Co-pyrolysis of the seaweed Sargassum and polystyrene was investigated as a potential source of renewable energy. Sargassum is a brown macroalgae, posing a large disposal problem for beaches worldwide, and polystyrene is the plastic least recycled in the U.S. Although macroalgae bio-oil cannot be directly used as a result of a high oxygen content and low heating value, co-pyrolysis of macroalgae with low-oxygen-content waste polystyrene can enhance oil quality. Pyrolysis of pure Sargassum was conducted to determine the temperature producing the highest percent oil (600 °C). Co-pyrolysis of four different mixture ratios of Sargassum and polystyrene (5, 15, 25, and 33% by weight) was then conducted at 600 °C. Feedstocks and pyrolysis products (liquid oil and water, gas phase, and solid phase) were characterized using elemental analysis, thermogravimetric analysis, gas chromatography, surface area and adsorption isotherm analysis, and nuclear magnetic resonance. Co-pyrolysis with polystyrene improved the quality and quantity of the oil compared to pyrolysis of Sargassum alone. The oil quantity increased, from 3% for Sargassum alone to 29% for a mixture of 67% Sargassum and 33% polystyrene. Co-pyrolysis improved the oil potential heating value and decreased its potential for producing air pollution when combusted, by lowering its nitrogen content. Co-pyrolysis produced a gas with up to 7% hydrogen and 30% methane, which can be burned as a fuel. Co-pyrolysis of Sargassum and polystyrene, therefore, shows promise as a method for generating fuel and reducing disposal problems.

Biomass renewable energy has become a major target of the Thailand Alternative Energy Development Plan (AEDP) since the country's economy is largely based on agricultural production. Rice husk (RH) is one of the most common agricultural residues in Thailand. This research aims to investigate yields and properties of biochar produced from copyrolysis of RH and plastic (high-density polyethylene (HDPE)) at different ratios, temperatures, and holding times. For both individual and copyrolysis, the temperature variation generated more pronounced effects than the holding time variation on both biochar yields and properties. For individual pyrolysis of RH, the maximum biochar yield of ∼54 wt % was obtained at 400 °C. A shift in temperature from 400 to 600 °C resulted in RH biochars with higher fixed carbon (FC) and carbon (C) contents by ∼1.11−1.28 and 1.06−1.22 times, respectively, while undetectable changes in higher heating values (HHVs) were noticed. For copyrolysis, obvious negative synergistic effects were observed due to the radical interaction between the rich H content of HDPE and RH biochars, which resulted in lower biochar yields as compared to the theoretical estimation based on individual pyrolysis values. However, the addition of HDPE positively impacted the FC and C contents, especially when 10 and 20 wt % HDPE were added to the feedstock. Besides, higher HDPE blending ratios resulted in biochars with improved HHVs, and >1.5 times improvement in HHV was reported in the biochar with 50 wt % HDPE addition in comparison with RH biochar obtained under the same conditions. In summary, biochars generated in this study have the potential to be utilized as a solid fuel or soil amendment.

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