L11 Flashcards
What is biodiesel?
A non-toxic, biodegradable, combustible liquid fuel. It should be:
- Renewable
- Made from vegetable oils or animal fats
- The most diverse liquid fuel
- EPA classifies biodiesel as an advanced biofuel
- coming from vegetable oil = 1st generation biofuel
Oil feedstocks for biofuel
- Soybean oil
- Coconut
- Rapseed/canola
- Peanut
- Canola oil
- Sunflower oil
- Mustard oil
- Fish oil
- Cooking grease
- Reuse increases the energy return on energy invested
- Go local
- Be flexible
Oil palm
Fruits are 45-55% oil High yields per acre Destructive for rainforests - Decrease biodiversity - Decrease wildlife habitats
Canola / rapeseed
- Major commercial crop
- Temperate zone crop
- 127 gallons per acre, highest for conventional oilseed crop
- Largest global source for biodiesel feedstock
Used cooking oils
Big advantages
- Abundant, particularly in cities
- Inexpensive
- High EROI
Disadvantage
- High free fatty acid content from high and repeated heating
- Contamination with water, crumbs etc
- Requires extra processing steps to produce commercial biodiesel
Animal fat
Advantage
- Abundant
- Inexpensive
- High EROI
- Lower NOx levels than biodiesel from plant oils
Disadvantages
- High cloud point and poor cold-weather properties, but this isn’t a problem in warmer climates
What’s the oil
Combination of mono, di, and tri-acylglycerides
Oil extraction
Cold pressing: pressing without heating seeds first
Screw press: uses an auger to press seed into an increasingly narrow space, often surrounded by a screen. As the seed is compressed it cracked and increasing pressure forces oil to flow out of the seed.
Oil seed cake or meal
Solids produced by pressing oil seeds
- Cellulosic
- Calorific and high in fat
- Nutritional
Used in livestock feeds
- Limited by the high amount of oil
- Soymeal is especially valuable
Other uses
- Fertilizer
- Pelletized for combustion fuel
Making biodiesel: the trans-esterification reaction
A glyceride reacts with an alcohol in the presence of a catalyst forming fatty acid alkyl esters and glycerol (25 - 60 Celsius)
1 mol of TAG + 3 mol alcohol = 3 mol ester + 1 mol glycerol
Structures: Petroleum fuels
- Molecules are straight chain hydrocarbons of varying length
- — length determines fuel type
- — Some branched and cyclic molecules are also present
Biodiesel process overview
Draw diagram
Batch or continuous?
Small-scale conversion usually done by using a batch process
- A single container is used for entire process
- To make more, start a new batch
Continuous-flow process is often used at larger scales
- Different containers are used for each phase of the process
- Feedstock flows from one container to the next as the process continues
- Oil feedstock is continuously fed into one end of the process and finished biodiesel continuously flows out the other
Batch process
Draw diagram
- Each tank is drained as the material is moved to the next tank
- Allowing the next batch to be started
Continuous process
Draw diagram
- Inputs flow in continuously
- Products flow out continuously
- A second reactor ensures complete conversion of feedstock to biodiesel
