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.
|US2015 001061||2015||JBI Inc. (Plastic2oil)||System and process for converting plastics to petroleum products||Solid waste plastics are processed by melting (250-340 oC), pyrolysis (340-445 oC), vaporization, and selective condensation, whereby final in-spec petroleum products are produced (diesel, gasoline, furnace fuel, kerosene, propane, butane, ethane or methane).|
|US8927797||2015||Natural State Research Inc||Method for converting waste plastic to lower-molecular weight hydrocarbons, particularly hydrocarbon fuel materials, and the hydrocarbon material produced thereby||Waste plastic (HDPE, LDPE, PP, PS) melted in an aerobic atmosphere, thermally decomposing the plastic melt, adding cracking catalyst to the melt, distilling at least a portion of the mixture whereby a liquid hydrocarbon fuel/distillate is produced (gasoline & diesel, C3 to C27).|
|US2014 371385||2014||Black Bear Carbon B.V.||Method for obtaining a carbon black powder by pyrolyzing scrap rubber, the carbon black thus obtained and the use thereof||Scrap rubber, in particular tires undergo pyrolysis (630-670 oC), the resulting char material is milled to carbon black powder (60-98 percent carbon black, less than 2.0 weight percent of volatiles, and 0-30 weight percent of silica) – carbon black powder is used as a filler or a reinforcing agent in a rubber composition, an ink, a paint, a bitumen, a thermoplastic composition or a thermoplastic elastomer.|
|US8344195||2013||J. Srinakruang (Thailand, Individual Inventor)||Process for producing fuel from plastic waste material by using dolomite catalyst||Pyrolysis (330-400 oC) of plastic waste (PE, PP, PS), the resulting liquid is first subjected to a semi-batch catalytic cracking reaction over a dolomite catalyst to obtain high quality oil for fuel (mainly light and heavy naphtha).|
|US8425731||2013||Advanced Pyrotech SDN BHD||Pyrolysis process for decomposing rubber products||Shredded tires are fed constantly into the pyrolysis vessel while the by-products of the pyrolysis are continually discharged – the waste tire particles fed into carbonizing reactor are conveyed through the reactor by a continuously rotating drag chain conveyor that travels bi-directionally in a continuously loop in transfer cylinders that operate in a partial vacuum (oxygen is below its stoichiometric level to prevent combustion). As the waste tire chemically decomposes through a pyrolysis process inside the reactor, oil vapor, referred as second by-product, and a synthesis gas (SynGas) are recovered from the waste tire particles while the waste tire is conveyed through the first transfer cylinder leaving small a quantity of partially decomposed waste tire, carbon black, referred as fifth by-product and the remaining steel wire to be transferred through the second transfer cylinder.|
|US2012261247||2012||Cynar Plastics Recycling Ltd.||Conversion of waste plastics material to fuel||pyrolysis in an oxygen-free atmosphere (240-280 oC) to provide pyrolysis gases followed by conversion to diesel and kerosene|
|US7959890||2011||RIPP Resource Recovery Corp.||Method of reclaiming carbonaceous materials from scrap tires and products derived therefrom||Tires are shredded and pyrolyzed (450-550 oC) under an anaerobic environment to produce a char, volatile organics and the char are removed from the reaction chamber, the char is cooled in a second anaerobic environment, metal and textile components (steel & fiber cords) are removed to obtain pyrolytic carbon black which is milled into particles of 325 mesh size or smaller, and utilized in a polymerization process that produces recycled rubber.|
|US7758729||2010||Agilyx Corp. and Plas2Fuel Corp.||System for recycling plastics||The plastic material is placed in a treatment chamber and heated to 270-375 oC that results in pyrolytic cracking in absence of oxygen so as to prevent combustion as a potential reaction pathway from occurring. A vacuum removes vapor (pyrolyzed inorganic species and gaseous organic species) from the chamber – the chamber is heated in incremental steps – the vapor from pyrolytic cracking is contacted with a pH buffered aqueous media resulting in condensation of gaseous organic species contained within the vapor. Chlorine and bromine are separated from the oil end-product.|
|US7626061||2009||MPCP GmbH||Method and apparatus for continuous decomposing waste polymeric materials||Waste polymeric material (scrap tires, rubber, polyurethane) are turned into valuable liquid chemicals and/or liquid fuels. Decomposition process is carried out under moderate temperatures (less than 850 oC) and atmospheric pressure in the presence of air and a feed of liquids containing oxygen. This continuous process is characterized by the low residence time (3-25 minutes). The liquid containing oxygen is acetone, methanol, ethanol, water or mixtures thereof. At least one of hydrogen, carbon monoxide, a gaseous hydrocarbon and carbon is also recovered in this process. Liquid oil and solid, oil free carbon is also recovered.|
|US5811606||1998||Plastic Advanced Recycling Corp.||Process and equipment for treatment of waste plastics||Waste plastics (PE, PP and PS) and a catalyst are mixed into a reactor for catalytic cracking reaction (280-480 oC) removing the solid impurities in the generated vapor, condensing the vapor in condenser, and returning the non-condensable gas to be burnt in the heating furnace, distilling and separating the condensate to obtain gasoline and diesel oil which will be stabilized to get high quality gasoline and diesel oil.|
|US5821396||1998||Fabspec, Inc.||Batch process for recycling hydrocarbon containing used materials||A pyrolysis batch process is described for recycling scrap tires and plastics (ABS, polystyrene and other non-chlorinated thermoplastics) so as to obtain useful light oil and fuel gases. Used tire cuttings are loaded into a rotatable reactor which is closed, evacuated, rotated and heated until exothermic reaction is initiated.|
|US5414169||1995||Mazda Motor Corp.||Method of obtaining hydrocarbon oil from waste plastic material or waste rubber material and apparatus for carrying out the method||Thermal cracking of waste plastic/rubber followed by acid catalysis|
|US4515659||1985||Ford Motor Co.||Pyrolytic conversion of plastic and rubber waste to hydrocarbons with basic salt catalysts||Pyrolysis under nitrogen at 400-700 oC and in the presence of one percent basic salt catalyst|
|US4251500||1981||Bridge-stone Tire||Process for hydrocracking a waste rubber||Hydrocracking (350-500 oC) under a hydrogen partial pressure of 100-300 atm. Waste rubber such as used tires, used conveyor belts, used hoses etc.|
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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