Brewer's Spent Grain to Xylitol & Polylactic Acid
With this project, the authors seek to present a desirable and novel process for converting brewers’ spent grain into two value-added products: the alternative sweetener, xylitol, and a biodegradable plastic, polylactic acid. This particular process is based in the Philadelphia Naval Yard, and uses the spent grain from surrounding breweries and microbreweries as its input. However, while the collection logistics and input quantity may change, the process is one that may be implemented anywhere, with varying degrees of success. The process consists of collection, universal pretreatment, then a split to feed one of two continuous fermenters. A highly acidophilic strain of the yeast Candida tropicalis ferments xylose into xylitol, which is then purified and pelleted in a marketable state. Lactobacillus delbrueckii bacteria ferments glucose into lactic acid, which is then polymerized to form polylactic acid of the desired molecular weight. This polymer is then purified and processed for sale. This product profile is optimal, as it incorporates both of the major constituents of the grain – cellulose and hemicellulose. Under the current market conditions, this process is expected to be financially desirable. We estimate a return on investment of 25.5%, with an internal rate of return of 30.95% and a net present value of $34.5M by 2032. However, if the price of polylactic acid were to rise, as market patterns suggest it may, this process could quickly become even more profitable. We therefore recommend pursuing the proposed process, and possibly expanding to other densely populated areas.