(485d) Evaluating Impacts of Carbon Taxes on the Economic Viability and Carbon Footprint of Plastic Production Pathways

Plastics are indispensable in modern society due to their exceptional functional properties of lightweight, good durability, and inexpensive production cost. Global production for plastics has reached 380 Mt in 2015, with a compound annual growth rate of 8.4% [1]. Most plastics used in our daily life are manufactured from fossil fuels, including petroleum, coal, and natural gas. For example, polyethylene (PE) is made from ethylene, which is produced from steam cracking of petroleum naphtha [2]. However, the reliance on the non-renewable fossil fuels will cause the problems of resource depletion [3]. Moreover, the use of fossil fuels will result in substantial greenhouse gas (GHG) emissions [4]. Therefore, several new production methods using renewable resources have been proposed to avoid the usage of fossil fuels [5–7].

A promising strategy to achieve more sustainable plastic production is to use biomass as feedstock, since this feedstock is renewable and can absorb carbon dioxide from the atmosphere [8]. Recently, researchers have successfully converted various biomass feedstocks to petrochemicals for further polymer processing [9–11]. For instance, Machado et al. demonstrated the process of propylene production from sugarcane [12]. However, most bio-based products are still not economically feasible nowadays. To address this problem, it is necessary to advance technologies for biomass conversion to increase product yields, which can make the production costs lower. Nevertheless, this requires significant time and effort and cannot be achieved over a short period of time. Another approach is to incentivize bio-based products through government regulations, such as imposing carbon taxes.

In this work, we propose an optimization formulation for determining optimal production pathways for various plastics from either fossil or biomass feedstocks. This problem is formulated as a network flow problem, where the total production cost is minimized. The nodes consist of raw materials, intermediates, products, and technologies. When materials are used as raw materials or processed in technologies, there are the associated costs and CO2 emissions. Our objective is to find out the production schedule with minimized total cost while satisfying the global demands for various plastics. At the same time, the total CO2 emission is calculated. We started with the analysis without the carbon tax imposed in the system as the base case scenario. In this scenario, most products are produced from fossil fuels in the optimized schedule. In addition, the contribution for CO2 emission from each plastic is calculated, and the most CO2 intensive product and intermediate are determined. Next step, we considered the imposition of carbon tax in the system. As a carbon tax is imposed, the feedstock of some plastics changes to biomass under the optimized production schedule, and the total CO2 emission decreases. Then, we increased the carbon tax to different levels and solved the optimization problem at the level. When the carbon tax increases to a certain level, carbon neutrality can be achieved. In other words, the net CO2 emission is zero under the optimized production schedule at the carbon tax rate. Since governments around the world are committed to achieve carbon neutrality by 2050 in order to attain the goals of the Paris Agreement, this work can be a preliminary guideline for policymakers to determine the carbon pricing system in their countries to combat global warming problem.

References

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