A Review of the Chemical and Physical Mechanisms of the Storage Stability of Fast Pyrolysis Bio-Oils

........................................................................................................................ 1 1.0 Introduction .......................................................................................................................... 1 1.1 Storage Stability Problem.......................................................................... 1 1.2 Combustion Problems Caused by Aging or Excessive Heat...................... 5 2.0 Composition of Bio-Oils ........................................................................... 5 2.1 Organics in Bio-Oil .................................................................................... 6 2.2 Inorganics in Bio-Oil .................................................................................. 6 3.0 Probable Chemical Mechanisms of Storage Instability........................................ 11 3.1 Reactions of Organic Acids ..................................................................... 12 3.1.1 Esterification................................................................................ 12 3.1.2 Transesterification ....................................................................... 15 3.2 Reactions of Aldehydes........................................................................... 15 3.2.1 Homopolymerization.................................................................... 15 3.2.2 Hydration ..................................................................................... 16 3.2.3 Hemiacetal Formation.................................................................. 16 3.2.4 Acetalization ................................................................................ 17 3.2.5 Transacetalization ....................................................................... 20 3.2.6 Phenol/Aldehyde Reactions and Resin........................................ 20 3.2.7 Polymerization of Furan Derivatives ............................................ 21 3.2.8 Dimerization of Organic Nitrogen Compounds............................. 21 3.3 Sulfur-Containing Compounds ................................................................ 22 3.4 Unsaturated Organic Reactions .............................................................. 22 3.4.1 Alcohol Addition........................................................................... 22 3.4.2 Olefinic Condensatio ................................................................... 22 3.5 Oxidation................................................................................................. 22 3.6 Gas-Forming Reactions .......................................................................... 23 3.6.1 Carbon Dioxide............................................................................ 23 3.6.2 Hydrogen..................................................................................... 24 3.7 Insights to Be Gained from the Chemical Mechanisms of Aging.............. 24 4.0 Observed Chemical Reactions in Wood Distillates, Wood Smoke, and Bio-Oils............................................................................................................... 26 4.1 Wood Distillates ...................................................................................... 26 4.2 Wood Smoke .......................................................................................... 27 4.3 Bio-Oils ................................................................................................... 27 4.3.1 Aging ........................................................................................... 27 4.3.2 Esterification and Acetalization .................................................... 28 4.3.3 Hydrogenation ............................................................................. 29 4.3.4 Polymerization with Formaldehyde .............................................. 30 4.3.5 Air Oxidation................................................................................ 30