Graduate Studies


First Advisor

Sibel Irmak

Date of this Version



A THESIS Presented to the Faculty of The Graduate College at the University of Nebraska In Partial Fulfillment of Requirements For the Degree of Master of Science, Major: Agricultural and Biological Systems Engineering, Under the Supervision of Professor Sibel Irmak. Lincoln, Nebraska : August, 2019

Copyright 2019 Ozge Nayman Tiryaki


Aqueous-phase reforming (APR) of carbohydrate-based oxygenated compounds from renewable materials is a promising approach for gas biofuel, hydrogen production.

Hydrogen has the highest specific energy content of all conventional fuels and its only waste/byproduct is pure water, while hydrocarbon fuels produce massive amounts of carbon dioxide, a greenhouse gas. Currently, energy intensive process natural gas reforming is used as the most effective way to produce hydrogen. Approximately 3-5% of the world's natural gas is consumed to produce hydrogen for ammonia synthesis in production of fertilizer. Sustainable alternatives that produce hydrogen in higher yield and richer composition could significantly reduce the cost of hydrogen that can be used as fuel or reactant in many industrial processes.

Carbohydrates and their breakdown products can be efficiently converted to hydrogen-rich gas mixtures at relatively mild processing conditions by APR. Since carbohydrate fraction in corn kernel is high and consists of mostly one type of carbohydrate (mainly starch), corn kernels from excess corn production are promising materials for high yielding hydrogen gas production by APR. The objectives of this study were to investigate solubilization efficiency of various corn kernels (field corn, non-GMO field corn, yellow field corn, white field corn and popcorn) in subcritical water to prepare feed solutions for gasification process and evaluate gasification performance of these hydrolysates by APR based on hydrogen gas produced and carbon consumed in the process.

The corn kernels subjected to thermal treatment at various temperature in subcritical water resulted in optimum solubilization at 200 °C. Hydrolysis of various corn varieties at this temperature was in the range of 89-91%. The hydrolysates obtained from solubilization process were rich in organics with a 5,200-5850 mg/L total organic carbon concentration range. Gasification of the hydrolysates from different corn varieties produced the same amount of hydrogen gas with a yield of 130 mL/g corn on average. Evaluation of gasification results based on carbon balance showed that only small fractions of organic carbons converted to carbon-containing gaseous products (CO and CO2) and remaining carbons were precipitated as ungasified solid residue. Thus, gas mixtures produced from corn kernels were mostly composed of hydrogen (83%).

Advisor: Sibel Irmak