The technological and economic potential of various routes to produce Plastics from Trees have been discussed in a report by Nexant. Trees are a prolific and renewable source of raw materials for a host of conversion processes, and have been used as raw materials for centuries (pulp and paper, building materials). The next stage in this evolution of trees and tree-based raw materials is being explored in a host of value-added products, including combined heat and power, liquid biofuels, and renewable chemicals, such as renewable plastics and intermediates. Trees absorb carbon dioxide from the atmosphere as they grow and provide a wide range of feedstocks. Technologies to tap the chemical precursors locked within biomass feedstocks (such as from trees) have improved over time. Products and pathways explored in this report include the following:
• Catalytic Fast Pyrolysis of wood to the key aromatic compounds, Benzene, Toluene, and Xylene (BTX), with generation of paraxylene from the BTX and subsequent conversion to purified terephthalic acid (PTA) and polyethylene terephthalate ( PET).
• Gasification of woody biomass to syngas with subsequent synthesis of methanol, plus methanol to propylene and polymerization to polypropylene.
• Enzymatic hydrolysis of wood to ethanol, with subsequent catalytic dehydration to ethylene and production of high density polyethylene (HDPE).
• Cellulosic plastics pioneered by Eastman (Tenite™ Cellulosics), which find commercial application in tool handles, toothbrushes, golf putters, alternatives to urethanes, etc.
These are compared to traditional fossil-fuel-based routes.
Gasification to Polypropylene (Tree-Based Propylene)
Gasification of woody feedstock generates syngas, which is subsequently converted to methanol via the well-known Methanol-to-Propylene (MTP™) process, and polymerization of the propylene to polyolefin, as shown below:
This process has multiple steps but is rather straightforward, with each of the technologies having been proven commercially.
Enzymatic Hydrolysis in SSF to HDPE (Tree-Based HDPE)
The simultaneous saccharification and fermentation (SSF) of wood chips to ethanol using enzymatic hydrolysis to generate sugars from wood chip feedstock is followed by the dehydration of ethanol to ethylene, which is subsequently polymerized to HDPE.
The pathway assessed here begins with technologies that have been long studied to extract sugars from cellulosic feedstock. The subsequent processes to ferment those sugars to ethanol, from which ethylene and HDPE are derived, are in practice commercially around the world.