Process units needed to make biodiesel continuously Michael Allen Department of Mechanical Engineering Prince of Songkla University Thailand
Why continuous? #For a reactor having volume V R and mean residence time T, throughput =V R /T # For the same reactor used batchwise, throughput is V R /(T+t) where t is the turnaround time between batches So the same reactor volume will provide more product when operated continuously
Continuous Reactors #Easy to control " Automated easily # Quality control is good with a consistent product being produced # Are smaller than a batch reactor producing at the same rate
Stirred-tank or Plug-flow? Q,c 0 V R Q,c 1 Mass balance gives: Qc Qc V dc 0 = 1 R dt Where c is the concentration of the reactant/unit volume so dc dt Q = ( V c c 0 1) R
We can measure how dc/dt varies with C, the oil concentration dc dt And then calculate the conversion achieved by a single CSTR Q/ V R C 1 c C 0
Stirred-tank Reactors Q,c 0 Q,c 1 Q,c 2 V R V R V R Q,c 3 They can be connected to each other in cascade:
dc dt Q/ V R2 Q/ V R1 and then calculate the conversion achieved by a several CSTR S Q/ V R3 C 3 C 2 C 1 c C 0
Conclusion The more continuous stirred tanks we have in series, the better conversion we get. A large number of CSTR s in cascade gives the same results as a plug-flow reactor (PFR)
The laboratory equipment used by Darnoko & Cheryan is a simple one-stage CSTR Condenser Thermometer Sample Separator Methyl Ester Palm Oil MeOH KOH Heater-stirrer Glycerol D. Darnoko and Munir Cheryan: Continuous Production of Palm Methyl Esters : JAOCS, Vol 77 no 1 2 (2000)
Typical reactions taking place CH 2 -OOR 1 CH 1 -OOR 2 + CH 3 -OH k 1 2 k CH 2 -OH CH 1 -OOR 2 + CH 3 -OOR 1 CH 2 -OOR 3 CH 2 -OOR 3 Triglyceride Methanol Diglyceride methyl ester CH 2 -OH CH 2 -OH CH 1 -OOR 2 + CH 2 -OOR 3 CH 3 -OH k 3 4 k CH 1 -OOR 2 + CH 2 -OH CH 3 -OOR 3 Diglyceride Methanol Monoglyceride methyl ester CH 2 -OH CH 2 -OH k 5 CH 1 -OOR 2 + CH 3 -OH 6 CH 1 -OH + CH 3 -OOR 3 CH 2 -OH k CH 2 -OH Monoglyceride Methanol glycerol methyl ester
The Rate Equations d[tg] dt d[dg] dt d[mg] dt d[gl] dt d[e] dt d[a] dt = k 1 [TG][A] + k 2 [DG][E] = k 1 [TG][A] k 2 [DG][E] k 3 [DG][A] + k 4 [MG][E] = k 3 [DG][A] k 4 [MG][E] k 5 [MG][A] + k 6 [GL][E] = k 5 [MG][A] k 6 [GL][E] = k 1 [TG][A] k 2 [DG][E] + k 3 [DG][A] + k 4 [MG][E] +k 5 [MG][A] k 6 [GL][E] = d[e] dt where [TG] denotes the molar concentration of the triglyceride, [DG] of the diglyceride, [MG] of the monoglyceride, [A] of the methanol and [E] of the ester.
The effect of increasing methanol concentration 3 Transesterification of soybean oil at 60 C Methanol:oil = 3:1 0.25 2.5 2 1.5 1 0.5 0.2 0.15 0.1 0.05 0 [TG] [Gly] [ME] [DG] [MG] 0 0 240 480 720 960 1200 1440 1680 secs -0.05 From data supplied by Noureddini and Zhu
3 2.5 2 1.5 1 0.5 0 Transesterification of soybean oil at 60 C Methanol:oil = 6:1 0 240 480 720 960 1200 1440 1680 secs 0.2 0.15 0.1 0.05 0-0.05 [TG] [Gly] [ME] [DG] [MG] From data supplied by Noureddini and Zhu
3 2.5 2 1.5 1 0.5 0 Transesterification of soybean oil at 60 C Methanol:oil = 9:1 0 240 480 720 960 1200 1440 1680 secs 0.2 0.15 0.1 0.05 0-0.05 [TG] [Gly] [ME] [DG] [MG] From data supplied by Noureddini and Zhu
Pilot-plant 5 litre, 6 CSTR in cascade Outlet detail 2.5 approx 110 65 97 10 10 mm ID 3 approx 120 40 10 Spinner cone detail Product outlet (see detail) 60 60 405 416 60 60 60 29 13 390 137 38 88.16 10 88.16 52 7.35 60 60 88.16 Insulation 60 50 148 144 16 16 8 60 10 Oil feed Methanol/methoxide feed glycerol outlet 10 50 72 190 28 21 100 133 160 166 Locator bar 5 CONTINUOUS REACTOR TO MAKE VEGETABLE OIL METHYL ESTERS Designed and drawn by Michael Allen, Visiting Professor Prince of Songkla University Last Revised September 2003
DeepThort 5 100 litre Continuous Transesterification Reactor 9 CSTR s in cascade 100 Detail of glycerol separator basket 125 125 125 190 Side view 125 125 125 200 25 50 Feed valves 5 x 4mm dia holes 150 100 350 407 436 View on base
Wash water Simplified flow diagram Alcohol 60 mm x 100 mm Separator Vegetable/ Animal oil Reactor 50 Ester Glycerol
Oil strainer Used-oil feed Wire basket To feed pump
Methoxide/Ethoxide mixer Wire basket Pumparound NaOH /KOH Alcohol To feed pump
Reactor Product 60 mm x 100 mm Feed 50 Reactor glycerol
Detail of glycerol separator basket 20 DeepThort 5 Continuous Transesterification Reactor 1370 715 Insulation Glycerol drain valve Drain valve
Reactor product Crude glycerol separator Alcohol recovery Glycerol Heater speeds up ester separation from glycerol Crude ester
`External view `Internal view
SOME DIMENSIONS OF THE SEPARATOR 1200 210 475 199 160 97
Vent Wash-water Washed Ester Ester washing in a packed tower Crude Ester Spent Wash-water
Vent 3-stage countercurrent washing in packed towers Vent Vent Washed Ester Washwater Crude Ester Spent Wash-water
Washed ester Ester separator Vent to atmosphere Spent washwater Ester
Washed Ester Ester clarifier Spent Wash-water Ester
Ester clarifier Plan view
Washed Ester Ester separation using a centrifuge But centrifuges are expensive...... Ester Spent Wash-water
Wash water Simplified flow diagram Alcohol 60 mm x 100 mm Separator Oil Reactor 50 Ester Glycerol
Mobile Palm Oil Transesterification Unit PO PO MeOH Gly Gly Water Water Water POME POME
Patent Rights There are several possibly unique features to my reactor design for the transesterification of oils: 1) The oil and the alcohol are introduced into the base of the reactor co-currently so that the alcohol can rise through the reacting fluids (Methanol and ethanol have a lower density than vegetable oil or the esters); 2) The spinning cones create separate CSTR s within the body of the reactor; 3) The cones also slightly reduce the glycerol concentration in the upper part of the reactor thus improving the yield and purity of the ester formed. 4) They also have the effect of recycling some catalyst and excess methanol back to the base of the reactor.
Patent Rights The main reason for placing my intellectual property into the public domain is to ensure that it is NOT patented. The only payment I require from any user or developer is that : 1) They acknowledge Michael Allen and JourneyTo Forever as their source; 2) That they challenge any person or company who would seek to remove this information from the public domain by patenting, licensing or otherwise restricting access to it.
Disclaimer This information is placed in the public domain in goodfaith. But as with any good developmental technology, the real objective is to build upon it and utilise it for the benefit of all (possibly in ways unforeseen by its author!) As a consequence, neither I or JourneyToForever can be held liable in any way for any accidents or problems that arise from the fabrication or use of this equipment. ALL CARE TAKEN BUT ABSOLUTELY NO RESPONSIBILITY, NO WARRANTIES, NO GUARANTEES!
Michael Allen BSc (London), ME (Auckland) Chemical Engineer Visiting Professor Prince of Songkla University Thailand (2004) Tamarisk Technology New Zealand