| Diesel is a very complex mixture of hydrocarbons, the number of carbon atoms is generally between10to22. The hydrocarbons include paraffins, naphthenes, olefins, and aromatics. Development of human society will be constrained by energy shortage problem. Development of renewable, environmentally friendly, alternative green fuel has become an important topic for the21st century. Biodiesel (Fatty Acid Methyl Ester; FAME) is poor in low temperature fluidity and oxidation stability, and its heat value is9%-13%lower than that of petroleum diesel. It is a promising approach to derive renewable hydrocarbon fuel from waste vegetable oil or animal oil via fatty acid decarboxylation. The purpose of the present study is to explore hydrocarbon generation mechanism by polarizing the carboxy-terminal of soap with microwave radiation at different carbon chain length, unsaturation, metal salts, and hydrogen donor, and much precise control of the energy input of the microwave radiation. The pyrolysis products were analyzed by GC, GC-MS, HPLC, and FT-IR. A chemical reaction kinetics model about hydrocarbon formation was developed, and the decarboxylation mechanism of fatty acid salt was explored. This research will help to open up a new area of application in theoretical research for microwave chemistry. This approach not only possesses higher scientific value but also provide a theoretical basis for developing innovative technology of renewable hydrocarbons fuel production. It can guide the preparation of renewable hydrocarbon bio-diesel production through non-edible oil (Swida wilsoniana fruit oil; Sapium oil) pyrolysis decarboxylation.First, the pyrolysis characteristics of sodium stearate, sodium oleate, sodium laurate, potassium stearate, calcium stearate and Swida wilsoniana fruit oil soap were studied by means of TG/DTA PYRIS DIAMOND thermo gravimetric apparatus. The process was carried out with heating rates of10℃/min and final temperature of800℃under the atmosphere of nitrogen. The study of the pyrolysis characteristics and mechanism was to understand the pyrolysis process in-depth and to predict the reaction rate and easiness. The activation energy of Swida wilsoniana fruit oil soap was proven to be the lowest, andeasy for the decarboxylation reaction. The study provides a good reference for Swida wilsoniana fruit oil waste recycling and animal and vegetable grease pyrolysis device design, as well as process parameters optimization.Sodium stearate (C18) was chosen as a model compound, the carboxy-terminal of this di-polar molecular was further polarized with microwave radiation. The Lorentz force of ions or dipolar mole-cules were moved in accordance with the electromagnetic waves and contributed to the formation of car-banion, which effectively promoted the decarboxylation reaction. Glycerol possessing high dielectric constant were added which formed "High-temperature Locus" that lowed the activation energy of decarboxylation reaction and played a role as the hydrogen donor. The liquid products were analysed and the results showed C8-C20n-alkanes and n-alk-1-enes were arranged regularly which agreed with the principle of hydrocarbon pyrolysis. All the work proved the feasibility of deriving renewable hydrocarbon fuel from fatty acid sodium salt using microwave pyrolysis.Sodium stearate; Potassium stearate; Sodium oleate and Laurate sodium was chosen as model compounds, it was compared to study the pyrolysis mechaniam and the decarboxylation process with microwave radiation at different carbon chain length, unsaturation, metal salts, and hydrogen donor. The peak area of C15-C17n-alkanes and n-alk-1-enes were larger than the other three kinds of material. Because the carboxyl terminal of potassium stearate was kalium with atomic radius and polarity larger than sodium, the carboxy-terminal of this dipolar moleacular was further polarized with microwave radiation, the Lorentz force of ions of dipolar molecules were moved in accordance with the electromagnetic waves, contribute to the formation of carbanion, which effectively promote the decarboxylation reaction, moreover, the polarity of carboxy-terminal was stronger and stable and therefore easier for decarboxylation. The decarboxylation mechanism of sodium salts of fatty acid proved to be correct by another way in microwave radiation. Carbanion formation in the microwave pyrolysis reaction formed stable P-π conjugated system with the double bond of sodium oleate, which promoted the decarboxylation. Therefore, pyrolysis liquid yield of sodium oleate was the highest, the double bonds were harder to be cracked than the single bonds during pyrolysis decomposition, so the sodium oleate double bonds were kept in the liquid final product. At the same time, the existence of double bonds promoted the cyclization reaction. Pyrolysis liquid color of potassium stearate was translucent. Its density and dynamic viscosity were0.783±0.14g/cm3and1.02±0.12mm2/s, respectively, similar to gasoline. The density and dynamic viscosity for the other three materials were ranged0.810～0.875g/cm3and2.09-2.85mm2/s, respectively, also similar to petroleum diesel.Finally, sodium soap made from Swida wilsoniana fruit oil was chosen as a model compound with significant molecular polarity for preparing hydrocarbon fuel by microwave-assisted pyrolysis. The experimental results showed that:1) Both of the yield of the liquid pyrolyzate over the dry mass of the soap and hydrocarbon content of the liquit pyrolyzate was usually above70%. In addition, its dynamic viscosity and density are2.09-2.85mm2/s and0.850～0.875g/cm3, respectively, similar to prtrodiesel. The highest peak in the GC-MS profile of the liquid pyrolyzate of the soap is fifteen carbon alkenes, which indicated that using microwave heating technology, which may preferentially activate the polar partial of the soap molecular, can lead to the high selectivity of decarboxylation, which is the most significant thermochemical reaction in this experiment.2) The hydrocarbons content in the liquid product increased with the increase of the microwave power input.3) In addition with decarboxylation, carbon chain cleavage is very common in the process of sodium soap microwave pyrolysis, C-C single bond is easier to be destroyed than C=C double bond, the later mostly remained in the liquid pyrolyzate.4) Adding CaCO3, FeCl3, Kaolinite as catalyst respectively, have significant impact on both the yield of the liquid pyrolyzate and its hydrocarbons content, and their alkenes, alkanes and aromatics composition. |
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