Enzymatic Hydrolysis Processes

This first process is an old approach to enzymatic hydrolysis from wood. It involves five essential steps. These steps have been modified through research and development but are not shown; only the basic elemental steps are shown.

  • Pretreatment of the cellulose-rich feedstock by removing the lignin usually through ball milling.

  • Production of cellulase enzymes by growing a cellulose-producing organism with the primary source of carbon coming from cellulose or other suitable cellulose-inducing carbohydrates. This process is aerobic and contaminant free.

  • Saccharification of the pretreated cellulose carried out by suspending it in the cellulase broth.

  • Fermentation of the sugar syrups in conventional batch or continuous fermentation processes. This step has been researched to include the fermentation of sugars produced from enzyme hydrolysis of lignocellulosic materials.

  • Recovery of the ethanol by stripping or extractive distillation processes.

    Schematic for basic process of enzymatic hydrolysis

    Schematic
    There is a process that simultaneously hydrolyzes cellulose to sugars and ferments the sugars to ethanol and side products. This system eliminates the need for a separate enzyme production vessel since the cellulolytic enzyme is produced and used in the same vessel. The thermophilic, anaerobic bacteria used in this culture system are Clostridium Thermocellum and Clostridium Thermosaccharolyticum.

    Schematic

    This process is very useful because a single organism C. Thermocellum is used to convert cellulose feed directly to ethanol with by-products. The other bacteria is used to make ethanol production more efficient from the first products. I do not know what the DOE knows of this process and how pure the ethanol process is but I suspect it is hard to control mass quantities of these bacteria and their media because of the ideal environment needed. With more research this process could prove to be very cost effective.

    A question to think about: What other factors might influence the production of ethanol from these bacteria?