Pyrolysis of Woody Biomass Peter Fransham ABRI-Tech Inc.

Lecture Outline Introduction A few definitions Something about Wood Pyrolysis Technologies Challenges of Modelling Why is this important – applications

What are We Trying To Do Take the complex organic polymer called “wood” and shatter the polymer into smaller molecules Ultimately develop models that will help predict the chemical outcomes

Definitions Thermolysis – Thermal Decomposition of a substance – can be organic or inorganic. eg. Calcium carbonate to CaO and CO2. Pyrolysis – irriversable chemical change through heat and limited oxygen – what we are interested in. Not a new process. Egyptians used pyrolysis to make pitch for caulking boats over 2000 years ago. Destructive Distillation – an older term for pyrolysis. Estabilshed technology pre 1950 to produce chemicals. Petroleum industry killed “green chemistry”.

Cracking Petroleum Industry method for breaking long chain hydrocarbons into smaller and lighter ones. Stongly dependent on temperature and presence of catalysts Non-petroleum industry refers to any type of process that splits an organic molecule (eg wood). Also dependent on temperature, catalysts, and rates – ie very process dependent.

Structure of Wood Cell Structure contains the following: Cellulose – Long replicating chain Hemicellulose – more amorphous little structure Lignin – large complex polymer In rough numbers wood contains 52% carbon, 42% oxygen and 6% hydrogen Smaller percentages of nitrogen and chlorine

Cellulose Long chain Average MW 100,000 (C6H10O5)n 40%-50% of wood Polysaccharide - sugar Most abundant organic polymer on earth Crab and lobster shells exoskeletons are polysaccharide cellulose

Hemicellulose Heteropolymer Polysaccharide Differences between hardwood and softwood Average Molecular wt 30,000 15% - 25% of wood Important source of dietary fibre.

Lignin Complex polymer Aromatic alcohols (C31H34O11)n 63% carbon 6% hydrogen 30% oxygen 1% ash Provides structural support for the plant

Shattering the Polymer We want to do something with wood other than lumber and firewood Densify energy Liquids are easier to store and burn than chips, sawdust and round wood. Potential source of chemicals

Fast vs Slow Pyrolysis Very different outcomes depending on the heating rates. Graphic showing yield split for fast and slow pyrolysis

Quick Overview of Fast Auger Pyrolysis Concept of steel shot – dense phase, high thermoconductivity Biomass is rapidly incorporated into the hot ( C) steel shot and volatile matter is driven off. Heating rates are in the order of 1000C/sec for fast pyrolysis Vapours are condensed leaving non condensing gas Char is separated from steel shot.

Endothermic vs Exothermic Lots of debate over this concept. Also concept that pyrolysis may be exothermic but torrifaction and gasification are endothermic On a laboratory scale we can have enough instrumentation to determine the reaction heats On a commercial scale, parasitic loss and energy transfer in a dynamic environment makes the calculations difficult. Position of temperature probes and their reaction times can be cause a false interpretation.

Thermogravimetric 500 C LIGNIN HEMI C

500 C

Empirical Observations Temperature vs yield Include graphic

Where to Start with a Kinetic Model Go simple at the start Look macroscopically at the production of liquid, solid and gas. One dimensional analysis is much easier than two dimensional. Static is easier than dynamic.

Advanced Models Model cellulose, hemicellulose and lignin as separate entities. We know from TGA experiments that thermodecomposition occurs at different temperatures.

Why is This Important We need to predict the outcome of fast pyrolysis for design purposes. Whether the reactions are exo or endothermic impact on the reactor design and the design of the cooling/condensation system. If we have an accurate model we can simulate various production stategies to maximize certain compounds.

Ultimate and Proximate Analysis of Wood Differences in CHONS + ash between species and bark. Volatile matter and fixed carbon Variation in composition makes prediction difficult. Proximate analysis is a simple form of pyrolysis – volatile matter is driven off in an inert atmosphere leaving fixed carbon and ash behind. Proximate analysis give a general estimate of possible biooil production