# HW3

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Homework Set 3

ChE 5551                                                    Due Tuesday Sept 28, 2010

Biodiesel Problem
Minnesota law requires that all diesel fuel sold in Minnesota must contain 2% biodiesel
starting in September 2005.
a. Biodiesel (the methyl ester of soy oil) is produced from soy beans by esterification of
the oil in the beans. Soy beans are 25% oil, 45% protein, and 30% carbohydrate and
fiber. The oil is the triglyceride of C18 fatty acids. Biodiesel is produced by
esterification of the triglyceride with methanol. How many gallons of biodiesel can be
produced from a bushel of soy beans? (Assume 60 pounds of soy beans per bushel
and that biodiesel has a density of 6 pounds per gallon).
b. Soy beans are dehulled, flaked, and the oil is extracted with hexane. The hexane is
removed, and the triglyceride is reacted with methanol in KOH. Excess methanol is
recycled. Glycerine and biodiesel are immiscible and separated. The hulls, protein,
and fiber are dried and palletized and sold as animal feed. Sketch the flow sheet of
this process.
c. A typical plant produces 25 million gallons per year. Soy beans cost \$8 per bushel,
biodiesel sells for \$2.50/gallon, soy bean meal sells for \$180/ton, and glycerine sells
for \$0.10/pound. What is the cash flow per gallon of biodiesel and per year, ignoring
capital and labor?
d. The plant requires 25 employees at \$50,000 per employee per year. Recalculate
income and profit including labor.
e. Natural gas costs \$250,000 per month and electricity \$50,000 per month. Recalculate
the income and profit including these utilities.
f. (ChEs only) Capital costs for construction of a plant are \$2/gallon year. What is the
payback period and discounted cash flow rate of return for a 25 million gallon per year
plant?

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