Biofuel''''s Engineering Process Technology Part 18 pdf

Recent Development of Miniatured Enzymatic Biofuel Cells 671 We have introduced three types of functionalization on carbon surface in this session. In the future work, we will immobilize different biomolecules based on these functionalization methods for EBFCs device. Work on building a prototype EBFC consisting of glucose oxidase immobilized anode and a laccase immobilized cathode using C-MEMS based interdigitated electrode arrays is underway. Fig. 5. Cyclic voltammograms showing the first and second cycle confirming the surface functionalization completed in the first irreversible cycle. 5. Simulation of C-MEMS based EBFCs 5.1 Finite element approach for optimization of electrodes design For our simulation approach, we used commercially available COMSOL 3.5 software multiphysics software, which solves partial differential equations (PDEs) by finite element technique. In the model we assume that 3D carbon microelectrode arrays were uniformly immobilized with glucose oxidase and laccase on anode and cathode respectively with out the use of any mediators. The proposed implantable membraneless EBFC is assumed to be placed inside a blood artery of the human body thus utilizes the glucose extracted from blood as a fuel. In principle, glucose oxidase reacts with glucose and produces gluconolactone and hydrogen peroxide. This hydrogen peroxide oxidizes on the anode to generate electron and hydrogen ions. The hydrogen ions travel from electrolyte to cathode, while electrons flow through an external load and generate electricity. On cathode, dissolved oxygen is reduced via laccase enzyme and by combining with electrons and hydrogen ions forms water. We applied Michaelis-Menten theory in our 2D model to analyze phenomenon between enzyme kinetics on the electrode surface and glucose diffusion and thus optimize the electrode microarray design rule according to the enzyme reaction rate In order to determine the output potential in developing biofuel cell, we also incorporated Nernst equation. The numerical simulations have been performed with various electrodes heights and well widths (distance between any two electrodes) to obtain the relation between design Biofuel's Engineering Process Technology 672 rule and EBFCs performance. Various 2D models are investigated for same foot print length (600 µm) of SiO 2 , with fixed electrode diameter of 30 µm and fixed enzyme layer thickness of 10 µm. The height of electrodes is chosen as 60 µm, 120 µm and 240 µm for different well widths (WW-distance between any two electrodes) of 10µm, 20 µm, 40 µm, 60 µm, 80 µm, 100 µm, 120 µm, 140 µm, 160 µm, 180 µm and 200 µm. The quantification of reaction rates of enzymes on anode and cathode is showed in Fig. 6. (a) (b) (c) (d) Fig. 6. (a) Subdomain plot of anode reaction rate (R1); (b) reaction rates from the whole surface of anode. (c) Subdomain plot of cathode reaction rate (R2); (d) reaction rates from the whole surface of cathode. From the results, we observe that the reaction rate decreased from the top to the bottom along the surface of both electrodes due to the lack of diffusion of the substrate as we go towards the bottom; also the outer surfaces of the electrodes have the larger reaction rate in the enzyme layer. The reaction rate along the surface of both electrodes is plotted in Fig. 6. The reaction rate is increased from the bottom to the top along the electrode surface and reached the maximum at edge of the top due to the edge effect. The maximum reaction rates of GOx enzymes vs. different well widths is shown in Fig. 7. for three different heights of electrodes: 60 µm, 120 µm and 240 µm, with 10 µm, 20 µm, 40 µm, 60 µm, 80 µm, 100 µm and 120 µm well widths, respectively. In the case of 60 µm height of electrodes, the maximum reaction rate is obtained when the well width is about 30 µm. For the height of 120 µm and Recent Development of Miniatured Enzymatic Biofuel Cells 673 240 µm, reaction rate reached the highest at the well width of 60 µm and 120 µm respectively. From all these three sets of models both in anode and cathode, we can conclude that the reaction rates of one pair of electrodes reach the maximum when the well width is half as the height of electrodes. Fig. 7. (a) Anode reaction rate curves vs. well width at different ratio of electrode dimensions; (b) Cathode reaction rate curves vs. well width at different ratio of electrode dimensions. The open circuit output potential also has been simulated for the same heights and well widths of electrodes by applying the Nernst equation. The current collectors are assumed at the bottom of the electrodes and hence these potentials are calculated from the bottom. Fig. 8. shows the open circuit output potential vs. well width of electrodes at different height of electrodes. From the results of simulation, we could find out an empirical relationship between electrodes height and well width to achieve optimized output potential is when height of electrodes is twice than that of well width which is in agreement to the results we obtain for the diffusion of the substrate. 5.2 Finite element approach for optimization of orientation of microelectrodes chip for enzymatic biofuel cells Until now, majority of the research was focused on in-vitro experiments by mimicking physiological conditions. The additional complex problems may arise when a BFC chip is placed inside a blood artery. The first is with implantation process itself, which involves a surgery for the insertion of a BFC, and other necessary electronics components. The second is the stability of this chip inside an artery and how/where this chip can be fixed such that it can survive against the blood flow. Third problem is the clotting of the blood. The goal is to put this EBFC chip in such a way that it does not obstruct the flow of blood and lead to substantial pressure drop inside an artery. The fixation of this chip with the blood artery also should not harm the blood vessel walls (Parikh et al., 2010). In order to improve mass transport around microelectrodes by optimizing the positioning of an EBFC chip, we have adopted the finite element analysis approach to look into the stability of an EBFC inside a blood artery. On the initial stage, we have analyzed only two orientations: horizontal position (HP) and vertical position (VP). The stability of the chip in these positions, diffusion and convectional fluxes around microelectrodes has been finely Biofuel's Engineering Process Technology 674 investigated. We have proposed a novel chip design, with holes in between all electrodes on the substrate, which can drastically improve the diffusion in between microelectrodes. Fig. 8. Output potential vs. well width for different ratio of electrode dimensions. The diffusion between the microelectrodes has shown in Fig. 9, where Fig. 9a and b shows the simulation profiles for diffusive flux along with the streamlines around microelectrodes in HP and VP, respectively. In HP, it is observed that the diffusive flux is less near the central electrodes and increases when going towards outer electrodes. However, the diffusive flux is almost same on top of all electrodes in VP. It is observed that in both the positions, the diffusive flux is following laminar pattern. The diffusive flux from bottom of an electrode to top of an electrode is investigated in HP and VP as shown in Fig. 9c and d, respectively. The flux is not uniform from the central to outer electrodes. The electrodes located at the circumference of a chip are having more flux compared to those located in the centre of the chip. The variation of the diffusive flux distribution around inner to outer electrodes is high in HP. The flux is not constant at every instance, but it is oscillating as shown in inset figures. The diffusive flux profiles in these figures are considered at the time, when the flux reaches its maximum value. This is also evident from Fig. 9e and f, the flux is higher exactly at the top of electrodes while lesser in the vicinity between any two electrodes. In comparison of HP and VP, the diffusive flux is 8 orders larger in case of VP than in HP. Total flux is the combination of a diffusive flux and a convective flux. Fig. 10 depicts the total flux data for (a) HP and (b) VP of a chip. In HP, flux is negligible up to almost 275 µm height of electrodes and then increasing at the top. Total flux is highest at the top of outer most electrodes and then reducing to the central electrodes. In case of VP, the flux is almost uniform on top of all electrodes, with negligible value in between electrodes up to 200 µm height and then gradually increasing to about 2000–3500 mmol m− 2 s− 1 at the top of all electrodes. Based on the results, the new design with the holes in between all microelectrodes has been inspected precisely and compared with the prototype design. The diffusive flux (Fig. 11a, c, e) and convective flux (Fig. 11b, d, f) profiles for the new design are compared with diffusive flux and convective flux profiles of the prototype model, respectively. The streamlines present the lines of motion of glucose at a particular instance. Recent Development of Miniatured Enzymatic Biofuel Cells 675 (a) (b) (c) (d) (e) (f) Fig. 9. Surface plot with streamlines for convective flux of glucose around microelectrodes for a) HP, b) VP, convective flux in between all 24 electrodes from bottom of electrodes to up to 300 µm height is shown for c) HP and d) VP, convective flux at top of all the electrodes from leftmost to right most electrodes for 0 – 10 secs in e) HP and f) VP. Biofuel's Engineering Process Technology 676 a) b) Fig. 10. Total fluxes in between micro-electrodes for a) HP and b) VP. Insets provide the total flux on top of all electrodes. From Fig. 11 it is inferred that the total flux (combined diffusive and convective flux) has been improved between all microelectrodes in terms of values and their uniformity for the chip with the holes. This enhanced mass transport around microelectrodes is significantly important for an EBFC performance. This proposed design could also be advantageous to prevent blood clotting. Human blood is mainly consisted of red blood cells and white blood cells. The sizes of all these cells such as red blood cells (6 µm), lymphocyte (7–8 µm), neutrophil (10–12 µm), eosinophil (10–12 µm), basophil (12–15 µm), and monocytes (14– 17 µm) are mostly smaller than 20 µm, the size of the holes provided in the chip. So these cells can pass through the holes in between microelectrodes without blocking the way in between micro-electrodes. These holes can be made bigger depending on the requirement. The improved convection in between microelectrodes may also be forceful enough to eliminate the bubble formation. However, the biomechanical process and hemodynamic process are more complex than convection and diffusion, especially on the micro-scale level. Cell growth and clotting phenomenon are related to many aspects, such as: biocompatibility, bending of blood artery, platelet and protein components. More detailed research needs to be done with biologists in order to obtain more sufficient and helpful information and further reach the applicable level of the EBFCs. Recent Development of Miniatured Enzymatic Biofuel Cells 677 (a) (b) (c) (d) (e) (f) Fig. 11. Surface plot with streamlines for (a) diffusive flux and (b) convective flux of glucose around microelectrodes; (c) diffusive flux and (d) convective flux in between all 24 electrodes from bottom of electrodes to up to 300 µm height; (e) diffusive and (f) convective flux at top of all the electrodes from leftmost to right most electrodes for 0 – 10 secs. Biofuel's Engineering Process Technology 678 6. Conclusion In this chapter, we have introduced the two major kinds of biofuel cells-microbial fuel cells and enzymatic biofuel cells. Significant development on both biofuel cells has been achieved in the past decade. With the demands for reliable power supplies for medical devices for implantable applications, great effort has been made to make the miniaturized biofuel cells. The past experiment results revealed that the enzymatic miniature biofuel cells could generate sufficient power for slower and less power-consuming CMOS circuit. In addition, we have also presented simulation results showing that the theoretical power output generated from C-MEMS enzymatic biofuel cells can satisfy the current implantable medical devices. However, there are some challenges for further advancements in miniaturized biofuel cells. The most significant issues include long term stability and non-sufficient power output. Successful development of biofuel cell technology requires the joint efforts from different disciplines: biology to understand biomolecules, chemistry to gain knowledge on electron transfer mechanisms; material science to develop novel materials with high biocompatibility and chemical engineering to design and establish the system. 7. Acknowledgements This project is supported by national Science Foundation (CBET# 0709085). 8. References Aelterman, P.; Versichele, M.; Marzorati, M.; Boon, N. & Verstraete, W. (2010). Loading rate and external resistance control the electricity generation of microbial fuel cells with different three-dimensional anodes, Bioresource Technology 99 (18), pp. 8895–8902. Akers, N.L.; Moore, C.M. & Minteer, S.D. (2005). Development of alcohol/O 2 biofuel cells using salt-extracted tetrabutylammonium bromide/Nafion membranes to immobilize dehydrogenase enzymes, Electrochim. Acta 50 (12), pp. 2521–2525. Allen, R.M. & Bennetto, H.P. (1993). 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[...]... steam process is approximatively 7% of the net biomass calorific value which represents approximatively 1.4 GJ per tonne of biomass process A two step process could easily lead to a 15 % which now justifies investigations towards a one step process Using triticale, our group compared the two- and one- step steam process Since lignin has to be partially hydrolysed and removed, the one step steam process. .. impregnation process as well as the following excess water removal Once excess water is removed, the biomass is transferred in the FIRSST reactor where it is cooked for 2-4 minutes whilst monitoring the severity factor of the whole process In a two step FIRSST process, one must ensure that the severity factor of the first process is not excessively high or the following delignification process, although... Eastern white cedar White spruce Jack pine Tamarack Sprucet Loblolly pineu Balsam-fir Biofuel's Engineering Process Technology Cellulose Hemicellulose (wt%) (wt%) 45 33 40 39 49 29 49 27 42 36 41.4 23.7 52.8 27.7 55.9 53 43.5 42 44 44 41 43 54.1 43.6 44 13.7 15.8 20.3 26 25 29 30 28 21.4 21.2 27 Lignin (wt%) 18 21 19 24 22 24.5 20 Extractives (wt%) 5 Ashes (wt%) 0.3 6 - 0.4 - 26.2 23.7 33 31 27 29 29... Biofuel's Engineering Process Technology Possible Production of ethanol (Millions of liters per year) from Agricultural residues (25%) Quebec Canada North America Forest residues (25%) Unexploited Forest 5097(e) 584 3353 1638 - 41483(e) 20322(c) - Production of ethanol operational Gasoline from energy consumption crop (Millions of (Millions of liters per year) liters per year) 9000(d) 155(a) 182 1(a)... biofuel Production (Milliard of liters) 160 140 120 100 80 Cellulosic biofuel 60 All types of biofuel 40 20 0 2012 2014 2016 2 018 2020 2022 Year Fig 1 Biofuel Mandate from lignocellulosic materials in the United States Renewable Fuels Standard 694 Biofuel's Engineering Process Technology 3 Fractionation 3.1 Basics informations about steam treatments The first technological challenge restraining the commercialisation... used at this point Biomass is then impregnated with water to ensure 698 Biofuel's Engineering Process Technology Original Biomass Size reduced to 3-6 cm Maceration Mostly cellulose Temperature : Room Time : 24 hours Sol: H 2 O + EtOH (50% vol) FIRSST Pulp Filtration Filtration Mostly extractives Mostly Lignin FIRSST process (2) Washing Temperature : 160-200 °C Time : 2 minutes Temperature : Room Sol:... Temperature : room Repetitions : 5 Time : 5 minutes • Pressure : 100 PSI FIRSST process (1) Washing Filtration Temperature : 180 210 °C Time : 2 minutes Temperature : Room Sol : Water + 2 -8% NaOH Time : 5 minutes Mostly Hemicellulose + proteins + other carbohydrate -based compounds Fig 4 Process flow diagram for the two step FIRSST process allowing isolation of the cellulose fibre as well as lignin, hemicelluloses... classical yeast strands (Gírio, 2009) Studies have shown that fermentation of all the glucidic part of the hemicelluloses, both C6 and C5 sugars, was feasible using nontraditional microorganisms (Agbogbo & Coward-Kelly, 2008; Casey et al., 2009; Chu & Lee, 2007) It is also well known 686 Biofuel's Engineering Process Technology that hydrolysis of hemicelluloses produces / liberates organic acids that could... shown sufficient The uncatalyzed steam explosion process can be related to the severity factor that is calculated from the cooking temperature and time, needless to underline the fact that similar severity could be obtained by increasing the cooking period whilst decreasing the temperature The 2 minutes cooking time usually 700 Biofuel's Engineering Process Technology excludes the heating period where... and to reduce to chemical alterations that the process may have induce to the cellulose fibres On the other hand, if hydrolysis of glucose is intended, it was previously reported that severe steam explosion process could have a beneficial effect on enzyme hydrolysis and therefore, reaching higher severity may be beneficial to the whole process even if part of the cellulose is solubilized in the lignin . Biofuel's Engineering Process Technology 680 Katz, E.; Shipway, A.N. & Willner, I. (2003). Biochemical fuel cells. In: Handbook of Fuel Cells —Fundamentals, Technology and Applications,. 35.5 18. 8 29 - - European oak q 38 29 25 4.4 0.3 White oak r 44 24 24 5.4 1 Chesnut oak r 41 30 22 6.6 0.4 Post oak r 38 30 26 5.8 0.5 Biofuel's Engineering Process Technology. leftmost to right most electrodes for 0 – 10 secs in e) HP and f) VP. Biofuel's Engineering Process Technology 676 a) b) Fig. 10. Total fluxes in between micro-electrodes for a)