Abstract

In this study, we performed fast pyrolysis, catalytic fast pyrolysis (CFP), and catalytic hydropyrolysis (CHP) of cotton gin byproducts (CGB) to investigate their conversion into hydrocarbon-rich liquid fuels and high-value aromatic chemicals. Five CGB fractions (CC1, CC2, SM, TM, and FCGB) were collected from different stages of cotton ginning operation and characterized by proximate, ultimate, and higher heating value (HHV) analysis. The feedstocks contained 41.5 44.8 wt.% carbon, 54.2–58.5 wt.% volatile matter, 6.0–15 wt.% ash, and higher heating values of 15.2–16.8 MJ kg⁻¹. All pyrolysis experiments were performed using a Pyroprobe 5200 coupled with GC-MS/FID, while catalyst loading, hydrogen pressure, metal loading, catalyst morphology, feedstock pretreatment, and operating conditions were systematically investigated. Non-catalytic fast pyrolysis of these fractions produced carbon yields of 1.3 2.3%, dominated by oxygenated compounds such as acids, aldehydes, ketones, and esters. SM-CGB, which exhibited one of the highest fast pyrolysis carbon yields (2.3 C%) together with a high carbon content (44.6 wt.%), the lowest ash content (6.6 wt.%), and the highest volatile matter (58.5 wt.%), was selected for all subsequent catalytic experiments. Catalytic Fast Pyrolysis with HZSM-5 increased hydrocarbon yield from 3.0 C% at a catalyst-to-biomass ratio of 1:1 to 11.4 C% at a catalyst-to-biomass ratio of 10:1 and shifted product selectivity toward BTX-range aromatics. During CHP, hydrocarbon yield increased with hydrogen pressure and reached a plateau of 7.7–7.8 C% between 7 and 17 bar before declining to 5.8 C% at 21 bar. Nickel-doped HZSM-5 reduced hydrocarbon yield as loading increased, from 7.8 C% with no nickel to 2.8 C% at 5 wt.% nickel but suppressed the formation of polycyclic aromatic hydrocarbons (PAHs). Adding molybdenum to a fixed nickel loading increased hydrocarbon yield to a maximum of 8.6 C%, which occurred when the Ni and Mo loadings on the HZSM-5 were 3 wt.% and 9 wt. Mo respectively. Response surface methodology using a Box–Behnken design identified significant effects of temperature, hydrogen pressure, and catalyst-to-biomass ratio on hydrocarbon yield (R² = 77.08%, p < 0.001). The model predicted a maximum hydrocarbon yield of 8.5 C% at 517°C, 17 bar, and a catalyst-to-biomass ratio of 6, which was experimentally confirmed at 8.6 C%. Warm-water washing of SM-CGB reduced ash content by approximately 50%, from 6.6 to 3.3 wt.%, and increased hydrocarbon yield under these optimal conditions to 11.2 C%. Washing of the samples did not change product selectivity. Replacing conventional HZSM-5 with a flower-like hierarchical HZSM-5 catalyst lowered total hydrocarbon yield (4.4 vs. 5.7 C%) but shifted product distribution toward heavier aromatic species, including C9+ aromatics and PAHs. These findings show that CGB can be converted into hydrocarbon-rich liquid fuels through catalytic hydropyrolysis, and that feedstock pretreatment, reaction conditions, catalyst composition, and morphology each provide distinct ways to improve yield and product quality from this underutilized agricultural residue.

Date of publication

8-2026

Document Type

Thesis

Language

english

Persistent identifier

http://hdl.handle.net/10950/5134

Committee members

Fernando Resende, PhD., Zishu Cao, PhD., Mohammad R. Biswas, PhD

Degree

Master of Science in Mechanical Engineering

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