Uncertainties and sustainability concepts in biofuel supply chain management: A review

Biofuel energy as an alternative and additive form of energy to fossil fuel has gained much attention in recent times. In order to sustain such a vision, a robust supply chain is of extreme importance in helping to deliver competitive biofuel to the end user markets. In this paper, firstly, an introduction of the evolution of biofuels and the general structure of the biofuel supply chain are presented. Secondly, the three types of decision making levels and uncertainties that are inherent within the biofuel supply chain are discussed. Thirdly, important methodologies for modeling uncertainties in the decision making process are provided. Fourthly, sustainability concepts and models that give perspectives to the social, economical and environmental concepts are reviewed. Finally, conclusions and future research based on incorporating uncertainties and sustainability concepts within the biofuel supply chain are drawn and suggested, respectively.     

A quinhydrone biofuel cell based on an enzyme-induced pH gradient

We report on an alternative concept of biofuel cell functioning based on the unconventional use of enzymes to create a pH difference generating a potential difference between electrodes soaked in quinhydrone solutions. The electrode and quinhydrone solution were confined in a dialysis bag placed into a compartment containing either glucose oxidase and catalase for the biocathode or urease for the bioanode. In presence of 0.4 mol L⁻¹ glucose and urea, the enzyme reactions generate a pH difference of 3.55, both compartments being separated by an agar-agar wall. The resulting biofuel cell exhibits an open-circuit voltage and maximum power of 208 mV and 30.6 μW, respectively, without immobilization and electrical connection of the involved enzymes. In addition, this biofuel cell was able to provide continuously10 μA during 23 h, producing 0.133 J and 0.828 C. A similar biofuel cell configuration based only on dialysis bags was also developed. A graphite disk electrode elaborated by mechanical compression of graphite particles and quinhydrone, was placed in a dialysis bag itself confined into another dialysis bag containing enzyme solution. The resulting power and open-circuit voltage at saturating substrate conditions are 7.6 μW and 157 mV, respectively.     

Opportunities for integration of biofuel gasifiers in natural-gas combined heat-and-power plants in district-heating systems

As political pressure to improve efficiency and reduce CO₂-emissions increases, natural gas combined cycle (NGCC) combined heat-and-power (CHP) technology is an increasingly attractive option for district-heating systems. However, as CO₂-emissions reduction targets become more ambitious, it is expected that there will be pressure to reduce CO₂-emissions from such units well before they reach the end of their useful lifetime. One way to achieve this goal is to integrate a biofuel gasification unit at the plant site. After clean-up, the produced syngas can be co-fired in the CHP unit. This paper discusses the economic performance of this type of retrofit, with specific emphasis on the impact of the following parameters: (i) the original NGCC CHP plant’s power-to-heat ratio; (ii) the size of the district-heating system’s annual heat-energy demand; (iii) the fuel mix in the district-heating system; and (iv) the availability of low-cost waste-heat that can be delivered to the district-heating system. The economic performance of the retrofitted CHP unit is measured as the overall cost of electricity production (COE). COE is analysed for four different energy-market parameter sets (referred to as Scenarios), including fuel prices, costs associated with energy and climate change policy instruments, and market electricity prices. The results indicate that even relatively high costs associated with CO₂ emissions are insufficient to motivate retrofitting an NGCC CHP unit with an integrated biofuel-gasification unit. To promote this type of retrofit, an additional premium value for electricity generated from renewable fuel sources is required (such as the Swedish REC renewable energy certificate system). An unexpected result of this study is that the required value of REC is essentially independent of the energy market scenario considered.     

Microfluidic fuel cells: A review

A microfluidic fuel cell is defined as a fuel cell with fluid delivery and removal, reaction sites and electrode structures all confined to a microfluidic channel. Microfluidic fuel cells typically operate in a co-laminar flow configuration without a physical barrier, such as a membrane, to separate the anode and the cathode. This review article summarizes the development of microfluidic fuel cell technology, from the invention in 2002 until present, with emphasis on theory, fabrication, unit cell development, performance achievements, design considerations, and scale-up options. The main challenges associated with the current status of the technology are provided along with suggested directions for further research and development. Moreover, microfluidic fuel cell architectures show great potential for integration with biofuel cell technology. This review therefore includes microfluidic biofuel cell developments to date and presents opportunities for future work in this multi-disciplinary field.     

Trends of biofuel cells for smart biomedical devices

Due to the increasing demand for monitoring diseases such as rising heart rate, diabetes, and ocular disorders wearable and implantable biomedical devices seems too essential for patients not only in the hospital but also at home or during working time. Researchers mostly try to offer valuable information on the conditions of patients as non-invasive, by using comfort biomedical device with a minimum side effect. So, small and self-powered with high sensitivity biomedical devices are recommended, among different power sources that introduced for devices, biofuel cells would be produced as power source for a range of medical devices because of its capability to generate sufficient power output compared to the primary power source. The nature of the electrode reaction and the nature of the biochemical reactions are some of the important parameters that are considered for the classification of fuel cells. Enzymatic biofuel cells due to high activity at mild conditions widely applied in pacemaker; glucometer; and smart contact lenses when compared to other kinds of biofuel cells. On the other hand, short lifespan is one of important limitations in this type of biofuel cells. So, the easiest way to overcome these challenges is to apply non-enzymatic ones. Recent studies have attempted to issue novel method for fabrication of non-enzymatic biofuel cell in order to produce a new generation which are inexpensive, disposable, selective, and sensitive in properties. However, consideration of researchers to the development of self-powered biomedical devices by using body fluids or providing electricity storage is rising.     

Structural studies of enzyme-based microfluidic biofuel cells

An enzyme-based glucose/O₂ biofuel cell was constructed within a microfluidic channel to study the influence of electrode configuration and fluidic channel height on cell performance. The cell was composed of a bilirubin oxidase (BOD)-adsorbed O₂ cathode and a glucose anode prepared by co-immobilization of glucose dehydrogenase (GDH), diaphorase (Dp) and VK₃-pendant poly-l-lysine. The consumption of O₂ at the upstream cathode protected the downstream anode from interfering O₂ molecules, and consequently improved the cell performance (maximum cell current) ca. 10% for the present cell. The cell performance was also affected by the channel height. The output current and power of a 0.1 mm-height cell was significantly less than those of a 1 mm-height cell because of the depletion of O₂, as determined by the shape of the E–I curve at the cathode. On the other hand, the volume density of current and power was several times higher for the narrower cell.     

A review: Metal-organic framework based electrocatalysts for methanol electro-oxidation reaction

Energy crisis is the most important issue of the current society, which needs to be addressed on a priority base. A number of energy sources are under research consideration to fulfil the energy needs of the modern society. Methanol electro-oxidation is one of the best energy sources, but still requires electrocatalytically active materials. Different materials, especially metal-organic frameworks (MOFs), have been extensively studied in the last few years. This review summarizes recent studies on the electrocatalytic methanol oxidation reaction, concluding that Ni-based MOFs materials were favoured compared to other metal-based MOF. Additionally, the synergism of two metals, especially Ni and Fe provided an outstanding response for the methanol electro-oxidation reaction. Moreover, the activity of MOFs was further improved as the size of materials was reduced. The introduction of carbon-based support, such as reduced graphene oxide (rGO), also increased catalytic performances due to the well dispersion of the catalyst on the surface. The dispersion of the active material enhanced the reactive surface area and the number of active reaction spots. Thus, performances of materials toward methanol oxidation reaction can be further enhanced if the size of the catalyst is reduced and morphology is controlled in terms of a large number of pores. Similarly, the deposition of the electrocatalyst on the surface of a conductive support avoids agglomeration and facilitates the electron transport, thus enhancing electrocatalytic performances. In addition, multi-metal (i.e., tri and tetra-metal) based materials are needed to be further studied to develop the most efficient electrocatalyst for electrochemical methanol oxidation.     

High-performance biofuel cell made with hydrophilic ordered mesoporous carbon as electrode material

A highly hydrophilic ordered mesoporous carbon has been synthesized by a microwave assisted method from a mixture containing glucose and poly(vinyl alcohol) and with a silica template to have high hydrophilicity, low charge transfer resistance and large specific surface area. The new carbon material is further used as an electrode material to fabricate an anode-limited glucose/O₂ biofuel cell, which gives an output power density of 110 μW cm⁻² with cell voltage of 0.72 V, a performance much higher than the reported anodes made from SWNT, bi-polymer layer and carbon black at the same or even higher glucose concentration. This work provides a universal approach to synthesize functional carbon nanomaterials with desired architectures and properties for various important applications in energy conversion systems such as fuel cells and solar cells.     

Enzymatic biofuel cell based on electrodes modified with lipid liquid-crystalline cubic phases

Two glassy carbon electrodes modified with enzymes embedded in lyotropic liquid-crystalline cubic phase were used for the biofuel cell construction. The monoolein liquid-crystalline film allowed to avoid separators in the biofuel cell. Glucose and oxygen as fuels, and glucose oxidase and laccase as anode and cathode biocatalysts, respectively were used. The biofuel cell parameters were examined in McIlvaine buffer, pH 7 solution containing 15 mM of glucose and saturated with dioxygen. A series of mediators were tested taking into account their formal potentials, stability in the cubic phase and efficiency of mediation. Most stable was the biofuel cell based on tetrathiafulvalene (TTF) and 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonate) (ABTS) as anode and cathode mediators, respectively. The open-circuit voltage was equal to 450 ± 40 mV. The power densities and current densities were measured for all the systems studied.     

Mandates,buyouts and fuel-tax rebates: Some economic aspects of biofuel policies using the UK as an example

Many governments mandate the blending of biofuels with fossil fuel supplies. The paper raises the possibility that some firms might choose not to respect such mandates, and cites the UK's experience, where a buyout of the obligation is possible. A simple economic framework is then used to explore some implications of mandate buyouts, including situations when buyouts and road-fuel-tax rebates are applied together. Finally, it discusses the design of buyout-mandate schemes that could release raw materials from biofuel production, following a future world food price shock.     

Electrochemical performance of a glucose/oxygen microfluidic biofuel cell

A microfluidic glucose/O₂ biofuel cell, delivering electrical power, is developed based on both laminar flow and biological enzyme strategies. The device consists of a Y-shaped microfluidic channel in which fuel and oxidant streams flow laminarly in parallel at gold electrode surfaces without convective mixing. At the anode, the glucose is oxidized by the enzyme glucose oxidase whereas at the cathode, the oxygen is reduced by the enzyme laccase, in the presence of specific redox mediators. Such cell design protects the anode from interfering parasite reaction of O₂ at the anode and works with different streams of oxidant and fuel for optimal operation of the enzymes. The dependence of the flow rate on the current is evaluated in order to determine the optimum flow that would provide little to no mixing while yielding high current densities. The maximum power density delivered by the assembled biofuel cell reaches 110 μW cm⁻² at 0.3 V with 10 mM glucose at 23 °C. This research demonstrates the feasibility of advanced microfabrication techniques to build an efficient microfluidic glucose/O₂ biofuel cell device.     

Impacts of a United States’ biofuel policy on New Zealand's agricultural sector

The rise in oil prices has spurred interest in biofuels. Policies in the United States like the renewable fuel standard (RFS) have led to an expansion of ethanol production, while the New Zealand government has mandated a minimum level of biofuel sales.The research used a partial equilibrium model of international trade to quantify the price and farmgate income effects of the US RFS policy. The goal was to examine the competition between food and biofuel production and to quantify the impact of the policy on the agricultural sector in New Zealand.The RFS policy has a significant impact on corn prices, but a small effect on livestock prices and production. There thus appears to be little conflict between food and fuel uses for corn at the level of the RFS mandate. New Zealand's pasture-based livestock sector benefits from the use of corn for ethanol production: it receives better prices for its products, but does not face the same input cost increases as competitors. The results suggest that New Zealand faces an interesting decision: it could support investment in biofuels research, or benefit from the biofuels boom through the indirect impacts on demand and prices for meat and milk.     

Investigation of multi-donor bulk-heterojunction photovoltaic cells based on P3HT:PCBM system

(2,7-bis[5′-(9,9-dioctylfluorene-2-yl)-2,2′-dithienyl-5-yl]-9,9-dioctylfluorene) (F3Th4) was used as a secondary electron donor material in the poly(3-hexylthiophene) (P3HT):[6,6]-phenyl C61-butyric acid methyl ester (PCBM) bulk-heterojunction photovoltaic cell. It is shown that the combination of F3Th4 with P3HT allows strong light absorption. The mechanism of charge transfer in the multi-donor PV cell was investigated; it shows that efficient energy transfer takes place from F3Th4 to P3HT. However, the short-circuit current (J_SC) of the multi-donor bulk-heterojunction photovoltaic (PV) cell still decreased. The possible reason for the smaller photocurrent is worsening of transport property after addition of F3Th4.     

Integrating multimodal transport into forest-delivered biofuel supply chain design

An integrated multi-stage, mixed integer programming (MIP) model using multimodal transport was designed for a forest biomass biofuel supply chain to manage logistics. The two transport modes are rail and truck. The objective was to minimize the total cost for infrastructure, feedstock procurement harvest, transport, storage and process. The model coordinated strategic and tactical decisions. Strategic decisions include the number, capacity, and location of storage yards and biorefineries. Tactical decisions included the amount of biomass shipped, processed and inventoried during a time period. The model was validated using the state of Michigan, in the Midwest United States, as the base case. It was uncovered that trucks are preferred over rail for short-haul deliveries while rails are more effective for long-haul transport. Taking advantage of these benefits, the multimodal transport model provided more cost effective solutions.     

A GIS-based method for identifying the optimal location for a facility to convert forest biomass to biofuel

There is growing interest in the production of biofuels from woody biomass. Critical to the financial success of producing biofuel is identifying the optimal location for the facility. The location decision is especially important for woody biomass feedstock owing to the distributed nature of biomass and the significant costs associated with transportation. This study introduces a two-stage methodology to identify the best location for biofuel production based on multiple attributes. Stage I uses a Geographic Information System approach to identify feasible biofuel facility locations. The approach employs county boundaries, a county-based pulpwood distribution, a population census, city and village distributions, and railroad and state/federal road transportation networks. In Stage II, the preferred location is selected using a total transportation cost model. The methodology is applied to the Upper Peninsula of Michigan to locate a biofuel production facility. Through the application of the two-stage methodology, the best possible location for biofuel production was identified as the Village of L’anse in Baraga County. Also investigated are the sensitivity of transportation cost and the optimal site for biofuel production to changes in several key variables. These additional variables included fuel price, transportation distance, and pulpwood availability. By applying sensitivity analysis based on limited availability of feedstock, the City of Ishpeming emerged as another viable location for the production facility.     

Laccase electrodes based on the combination of single-walled carbon nanotubes and redox layered double hydroxides: Towards the development of biocathode for biofuel cells

Single-walled carbon nanotubes (SWCNT) were combined with layered double hydroxides (LDH) intercalated with 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonate) diammonium salt [ZnCr-ABTS] to entrap and electrically connect laccase enzyme. The resulting laccase electrodes exhibited an electro-enzymatic activity for O₂ reduction. To improve this electrocatalytic activity, varying SWCNT quantities and loading methods were tested to optimize the configuration of the laccase electrodes. Furthermore, the resulting bioelectrode was successfully used as a biocathode for the elaboration of a membrane-less glucose/air biofuel cell. In 0.1 M phosphate buffer (PBS) of pH 6.0, containing glucose (5 mM) under ambient conditions, the assembled biofuel cell yielded a maximum power density of 18 μW cm⁻² at a cell voltage of 0.3 V whereas this power decreased to 8.3 μW cm⁻² for a biofuel cell based on the identical biocathode setup without SWCNT.     

Electrochemical properties of enzyme electrode covalently immobilized on a graphite oxide/cobalt hydroxide/chitosan composite mediator for biofuel cells

A critical factor for the performance of a biofuel cell is an immobilization of the redox enzyme for continuous catalytic reaction and efficient electron transfer. However, the main obstacle associated with enzyme electrode is the reduced surface area for the accommodation of enzymes, leading to poor power output. This study aimed to optimize the efficient electrical communication for glucose oxidase (GOx) on the surface of a graphite oxide/cobalt hydroxide/chitosan composite as mediator, thereby enhancing the generation of power output. Immobilization efficiency was affected by the different concentrations of 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide (EDC)/N-hydroxysuccinimide (NHS). Also, the surface of enzyme electrode was observed by XPS, Raman, and AFM, respectively. The electrochemical characterization showed that the immobilized GOx possesses the highest activity at EDC:NHS(40:80 mM) concentration. The power output under the optimal condition was found to be 2.24 mWcm^?2 of power density using the three-electrode cell in 0.1 M PBS solution at room temperature.     

Energy harvesting by implantable abiotically catalyzed glucose fuel cells

Implantable glucose fuel cells are a promising approach to realize an autonomous energy supply for medical implants that solely relies on the electrochemical reaction of oxygen and glucose. Key advantage over conventional batteries is the abundant availability of both reactants in body fluids, rendering the need for regular replacement or external recharging mechanisms obsolete. Implantable glucose fuel cells, based on abiotic catalysts such as noble metals and activated carbon, have already been developed as power supply for cardiac pacemakers in the late-1960s. Whereas, in vitro and preliminary in vivo studies demonstrated their long-term stability, the performance of these fuel cells is limited to the μW-range. Consequently, no further developments have been reported since high-capacity lithium iodine batteries for cardiac pacemakers became available in the mid-1970s. In recent years research has been focused on enzymatically catalyzed glucose fuel cells. They offer higher power densities than their abiotically catalyzed counterparts, but the limited enzyme stability impedes long-term application. In this context, the trend towards increasingly energy-efficient low power MEMS (micro-electro-mechanical systems) implants has revived the interest in abiotic catalysts as a long-term stable alternative. This review covers the state-of-the-art in implantable abiotically catalyzed glucose fuel cells and their development since the 1960s. Different embodiment concepts are presented and the historical achievements of academic and industrial research groups are critically reviewed. Special regard is given to the applicability of the concept as sustainable micro-power generator for implantable devices.     

Design of biomass processing network for biofuel production using an MILP model

This paper presents a general optimization model that enables the selection of fuel conversion technologies, capacities, biomass locations, and the logistics of transportation from the locations of forestry resources to the conversion sites and then to the final markets. A mixed integer linear programming (MILP) model has been formulated and implemented in a commercial software package (GAMS) using databases built in Excel. The MILP represents decisions regarding (1) the optimal number, locations, and sizes of various types of processing plants, (2) the amounts of biomass, intermediate products, and final products to be transported between the selected locations over a selected period, and maximizes the objective function of overall profit. The model has been tested based on an industry-representative data set that contains information on the existing wood resources, final product market locations and demands, and candidate locations and sizes for different types of processing plants, as well as the costs associated with the various processing units and transportation of materials, covering the Southeastern region of the United States. The model is applied to design both a distributed, and a more centralized, conversion system. The overall profits, values, cost, and supply network designs of both systems are analyzed using the optimization model. In particular, we investigate: 1) which parameters have major effect on the overall economics, and 2) the benefits of going to more distributed types of processing networks, in terms of the overall economics and the robustness to demand variations.