XXVI Congresso Nazionale della Società Chimica Italiana XXX Y000
Effects of biomass, temperature and thermochemical process on PAH
concentration in biochar
Janeth Tafur Marinos, Marco Ginepro, Vincenzo Zelano
Dipartimento di Chimica – Università di Torino; Via Pietro Giuria 5, Torino, Italia 10125;
janethalicia.tafurmarinos@unito.it
Biochar is the solid carbonaceous material produced by the pyrolysis of biomass for a variety of applications in the agro/environmental field (1). The thermochemical processes of biomass also produce a variety of organic compounds including PAHs, highly harmful compounds to man and to the environment.
The effects of biomass, temperature and type of process (pyrolysis and gasification) on 16 US EPA PAH concentration in biochar were investigated. To this end, 47 biochars were analyzed for their PAH content. 38 of them were produced in laboratory furnace, in highly controlled pyrolysis conditions, from 11 biomasses of which 7 were of wood (beech, chestnut, pine, poplar, spruce pine, commercial conifer, and pruning from fruit tree and grape vine) and 4 of grass (thistle, giant cane, rice straw and miscanthus leaves). The temperatures of pyrolysis were 350, 550, 750 and 1000 °C. In addition, 6 biochars were produced in industrial plants of pyro-gasification or pyrolysis. These plants were fueled with six of the biomasses used in the laboratory pyrolysis (spruce pine, conifer, pruning, thistle, giant cane and rice straw). Finally, 2 biochars (named STG and SPG), produced in a small experimental plant of gasification, and a biochar commercially available were considered. For the latter the production conditions were not known.
Examining the sum of the concentrations of 16 PAHs (Σ16PAH) of each laboratory biochar, it can state that the type of biomass (wood or grass) does not affect the Σ16PAH, but this Σ16PAH depends on single biomass. Although the highest Σ16PAH values related to the type of biomass were found at 350 °C for wood biochars and 550 °C for grass biochars. The Σ16PAH at the highest temperatures studied (750 and 1000 °C) were always lower than values of the other temperatures. Other interesting considerations that can be made concern single PAHs trapped on biochar at 350, 550 and 750 °C. For instance, all 16 PAHs were present at 550 °C except acenaphthene, and naphthalene and phenanthrene were found to be the most common and abundant PAHs. The process (pyrolysis or gasification) influences on the concentration of PAHs in biochar, however, the design of the reactor used and the working temperature are also important. The fact that the produced gas passes through or not the char bed to exit from reactor is an important factor. The lab. pyrolysis, in which the produced gas is continuously brought away by inert gas, gave biochar with Σ16PAH lower than pyro-gasification, in which the syngas passes through the char bed. For example, Σ16PAH were 455 and 3989 μg/kg for lab. pyrolysis and ind. gasification biochars, respectively. In this study the ind. pyro-gasification biochars were generally characterized by PAHs that did not include those with MW > 228 uma, unlike the biochar from ind. pyrolysis that contained 15 of the 16 US EPA PAHs. Considering the TEC (toxic equivalent concentration) values, the ind. pyro-gasification biochars investigated are suitable for their potential use as soil amendments. In conclusion, it can be said that to produce biochar with lower PAH content is necessary choose the suitable parameters concerning the feedstock, temperature, process and design of the reactor.
Reference: 1. M. Ghidotti, D. Fabbri, A. Hornung, Profiles of Volatile Organic Compounds in Biochar: Insights into Process Conditions and Quality Assessment, ACS Sustain. Chem. Eng. 5 (2017) 510–517. doi:10.1021/acssuschemeng.6b01869.
XXVI Congresso Nazionale della Società Chimica Italiana XXX Y000
