2-04: A new low cost design for the AFEX™ process: application in distributed biofuel production systems

The ammonia fiber expansion (AFEX™) process is an effective and promising pretreatment for cellulosic biomass including grasses, crop residues and some woody materials.  AFEX™ uses little water and generates very few inhibitors, so high sugar concentrations are achievable.  However, AFEX™ scale up for commercial applications has been limited by the capital and operating costs of ammonia recovery.  We describe a new packed bed AFEX™ design in which ammonia is recovered directly onto the next batch of biomass, thereby enabling low capital and operating costs.  This new low cost design further enables distributed biomass processing systems, in contrast to the prevailing cellulosic biofuels paradigm in which all biorefinery operations are performed at a single central facility.  In contrast, distributed systems perform biomass size reduction, AFEX™ pretreatment and densification in local biomass processing depots (LBPDs), separate from the biofuel production facility.  Feedstock supply, contracting and logistics are greatly aided by this distributed system and the capital cost of the biorefinery is reduced significantly. Furthermore, the AFEX™ pretreated biomass is a potentially valuable cattle feed, thereby helping “jump start” the formation of feedstock supply chains and reducing the cost of pretreated biomass for the biorefinery.  System economics depend strongly on the animal feed value of AFEX™ pretreated biomass.  MBI International is currently scaling up the AFEX™ process for use in LBPDs under a $5.3 million project funded by the U. S. Dept. of Energy and the Michigan State University Foundation.