Research and Solutions: Making Biodiesel from Recycled Cooking Oil Generated in Campus Dining Facilities

Abstract

Made from vegetable oil, waste oil, or animal fats, biodiesel fuel is renewable and nearly carbon neutral; it requires little engine modification, and over time can reduce the United States' dependence on foreign oil. Over the past few decades, the production of biodiesel has increased significantly. Here at the University of Cincinnati (UC), biodiesel is being generated from fryer oil from campus dining halls to reduce diesel use and enhance sustainability on the campus. A secondary goal is to use this process as a real world classroom for students, K-12 teachers, and interested community members wishing to optimize conversion of waste cooking oil to biodiesel. The production of biodiesel at the UC is accomplished via transesterification, whereby waste fryer oil and methanol are converted, with the aid of the catalyst sodium hydroxide, to methyl esters, or biodiesel, and glycerol. The pretreatment, titration/pilot test, full-scale production, and purification processes are quantitatively described here, as are the estimated costs and potential uses of biodiesel on campus.

Esterification pretreatment of free fatty acid in biodiesel production, from laboratory to industry

“…Many studies have reported the production of biodiesel from waste oil feedstock with a few cited here to summarize the advantages and challenges of using waste oils [6][7][8][9]. The waste feedstock can range from used cooking oil from restaurants to animal fats from rendering companies.…”

“…However, it is not much practiced by the biodiesel producers due to the longer reaction time and lower yield [12]. Instead, the two-step conversion process: an acid-catalyzed esterification pretreatment to lower the FFA content followed by the traditional alkali-catalyzed transesterification [7], is widely used in both industry and laboratory. The acid-catalyzed esterification requires additional acid and methanol usage, but the majority of methanol can be reclaimed through a methanol recovery system, which is now commonly installed by biodiesel manufacturers.…”

Converting campus waste into renewable energy – A case study for the University of Cincinnati

“…For the pilot-scale system, waste cooking oil is collected from campus dining facilities and made into biodiesel in a 189 L (50-gal) batch reaction system. Biodiesel is made by the transesterification reaction between waste cooking oil and methanol with NaOH as the catalyst (Agnew et al, 2009). The production procedure consists of: (1) preheating waste cooking oil in the main reaction tank, (2) pre-mixing NaOH and methanol in the mixing tank, (3) adding the NaOH-MeOH mixture into the main reaction tank, (4) keeping the reaction going for 2.5 hr, (5) recovering the methanol by distillation, (6) separating biodiesel and glycerin by decanting after 24-hr settling time, and (7) water washing to purify the biodiesel.…”

“…The remaining methanol is recovered through distillation. A NaOH dose of 3.5 g/L is used to account for the amount of NaOH needed to neutralize the free fatty acids in the waste cooking oil, which is typically <2% by weight (Agnew et al, 2009). As a result, the annual biodiesel production for the entire campus would be 3712 L (982 gallons) with 269 L (71 gallons) of glycerin as a by-product (Table 1).…”

A Greener Alternative Titration Method for Measuring Acid Values of Fats, Oils, and Grease

“…For biodiesel, the AV should be less than 0.5 (mg KOH) g −1 to meet the specification in ASTM D6751 (“Standard Specification for Biodiesel Fuel Blend Stock (B100) for Middle Distillate Fuels” published by the American Society for Testing and Materials) in the US or EN 14214 (“Automotive fuels—Fatty acid methyl esters (FAME) for diesel engines—Requirements and test methods” published by the European Committee for Standardization) in Europe. FOGs with AVs less than 30 (mg KOH) g −1 are classified as yellow grease, otherwise as brown grease (Agnew et al, ; ASTM, ; Chai et al, ).…”