Energy And Greenhouse Gas Assessment Of Biodiesel Made From Food Waste Oil Based On Chemical Catalysis

Shortage of fossil energy and global warming has brought great challenge to human's existence and development. Developing bioenergy is an important measure to relieve energy's tension supply and global warming. Biodiesel as a biological liquid fuel which can be directly used in vehicles substituting petroleum diesel, its development is attached widely importance by a lot of countries. Biodiesel is not naturally existed, and processes of obtaining and processing of feedstock, trans-esterification for biosiesel are along with fossil energy consumption and greenhouse gas emissions. To analyze the life cycle energy consumption and greenhouse gas emissions of biodiesel is of important meaning to assess the sustainability of the development of biodiesel scientifically. China has a huge number of populations, agricultural land is relatively in shortage, agricultural products like vegetable oil mainly depends on import, and production of biodiesel directly by vegetable oil is of great threat to China's food security. Waste oil is the main feedstock for China to produce biodiesel. The present paper by using the life cycle assessment theoty, making 1 MJ of biodiesel as the unit function, analyzed the life cycle energy consumption and greenhouse gas emissions for biodiesel made from food waste oil by chemical catalysis in China. The results shows: producing 1MJ biodiesel, the life cycle total energy consumption is 1.3756MJ, life cycle total energy efficiency is 72.7%, life cycle fossil energy consumption is 0.3398MJ, fossil energy ratio is 2.94, life cycle global warming potential (GWP) is 29.2487 gCO2eq; comparing to petroleum diesel, life cycle fossil energy consumption and GWP of biodiesel have reduced by 76.42%and 62.74%respectively, energy output by unit fossil energy consumption is 3.94 times of petroleum diesel, so developing biodiesel plays a positive role to reduce fossil energy consumption and mitigate global warming; the life cycle emissions of CH4and N2O are 10.65 and7.24 times of petroleum respectively, and the great proportion of the use of coal in the production of biodiesel is the main reason for the rising of life cycle emissions of CH4 and N2O; the stage of trans-esterification for biosiesel causes the most energy consumption and greenhouse gas emissions in the life cycle, and promoting trans-esterification technology, reducing feedstock, methanol and steam consumption is the key to lower the life cycle energy consumption and greenhouse gas emissions; after allocation, life cycle energy consumption and greenhouse gas emissions all reduced by 5%, so strengthening byproducts'recovery and integrated use help to lower life cycle energy consumption and greenhouse gas emissions.