1. Green Polymer Chemistry: A Biologically-Derived Synthesis of Polyethylene
Adam Hildebrandt, Faculty Member: Dr. Carolyn Wanamaker
Concordia University St. Paul
As the global demand for plastics continues to increase, the petrochemical
industry as a whole should implement a biologically derived synthesis of
polyethylene. This will reduce greenhouse gas (GHG) emissions, lower
consumer prices and decrease environmental impact. Both high-density
polyethylene (HDPE) and low-density polyethylene (LDPE) can be
synthesized from the renewable source of ethanol. Ethanol is a renewable
source that is produced from the fermentation of corn or sugar cane.
LDPE is synthesized via a free radical reaction. While the Ziegler-Natta
Catalyst is used to synthesize HDPE [4]. Bio-based polyethylene
production reduces greenhouse gas emissions compared to the current
petroleum-based PE production methods [2].
Figure 1. Flow chart for converting ethanol into polyethylene. Adapted
from Kikuchi et al [2].
Polyethylene is the most common plastic in the world. It is commonly
used to make plastic bags and bottles. The petrochemical industry
produces mass amounts of CO2, a GHG, as a byproduct from the current
petroleum-based PE production [1]. CO2 is produced from the
combustion of fossil fuels. Decreasing the amount of CO2 produced from
this industry will positively benefit the environment and human health.
The second problem this research investigates is the cost of PE
production. As fossil fuel prices increase, the cost of PE also rises. The
idea of a bio-based plastics from natural sources such as ethanol has been
hypothesized and has resulted in successful production of polyethylene in
the 1980’s [2]. As fossil fuels become depleted and prices increase, there
will be a shift towards a sustainable bio-based plastic production. The
Petrochemical company, Brasken, located in Sao Paulo Brazil is currently
implementing large-scale productions of biologically-derived
polyethylene from sugar cane [3].
ABSTRACT
INTRODUCTION Ethanol ([3] bio-derived from sugar cane or corn) can be converted into ethylene, through a
simple dehydration reaction (Mechanism 1.) Ethylene is formed by adding an excess of
concentrated sulfuric acid [4]. The optimal temperature for this reaction is 170°C [4]. Once
ethylene is created via dehydration from ethanol, the process of polymerization can occur. Two
different densities of polyethylene can be synthesized. Low density polyethylene (LDPE) and
high density polyethylene (HDPE). LLDPE has high molecular branching due to the lack of
specificity of a free-radical reaction (Mechanism 2.) LDPE polymerization occurs optimally at
temperatures around 200°C, pressure of 2000 atmospheres, with limited amounts of oxygen to
act as the initiator [4]. A high pressure apparatus is required for LDPE synthesis. HDPE
polymerization occurs under distinctively different conditions compared to LDPE. HDPE
polymerization occurs at a temperature of 60°C, 2-3 atmospheres of pressure with the use of a
Ziegler-Natta catalyst. The Ziegler-Natta Catalyst is titanium(III) chloride used in tandem with
triethyl aluminum. This catalyst system is used to polymerize terminal alkenes (Mechanism 3).
Unlike LDPE, HDPE is not polymerized by a free-radical reaction. The efficient catalyst
allows for very few branching, this leads to plastics with higher densities and melting points.
REACTION SCHEMES
• [1] Tsiropoulos, I. (03/01/2015). Journal of cleaner production: Life cycle impact assessment
of bio-based plastics from sugarcane ethanol. Elsevier.
• [2] Kikuchi, Y., Hirao, M., Narita, K., Sugiyama, E., Oliveira, S., Chapman, S., . . . Cappra,
C. M. (2013). Environmental Performance of Biomass-Derived Chemical Production: A Case
Study on Sugarcane-Derived Polyethylene. J. Chem. Eng. Japan / JCEJ J. Chem. Eng. Japan
Jcej JOURNAL OF CHEMICAL ENGINEERING OF JAPAN, 46(4), 319-325.
• [3] Dijkmans, T., Pyl, S. P., Reyniers, M., Abhari, R., Van Geem, K. M., & Marin, G. B.
(2013). Production of bio-ethene and propene: alternatives for bulk chemicals and
polymers. Green Chemistry, 15(11), 3064-3076. doi:10.1039/c3gc41097h
• [4] Polymerisation of alkenes. (n.d.). Retrieved February 20, 2016, from
http://www.chemguide.co.uk/organicprops/alkenes/polymerisation.html
• [5] Poly(ethene). (n.d.). Retrieved February 20, 2016, from http://www.greener-
industry.org.uk/pages/poly(ethene)/7_polyethene_PM_2.htm
Biologically derived polyethylene reduces greenhouse gas emissions by 140%
compared to petrochemical derived polyethylene [1] (Figure 2). Bio-PE
production significantly increases human health and ecosystem quality
compared to pchem plastic production [1]. An assessment was conducted on
energy outputs such as electricity and heat as well as material outputs such as
ethanol and sugar cane to determine the effects PE has on human health and
ecosystem quality[1] (Figure 3). In addition to the environment and human
health benefits, there is no significant difference in plastic performance between
bio-PE or pchem-PE. Bio-LDPE and HDPE retain the same densities as
compared to their pchem counterparts. The density of LDPE is 0.92g/cm-3 while
the density of HDPE is 0.95g/cm-3 [4]. Figure 3 shows impacts of bio-HDPE on
human health and ecosystem quality compared to pchem HDPE production.
RESULTS
REFERENCES
Ethanol Dehydration Ethylene Polymerization Polyethylene
DISCUSSION
Overall, bio-PE reduces CO2 emissions and increases human health and ecosystem
quality. Note that CO2 is still produced through Bio-PE synthesis; CO2 is produced
through ethanol dehydration, polymerization and transportation [1]. The
performance of bio-PE is comparable to current PE synthesis methods. By using a
renewable source such as ethanol, bio-based plastics offer an competitive alternative
to pchem-based plastics in the presence of expensive or depleted fossil fuels. Bio-
based plastics retain enormous potential that can positively impact the environment
and human health in years to come.
MATERIALS & METHODS
Ti
Mechanism 3. Polymerization of ethylene using the Ziegler-Natta
catalyst
HumanHealth
[DALY/kgHDPE
HH EQ HH EQ
Bio-HDPE Pchem-HDPE
2.5E-04
2.0E-04
1.5E-04
1.0E-04
5.0E-05
0.0E+00
EcosystemQuality
[PDF-m2year/kgHDPE
O
2
4
6
8
10
Ethylene and ethanol
production
Polymerization, Energy and
Transportation
SE-C
Figure 2. GHG emission due to
polyethylene production through
naphtha cracking (fossil-PE) and ethanol
dehydration (bio-PE). Adapted from
Kikuchi et al [2].
Figure 3. Life cycle assessment of ethylene and ethanol
production with regards to transportation, energy usage and
polymerization. Adapted from Tsiropoulos et al [1].
Ti