Influência de variáveis físico-químicas de biomassas lignocelulósicas e de processo pirolítico no rendimento de biocarvão e potencial de aplicação no sequestro de carbono

Abstract

Pyrogenic carbonaceous material (PCM) is an aromatic, amorphous, porous carbonaceous structure with high total carbon and fixed carbon on a mass basis, and low H/C and O/C atomic ratios. In case the H/C and O/C ratios meet the limits imposed by the international certification bodies “International Biochar Initiative-IBI” and “European Biochar Certificate-EBC” (H/C ≤ 0.7 and O/C ≤ 0.4) the PCM will be classified as “biochar”, which is a PCM with a degree of aromaticity and carbon content that has sufficient stability for soil application, with similarities to the dark soil portions of the Amazon, known as “Terras Pretas de Índio” (TPI). Fast pyrolysis is generally aimed at producing bio-oil, while PCM solid waste is traditionally intended for burning by direct combustion to produce heat and is generally used by the reactor at the beginning of the plant. Currently, “biochar” has been used for carbon sequestration in soil, as a climate change mitigation strategy, in addition to other environmental applications. There is a growing interest in PCM for applications in acidic soils. The objective of this thesis was, through a literature review on the subject, to outline an overview of the production of biochar by means of pyrolysis in Brazil and in the world (Papers I and II) and, based on data from 23 experiments in mainly slow pyrolysis reactors obtained from the literature (Paper III), and 40 experiments in fast pyrolysis reactors (circulating fluidized bed) produced at the University of the Basque Country, Bilbao/ Spain (Paper IV), to investigate interactions between chemical composition variables of biomass used with raw material, pyrolytic process variables and the yield of biochar (Paper III), and biochar, bio-oil and bio-syngas (Paper IV). The study also evaluated characteristics of biochars from different biomasses and operational conditions, as to the characteristics that confer stability to the material (resistance to microbiological degradation and weathering for ≥100 years), using criteria established by the IBI and the EBC. A decision tree is proposed (Paper V) for application to any group of biochars and to assess their potential for application in soil, based on chemical stability. The multivariate (exploratory) statistical approach proved to be useful in reducing the dimensionality of the set of original variables to a maximum of 2 or 3 independent latent variables (Principal Components 1, 2 and 3). These were sufficient to capture the maximum amount of information retained by the original dataset, as well as reveal interactions and relative influences in relation to the dependent variables (biochar, bio-oil and syngas yields). A set of 40 PCMs described in Paper IV was also analyzed, regarding the main certification parameters of international organizations IBI and EBC, using a developed decision tree. This procedure allowed the pre-selection of biochars with physicochemical characteristics indicating stability, thus justifying additional investment in chemical analyzes to determine their levels of contaminants. Based on the results, it is concluded that fast pyrolysis, as well as slow pyrolysis/carbonization, enables the production of biochars (albeit with a lower yield), which can be used in environmental applications, as long as they meet the requirements of the certifying agencies.