Question

Biodiesel fuel—a sustainable alternative to petroleum diesel as a transportation fuel—is produced via the transesterification of triglyceride molecules derived from vegetable oils or animal fats. For every 9 kg of biodiesel produced in this process, 1 kg of glycerol, C₂H₈O₃, is produced as a byproduct. Finding a market for the glycerol is important for biodiesel manufacturing to be economically viable. A process for converting glycerol to the industrially important specialty chemical intermediates acrolein, C₂H₄O, and hydroxyacetone (acetol), C₃H₆O₂, has been proposed.

                                                       C₃H₈O₃?C₃H₄O + 2H₂O

                                                       C₃H₈O₃?C₃H₆O₂+ H₂O

The reactions take place in the vapor phase at 325°C in a fixed bed reactor over an acid catalyst. The feed to the reactor is a vapor stream at 325°C containing 25 mol% glycerol, 25% water, and the balance nitrogen. All of the glycerol is consumed in the reactor, and the product stream contains acrolein and hydroxyacetone in a 9:1 mole ratio. Data for the process species are shown below.

Species	?H?f°(kJ/mol)	Cp[kJ/(mol?°C)]
glycerol(v)	-620	0.1745
acrolein(v)	-65	0.0762
hydroxyacetone(v)	-372	0.1096
water(v)	-242	0.0340
nirtogen(g)	0	0.0291

a) Assume a basis of 100 mol fed to the reactor and draw and completely label a flowchart. Calculate the molar amounts of all product species.

b) Calculate the total heat added or removed from the reactor (state which it is), using the constant heat capacities given in the above table.

c) Assuming this process is implemented along with biodiesel production, how would you determine whether the biodiesel is an economically viable alternative to petroleum diesel?

Answer 1