No abstract

The economics of a process for the production of ethanol employing a hollow fiber extractive fermentor have been investigated. A computer simulation of the process incorporating a mathematical model of the fermentor was used to calculate the mass and energy balances. The results of the process simulation were read into a computer spreadsheet programmed with the economic calculations from which a final ethanol product cost was obtained. The process was found to be as competitive as conventional fermentation processes even at the currently high cost--$4/sq ft--of hollow fibers. It was determined that the 1986 price of 46.2 cents/L of ethanol produced by the process would be reduced by 1.8 cents/L for every $1/sq foot drop in the price of hollow fibers. A comparison of this process with conventional fermentation processes indicates that its potential savings lie in its ability to use a concentrated sugar feed, and the fermentor's increased productivity and ability to produce a concentrated ethanol stream which is removed by the extracting solvent.

In these two recent papers published in Biotechnology and Bioengineering we described the analysis of a novel approach for extractive fermentation, which we called the Hollow Fiber Extractive Fermentor (HFEF). Unfortunately, at the time of our writing we were not aware of two publications and a PhD thesis'-3 by G. T. Frank and K. K. Sirkar of Stevens Institute of Technology which described a similar concept. They provided both experimental behavior and a partial analysis of the HFEF concept. The major difference between the two approaches is that Frank and Sirkar immobilized the cells on wood chips. Our analysis indicates that with product inhibition minimized by solvent extraction significant cell densities should be achievable without cell immobilization. We apologize for this omis-