Researchers Convert “Green Tide” Macroalgae to Bio-oil
12 June 2010
Researchers at Fudan University (Shanghai, China) have converted the marine macroalgae Enteromorpha prolifera, one of the main algae genera for “green tide”—massive algal blooms caused by eutrophication of marine water bodies—to bio-oil by hydrothermal liquefaction in a batch reactor at temperatures of 220-320 °C.
Green tide, formed by green macroalgae, including Ulva sp. and Enteromorpha sp., has been one of the major marine environmental problems all over the world. An unprecedented scale of Enteromorpha prolifera green tide broke out in China’s Yellow Sea in Qingdao, Shandong province, during May and July, 2008.
A large number of drifting E. prolifera flocked to the shore, then became waste, and soon began to decay, resulting in negative effects to the coastal seawater quality and the ecological environment. Up to 1 million tons of algal waste was collected after the cleanup of E. prolifera; however, more algal waste was produced in the following waves of green tides (which have spread to the coast of Jiangsu province). Therefore, it is important to study how to achieve better resource use for algal waste to protect the environment.
—Zhou et al.
Their study, published online 11 June in the ACS journal Energy & Fuels, investigate the effects of the temperature, reaction time, and alkali catalyst (Na2CO3) on product yields were studied. The characters of liquid and solid products were analyzed using multiple analysis methods, such as elemental analysis, Fourier transform infrared (FTIR) spectroscopy, gas chromatography-mass spectrometry (GC-MS), and 1H nuclear magnetic resonance (NMR).
The hydrothermal liquefaction was performed using system consisting of a 250 mL GSH-0.25 zirconium cylindrical autoclave, an electrically heated furnace, a magnetic stirrer, a pressure holding circuit, and a controller. In a typical run, 20 g of E. prolifera powder, 150 mL of distilled water, and the desired quantities of Na2CO3 catalyst (0 or 5 wt %) were charged in the autoclave. Residue air was removed by purging with N2 for 5 min. The autoclave was pressurized to 2.0 MPa with N2. The operating temperature and reaction time are two important parameters for the hydrothermal liquefaction process.
A moderate temperature of 300 °C with 5 wt % Na2CO3 and reaction time of 30 min led to the highest bio-oil yield of 23.0 wt %. The higher heating values (HHVs) of bio-oils obtained at 300 °C were around 28-30 MJ/kg. The bio-oil was a complex mixture of ketones, aldehydes, phenols, alkenes, fatty acids, esters, aromatics, and nitrogen-containing heterocyclic compounds. Acetic acid was the main component of the water-soluble products.
Resources
Dong Zhou, Liang Zhang, Shicheng Zhang, Hongbo Fu and Jianmin Chen (2010) Hydrothermal Liquefaction of Macroalgae Enteromorpha prolifera to Bio-oil. Energy Fuels, Article ASAP doi: 10.1021/ef100151h
This isn't bad, but it really needs to go to the next step. Producing water-soluble products requires a separation process, with all the implied energy costs.
Adding hydrogen to de-oxygenate the products to alkanes and other insoluble compounds would increase the value and slash post-processing energy input. The question is what sort of catalyst is needed for this, and what is its cost (lifetime, regeneration expense, etc.).
Posted by: Engineer-Poet | 12 June 2010 at 09:34 PM