Analysis and Characterization of Metallic Nodules on Biochar from Single-Stage Downdraft Gasification

Tejasvi Sharma,Albert Ratner

doi:10.3390/pr9030533

Abstract

Biochar, which is a byproduct of gasification, is used in a wide range of fields such as water filtration, agriculture, and electronics, to name a few. The metals in the biomass were thought to end up either in the ash or distributed throughout the biochar. In this study, the goal was a more thorough characterization of biochar resulting from a single-stage downdraft gasifier. One of the first observations was that some metals actually localize into small (~25 micron diameter) metallic nodules on the biochar surface. Further analysis included ultimate and proximate analysis, Brunauer–Emmert–Teller (BET) analysis, and scanning electron microscopy X-ray spectroscopy (SEM-EDS). Biomass fuel included corn grains, soybeans, and wood pellets, with wood biochar showing the highest fixed carbon content, at 91%, and the highest surface area, at 92.4 m2/g. The SEM analysis showed that certain minerals, including potassium, phosphorus, calcium, iron, nickel, silicon, and copper, formed nodules with over 50% metal mass next to pores in the carbon substrate. Aluminum, chlorine, magnesium, and silicon (in certain cases) were mostly uniformly distributed on the biochar carbon substrate. Corn biochar showed a high concentration in the nodules of 9–21% phosphorus and up to 67% potassium. Soybean biochar showed a similar trend with traces of iron and nickel of 2% and 4.1%, respectively, while wood biochar had a significant amount of potassium, up to 35%, along with 44% calcium, 3% iron, and up to 4.2% nickel concentrations. A morphology analysis was also carried out.

Highlights

Today, 85% of the world’s energy is supplied using conventional fossil fuel, which releases 56.6% of anthropogenic greenhouse gas emissions [1]
Some studies have shown that the amount of fixed carbon increases with an increase in temperature and that most biochar fixed carbon content is in the range of 0–77% [49]
It was found that that some metals localize into small (~25-micron diameter) metallic nodules on the biochar surface

Summary

Introduction

85% of the world’s energy is supplied using conventional fossil fuel, which releases 56.6% of anthropogenic greenhouse gas emissions [1]. In addition to other renewable energy technologies, is one of the possible routes through which carbon-neutral energy can be produced. Gasification is a process that converts organic carbonaceous materials at high temperatures into fuel gas, heat, and biochar. There are several processes for producing biochar: slow pyrolysis, fast pyrolysis, and gasification [3]. Gasification is a state-of-the-art method through which energy is produced from biomass [4]. The advantage of this process over others is that it produces syngas composed of H2 , CO, CO2 , and CH4 , which can be used for energy and fuel. The highest biochar conversion rates so far are 35% using slow pyrolysis, 12% using fast pyrolysis, and about 10% through gasification. The lower percentage is due to the presence of a higher presence of oxygen and air [4,5,6,7]

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