A Patent Review on Pyrolysis of Waste Plastic and Scrap Tire into Liquid Fuel and Useful Chemicals

By Ben Bahavar, Ph.D.

Originally Published February 19, 2015

A Patent Review

In many aspects, the development, refining, and commercialization of plastic-to-liquid fuel is a classic example of the market forces being the main determining factor in adoption of a technology that is fairly well-developed. This article provides an overview of the recent efforts to produce a more efficient plastic/rubber-to-liquid fuel technology in order to make it a more commercially viable venture. Patent and non-patent activity worldwide is examined, the main drivers of technology are identified, and their unique contributions are briefly described.

The Drive Behind the Technology

Local and municipal jurisdictions are constantly exploring ways to deal with plastic (and rubber/tire) waste and promote reuse, recycling, and recovery of plastic waste over landfilling. Worldwide plastic production soared from 1.5 million m.t./year in 1950 to 245 million m.t./year in 2008, a trend that is expected to continue [2013 European Commission study on the impact of plastic waste]. Also of concern to the global community of nations is the plastic waste that is estimated to form 80% of the enormous waste patches in the Atlantic and Pacific oceans – this causes sea species to suffer from entanglement or ingestion of released plastic additives that can act as endocrine disruptors.

A Brief Description of the Technology

The production of gasoline-like fuels suitable for internal combustion engines (e.g., gasoline, diesel) via catalyzed or non-catalyzed thermal decompositions of waste plastic has been known for decades. The process is generally known as pyrolysis. Conventionally, pyrolysis implies a process in which organic substances are reduced or cracked by subjecting a material to heat in the absence of oxygen. The pyrolytic reactions are endothermic, i.e. they demand a delivery of heat to a reactor. pyrolytic cracking is carried out in absence of oxygen in order to prevent combustion as a potential reaction pathway.

Typically, the pyrolysis products are comprised of solids, oily liquid and vapors containing both valuable hydrocarbon gases as well as various contaminants to be removed. In the case of tires, the pyrolytic process reduces scrap tires into three product streams: an oily liquid, a gas, and carbon char (PyroChar). A related decomposition process to pylolysis is gasification whereby coal or biomass is heated under reduced oxygen levels, and the product is synthesis gas (SynGas, consisting mainly of H₂ and CO) that is utilized to produce fuels and platform chemicals via the Fischer-Tropsch process.

High-level Overview on Recent Patent Activity

The following Table depicts 14 inventions (1981-2015, mostly since 2009) representing some of the major improvements on the pyrolysis process to produce oil/fuel from waste plastic and scrap tire/rubber. This is followed by a discussion that also incorporates relevant non-patent information.

What is the Patent Activity Telling Us About the Challenges and the Opportunities?

A review of the full-text for the above patents point to some of the major drawbacks or challenges encountered in commercial-scale processes: A) chlorine/halogen removal when halogen-containing polymeric materials (e.g., PVC, PTFE) are among the plastic wastes, B) heat gradients due to poor heat conductivity of plastics, resulting in char accumulation at heat transfer surfaces, and C) economics, varying from high catalyst costs/consumption to high energy consumption. The object of the various inventions is to remedy one or more of these drawbacks.

Another challenge identified as an impetus for the above inventions is the need for the continuous operation as opposed to the batch mode so as to enhance the economic viability of the conversion process. It should be noted that the continuous operation mode for scrap tires is much more complicated than the continuous processing of other polymeric wastes because of a significant content of carbon (and steel) that cannot be completely converted into gaseous or liquid products and, therefore, should be permanently removed out of a decomposition reactor.

The Current Reality and Opportunities

As indicated at the outset of this article, the well-established pyrolysis process is further improved and is being improved, but the market adoption has been elusive. As indicated in one of the above inventions, some early commercial installations in Europe were short-lived for economic reasons, but commercial installations continue in Japan, and other countries. It is interesting to note that the three earlier patents (1981-1995) in the above Table are assigned to Bridgestone Tire, Ford Motor Company, and Mazda Motor Corporation. However, these patents do not seem to have been commercialized in any significant manner.

Even more revealing about the lack of commercial viability of this technology is the announcement in 1994 by BP Chemicals that it had put together a consortium of European petrochemical companies to help develop its polymer cracking technology [Miller, 1994, “Industry Invests in Reusing Plastics”]. Petrofina, DSM, Elf-Atochem, and Enichem were said to have participated in a pilot-plant at BP’s Grangemouth site in Scotland. Despite the very promising results from this pilot plant with a capacity of 50 kg/hr plastics waste, and despite a slated 2001 expansion to a demonstration plant by the consortium with a capacity of 25,000 m.t./year (a $30-40 million investment), we could not find any evidence of continuation of this high-profile effort.

Not all the news on commercialization of this technology is gloom! Indeed, two of the patent assignees in the above Table have been running commercial operations over the past few years: Plastic2Oil (Buffalo, NY – a 2015 patent assigned to JBI Inc.), and Cynar (Ireland – a 2012 patent assigned to Cynar Plastics Recycling Ltd.). There are also established pyrolysis operations in Asia. For instance, a joint venture between a Malaysian company and a South Korean company is said to be in operations since 2008 with a capacity of 120 m.t./year. This commercial plant was designed for scrap tire being broken down into carbon black (30%), recovered oil (50%), and non-condensable flammable gas and steel wires (10% each).

The only constant in this technology space is the variability of market forces. For instance, the tipping fee for tires (the cost to the transporter for tipping his truck’s contents at a disposal site) can range from $10/ton to $110/ton depending on the jurisdiction – the tipping fee at a Nevada landfill was at some point so low that the State had no tire processing or recycling/diversion industry. In recent years, the uncertainty in permitting the plants to burn tires (tire-derived-fuel, TDF) as well as lack of experience with TDF, has retarded the U.S. implementation of TDF. For instance, a TDF utility plant in Sterling, Connecticut had to shut down in 2013 after 22 years in operation because the State modified its regulations on the definition of renewable energy. Thus, various factors can make the price and supply of scrap tire to be quite volatile, and this further clouds the prospect of long term planning for adoption of pyrolysis technology.

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