Pyrolysis of urban pruning waste as a technological strategy to obtain valuable biomolecules

MUSCI, JUAN J.; LATORRE DAIANA C.; CHIOSSO M. EUGENIA; GIL, FELICITAS; NAVONE, MICAELA; CASELLA, MÓNICA L.; LICK, ILEANA D.

Congreso; WCCE11-11TH WORLD CONGRESS OF CHEMICAL ENGINEERING; 2023

There are numerous chemical and thermochemical processes that serve as an alternative for the revaluation and use of biowaste. Generally, these processes tend to optimize waste management, making a more efficient use of natural resources and promoting the development of circular economy. Naturally, the first point to optimize waste management is to reduce their generation. However, there are cases where the generation of waste cannot be avoided, for example, the seasonal generation of lignocellulosic biomass, from urban pruning that generates a high amount of waste. For an efficient use, strategies are required to reuse this waste, reintroducing it as a source of raw materials in production chains, in order to obtain more sustainable systems and promote the circular economy. In addition, it is worth mentioning that the planning of the use of pruning residues has the additional advantage of being selectively collected.Fast pyrolysis, heat treatment in the presence of a controlled (generally inert) atmosphere, appears in this context as a process capable of transforming biowaste into bioliquids rich in valuable molecules, many of which are considered platform molecules or building block molecules for the development of a lignocellulosic biorefinery . Although pyrolytic bioliquids have a complex and varied composition, made up of molecules from different families, one way to direct “a priori” the obtaining of a particular family of compounds is to carry out a pre-fractionation or chemical pre-treatment of the biomass to be pyrolyzed. This work shows the effect of pre-treatments with mineral acids (sulfuric acid and phosphoric acid) and with a base (KOH) on the yield and composition of bioliquids obtained from the pyrolysis of urban pruning waste from the city of Junín (Argentina). To meet the objective, various pretreatments of the biomass, dried and ground, were carried out. The concentration of the agent used was systematically varied (H2SO4 at 5 wt.%, H3PO4 at 2, 5, 10 and 20 wt.% and KOH at 2, 5, 10 and 20 wt.%). Preliminary experiences were then carried out using thermogravimetric techniques (TGA and TGA-FTIR) with the aim of obtaining information about the effect of pre-treatment on the thermochemical behaviour of depolymerization/degradation of polymer chains of sugars (hemicellulose and cellulose) and polyphenols (lignin) . From the results obtained, a temperature of 450°C was chosen to carry out the pyrolytic tests in a vertical fixed-bed reactor, fed with a N2(g) stream.During pyrolysis, a gaseous fraction (biogas), a solid fraction (biochar) and condensable gases are generated. From the latter , a bioliquid is obtained. In the case of the samples pre-treated with base, the maximum bioliquid yield was 29.33% with KOH at 5 wt.%, while with those pre-treated with H2SO4 at 5 wt.% and H3PO4 at 5 wt.%, higher proportions of bio-oil were obtained, 39.66 wt.% in the first case and 38.90 wt.% with phosphoric acid. The qualitative and semi-quantitative composition of the bioliquids was analysed by gas chromatography coupled to mass spectroscopy . As expected, the liquids obtained from pre-treated biomass contained a lower number of components than those obtained from untreated biomass. The acid pre-treatment promotes depolymerization reactions and subsequent dehydration of sugars, being furfural one of the main products obtained. On the other hand, basic pre-treatments generate an extraction/depolymerization of lignin, producing bioliquids richer in phenolic compounds such as 2,6-dimethoxyphenol.