Abstract
This work investigates the non-catalyzed supercritical methanol (SCM) process for continuous biodiesel production. The lab-scale setup was designed and used for biodiesel production in the temperature range of 520–650 K and 83–380 bar with an oil-to-methanol molar ratio ranging from 1:5 to 1:45. The experiments were performed in the coiled plug flow tubular reactor. The volumetric flow rate of the methanol/oil ranged from 0.1–10 mL/min. This work examines a new reactor technology involving preheating and pre-mixing of the methanol/oil mixture to reduce setup cost and increase biodiesel yield under the same reaction conditions. Work performed showed that FAME’s yield increased rapidly with temperature and pressure above the methanol critical points (i.e., 513 K and 79.5 bar). The best methyl-ester yield using this reaction technology was 91% at 590 K temperature and 351 bars with an oil-to-methanol ratio of 39 and a 15-min residence time. Furthermore, the kinetics of the free catalyst transesterification process was studied in supercritical methanol under different reaction conditions.
Highlights
Nowadays, there is a necessity to look for more economical renewable fuels like biodiesel
FAE is fatty acid ester G is glycerol. r1, r2, r3, r4, r5 and r6 are reaction rates k1, k2, k3, k4, k5, k6, k7, k8 are reaction constants It was found that the critical process variables affected the conversion in the supercritical method: temperature, pressure, oil/alcohol ratios, residence time, and mixing and solubility parameters
At the same molar ratio, temperature (520 K), and residence time, the fatty acid methyl ester (FAME) yield increased from 15% (83 bar) to 49% (380 bar), and the pressure makes a noticeable improvement
Summary
There is a necessity to look for more economical renewable fuels like biodiesel. R1, r2, r3, r4, r5 and r6 are reaction rates k1, k2, k3, k4, k5, k6, k7, k8 are reaction constants It was found that the critical process variables affected the conversion in the supercritical method: temperature, pressure, oil/alcohol ratios, residence time, and mixing and solubility parameters. The oil/alcohol ratios were reported to increase the biodiesel production if it was far beyond the theoretical stoichiometric molar ratios of transesterification reactions (i.e., 1:3 see Equation (4)) These factors interacted with each other; for example, the higher process temperature and pressure led to shorter residence time, but higher biodiesel decompositions and energy consumption should be expected [18]. That demands high conversion value; the low Peclet number could increase the reaction operating condition (i.e., reaction temperature and pressure) and the alcohol/oil ratio, resulting in high production costs. The two-step microwave transesterification process, which includes acid and base catalysts described in an earlier paper, was examined for comparison purposes
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