Biomasspyrolysisrefinery: Product Stability of Intermediates and Products

The BiomassPyrolysisRefinery is a dual step concept for biomass liquefaction and hydrogenation, intending production of liquid energy carriers. First step of this concept is liquid phase pyrolysis (LPP). During pyrolysis lignocellulose is dehydrated to form biochar and pyrolysis oil (Schwaiger et al., 2011, 2012) The LPP process has been scaled up to a capacity of 100 kg/h biomass (BDI bioCRACK facility) at OMV refinery Schwechat. The second step of the BiomassPyrolysisRefinery is product upgrading. Pyrolysis oil can pass a dewatering step to raise the calorific value. It may also be deoxygenated and hydrogenated. Biochar is separated from the heat carrier after liquid phase pyrolysis and then hydrogenated.

Figure 1: Stability of selected substances from liquid phase pyrolysis during storage at ambient temperature

During liquefaction biogenous material passes several heating and storing steps. Therefore sufficient chemical stability of intermediates and products is needed. Stability of pyrolysis oil for storing and upgrading purposes may be very limited (Fahmi et al., 2008; Kim et al., 2012), because of polymerization. The molar mass, viscosity and water content may rise significantly. The storing properties of liquid phase pyrolysis oil, upgraded liquid phase pyrolysis oil and liquified biochar at ambient temperature was monitored by GC-MS, GC-TCD, SEC and pH, and TAN analysis. Density and viscosity were recorded.

Figure 2: Liquid phase pyrolysis oil; molar mass versus storage time

Figure 1 shows the concentration of liquid key substances from liquid phase pyrolysis. During the first week of storage nearly one third of highly oxygenated substances vanish, afterwards degradation may cease. The same trend of property changes in the first days after pyrolysis is recorded with SEC-analysis. Figure 2 shows stabilization of molecular mass within day 15.

Figure 3: Viscosity and density at T = 20°C of liquid phase pyrolysis oil

Viscosity and density trends, shown in figure 3, confirm the findings. Liquid phase pyrolysis oil undergoes ageing through repolymerization within the first 15 days of storage. After upgrading stability of pyrolysis oil and liquified biochar is significantly better. Compared with flash pyrolysis oil the stability of liquid phase pyrolysis oil is seemingly achieved through separation from char based particulate matter and inorganics.

Fahmi, R., Bridgwater, A., Donnison, I., 2008. The effect of lignin and inorganic species in biomass on pyrolysis oil yields, quality and stability. Fuel 87, 1230--1240.

Kim, T.-S., Kim, J.-Y., Kim, K.-H., Lee, S., Choi, D., Choi, I.-G., Choi, J.W., 2012. The effect of storage duration on bio-oil properties. Journal of Analytical and Applied Pyrolysis 95, 118--125.

Schwaiger, N., Feiner, R., Zahel, K., Pieber, A., Witek, V., Pucher, P., Ahn, E., Wilhelm, P., Chernev, B., Schröttner, H., Siebenhofer, M., 2011. Liquid and Solid Products from Liquid-Phase Pyrolysis of Softwood. BioEnergy Research 4, 294--302.

Schwaiger, N., Witek, V., Feiner, R., Pucher, H., Zahel, K., Pieber, a, Pucher, P., Ahn, E., Chernev, B., Schroettner, H., Wilhelm, P., Siebenhofer, M., 2012. Formation of liquid and solid products from liquid phase pyrolysis. Bioresource technology 124, 90--4.