The Study On The Chemical Modification Of Shrimp Shell And Its Performance In Biodiesel Production

Biodiesel was renewable environmental-friendly fuel and excellent substitute of petroleum fuel. The study on biodiesel has important significance of relieving the crisis of energy sources and reducing environmental pollution. At present, most of the countries in the world have paid attention to biodiesel. Biodiesel can be synthesized from transesterification catalyzed by solid base under mild reaction conditions, and solid base catalyst shows high catalytic activity, a good prospect in avoiding the difficulty of products separation and purification and the problem of environmental pollution from the transesterification using homogeneous base in the traditional biodiesel production. Hence, the study on the synthesization of solid base catalyst and its performance in biodiesel production has an important significance in practices aspect.In order to resolve the problems which existed in the preparation of biodiesel catalyst at present, natural products shrimp shell was employed as raw material to prepare shrimp shell catalyst by incomplete carbonization of shrimp shell, loading modifier on the resultant and followed by activation for biodiesel production. The influence of different modifiers such as KF, KI, K₂CO₃, NH₄HCO₃ and NaNO₂ on the catalytic activity of shrimp shell catalyst was investigated, and it was fond that the catalytic activity of shrimp shell catalyst modified by KF or K₂CO₃ for the transesterification of rapeseed oil and methanol was relatively high. Hence, the influence of the preparation conditions on catalytic activity and its catalytic performance were further studied for shrimp shell catalyst modified by KF or K₂CO₃.For shrimp shell catalyst modified by KF, we investigated the influence of carbonization temperature, activation temperature, loading amount of KF and catalyst amount on the catalytic activity, and studied the influence of methanol/oil molar ratio and reaction time on the conversion. The results indicated that the optimum conditions of preparing shrimp shell catalyst were carbonization temperature at 450℃, loading KF of 25wt.% and activation temperature at 250℃. The transesterification rate of rapeseed oil to biodiesel reached 89.1% using the shrimp shell catalyst at reaction temperature 65℃with a catalyst amount 2.5wt.%, a methanol/oil molar ratio 12:1 and a reaction time 3h. The basicity of shrimp shell catalyst modified by KF was measured by the Hammett indicator method, and shrimp shell catalyst modified by KF was characterized by thermogravimetric analysis (TGA) and differential thermal analysis (DTA), scanning electron microscope (SEM), BET, X-ray diffraction (XRD), Energy Dispersive Spectrometer (EDS), Element Analyzer (EA) and Fourier transform infrared spectrometer (FT-IR). We explored the catalytic mechanism of shrimp shell catalyst modified by KF. Shrimp shell catalyst modified by KF possessed porous framework structure, catalytic active sites probably be -CH₂OK formed by the reaction of KF with incompletely carbonized shrimp shell and solid inorganic base formed by the reaction of KF with Ca₃(PO₄)₂ during the activation process.For shrimp shell catalyst modified by K₂CO₃, we investigated the influence of carbonization temperature, activation temperature, loading amount of K₂CO₃ and catalyst amount on the catalytic activity, and studied the influence of methanol/oil molar ratio and reaction time on the conversion using single factor method. The result indicated that when shrimp shell catalyst was prepared by carbonized at 450℃, loading 30wt. % of K₂CO₃ and activated at 300℃and the transesterification was carried out at reaction temperature 65℃with a catalyst amount 3.5wt.%, a methanol/oil molar ratio 12:1 and a reaction time 3h, the highest conversion of 97.9% can be achieved.For shrimp shell catalyst modified by KI, we investigated the influence of carbonization temperature, activation temperature, loading amount of KF and catalyst amount on the catalytic activity using single factor method. The result indicated that when shrimp shell catalyst was prepared by carbonized at 450°C, loading 30wt. % of KI and activated at 350℃and the transesterification was carried out at reaction temperature 65°C with a catalyst amount 2.5wt.%, a methanol/oil molar ratio 12:1 and a reaction time 3h, the highest conversion of 47.9% can be achieved.In the study, shrimp shell was employed as raw material to prepare catalyst for biodiesel production for the first time. The source of shrimp shell catalyst was abroad, the price of shrimp shell was low and shrimp shell was bio-degradable in the natural environment. Hence, shrimp shell catalyst has relatively high economic benefit and environmental benefit. In the experiment, we proposed a novel synthesize method of catalyst which was incomplete carbonization of shrimp shell, loading modifier on the resultant and followed by activation. Not only shrimp shell catalyst prepared by the method has high catalytic activity and good stability, but also the preparation processwas simple, unpolluted and has marked characteristic of green synthesis.