Benyamin Marcus S, Jahnke Justin P, Mackie David M
Army Research Laboratory, 2800 Powder Mill Road, Adelphi, MD 20740 USA.
Biotechnol Biofuels. 2017 Mar 17;10:68. doi: 10.1186/s13068-017-0755-7. eCollection 2017.
Concentration and purification of ethanol and other biofuels from fermentations are energy-intensive processes, with amplified costs at smaller scales. To circumvent the need for these processes, and to potentially reduce transportation costs as well, we have previously investigated bio-hybrid fuel cells (FCs), in which a fermentation and FC are closely coupled. However, long-term operation requires strictly preventing the fermentation and FC from harming each other. We introduce here the concept of the vapor-fed bio-hybrid FC as a means of continuously extracting power from ongoing fermentations at ambient conditions. By bubbling a carrier gas (N) through a yeast fermentation and then through a direct ethanol FC, we protect the FC anode from the catalyst poisons in the fermentation (which are non-volatile), and also protect the yeast from harmful FC products (notably acetic acid) and from build-up of ethanol.
Since vapor-fed direct ethanol FCs at ambient conditions have never been systematically characterized (in contrast to vapor-fed direct methanol FCs), we first assess the effects on output power and conversion efficiency of ethanol concentration, vapor flow rate, and FC voltage. The results fit a continuous stirred-tank reactor model. Over a wide range of ethanol partial pressures (2-8 mmHg), power densities are comparable to those for liquid-fed direct ethanol FCs at the same temperature, with power densities >2 mW/cm obtained. We then demonstrate the continuous operation of a vapor-fed bio-hybrid FC with fermentation for 5 months, with no indication of performance degradation due to poisoning (of either the FC or the fermentation). It is further shown that the system is stable, recovering quickly from disturbances or from interruptions in maintenance.
The vapor-fed bio-hybrid FC enables extraction of power from dilute bio-ethanol streams without costly concentration and purification steps. The concept should be scalable to both large and small operations and should be generalizable to other biofuels and waste-to-energy systems.
从发酵产物中浓缩和纯化乙醇及其他生物燃料是能源密集型过程，在小规模生产时成本会增加。为了避免这些过程的需求，并有可能降低运输成本，我们之前研究了生物混合燃料电池（FCs），其中发酵过程与燃料电池紧密耦合。然而，长期运行需要严格防止发酵过程和燃料电池相互损害。我们在此引入气相进料生物混合燃料电池的概念，作为在环境条件下从正在进行的发酵过程中持续提取能量的一种方式。通过将载气（N）鼓泡通过酵母发酵液，然后再通过直接乙醇燃料电池，我们保护燃料电池阳极免受发酵液中催化剂毒物（这些毒物是非挥发性的）的影响，同时也保护酵母免受有害的燃料电池产物（特别是乙酸）以及乙醇积累的影响。
由于在环境条件下气相进料直接乙醇燃料电池从未得到系统表征（与气相进料直接甲醇燃料电池不同），我们首先评估乙醇浓度、气相流速和燃料电池电压对输出功率和转换效率的影响。结果符合连续搅拌釜式反应器模型。在较宽的乙醇分压范围（2 - 8 mmHg）内，功率密度与相同温度下液相进料直接乙醇燃料电池的功率密度相当，获得的功率密度>2 mW/cm²。然后我们展示了气相进料生物混合燃料电池与发酵过程连续运行5个月，没有因中毒（燃料电池或发酵过程的中毒）而导致性能下降的迹象。进一步表明该系统是稳定的，能从干扰或维护中断中快速恢复。
气相进料生物混合燃料电池能够从稀生物乙醇流中提取能量，而无需进行昂贵的浓缩和纯化步骤。该概念应可扩展到大规模和小规模操作，并且应可推广到其他生物燃料和废物转化能源系统。
