BIOMASS PYROLYSIS LAB OVERVIEW Level: Grades 9-16 Estimated Time to Completion: 90 Minutes Prior Knowledge: Background Provided In this lab investigation, students will become familiar with pyrolysis, a method to fractionate biomass into solid, liquid and gaseous components under the influence of heat only. The lab allows the student to create three pyrolysis products consisting of: 1. The solid component, biochar, which may be used as a soil additive, or as activated carbon in absorption processes, or as solid fuel (charcoal). 2. The liquid component, pyrolysis oil, which can be directly used as replacement to #2 fuel oil or upgraded catalytically to be used as a transportation fuel. 3. The gas component, synthesis gas, consisting of hydrogen (H2), carbon monoxide (CO), carbon dioxide (CO2) and methane (CH4), which may be burned directly or catalytically converted to a liquid fuel. Upon completion, students will be able to: • Be able to create a simple pyrolysis unit. • Explain the process of pyrolysis and the resulting fuel forms. • Explain the potential advantages and disadvantages of pyrolysis. • Understand the impact of biomass types or temperature on the pyrolysis process. • Calculate mass yields of pyrolysis products. MATERIALS REQUIRED Meker or Bunsen burner Large glass test tube (thick borosilicate tubes work the best) Lab Balance Stopwatch Various Biomass Types and Forms Rubber Stopper Glass or Metal Tubing Matches or Lighter Type K Thermocouple (optional) NOTES TO INSTRUCTOR • Provide a variety of biomass types for the students to choose from including wood shavings, dried grasses, et cetera. Have the % moisture recorded from the biomass along with the literature value for the biomass. • Size reduced wood works well for this experiment and can be acquired from the size reduction lab. • Dense biomass such as wood chips or biomass pellets work better at transferring heat in the tube. Low density grasses tend to not pyrolyze the entire sample. • Have the students pyrolyze both a relatively dry (<10% moisture) and wet (20 – 30% moisture) sample to determine the double impact of moisture (change in mass content and decreased net energy content). • It is recommended that safety protocols are discussed before the lab and the importance of safety equipment to avoid burns or other fire hazards. Additionally, experiments should be conducted in a well-ventilated area such as a hood. • A student presentation on pyrolysis is available in the “Supporting Materials” folder of the downloadable lab package.
BIOMASS PYROLYSIS INTRODUCTION Pyrolysis has been practiced widely since the ancient times. The burning of wood into charcoal is an example of pyrolysis, and is still practiced in many parts of the world. Charcoal is produced by burning wood until complete carbonization, or pyrolysis, occurs. Complete carbonization is a process in which only carbon and inorganic ash are the products. As early as 1930s, various research has been done on the subject of pyrolysis. In its simplest term, pyrolysis is defined as a chemical process in which organic materials are heated and decomposed at very high temperatures in the absence of oxygen. The materials are usually biomass and agricultural wastes such as wood chips, corn husks, switchgrass and straws. The temperature of the pyrolysis process is usually around the range of 400 to 700°C. Generally, the three main types of pyrolysis are slow pyrolysis, rapid or fast pyrolysis, and pyrolysis in a medium. In slow pyrolysis, the biomass is usually heated for a long period of time at a temperature of around 400 °C. This process maximizes char formation due to the longer heating time. The carbonization of wood to produce charcoal is an example of slow pyrolysis. At the other end of the spectrum, the production of liquid biofuel and gas is maximized in fast pyrolysis. In this process, the biomass is heated rapidly at very high temperatures, sometimes as high as 1000 °C. . The by-products of the pyrolysis serve a wide range of applications. Depending on the parameters of the process such as temperature, furnace residence time and pressure, the by-products are different, although generally they still consist of 3 yields: solid, liquid and gas. In this lab we will attempt to produce all three through the application of high temperature.
Safety glasses must be worn at all times. No loose clothes or hair. Only perform experiments in a well-ventilated area (best done in a hood). Fire extinguisher should be present, but a box of baking soda or sand to pour on any excessive flames works best. • Pyrolysis apparatus will be hot after combustion. It is best to allow to cool for 10 minutes after each experiment and also use heat resistant gloves and tongs to handle samples. • • • •
PROCEDURE 1. Using a balance, determine the mass of an empty test tube (including the rubber stopper and tubing). This will be your tare weight. 2. Fill the test tube half full with biomass. 3. Determine the mass of the test tube half-filled with biomass (including the rubber stopper and tubing) and record. 4. From your determinations, calculate the mass of the biomass and record. 5. Clamp the test tube using the tube clamp. Use metal or fiberglass lined clamps as rubber clamps will smolder under heat. If you would like a recording of a relative temperature of the reaction place a type K thermocouple between the glass tube and the clamp. Position test tube approximately 10cm (4 inches) from the top of the burner. A picture of the assembly is shown below:
6. You are now ready to start the gasification. Have your instructor checks your setup before you light the burner and that you have your safety gear on. When you are ready and your instructor confirms it safe, light your burner. 7. Start your timer and reposition your burner if needed. The flame should just meet the bottom of the glass.
PROCEDURE (cont.) 8. Carefully record your observations throughout the experiment. Record the amount of time it takes for the gas to start to be released from the end of the tubing. You will see the gas begin to form in the test tube and eventually escape through the tubing. 9. Once a steady stream of gas is being produced, light a splint or match and hold it approximately 2 centimeters from the end of the glass tubing. 10. The gas will begin to burn. CAUTION: Hot gases and oil will be released from the glass tubing. Do not stand in front of glass tubing and keep hands, arms, and face away from this area. 11. Keep the burner lit for 2 minutes. Draw a diagram of what you see as the gas burns. 12. Turn the burner off and observe how long gas continues to be released from the tubing. Record this time. 13. Allow the apparatus to cool 10 minutes, using this time to record all observations. 14. Once the test tube is completely cooled, remove it from the ring clamp stand and determine the mass of the test tube (including the rubber stopper and glass tubing) and the mass of the remaining wood. 15. If time allows, repeat the previous steps using additional types or forms of biomass material or different temperatures. 16. Clean up your station and put away lab supplies as instructed.
DISCUSSION 1. Describe the process of pyrolysis you observed during these experiments.
2. How much of the biomass was lost as gas?
3. What impact did biomass type or pyrolysis temperature have on the experiments?