Fast Synthesis of Biodiesel at High Throughput in Microstructured Reactors

Abstract

Transesterification of cottonseed oil and methanol with KOH as the catalyst for biodiesel production was carried out in microstructured reactors at residence times of less than 1 min and high flow rates. The reaction system included a micromixer that was connected to either a stainless steel capillary (inner diameter of 0.6 mm) or a PTFE tube (inner diameter of 3 mm, packed with Dixon rings) where the reaction is supposed to take place. The influences of the type of the micromixer, the residence time, the methanol-to-oil molar ratio, the flow rate, the type of delay loop, and reaction temperatures below and above the boiling point of methanol were examined. Flow patterns under different conditions were also examined in transparent microtubes. The results indicated that multilamination micromixers exhibited higher efficiencies in biodiesel production than simple T-and J-type micromixers. A higher yield of biodiesel could be obtained at reaction temperatures above the normal boiling point of methanol. By using the stainless steel capillary as the delay loop, the yield of biodiesel reached 94.8% under the conditions of a methanol-to-oil molar ratio of 8:1, a flow rate of 2.5 mL/min, a residence time of 44 s, and a reaction temperature of 70 °C. Under such circumstances, the pressure drop was 0.8 MPa. By using the PTFE tube packed with Dixon rings as the delay loop, the yield of biodiesel reached 99.5% at the same methanol-to-oil molar ratio and reaction temperature, a flow rate of 10 mL/min, and a residence time of 17 s. The pressure drop was 0.7 MPa. Thus, very fast biodiesel production at high throughput can be achieved in microstructured reactors.

On-line monitoring of the transesterification reaction carried out in microreactors using near infrared spectroscopy

“…Depending on the reactional scheme and the thermokinetic properties of the system, continuous processes may withdraw existing obstacles of batch processes such as numerous steps, secondary reactions, stable equilibria and difficulties to separate the reaction products. Several works on biodiesel production using microreactors have recently been published [11][12][13][14]. The methanolysis system is complex due to changing phase equilibria [15]: two 4 immiscible phases are present at the beginning (vegetable oil and methanol), then a single phase appears after a few minutes of reaction.…”

Biodiesel synthesis in microreactors

“…In the course of the reaction, a quasi-homogeneous one-phase fl ow [ Figure 4B(c)] [26] is formed, resulting from the aggregation of the droplets, the volume reduction of the methanol phase during the reaction, and the formation of FAME. A similar slug fl ow at the outlets of the T-mixer and J-mixer is also observed, however, some slugs and many methanol droplets with diameters of 50 -500 µ m dispersed well into the oil phase are formed at the outlets of the RIMM and SIMM-V2 micromixers, after mixing cottonseed oil with methanol ( Figure 5 ) [34] . The fl ow patterns in SIMM-V2 change at different methanol-to-oil molar ratios, temperatures of 60 -80 ° C and residence times of 0 -44 s.…”

“…of 0.8 mm for transesterifi cation of sunfl ower oil and methanol. However, in a designed microstructured reactor, FAME yields increased with increase in reaction temperature from 60 to 70 ° C for transesterifi cation of cottonseed oil and methanol [34] , resulting from formation of gas-liquid two-phase slug-annular fl ow in the reactor. When the reaction is conducted at around room temperature, a long residence time (for example, 10 min) is needed, or CH 3 ONa is used as the catalyst to obtain a FAME yield of 91 % [33,42] .…”

“…Sun et al [34] employed microstructured reactors assembled with two multilamination micromixers and designed a 3 mm i.d. PTFE tube packed with Dixon rings as the delay loop for transesterifi cation of cottonseed oil and methanol with KOH as the catalyst ( Figure 2C).…”

“…However, the pressure drop will increase signifi cantly with decrease in the microchannel size, thus resulting in increased diffi culty in operating and production cost. An effective solution is packing Dixon rings into a large tube [34] , which can obviously reduce the pressure drop as well as get a high FAME yield in a short time.…”