Although some scientists have criticized the accuracy of the amino acid process when used on bones, the researchers say it works on ostrich egg shells because they are less porous than bone and thus more resistant to groundwater and other changes.
The enzymatic process entails greater GHG emissions than the dilute acid process owing to the large quantity of electricity consumed during enzyme manufacture, even though the dilute acid process has a somewhat lower ethanol yield.
The parameters with the greatest influence are the emissions factors for electricity, enzyme manufacture, biomass production, and, in the case of the dilute acid process, sulphuric acid.
The major drawback to these acid processes is the cost of acid and the requirement to neutralize the acid after treatment.
The approach is illustrated by reference to the sulphuric acid process.
The large quantity of electricity consumed during enzyme manufacture suggests that enzymatic conversion processes may give rise to greater greenhouse gas emissions than the dilute acid conversion process, even though the dilute acid process has a somewhat lower ethanol yield.
The acrylic acid process using air oxidation of propylene presents many interesting design trade-offs, particularly in the design of the reactor.
In the long run, cellulosic enzyme technology should provide cost reductions four times greater than the sulfuric acid process.
