生物燃料： 生产乙醇从纤维素材料
English
Condividere
Panoramica
资料来源： 玛格丽特工人和金伯利弗莱-Depaul 大学实验室
在这个实验中，纤维素材料 （如玉米秸秆、 树叶、 草等） 将被用于作为原料生产乙醇。纤维素材料首先经过预处理 （地面和加热），消化的酶，然后用酵母发酵而成。采用乙醇探头监控生产乙醇。可以扩展实验，以优化生产乙醇通过改变使用的原料、 预处理条件、 酶变异、 酵母变异等。监测反应的一种替代方法是测量二氧化碳 （使用气体传感器） 生产乙醇。作为一个技术含量较低的替代方案，可以使用血糖仪 （在任何药店中找到） 血糖监测过程中，如果一种乙醇探针或二氧化碳气体传感器不可用。
更加注重探究式学习”，科学探索正变得更受欢迎。手持设备一样与各种探头 （类电导率、 溶解的氧、 电压，和更多的） 结合使用游标卡尺实验室寻求允许少侧重于收集数据和/或制作图和更多的数据分析和预测。另一个好处是，这些是小，重量轻，而且可以考虑测量领域。
Principi
Procedura
Risultati
The % ethanol in the solution will be displayed on the handheld tablet screen using the software related to the brand of the ethanol sensor used (Figure 2).
Representative results of the percent ethanol produced by various feedstocks can be seen in Table 1.
| Feedstock | Ethanol produced |
| Sawdust | 0.70% |
| Corn Stalks | 0.60% |
| Cardboard | 1.67% |
| Switchgrass | 0.37% |
| Control | 0.11% |
Table 1. Representative results of the percent ethanol produced by various feedstocks.
Applications and Summary
The Energy Independence and Security Act of 2007 set into law a renewable fuel standard. It created a phase-in for renewable fuel volumes starting at 9 billion gallons in 2008 and ending at 36 billion gallons in 2022. Of that 36 billion, it was expected that 16 billion of that would come from cellulosic materials. For 2014, the original proposal was for 18.15 billion gallons of renewable fuel, 1.75 billion of that coming from cellulosic material. Unfortunately, based on the volume of cellulosic ethanol that is feasible to be produced currently, this number has had to be reduced to 17 million gallons according to a recent EPA proposal.1 Improving the process of creating ethanol from cellulosic material is currently a very hot area of research. In this experiment, students will be emulating the scientific practices that scientists in the top research labs are following.
A variety of biomass feedstock materials can be used to produce cellulosic ethanol for transportation. The U.S. Department of Energy’s Bioenergy Technologies Office is focused on developing cellulosic feedstock from non-food based plant material and the related technologies that will allow an economically feasible conversion of this biomass to transportation fuel. They are investigating biomass sources ranging from agricultural residue, herbaceous energy crops, and forest materials to waste materials and algae. In this laboratory activity, students can vary the feedstock they use and compare the amount of ethanol that results. Possibilities include corn stover, grasses, leaves, cardboard, newspaper, paper, flowers, etc.
One roadblock to large scale production of cellulosic ethanol is the costly nature (both in terms of money and energy) of the pretreatment process. Much research is being done on reducing these costs and making the breakdown of the cellulosic material easier. Enzyme companies are spending a lot of time and money developing new enzymes to increase the yield of ethanol. In this laboratory activity, students can vary the enzymes they use and compare the amount of ethanol that results. A variety of Cellulase enzymes can be purchased from chemical companies that sell to schools, such as cellulase from Aspergillus niger or cellulase from Trichoderma virde. Or proprietary enzymes can be purchased from specialty enzyme companies, however these are costly. Other enzymes can be used, like amylase, to compare their ability of producing ethanol from cellulosic material to that of the cellulases.
Another emerging area of research is improving the ability of yeast to convert cellulosic biomass into ethanol. Lignocellulose has evolved in plants to provide stability. This is due to the crosslinking between cellulose and hemicellulose and the ester linkages in lignin. It is necessary to separate the cellulose from the lignin and then treat the cellulose to break it down into a monosaccharide. In addition, the hemicellulose has a high percentage of pentoses like xylose, which is more difficult to ferment than a hexose like glucose.4
Riferimenti
- The Energy Independence and Security Act of 2007. United States Congress, Washington DC. January 4, (2007).
- Balat, M., Balat, H., Oz, C. Progress in bioethanol processing. Progress in Energy and Combustion Science. 34 (2008).
- Ragauskas, A.J., Williams, C.K., Davison, B.H., Britovsek, G., Cairney, J., Eckert, C.A., Frederick Jr, W.J., Hallett, J.P., Leak, D.J., Liotta, C.L., Mielenz, J.R., Murphy, R., Templer, R., Tschaplinski, T. The Path Forward for Biofuels and Biomaterials. Science. 311 484 (2006).
- Demirbas, A. Bioethanol from Cellulosic Materials: A Renewable Motor Fuel from Biomass. Energy Source. 27 327-337 (2005).
Trascrizione
Biofuels are fuels that are derived from biological matter, such as plants. Biofuels serve as an alternative to fossil fuels, as they can be sourced from crops in many parts of the world. Additionally, they are cleaner burning, thereby reducing greenhouse gas emissions.
One of the most widely used biofuels is ethanol derived from plant biomass, typically sugar cane and corn. In the US, the majority of ethanol biofuel is produced from corn.
The use of corn crops as a feedstock is controversial, as corn is energy intensive to grow, uses a large quantity of fertilizers, and its use as a feedstock removes a large quantity of corn from the food supply, especially feed for livestock. As a result, the use of other plant materials, or lignocellulosic materials, such as grass, leaves, paper, and non-edible parts of crops is increasing.
This video will cover the basics of deriving ethanol from lignocellulosic material, and demonstrate the production of ethanol from lignocellulosic feedstocks in the laboratory.
Lignocellulosic biomass refers to plant matter with woody cell walls. This type of plant matter is one of the most abundant raw materials available, as it is frequently a waste product of agriculture and manufacturing.
The cell walls are composed of the highly crosslinked polymer, lignin, and two complex carbohydrates, hemicellulose, and cellulose. Cellulose is the primary source of fermentable sugars, such as glucose, but it must be first separated from the lignin and hemicellulose components.
The first step in processing of the lignocellulosic material is to finely grind the dry plant matter into a powder. The ground feedstock then undergoes pretreatment to break down the lignin and hemicellulose barrier in the cell wall, and enable access to the cellulose.
Next, the cellulose is treated with hydrolytic enzymes, such as cellulase and hemicellulase. The enzymatic hydrolysis breaks down cellulose into glucose. Finally, the glucose is fermented with yeast to produce ethanol.
The following experiment demonstrates this step-wise method of producing ethanol from cellulosic biomass through the removal of lignin and hemicellulose, followed by the enzymatic treatment of cellulose, and the fermentation of glucose to produce ethanol.
In this experiment, ethanol will be produced from corn stover, the leaves and stalks from corn plants. Using a ball mill grinder, grind the feedstock into a fine powder, and ensure that no large pieces remain.
Weigh 1 g of feedstock, place it into a 50-mL centrifuge tube, and label it. Label a second tube as the control sample, and do not add any feedstock. To pretreat the samples, set up a 500-mL beaker with approximately 400 mL of water, and bring it to a gentle boil.
Add 25 mL of distilled water to the two prepared centrifuge tubes and cap them loosely. Swirl the tubes to mix. Place the tubes in the boiling water, and ensure that the water from the bath does not leak into the tubes. Allow them to boil for 30 min, then remove and let them cool to room temperature.
Once the tubes have cooled, add 1 mL of cellulase enzyme to both tubes. Place the tubes in an incubator for 24 h. After 24 h, remove the tubes and allow them to cool to room temperature. Ethanol is produced from the digested cellulosic material through fermentation by yeast. To begin this process, add 1 g of active yeast to each of the centrifuge tubes, and swirl to mix.
Place an airlock on the centrifuge tubes. The airlock allows the carbon dioxide that is generated during the fermentation to escape so pressure does not build up in the tube. Place the centrifuge tubes in a rack, and place in an incubator at 37 °C. Once fermentation is complete, use an ethanol sensor to measure the ethanol concentration in the control and sample tubes.
To make biofuels a competitive energy source, certain questions about the structure and performance of the feedstocks must be answered.
It is important to understand the distribution of lignin in various plants, so its removal can be performed efficiently. In this example, the lignin distribution in plant cell walls was analyzed by slicing thin layers from a plant stem. The thin slices were then imaged using confocal microscopy with 532 nm laser light to create three-dimensional images of the plant stem.
Lignin content was determined using Raman spectroscopy. By combining the confocal images and the Raman spectra, a three-dimensional map of lignin distribution was generated.
In order to maximize the amount of bioethanol derived from plant feedstocks, the types of feedstocks must be compared. In this example, ethanol was produced from cardboard, and compared to corn stover.The cardboard was prepared as shown previously, where the ground cardboard was subjected to pretreatment, followed by enzymatic digestion in order to separate lignin and hemicellulose from the material and break down the cellulose to glucose. The extracted glucose was then fermented with yeast to produce ethanol. Cardboard proved to be a superior feedstock to corn stover, as it produced more than double the concentration of ethanol in solution.
In the United States, the vast majority of bioethanol is produced from corn. While the production of ethanol from corn is energy intensive, it is less complex than the production of ethanol from cellulosic biomass.
In order to transition away from corn feedstocks, the yield from cellulosic biomass must be better than that of corn. In this example, cornmeal and corn stover were compared using the same procedure as shown previously.
Cornmeal produced a higher concentration of ethanol than corn stover, showing that corn is a slightly better feedstock than the corn stalks themselves. However, corn stalks and other cellulosic feedstocks, are more plentiful and inexpensive and may provide a viable alternative.
You’ve just watched JoVE’s Introduction to Biofuels. You should now understand the production of ethanol from plant feedstocks, and the challenges associated with the process. Thanks for watching!
