Lignocellulosic Biomass Pretreatment Using Gaseous Ammonia and Combinations with Hot Inert-Carrier Gases

Introduction

To achieve high yields of glucose and other products for use in biofuels and bio-based chemicals, lignocellulose must first be pretreated. The goal of pretreatment is to decrease the crystallinity of cellulose, increase the biomass surface area, remove hemicellulose, and break the lignin seal. Current pretreatments use liquid ammonia, dilute acid, organosolvents, and steam, among others. Each of these methods has drawbacks in its ability to effectively and efficiently pretreat and process lignocellulosic biomass.

Description of Technology

Michigan State University’s invention, Gaseous Ammonia Pretreatment (GAP), uses hot ammonia gas rather than liquid ammonia to pretreat biomass in a reactor. The hot ammonia gas condenses on the biomass and reacts with the water that is used to wet the biomass prior to adding the ammonia gas. During the GAP process, the raw biomass is more uniformly treated by ammonia and requires much shorter pretreatment time. Therefore, this method has the potential to be a less expensive and more effective raw biomass pretreatment process. At present, pretreatment cost is considered one of the primary bottlenecks for the development of biorefinery technology.

Key Benefits

Faster pretreatment time: Using the GAP process, it is possible to rapidly reach the desired pretreatment temperature of 100-150 degrees Celsius instantly, thereby reducing the biomass residence time to 5-15 minutes in total. Ammonia in the delivery vessel is preheated and ensures condensation of hot ammonia gas on the raw biomass, causing an instantan rise in temperature.
Limited or no ammonia recovery: Use of hot gaseous ammonia along with hot steam and inert gas/air limits the need to recover ammonia as is required in other pretreatment processes. In competing processes, the ammonia recovery step is expensive in terms of time and energy costs.
Less temperature degradation of raw biomass: Current biomass pretreatments, such as dilute acid pretreatments, tend to “over degrade” the raw biomass due to higher temperatures.
Pretreatment residence time reduction: Competing processes can require long biomass residence time (hours to weeks), which are expensive and inconvenient to scale up.
No impact on downstream processing: GAP does not inhibit downstream processing of the raw biomass hence there is no need to wash the biomass to remove inhibitors.
Flexibility of GAP process: Potential exists for coupling the GAP process with other processes, such as the steam toasting process used in the edible oilseed and oilcake industry.

Applications