| Biodiesel is a mixture of long-chain fatty acid esters derived from the transesterification of various animal fats or vegetable oils with short alcohols. It has three advantages of superior renewability, cleanness, and safety, thereby attracting considerable attention of government in countries around the world, biodiesel contains a relatively high content of high-melting point saturated fatty acid methyl esters (FAMEs); these are easy to crystallize and gel at low temperatures, causing the fuel pipe and filter of the diesel engine to be blocked, and cannot be used in the bus. Thus, the poor cold flow property is the major technical obstacles confronting the promotion and application of biodiesel.In this work, waste cooking oil was used to prepare the waste cooking oil biodiesel(BWCO). Blending with diesel, adding pour point depressants, formulation, and mixed depression methods are comprehensive utilized to improve the cold flow properties of biodiesel. Also, viscosity-temperature curves, differential scanning calorimetry (DSC),polarized optical microscopy (POM), and low-temperature X-ray diffraction (XRD) were used to explore the performance mechanism for enhancing the cold flow property of biodiesel.To further improve the biodiesel low temperature fluidity, promote the use of bio-diesel scale,ease the energy and environmental problems, lay the theoretical basis. The results of the present investigation are expected to be beneficial for further improving the cold flow property, promoting the utilization, easing the energy and environmental problems, and providing a theoretical basis.The specific contents of this paper are as follows:(1) A multifunctional integrated biodiesel reactor was developed for the production of high-quality biodiesel from waste cooking oil by using the transesterification reaction. The biodiesel yield reached the maximum of 97.3% under follow conditions: methanol to oil ratio,8:1; catalyst amount, 0.75%; reaction temperature, 65 ?; reaction time, 120min; stirring speed, 250 rpm/m. The CP, CFPP and PP of BWCO are 6?, 5?, and 4?.All the fuel properties, except for the oxidation stability, are within the EN142114 and ASTM D6751 limits.(2) The cold flow properties of biodiesel were improved by ternary complementary blending 0# petro-diesel (PD) and diesel from direct coal liquefaction (DDCL) with BWCO.PD and DDCL were firstly together introduced into BWCO to enhance the cold flow properties. The cold flow properties of BWCO-PD-DDCL ternary blends, and BWCO-PD,BWCO-DDCL binary blends were comparative evaluated. Ternary phase diagrams were used to present the blending effect on the CP, CFPP, and PP of biodiesel. In addition, to explore the performance mechanism, DSC and POM were used to observe the crystallization behavior and crystal morphology of blends fuel.(3) The depression effect of various pour point depressants on the BWCO was studied.The effective pour point depressant was mixed with usual surfactants or dispersants (Tween 20, 40, and 80; Span 20, 40, and 80; PEG 200, 400, and 800) in various ratios. Effects of the mixed improvers on the cold flow properties of biodiesel were studied. Also, the performance mechanism was explored by using the DSC and POM. PMA-Span 80 exhibited positive synergistic effects on depressing the CFPP of BWCO. For PMA-Span 80 mixed in 2:1, 0.5%addition in BWCO exhibited the best depression of 7 ? on CFPP. Such mixed improver in biodiesel effectively changed the crystallization behavior via transforming their shape and depressing the formation of large wax crystals, thereby delaying the formation of wax crystals and enhancing the cold flow property of biodiesel.(4) Mixed depression method was used to improve the cold flow properties of BWCO.The effects of PAO additions on the PP, CFPP, and CP of biodiesel/diesel blends are studied.Viscosity-temperature curves, DSC, POM, and low-temperature XRD were comprehensive utilized to explore the performance mechanism, and established theoretical model between PAO and biodiesel blends for enhancing the cold flow property of biodiesel. PAO is more sensitive to B20 than to others blends. The addition of PAO up to 0.04% decreased the CP,CFPP, and PP of B20 by 8 ?, 9 ? and 7 ?, respectively. PAO effectively delays the aggregation of wax crystals and modifies their crystallization behavior by transforming their shape and restricting the formation of large wax crystals, thereby exerting better cold flow properties in biodiesel blends. |
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