Photocatalytic bioethanol Production

21世纪最大的挑战之一是满足全球能源需求。化石燃料供应的减少，加上温室气体(GHG)的有害排放，导致了对可再生燃料/能源的追求，欧盟的目标是到2020年可再生能源占能源的10%。风能、太阳能、潮汐和来自农作物(甘蔗和玉米)的生物燃料正迅速被引入作为替代能源。然而，由于人口、粮食价格和砍伐森林用于种植能源作物，粮食作物的使用受到了广泛的批评，因此迫切需要开发更可持续的替代方案，而不影响全球粮食生产。一种方法是开发大量可利用的纤维废物，这些废物主要由纤维素组成。这些由农业、林业和工业(如造纸业)产生的废物可用于生产生物燃料。据估计，仅在英国，每年过剩的秸秆就超过570万吨。这种丰富的废物资源，再加上它们在地理上均匀分布在全国各地，可以为生物燃料的生产提供本地化的低能源解决方案。作为一种碳水化合物，纤维素由糖分子组成，可以发酵来提供乙醇，但与淀粉不同的是，纤维素的结构阻止了结合糖的简单释放。以前利用纤维素废物的尝试都使用了极端的处理条件来释放可用糖。在现有的前处理程序中，酶法、酸碱爆破法、湿式氧化、蒸汽爆破法都可能与高压、高温相结合。这些过程昂贵，耗能高，并且产生危险废物。在这个项目中，我们提出了一种低成本，低环境影响的方法，通过光催化结合单一反应器中的发酵来从纤维素废物中生产生物乙醇。光催化是一种使用催化剂通过产生自由基来加速光反应的过程，通常被用于一系列应用(废水处理、防污涂料、自清洁玻璃)。光催化将被用来从纤维素中释放糖，这些糖将通过半透膜，在那里它们将被酵母(或其他选定的微生物)发酵以产生生物乙醇。这种方法有多个优点：催化剂成本低、无毒、自清洁、可回收，并可由收获的自然光激活(需要时可通过低能LED来增强)。这一综合工作计划由微生物学(Linda Lawton-RGU教授)、工程学(Peter Robertson-RGU教授)和化学(John Irvine-St Andrews教授)专家领导，他们都在应用驱动的研究方面拥有成熟的记录。工作计划的关键组成部分包括：底物定向设计和合成新型催化剂，其将被筛选以最大限度地释放可发酵糖，筛选微生物以最大限度地生产生物乙醇，设计、制造、测试和优化平行小试规模的反应器。该反应器的一个关键特点是使用选择性膜将释放出的糖从催化剂中分离出来。在典型的条件下，光催化反应会完全降解与催化剂接触的化合物，因此释放出来的糖将穿过膜，在那里它们将被微生物降解。这种新型的反应器将是简单和可规模化的，便于在地方或市政规模上实施。为了获得最大的通用性，该反应器将进行优化，以从一系列来自农业和工业的废物原料中生产生物乙醇。这一多学科项目将应对可再生能源的挑战，开发一种可持续、成本效益高、环境影响低的工艺，将低价值纤维废物转化为高价值生物乙醇。

One of the greatest challenges in the 21st century is to meet the global energy demand. Dwindling supplies of fossil fuel, combined with detrimental release of green house gases (GHG) have lead to the quest for renewable sources of fuel/energy with EU targets of 10% energy from renewable by 2020. Wind, solar, tidal and biofuel from crops (sugar cane and corn) are rapidly being introduced as alternative energy supplies. However, use of food crops has been widely criticised due to escalating population, food prices and deforestation for cultivation of energy crops hence there is an urgent need to develop more sustainable alternatives that do not impact global food production. One approach is the exploitation of significant quantities of available fibrous waste, which consist largely of cellulose. This waste, generated by agriculture, forestry and industry (e.g. paper manufacturing) can be exploited for biofuel production. It has been estimated that in the UK alone, annual excess straw exceeds 5.7 million Tonnes. This abundant waste resource, coupled to the fact that they are geographically evenly distributed across the country, could offer localised, low energy solutions for production of biofuel. As a carbohydrate cellulose consists of sugar molecules which can be fermented to provide ethanol but unlike starch the structure of cellulose prevents simple release of bound sugars. Previous attempts to harness cellulosic waste have used extreme treatment conditions to release the usable sugars. In existing pre-treatment procedures, enzymes, acid and alkali explosion, wet oxidation, steam explosion may be combined with high pressure and temperature. These procedures are expensive, energy demanding and generate hazardous waste.In this project, we propose a cost effective, low environmental impact approach to produce bioethanol from cellulosic waste by photocatalysis combined with fermentation in a single reactor. Photocatalysis is a process which uses a catalyst to accelerate a photoreaction by generating free radicals, and is commonly exploited in a range of applications (waste water treatment, antifouling paints, self-cleaning glass). Photocatalysis will be used to release sugars from the cellulose which will pass through a semi-permeable membrane where they will be fermented by yeast (or other selected microbes) to yield bioethanol. This approach has multiple advantages; catalyst is low cost, non-toxic, self cleaning, recoverable and activated by harvested natural light (augmented by low energy LED's where required). This integrated work programme is led by the experts in microbiology (Professor Linda Lawton - RGU), engineering (Professor Peter Robertson-RGU) and chemistry (Professor John Irvine - St Andrews) all of whom have a proven track record in application driven research.Key components of the work programme include; substrate targeted design and synthesis of novel catalysts, which will be screened for maximum liberation of fermentable sugars, screening of microbes for maximum production of bioethanol, design, fabrication, testing and optimisation of the parallel bench scale reactor. A key features of the reactor is the use of selective membranes to separate the liberated sugars from the catalyst. Under typical conditions the photocatalytic reaction would completely degrade compounds in contact with the catalyst hence liberated sugars will pass through the membrane where they will be available for microbial degradation. This novel reactor will be simple and scale-able facilitating implementation at local or municipal scale. For maximum versatility, the reactor will be optimised to produce bioethanol from an array of waste feed stocks from agriculture and industry. This multidisciplinary project will address the challenge of renewable energy with the development of a sustainable, cost effective, low environmental impact process for conversion of low value fibrous waste into high value bioethanol.