Chemical Recycling of Plastic Waste using Pyrolysis

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Recycling has been popular for over 50 years, but there are still growing pains.

Mechanical recycling of plastic has been the primary approach, yet it remains to have serious issues. Recycling plastic using mechanical techniques (shredding, grinding, melting, etc.) is a challenge since a) it degrades the properties of the polymer during processing and b) improper sorting will affect the purity of the output. Chemical recycling, though, has been slow to catch on. Until now.

Chemical Recycling Using Pyrolysis

Pyrolysis is the thermal decomposition of any organic compound when heated in the absence of air. The products of this process, depending on the conditions, can consist of (H2/CO)/lower hydrocarbons/aromatics.

Products of the pyrolysis of organic material have been used as early as the 12th century. The process produced pine resin used for waterproofing wooden ships and impregnating ropes. It became commercial in the 16th century for this application. WWI precipitated the need for aromatic compounds from the pyrolysis of biomass to make the explosive TNT. After that, the production of aromatic compounds from waste languished for 60 years.

The first interest in the pyrolysis of mixed plastic waste to form the aromatic compounds benzene, toluene, xylene, referred to as BTX, began in the early s in both the academic as well as patent literature. During this period, environmental conservation came to the forefront in the US and around the world precipitating an interest in recycling on a large scale.

In there were the first three academic articles from a group in West Germany discussing the use of pyrolysis of waste plastic and tires for chemical recycling. Fast forward to the s and the number of papers ballooned exponentially, with 123 papers published in alone, up from 100 in and 62 and 45 in and , respectively. In this sector, most of the academic funding for chemical recycling to produce BTX is from government agencies in China, followed by the EU. While hurdles remain at the federal level within the US on utilizing pyrolysis techniques for chemical recycling due to it being energy intensive and environmental concerns, states are promoting its use. As of , 18 states have passed laws regarding this as a viable recycling technique (read the article here).

Patent activity has also exploded recently. SABIC is the leading company with the most first-time patent filings for the conversion of waste plastic to BTX &#; these filings were published in and . SABIC has only filed world patent applications for their recent innovations in the production of BTX using pyrolysis (no first-time US patent applications yet since ). Overall, SABIC has 11 pending, eight granted, and four dead patents in BTX production from pyrolyzed waste plastic. Coverage ranges from China, World, US, Japan, EU, and Korea and a few other individual countries, so it is anticipated that these recent patent applications will be filed in the US and other countries. SABIC&#;s first patent application, specifically in this area, occurred in .

Eastman Chemical and Anellotech have published four recent patent application each. Eastman Chemical has been patenting in pyrolysis of waste for several decades. The start-up, Anellotech, is a recent entrant starting pilot operations over the past decade. They recently announced the possibility of advancement of their technology from the lab to commercial scale with assistance from potential partnering companies. Their technology can use mixed textile wastes, including cotton, polyester, nylon, elastane, acrylic, and polyurethane, a unique application of pyrolysis to a significant waste stream (read the article here).

A recent advancement in commercial chemical recycling of waste mixed plastics to BTX was signed (read the article here) through a Joint Development and Cooperation Agreement with Synova, SABIC Global Technologies, and Technip Energies with their respective MILENA, OLGA, and Pure.rGas processes. This collaborative effort will focus on the development and launch of a new commercial plant to produce olefins and aromatics from mixed plastic waste.

Eastman Chemical has been very active in the circular economy, improving recycling, including chemical recycling. Though several of their processes are in the process of commercialization, their pyrolysis technology has not yet been implemented commercially.

Making new renewable sources for deriving BTX available can have many supply-chain benefits to the petrochemical, polymer, and coating/formulation industry. This will also improve the value of recycling mixed plastic waste and usher plastic waste recycling into today&#;s circular economy.

So, why is this important to you?

Are you interested in emerging technologies that may impact your business?

How Can Nerac Help?

Nerac can provide you with the backstory for new technologies, who the players are in the space, both in the market as well as the patent literature. These may be your competitors and/or new entrants who could be potential targets for partnership or acquisition. We can provide you with the intelligence you need to understand how these players may impact your business, either positively or negatively.

In parallel, should you desire, we can investigate the academic contributions to a technology area, who is funding the research, and the key players involved. In this latter case, it will allow you to identify academic partners or potential consultants to help you move forward with more arrows in your quiver to keep you on top of your game as you move your company towards a more circular economic model.

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Petroleum substitute

This article is about synthetic liquid fuel derived by pyrolysis from biomass. For other uses, see Pyrolysis oil (disambiguation)

Pyrolysis oil, sometimes also known as biocrude or bio-oil, is a synthetic fuel with few industrial application and under investigation as substitute for petroleum. It is obtained by heating dried biomass without oxygen in a reactor at a temperature of about 500 °C (900 °F) with subsequent cooling, separation from the aqueous phase and other processes. Pyrolysis oil is a kind of tar and normally contains levels of oxygen too high to be considered a pure hydrocarbon. This high oxygen content results in non-volatility, corrosiveness, partial miscibility with fossil fuels, thermal instability, and a tendency to polymerize when exposed to air.[1] As such, it is distinctly different from petroleum products. Removing oxygen from bio-oil or nitrogen from algal bio-oil is known as upgrading.[2]

Standards

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There are few standards for pyrolysis oil because of few efforts to produce it. One is from ASTM.[3]

Feedstock decomposition

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Pyrolysis is a well established technique for decomposition of organic material at elevated temperatures in the absence of oxygen into oil and other constituents. In second-generation biofuel applications&#;forest and agricultural residues, waste wood, yard waste, and energy crops can be used as feedstock.

Wood

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When wood is heated above 270 °C (518 °F) it begins a process of decomposition called carbonization. In the absence of oxygen, the final product is charcoal. If sufficient oxygen is present, the wood will burn when it reaches a temperature of about 400&#;500 °C (752&#;932 °F) leaving wood ash behind. If wood is heated away from air, the moisture is first driven off and until this is complete, the wood temperature remains at about 100&#;110 °C (212&#;230 °F). When the wood is dry its temperature rises, and at about 270 °C (518 °F) it begins to spontaneously decompose and generate heat. This is the well known exothermic reaction which takes place in the burning of charcoal. At this stage evolution of carbonization by-products starts. These substances are given off gradually as the temperature rises and at about 450 °C (842 °F) the evolution is complete.

The solid residue, charcoal, is mainly carbon (about 70%), with the remainder being tar-like substances which can be driven off or decomposed completely only by raising the temperature to above about 600 °C to produce Biochar, a high-carbon, fine-grained residue that today is produced through modern pyrolysis processes, which is the direct thermal decomposition of biomass in the absence of oxygen, which prevents combustion, to obtain an array of solid (biochar), liquid&#;Pyrolysis oil (bio-oil/pyrolysis-oil), and gas (syngas) products. The specific yield from the pyrolysis is dependent on process conditions. such as temperature, and can be optimized to produce either energy or biochar.[4] Temperatures of 400&#;500 °C (752&#;932 °F) produce more char, while temperatures above 700 °C (1,292 °F) favor the yield of liquid and gaseous fuel components.[5] Pyrolysis occurs more quickly at higher temperatures, typically requiring seconds instead of hours. High temperature pyrolysis is also known as gasification, and produces primarily syngas.[5] Typical yields are 60% bio-oil, 20% biochar, and 20% syngas. By comparison, slow pyrolysis can produce substantially more char (~50%). For typical inputs, the energy required to run a &#;fast&#; pyrolyzer is approximately 15% of the energy that it outputs.[6] Modern pyrolysis plants can use the syngas created by the pyrolysis process and output 3&#;9 times the amount of energy required to run.

Algae

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Algae may be subjected to high temperatures (~500 °C) and normal atmospheric pressures. The resultant products include oil and nutrients such as nitrogen, phosphorus, and potassium.[7]

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There are numerous papers on the pyrolysis of lignocellulosic biomass. However, very few reports are available for algal bio-oil production via pyrolysis. Miao et al. (b) performed fast pyrolysis of Chllorella protothecoides and Microcystis areuginosa at 500 °C, and bio-oil yields of 18% and 24% were obtained, respectively. The bio-oil exhibited a higher carbon and nitrogen content, lower oxygen content than wood bio-oil. When Chllorella protothecoides was cultivated heterotrophically, bio-oil yield increased to 57.9% with a heating value of 41 MJ/kg (Miao et al., a). Recently when microalgae become a hot research topic as the third generation of biofuel, pyrolysis has drawn more attention as a potential conversion method for algal biofuel production. Pan et al. () investigated slow pyrolysis of Nannochloropsis sp. residue with and without the presence of HZSM-5 catalyst and obtained bio-oil rich in aromatic hydrocarbons from catalytic pyrolysis. Algal pyrolytic liquids separate into two phases with the top phase called bio-oil (Campanella et al., ; Jena et al., a). The higher heating values (HHV) of algal bio-oil are in the range of 31&#;36 MJ/kg, generally higher than those of lignocellulosic feedstocks. Pyrolytic bio-oil consists of compounds with lower mean molecular weights and contains more low boiling compounds than bio-oil produced by hydrothermal liquefaction. These properties are similar to those of Illinois shale oil (Jena et al., a; Vardon et al., ), which may indicate that pyrolytic bio-oil is suited for replacing petroleum. In addition, the high protein content in microalgae led to a high N content in the bio-oil, resulting in undesirable NOx emissions during combustion and deactivation of acidic catalysts when co-processed in existing 10 crude oil refineries. Algal bio-oil had better qualities in many aspects than those produced from lignocellulosic biomass. For example, algal bio-oil has a higher heating value, a lower oxygen content and a greater than 7 pH value. However, upgrading towards the removal of nitrogen and oxygen in the bio-oil is still necessary before it can be used as drop-in fuels.[8]

Hydrothermal liquefaction

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Hydrothermal liquefaction (HTL) is a thermal depolymerization process used to convert wet biomass into an oil[9]&#;sometimes referred to as bio-oil or biocrude&#;under a moderate temperature and high pressure[10] of 350 °C (662 °F) and 3,000 pounds per square inch (21,000 kPa). The crude-like oil (or bio-oil) has high energy density with a lower heating value of 33.8-36.9 MJ/kg and 5-20 wt% oxygen and renewable chemicals.[11][12]

The HTL process differs from pyrolysis as it can process wet biomass and produce a bio-oil that contains approximately twice the energy density of pyrolysis oil. Pyrolysis is a related process to HTL, but biomass must be processed and dried in order to increase the yield.[13] The presence of water in pyrolysis drastically increases the heat of vaporization of the organic material, increasing the energy required to decompose the biomass. Typical pyrolysis processes require a water content of less than 40% to suitably convert the biomass to bio-oil. This requires considerable pretreatment of wet biomass such as tropical grasses, which contain a water content as high as 80-85%, and even further treatment for aquatic species, which can contain higher than 90% water content. The properties of the resulting bio-oil are affected by temperature, reaction time, algae species, algae concentration, reaction atmosphere, and catalysts, in subcritical water reaction conditions.

Biocrude

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Bio-oil typically requires significant additional treatment to render it suitable as a refinery feedstock to replace crude oil derived from petroleum, coal-oil, or coal-tar.

Tar is a black mixture of hydrocarbons and free carbon obtained from a wide variety of organic materials through destructive distillation.[14][15][16] Tar can be produced from coal, wood, petroleum, or peat.[16]

Wood-tar creosote is a colourless to yellowish greasy liquid with a smoky odor, produces a sooty flame when burned, and has a burned taste. It is non-buoyant in water, with a specific gravity of 1.037 to 1.087, retains fluidity at a very low temperature, and boils at 205-225 °C. When transparent, it is in its purest form. Dissolution in water requires up to 200 times the amount of water as the base creosote. The creosote is a combination of natural phenols: primarily guaiacol and creosol (4-methylguaiacol), which will typically constitute 50% of the oil; second in prevalence, cresol and xylenol; the rest being a combination of monophenols and polyphenols.

Pitch is a name for any of a number of viscoelastic polymers. Pitch can be natural or manufactured, derived from petroleum, coal tar[17] or plants.

Black liquor and Tall oil is a viscous liquid by-product of wood pulp manufacturing.

Rubber oil is the product of the pyrolysis method for recycling used tires.

Biofuel

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Biofuels are synthesized from intermediary products such as syngas using methods that are identical in processes involving conventional feedstocks, first generation and second generation biofuels. The distinguishing feature is the technology involved in producing the intermediary product, rather than the ultimate off-take.

A Biorefinery is a facility that integrates biomass conversion processes and equipment to produce fuels, power, heat, and value-added chemicals from biomass. The biorefinery concept is analogous to today's petroleum refinery, which produce multiple fuels and products from petroleum.[18]

Atmospheric carbon dioxide removal

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Bio-oil is a recent contender technique for carbon sequestration. Corn stalks are converted by pyrolysis into bio-oil, which is then pumped underground.[24]

Industrial applications

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Currently, bio-oil has few industrial uses. A reported application is in the production of zinc oxide as thermal source.[25] In this use, the fuel has substituted heavy fuel oils as a biogenic source of heat.[26] The bio-oil is used in the kiln burners as a direct substitute with little to no change in the operational results. The fuel has higher water and oxygen content which makes a higher volumetric flow for the same heat capacity.

See also

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References

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