Figure A F.1 provides an overview of bio-ethylene manufacturing process, including feedstock and resin production. The production bioethanol from sugarcane includes the plantation, the conversion of sugarcane into molasses by sugar milling and refining. Molasses is processed through fermentation and distillation to produce bioethanol. Bio-ethylene is then produced from catalytically dehydrated bioethanol The bio-ethylene obtained from this conversion process is used as an input in the polymerisation phase to produce biopolyethylene.
Implementing the OECD Framework for Industry’s Net‑zero Transition in Thailand
Decarbonising the Petrochemical Sector and Plastics Value Chain
PLA is produced from the fermentation of plant-derived carbohydrates such as sugars or starch. The main production process of PLA consists in (Figure A F.2):
Feedstock collection and conversion, for example, sugar from sugarcane to the processing mill.
Next, the raw materials (i.e. sugar) are transformed into lactic acid using a fermentation process. The optical purity of the lactic acid plays a significant role in determining the crystallinity and biodegradability of PLA. Therefore, it is crucial to give careful attention to the processing of lactic acid downstream as the fermentation broth contains significant levels of impurities. Identifying and removing these impurities is a critical step that may affect the properties of the final PLA product (Cheroennet et al., 2017[1]).
Finally, the lactic acid is polymerised by combining it with lactide, which is the dimer form of lactic acid. Other inputs for producing PLA resin include potassium hydroxide, sulfuric acid, lime, steam and electricity This polymerisation process, known as ring-opening polymerisation, is used to produce PLA pellets.
PBS is synthesised through bacterial fermentation utilising succinic acid and 1,4 butanediol as the primary precursors (Figure A F.3):
The production of succinic acid uses raw materials such as sugar from sugarcane. The process involves hydrolysis and fermentation to produce dextrose through a series of enzymatic reactions. Subsequently, dextrose is combined with sodium chloride and carbon dioxide to produce succinic acid (Rajendran and Han, 2023[2]).
The production of butanediol involves the use of bioethanol, succinic acid, electricity and natural gas.
PBS pellets are then produced through the esterification of succinic acid and 1,4-butanediol, followed by a condensation process.
TPS is formed through the de-structuring of native starch granules by heating (Tongsumrith, 2015[3]). TPS production involves conventional polymer processing techniques such as compression, extrusion and injection molding that can be used to melt the granular structure of starch with a plasticiser such as glycerol (Tongsumrith, 2015[3]).
Figure A F.5 provides an overview of olefin production through steam cracker, involving the main following steps:
Cracking furnace: The feedstock is mixed with steam and heated to around 900°C in a cracking furnace. The high temperature causes thermal cracking, forming ethylene, propylene and other byproducts, depending on the feedstock. The furnace outlet stream is subsequently fed to a water-based quench, to prevent further reactions and formation of undesirable byproducts.
Quenching: The cracked gas is cooled to stop further reactions and the formation of undesirable byproducts. Cracked gas from the quench is then directed to compression and separation.
Compression, drying, acid gas removal: The cooled gas is compressed and acid gases like CO2 and H2S are removed using chemical scrubbers. The compression of the cracked gas is performed across five stages. The compressed cracked gas is cooled and subsequently dried.
Separation and purification: The mixture contains products including ethylene, propylene, butadiene, hydrogen, methane, other light hydrocarbons. The light components from the compressed stream are sequentially separated from the heavy fractions using a separation train of distillation columns that ultimately yield high-purity ethylene and propylene.
Note: Illustration for a naphtha-based steam cracker.
Source: (Haribal et al., 2018[4])
References
[1] Cheroennet, N. et al. (2017), “A trade-off between carbon and water impacts in bio-based box production chains in Thailand: A case study of PS, PLAS, PLAS/starch, and PBS”, Journal of Cleaner Production, Vol. 167, pp. 987-1001, https://doi.org/10.1016/j.jclepro.2016.11.152.
[4] Haribal, V. et al. (2018), “Intensification of Ethylene Production from Naphtha via a Redox Oxy-Cracking Scheme: Process Simulations and Analysis”, Engineering, Vol. 4/5, https://doi.org/10.1016/j.eng.2018.08.001.
[2] Rajendran, N. and J. Han (2023), “Techno-economic analysis and life cycle assessment of poly (butylene succinate) production using food waste”, Waste Management, Vol. 156, pp. 168-176, https://doi.org/10.1016/j.wasman.2022.11.037.
[3] Tongsumrith, T. (2015), Production of thermoplastic cassava starch reinforced by natural fiber : performance, biodegradability, and environmental impacts, https://d.lib.msu.edu/etd/3759.