Influence of corn oil recovery on life-cycle greenhouse gas emissions of corn ethanol and corn oil biodiesel.

Zhichao Wang,Jennifer B Dunn,Michael Q Wang,Jeongwoo Han

doi:10.1186/s13068-015-0350-8

Abstract

BackgroundCorn oil recovery and conversion to biodiesel has been widely adopted at corn ethanol plants recently. The US EPA has projected 2.6 billion liters of biodiesel will be produced from corn oil in 2022. Corn oil biodiesel may qualify for federal renewable identification number (RIN) credits under the Renewable Fuel Standard, as well as for low greenhouse gas (GHG) emission intensity credits under California’s Low Carbon Fuel Standard. Because multiple products [ethanol, biodiesel, and distiller’s grain with solubles (DGS)] are produced from one feedstock (corn), however, a careful co-product treatment approach is required to accurately estimate GHG intensities of both ethanol and corn oil biodiesel and to avoid double counting of benefits associated with corn oil biodiesel production.ResultsThis study develops four co-product treatment methods: (1) displacement, (2) marginal, (3) hybrid allocation, and (4) process-level energy allocation. Life-cycle GHG emissions for corn oil biodiesel were more sensitive to the choice of co-product allocation method because significantly less corn oil biodiesel is produced than corn ethanol at a dry mill. Corn ethanol life-cycle GHG emissions with the displacement, marginal, and hybrid allocation approaches are similar (61, 62, and 59 g CO2e/MJ, respectively). Although corn ethanol and DGS share upstream farming and conversion burdens in both the hybrid and process-level energy allocation methods, DGS bears a higher burden in the latter because it has lower energy content per selling price as compared to corn ethanol. As a result, with the process-level allocation approach, ethanol’s life-cycle GHG emissions are lower at 46 g CO2e/MJ. Corn oil biodiesel life-cycle GHG emissions from the marginal, hybrid allocation, and process-level energy allocation methods were 14, 59, and 45 g CO2e/MJ, respectively. Sensitivity analyses were conducted to investigate the influence corn oil yield, soy biodiesel, and defatted DGS displacement credits, and energy consumption for corn oil production and corn oil biodiesel production.ConclusionsThis study’s results demonstrate that co-product treatment methodology strongly influences corn oil biodiesel life-cycle GHG emissions and can affect how this fuel is treated under the Renewable Fuel and Low Carbon Fuel Standards.

Highlights

Corn oil recovery and conversion to biodiesel has been widely adopted at corn ethanol plants recently
This study considers issues that arise in applying various co-product treatment methods to a corn ethanol facility that produces corn ethanol, distiller’s grain with solubles (DGS), and corn oil biodiesel, examining four potential techniques that avoid double counting of greenhouse gas (GHG) emission reductions, and allocates burdens appropriately between the facility’s two fuel products
Co‐product handling approaches and key analysis parameters In this study, we developed four approaches (Fig. 2; Table 1) to investigate how corn oil recovery influences the life-cycle GHG emissions of corn ethanol and corn oil biodiesel with the intention of avoiding double counting of the benefits of co-producing corn oil as a biodiesel feedstock

Summary

Introduction

Corn oil recovery and conversion to biodiesel has been widely adopted at corn ethanol plants recently. Wang et al Biotechnol Biofuels (2015) 8:178 of biodiesel could be produced from corn oil recovered from corn ethanol plants in 2022, compared to 2.5 billion liters of biodiesel that could be supported by domestic soy oil production [4]. This volume (2.6 billion liters) is nearly 70 % of the Energy Independence and Security Act mandated level of biomass-based diesel, which was 3.8 billion liters by 2012 [5]. Over 50 % of this volume was produced from soybeans [6] If it achieves a greater than 50 % reduction in lifecycle greenhouse gas (GHG) emissions compared to conventional diesel, corn oil biodiesel may be eligible to receive renewable identification numbers (RIN) under the Renewable Fuel Standard (RFS2). Under either structure (RFS2 or LCFS) it is important to have a GHG intensity (RFS2) or CI (LCFS) that is calculated with a life cycle analysis (LCA) technique that avoids double counting

Methods

Results

Conclusion