Economic analysis of enzyme recycling during enzymatic hydrolysis of sugar beets for soluble sugars production

Enzymatic hydrolysis of sugar beets is an efficient alternative to conventional hot water extraction where overall soluble extraction is valued. The economic analysis of a sugar beet soluble sugar production plant was designed and developed using SuperPro Designer software. The commercial scale operation was sized to process 100 million metric ton (MT)/day of sugar beets. The base case process includes transportation, grinding, thermal pretreatment, enzymatic hydrolysis, solid–liquid separation, and evaporation. The final product from the model was assumed to be a sugar syrup stream at 65% total solids content. Since the breakeven selling price was sensitive to the cost of enzymes, alternative scenario A added an ultrafiltration unit operation to separate the enzymes and reuse them in subsequent batches of hydrolysis. Steam was another major contributor to the operating cost. Alternative scenario B included a natural gas boiler to generate steam from biogas produced from a co-located dairy manure digester. The breakeven selling price of the sugar syrup from the base case, alternative scenario A, and alternative scenario B were $965, $911, and $955 per metric ton, respectively. Sensitivity analysis showed that the breakeven selling price is sensitive to the raw material cost, especially for the pectic enzymes.