Development of Carbon-Based, Controlled-Release Soil Ameliorants Through Chemical Pathways

Stephanos Horvers, Institute for Chemicals and Fuels from Alternative Resources

Abstract

This thesis aimed to develop and validate the Carbon Control Technology (CCT®), a novel, patented process for converting waste agricultural residues into carbon-based controlled-release fertilizers (CBCRFs) through chemical carbonization followed by nutrient impregnation. The process involved treating lignocellulosic biomass with 93% sulfuric acid to produce a stable carbon matrix, subsequently neutralized with anhydrous ammonia to incorporate nitrogen. In partnership with Sulvaris Inc. and the Institute for Chemicals and Fuels from Alternative Resources (ICFAR), pilot-scale reactors were designed, improved, and operated, producing over 600 kg of CCT® material for field trials. These products demonstrated nitrogen contents of 15–17% and sulfur levels of 18–20%. The second phase of this work investigated how lignocellulosic composition influenced CBCRF properties. Chars derived from pine, spruce, coconut, and switchgrass were characterized using elemental analysis, FTIR, TGA/DTG, BET, SEM-EDX, and XPS. Switchgrass chars exhibited the highest porosity (423.97 m²/g) and surface oxygenation (COOH up to 13.51%), promoting nutrient loading but associated with lower thermal stability. Coconut chars, with high aromaticity (C-C/C=C 48.17%), offered greater structural durability but fewer reactive sites for nutrient binding. Pine and spruce chars provided a balance, with moderate porosity and oxygen functionality supporting both nutrient retention and controlled-release potential. Across all feedstocks, nutrient impregnation was successful: nitrogen contents of up to 4.59% (spruce) and sulfur up to 2.11% (coconut) were retained post-washing, with XPS confirming incorporation as quaternary nitrogen (NR₃⁺) and sulfonic (SO₃^-) groups. SEM-EDX showed uniform distribution of nitrogen and sulfur, while TGA/DTG analysis revealed that washed CBCRFs exhibited more gradual degradation profiles, consistent with chemical stabilization rather than mere physical adsorption. Collectively, these results confirm that the CCT® process effectively carbonizes diverse lignocellulosic residues and produces nutrient-functionalized matrices suitable for use as slow-release fertilizers, with structural and chemical traits tunable via feedstock selection and process conditions.