application and Market Studies

Mir Mohammad Alavi Nikje, Imam Khomeini International University, Qazvin, Iran

Polyurethane, market and consumption

Polyurethane is a polymer, invented by Otto Bayer in 1930s, during developing research on polymer fibers.  Polyurethane (PU) is formed by reacting a polyether or polyester polyol (a polymeric alcohol with more than two reactive hydroxyl groups per molecule) such as polypropylene glycol (PPG) or polytetramethylene glycol (PTMG) with diisocyanate or polymeric isocyanate e.g. diphenylmethane diisocyanate (MDI) or toluene diisocynate or (TDI) in the presence of suitable catalysts and additives, especially chain extenders e.g. 1,4-butanediol. With the diverse range of high performance properties, polyurethanes are essential to a multitude of end-use applications.  The producers of PU are organized within the Isocyanate Producers Association (ISOPA) in Europe and API in North America. Total production volume of PU in Europe is more than 3 million tons per year. Rigid and flexible PU foams are highly produced and consumed in many industries and some of the main applications of PU based products are detailed below:

• Flexible PUF:  automobile seating, furniture, carpets

• Rigid PUF: refrigerator, insulation board

• Elastomers: footwear, adhesives, medical

• RIM: automobiles (bumpers, side panels)

• Other: carpets, casting, sealants

Waste reduction

Polyurethane is disposed generally via landfill, incineration or recycling. In 2003, 55.4% of all the municipal solid waste generated ended up in a landfill, while only 30.6% was recycled. Polyurethanes often are recyclable materials. Leading raw materials suppliers of the polyurethane industry have committed themselves over the years to find economically viable ways to reclaim discarded polyurethane-containing products and have successfully recycled a variety of consumer products, including:

• Appliances

• Automobiles

• Bedding

• Carpet cushion

• Upholstered furniture

 

Recycling methods

There are various recycling methods has been industrialized in the World and all of them have their own merits and drawbacks.

Physical recycling (Rebinding, Regrinding, Adhesive pressing, Compression molding and injection molding, Energy recovery (combustion – incineration)

Thermochemical recycling (Pyrolysis-Gasification, Hydrogenation)

Chemical recycling (Hydrolysis, Aminolysis, Glycolysis, Other chemical recycling methods)

As the goal of this proposal is finding the economical roots toward chemical recycling, the chemical one studied in detail in this report.

 

Chemical recycling

In the chemical recycling, the urethane bonds can be broken down releasing some useful material by means of a suitable reagent. However there are 3 main methods for chemical recycling of PU wastes: Hydrolysis, Aminolysis and Glycolysis, nowadays some binary processes are also presented as recycling methods.

Flexible Polyurethane Foam Recycling in Pilot Scale

The scraps of flexible PU foam (450 Kg), sodium hydroxide (1% w/w) and glycolysis agents (the mixture of ecofriendy solvents namely glycerol, pentaeritritol and sorbitol) were placed in a fully equipped 1 ton reactor and the reaction temperature was raised to 180 ºС by using circulated heating oil. After reaction completion, the reactor was reload, the liquid sieved in order to sieving unreacted polymers and contaminants and decanted within 1 h two split phases collected. The upper phase was slightly yellowish color and characterized as polyol. The lower phase had dark brown color and assigned as highly hydroxyl and amine functionalized materials what was suitable for rigid polyurethane foam formulation. All QC test were performed on recycled polyol and data compared by virgin one.

New rigid PU foam preparation

One of the main goal in the studying of recovered polyol performances is the compatibility of the recycled polyol with virgin one which causes it to be usable in a similar formulation for production of new rigid PU foam. We focused on reactivity factors, densities and foam qualities in this study and data are collected in table 1. According to the table, increasing the bottom phase till to 20% causes an increment in density and decreasing the quality of new rigid PU foams. By the way results showed the performance of lower phase up to 20% in the rigid PU foam formulations.

Table 1

Reactivity parameters, density and foam qualities of PU rigid foam samples during formulation

 

Project Abstract (Background, Hypothesis, Aims & Performing Method):

Thermoset waste polyurethane from flexible and rigid foams products is recycled and the recycled is reused in formulation of new foam products.

• Rigid polyurethane foam waste is converted to single liquid phase which containing unreacted destroying solvents, recovered amines, recovered polyols and oligomers. The recovered polyol can be used in rigid polyurethane rigid foams in blending with virgin one.

• Flexible foam wastes, is converted to two split phases. The upper phase containing recovered polyol as a main product which contaminate with unreacted solvents and some diphenylmethylene diamine. By using additional headings and/or additional microwave irradiations in the controlled conditions, the recovered polyol assay will be high and comparable with virgin one. This phase is applicable in the new foam formulation in blending with virgin and commercially available polyols. As the recycled polyol would not provide the product which is exactly similar to virgin polyol, thus it is required to provide some extra advanced processes to optimize the structure and characteristics of recyclate. This would enable the formulator to use more amount of recycled polyol in formulation. The optimization procedure consists of some physico-chemical processes to make the recycled as similar as possible to virgin polyol.

• The “system housing of recovered polyol” idea can be discussed as a separated proposal. The upper phase yield is calculated as 45% of total mass.

The lower phase which containing a lot of unreacted solvent, released amine products from glycolysis, oligomers and other polar molecules has high hydroxyl number and applicable as a portion of highly functionalized polyol in rigid foam production in blend with virgin polyol. The lower phase yield is calculated 55% of total mass.

 

Goals

Reduction in amount of polyurethane wastes as an environmental pollutant chemical, reducing the amount polyol import by PU industries from abroad, producing a valuable product from wastes, earning the technical knowledge of recycling and polyol recovery which is now limited to few countries e.g. USA, Germany and Japan.

 

Applications and Usages (Technical Sciences Production, Yield Production, Science Offering)

The earned technical knowledge of this project is possible to be easily scaled up for industrial applications and the industrial application of this knowledge would reduce the amount of imported polyol.

 

Scientific Demonstration & Technical-Laboratory Features of the Project (If Necessary)

In the first step, polyurethane foam is recycled by solvolysis process. This procedure is conducted by a two (or multi) component solvent systems. Characterization of recycled polyol i.e. molecular weight, viscosity, density, acid number, OH number, etc. and comparison with virgin polyol would provide the initial condition for optimization and preparing the most similarity within their structure. The optimized recycled would be reused in foam formulation with different ratios. This foam is synthesized by polyether polyol and MDI.

 

Method (Containing Research Method or Designing & Building System)

Literature survey, evaluating the documents for research route decision

Investigating the effect of different solvent systems on glycolysis process 

Quality control and characterization of product

Application of recycled as a substituent of virgin polyol in polyurethane foam formulation

Quality control and comparison of synthesized foam with original sample

Conducting the physic-chemical processes for optimization of recycled

Studying the efficiency of optimization approach to make the recycled as similar as possible to virgin polyol

 

Estimated product price: recycling pilot in 1 ton / day scale

Solvent/ waste foam: 1/1.5

Waste cost: zero US$

Destroying solvent (solvent and catalysts) cost: 0.6 US$/Kg (according to world solvent costs)

Batch capacity: 1 ton

Total solvent cost in batch: 210 US$

Energy cost (heating using oil system):  about 3 Cent/Kg

Total heating cost: about 100 US$

Total cost (without investments and….) 310 US$/ton

Polyol world price (considered in Iran): 1800−2300 US$/ton

 

Estimated equipments investment:

About 200000 US$ is estimated to designing, manufacturing and turning key for 1 ton/day pilot plant

Requested area: 200 square meter

 

Important comments:

All products should be quality controlled using an authorized person and laboratory and all polyol ASTM tests will be performed on recycled materials.

The final polyol will be check in chemical and physical specifications and data should be compared with virgin one.

All reactivity factors will be control and the foam data should be compared with virgin produced foam data.

 

Main Factors what should be considered in total recovered polyol cost estimation:

1.   Total yearly all PU scraps rising

2.   Region studies and Nominal plant capacity

3.   Total Investment and financing for 2 years with nominal 6% of interest

4.   Price difference between the virgin Polyol system house and virgin/ recycled Polyol blends system house

5.   Recycled Polyol production capacity

6.   Yearly profit without financing and tax considerations

7. Investment return time (months)

 

 

 

Conclusion:

In conclusion, our Lab., and pilot studies toward chemical recycling, had been shown that all PU waste types are suitable for chemical recycling via our novel methods using green solvents containing highly economical interests. The recycled polyols are comparable by virgin one and can be use as a portion of industrially system house virgin polyol and / or alone before system housing.

 

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Mir Mohammad Alavi Nikje, Assoc. Prof., University Staff Member, Department of Chemistry, Faculty of Science, Imam Khomeini International University,  P. O. Box 288, Qazvin, Iran. Tel/fax +98 (281) 378-00-40. E-mail

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