Master of Engineering Science
Chemical and Biochemical Engineering
Maize is one of the most important agricultural products in terms of production, consumption, and economic importance. However, its contamination with mycotoxins, particularly deoxynivalenol (DON), frequently occurs around the world due to high humidity. This mycotoxin appears predominantly in grains associated primarily with pathogens such as Fusarium graminearum (Gibberella zeae) or Fusarium culmorum. This phenomenon, threatening both human and animal health, also affects the economy due to the disposal of large amounts of contaminated corn. The overall objectives of this study were to use thermochemical conversions (i.e. pyrolysis) for managing this seasonal waste by converting it into value-added industrial solid (bio-char), liquid (bio-oil) and gaseous products. The pyrolysis of vomitoxin-corn grains was carried out in a bench-scale batch reactor at temperatures between 450 to 650 °C with 15 to 20 °C/min heating rates and without carrier gas.
Pyrolysis resulted in the deterioration of deoxynivalenol (DON) from 5-7 ppm in raw corn grains to zero ppm in the treated biochar, making thermochemical conversion a promising method for industrial applications.
The effect of pyrolysis conditions, including temperature and heating rate, on the conversion of toxic corn grains, was investigated. The results showed the maximum bio-oil yield was achieved at 650 °C (47 wt.%). Bio-char and non-condensable gases were two other products with 28.6 wt.% and 24.5 wt.% yields, respectively.
Further, the chemical composition of the bio-oil was identified using Gas Chromatography-Mass Spectrometry (GC-MS) and quantified by High-Performance Liquid Chromatography (HPLC). The results showed that acetic acid and levoglucosan are the two major components in the bio-oil, which were measured to be 26 g/kg, and 13 g/kg of bio-oil, respectively. Both acetic acid and levoglucosan have potential applications in various industries, such as for the synthesis of polymers, solvents, and pharmaceuticals.
The bio-chars were analyzed using TGA for proximate analysis, FTIR for identification of significant functional groups, BET for surface area, SEM for measuring the development of the pores, and elemental analysis for CHNS content. Bio-char was upgraded by physical activation using a CO2 at 900 °C. Activation significantly increased the BET surface area of the bio-char from 3 to 419 m2g-1. The significant development of the pore structure was verified through SEM images. The performance of activated bio-char has been tested by utilizing three different model molecules, i.e. methylene blue, methyl orange, and ibuprofen. The results showed that adsorption capacity of the activated bio-char was similar to that of commercial activated carbons (CAC).
The gas composition from pyrolysis of corn was analyzed via micro-GC to investigate the potential use of gases as a renewable energy resource for combustion in engines or as for process energy recovery.
In this study, we demonstrated a successful process for eliminating DON from contaminated corn via pyrolysis, while producing value-added products.
Summary for Lay Audience
Maize (corn) has several applications for human consumption, animal feed, and ethanol production. However, contamination of corn with an ear mould in the areas with high humidity, turns this valuable cereal into a toxic product, which threatens both human and animal health, causing food refusal, vomiting, abdominal pain, and diarrhea. It also affects the economy due to large amounts of contaminated corn disposal. This phenomenon generally occurs in countries with humid climates, such as the United States, Europe, and Canada.
In this study, a thermochemical technology called pyrolysis was used to destroy the toxin and extract value from this wasted crop. Pyrolysis is the thermal decomposition of biomass, which occurs at elevated temperatures (300 to 700 °C) in the absence of oxygen. The products of this process, liquid bio-oil, solid bio-char, and gases, have many potential applications in the chemical, agricultural, and pharmaceutical industries.
The bio-oil is composed of many chemicals, such as acetic acid and levoglucosan. Acetic acid is used for the production of paints, adhesives, and coatings after separation from the bio-oil. Levoglucosan is an organic compound that can be used for the synthesis of polymers. Bio-char is a solid product, which is similar to charcoal and has high mineral contents. This product can be used as a soil amendment, an adsorbent for wastewater treatment and for air pollution control. Finally, the gases can be used for providing the required energy for the pyrolysis process, making it a more sustainable process.
Karami, Shokooh, "Slow Pyrolysis of Vomitoxin-Contaminated Corn in a Batch Reactor" (2021). Electronic Thesis and Dissertation Repository. 7687.