A Marine Waste Biorefinery.

Abstract

Biodiesel is a renewable alternative to ‘petro-diesel’. There is already an established, conventional production technology based on refined vegetable oils. However, this is always more expensive than producing petroleum-based diesel, mainly due to the feedstock cost. Use of a cheap, non-edible feedstock, such as waste shark liver oil (WSLO), would reduce the biodiesel production cost and make the process economically viable. WSLO is obtained by exposing sharks’ livers to the sun until they melt and collecting the oil produced. Sharks’ livers comprise 25-30% of their body weight. Historically, the discarded WSLO was used for waterproofing wooden boats. However, this application is no longer required, as modern boats are made of fibreglass. The excess WSLO derived from these discarded sharks’ livers has great potential for being further processed into valuable products, including biodiesel, squalene and omega-3 polyunsaturated fatty acids (PUFA), such as eicosapentaenoic (EPA) and docosahexaenoic (DHA). The glyceride components of the WSLO can be converted into biodiesel using existing biodiesel processing technologies, while the squalene, EPA and DHA may be extracted and sold as value-added products through biorefinery processes. This study investigated the production of fatty acid methyl ester (FAME) from WSLO using both acid (sulfuric acid, H2SO4) and base (sodium hydroxide, NaOH) catalysts. Due to the high levels of free fatty acids (FFA) in WSLO, homogeneous alkali-catalysed transesterification was less effective than the acid-catalysed process, resulting in a maximum WSLO to FAME conversion of only 40% after 15 min at a 60°C temperature, a 1.5 wt.% of NaOH catalyst and a 6:1 molar ratio of methanol to WSLO. The acid-catalysed transesterification of the WSLO was investigated, using Design of Experiments (DoE), by a response surface method. The acid-catalysed process achieved 99% FAME conversion during a 6.5 h reaction time at a 60°C temperature, a 5.9 wt. % of H2SO4 catalyst and a 10:3 molar ratio of methanol to WSLO. Saponification of WSLO for extracting squalene was also investigated using a DoE methodology to obtain the operating conditions for highest squalene extraction. The results showed 101.6 ± 1.3 % squalene recovery at the following operating conditions: a 5 min reaction time, a 9.9 wt. % of water loading and a 20:1 molar ratio of ethanol to oil. Aqueous silver nitrate (AgNO3) was employed for extracting EPA and DHA from fatty acid ethyl esters produced from the WSLO. The highest EPA and DHA recoveries achieved were 66.2% EPA and 83.4% DHA. These came from extractions using a 2 h reaction time, a mixing speed of 300 rpm, a 20°C reaction temperature, and a 50 wt. % of silver nitrate concentration. Techno-economic analysis was performed to assess the commercial feasibilities of acid-catalysed biodiesel production using WSLO and alkali-catalysed biodiesel production using refined vegetable oil (rapeseed oil). Aspen HYSYS-V9 was used to simulate both production types at plant capacity of 12,000 te/y and lifespan of 20 years. Net present values (NPVs) of US $34.8 and US $4.9 million were obtained for the acid-catalysed WSLO process and the alkali-catalysed vegetable oil process, respectively. The internal rate of return (IRR) was calculated to be 260% for the acid-catalysed process and 56% for the alkali-catalysed process. Therefore, the acid-catalysed process is more profitable than the alkali-catalysed process due to its higher IRR percentage. Sensitivity analysis was also conducted to show the effect of certain variables on the NPV of both biodiesel production types. It was concluded that the biodiesel selling price has more effect on the NPV than the glycerol variation price, whereas the triglyceride feedstock purchase prices have the largest influence on the NPV of the two processes.