Alcohol Production from Spent Sulfite Liquor

Spent sulfite liquor (SSL) has been used as raw material for ethanol production for over 50 years (mostly in Sweden until WWII). Now, the world production is about 500 million gallons per year, and the only plant in the U.S. is in Bellingham, Wash. (8,000 gal. per day). The system is built around: 1) Recovery of the SSL from a screened blowpit; 2) preparation for fermentation by stripping out the toxic sulfur dioxide; 3) addition of yeast and fermentation in seven 80,000 gallon fermentors; 4) recovery of yeast for re-use in stainless steel centrifruges; and 5) recovery and purification of the alcohol by steam stripping in a five-column distillation process. Special care is taken to prevent contamination. Most of the present production comes from other raw materials; mainly molasses, rain, potatoes, and petroleum hydrocarbons. Synthetic alcohol, from ethylene, is the least costly to make and provides over three-fourths of the industrial ethanol. Even though, the SSL process has no raw material cost, it has the highest production cost due to low concentration of alcohol obtained and the consequently high cost of purification.

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