Research On Reaction Process Intensification Of Biodiesel Production

Due to the depletion of petroleum-based sources and environmental concern, alternative renewable energy sources have attracted more attention in many countries. Biodiesel is non-toxic, bio-degradable and can be used directly or blended with conventional diesel, without modification of current engine systems. Generally, biodiesel is produced by a batch stirred reactor via homogeneous catalysis, which needs a long time of reaction leading to low efficiency and batch production. Using homogeneous catalysts would bring new environmental issue, e.g. waste water that will not fit the philosophy of "Green energy" Besides, the feedstock of biodiesel plays an important role since the price of biodiesel is closely related to the feedstock. Therefore, seeking for low-price feedstock is significant for reducing the cost of biodiesel. production. Considering of these points, the main contents and novel results are as follows:(1) Intensification of biodiesel synthesis using zigzag micro-channel reactorsZigzag micro-channel reactors have been fabricated and used for continuous biodiesel production. The influences of main geometric parameters on the performance of the micro-channel reactors were experimentally studied. It has been found that the zigzag micro-channel reactor with small channel size and more turns produces smaller droplets which result in higher efficiency of biodiesel synthesis. Compared to conventional batch stirred reactor, the zigzag micro-channel reactor could get the biodiesel yield of 99.5% in residence time of 28 s. Besides, the energy consumption of micro-channel reactor was 1/3 of that originated by batch stirred reactor. These results indicate micro-channel reactors can be designed as compact mini-fuel processing plant for distributive applications.(2) Intensification of biodiesel synthesis using metal-foam reactorsAs the production volume of micro-channel reactor is low, it is necessary to design a new continuous reactor for synthesizing biodiesel. Here, the metal-foam reactor was firstly designed as a tool for continuous biodiesel production. Three types (20PPI,30PPI,50PPI) of metal foam reactors were evaluated according to the mixing result of methanol/oil. It has been found that the metal foam reactor with the higher pore density produces smaller droplets which result in higher efficiency of biodiesel synthesis. Compared with the batch stirred reactor and micro-channel reactor, the metal foam reactor (50PPI) exhibited lower energy consumption per gram biodiesel of 1.14 J g-1, only 1.69% and 0.77% those of micro-channel reactor and batch stirred reactor.(3) Synthesis of biodiesel catalyzed by Li-doped MgO catalystsThe Li-doped MgO catalysts were prepared by incipient wetness impregnation method and used for biodiesel synthesis. The Li/Mg molar ratios and calcination temperatures on the performance of catalysts were investigated. It has been found that the catalytic activity is improved by Li doping, which is attributed by the defects of MgO lattice. The active sites were leached into the reactants leading to the deactivation of catalysts, indicating more studies are needed to stabilize the catalysts for its large-scale application.(4) Transesterification of Pistacia chinensis oil for biodiesel catalyzed by CaO-CeO2 mixed oxidesCaO-CeO2 mixed oxides were prepared for producing biodiesel from Pistacia chinensis oil. The molar ratios of Ce/Ca and calcination temperatures of catalysts were optimized. It has been found the replacing of Ca2+ for Ce4+ would enhance the stability of catalyst due to the defects. After the fourth reuse, the biodiesel yield exceeded 80% yet. Interestingly, after calcination of the used catalyst, the biodiesel yield could still reached 91.1%, which is close to the level of fresh use.(5) Biodiesel production from waste cooking oil catalyzed by TiO2-MgO mixed oxidesMixed oxides of TiO2-MgO were used as solid catalysts to convert waste cooking oil into biodiesel. The preparation parameters such as Mg/Ti molar ratios and calcination temperatures were studied. The metal leaching was serious when using MgO as catalyst. However, the catalyst stability was improved by Ti addition. The optimal result was obtained as the Mg/Ti molar ratio of 1 and calcination temperature of 923 K. The biodiesel yield reduced as the reuse time increased. Nevertheless, the biodiesel yield could exceed the fresh use after regeneration, which might be attributed to its larger BET surface area, pore volume and average pore diameter. The mixed oxides catalyst, TiO2-MgO, showed good potential in large-scale biodiesel production from waste cooking oil.