Session: 08-03-01: 4E Analysis and Optimization of Thermodynamic Systems

Paper Number: 69292

Start Time: Wednesday, 05:10 PM

69292 - Methods of Dealing With Co-Products in a Life-Cycle Assessment of Biodiesel Fuel Produced From Waste Cooking Oil 

METHODS OF DEALING WITH CO-PRODUCTS IN A LIFE -CYCLE ASSESSMENT OF BIODIESEL FUEL PRODUCED FROM WASTE COOKING OIL

Hannah Torres

Nelson Macken

Swarthmore College

Biodiesel fuel has received considerable attention as a more sustainable alternative to traditional fuel. This paper presents a life cycle assessment (LCA) for producing biodiesel fuel from waste vegetable oil (WVO).  Comparisons are made for different methods of dealing with co-products.

The LCA is a cradle to fuel model that includes the following unit processes: soybean farming, soy meal and soy oil extraction, processing of soy oil for the cooking industry, consideration of the net outflows from the cooking process, cleaning/drying waste oil and transesterification to produce useful biodiesel. In soybean farming, national historical data for yields, fuels (diesel, gasoline, LP gas, natural gas), and electricity for machinery and fertilizers (nitrogen, phosphorous and potassium) are considered. In soy oil extraction, extraction solvent (n-hexane), steam production using natural gas and electricity for machinery are considered inputs. Soy oil processing is modeled using alkaline refining followed by bleaching and deodorizing. Energy and material requirements for these operations are determined from the literature. In order to determine a mass balance for the cooking operation, food carry-out is determined. Data is obtained from typical users on oil amounts purchased and waste oil produced.  Waste oil is filtered and water removed. Energy requirements (fuel, electricity) for these operations are obtained from equipment manufacturers. Energy and material (primarily methanol) requirements associated with transesterification are also found from the literature. Transportation via diesel powered trucks to all sites is included. Metrics evaluated to determine sustainability include global warming potential (GWP) and cumulative energy demand (CED). Values are obtained using GREET1. We determine GWP as CO₂ equivalent (CO_2e) (kg, lb) and CED as (MJ, BTU)). The functional unit is the mass of biodiesel fuel (kg, lb).

Credits for additional products must be applied in the LCA. WVO is a byproduct of oil produced for cooking fried products. We account for oil consumed in the cooking process using two approaches. In the first approach, the WVO is considered a “free” product. This means only the CED and GWP associated with WVO transportation, processing and transesterification are included in the LCA. In the second approach, the amount of oil consumed in the cooking process is credited to the WVO. All the cooking oil is considered WVO. Other coproducts are considered applying two traditional methods used in LCA: mass-based allocation and displacement. In mass-based allocation, CED and GWP are adjusted considering the mass fraction of soymeal produced in soy oil production and the mass fraction of glycerin produced in the transesterification process. In the displacement method, soymeal is considered to displace soybeans as animal feed and glycerin displaces synthetic glycerin. The CED and GWP of the displaced products are subtracted as credits.

LCA results for the various approaches to co-products are compared. We demonstrate a wide range of results are possible. These results should provide useful information on the consideration of co-products in determining the sustainability of producing biodiesel fuel from waste vegetable oil.

Presenting Author: Nelson Macken Swarthmore College

Authors:

Hannah Torres Swarthmore College
Nelson Macken Swarthmore College