Pentenoic acid pathways for cellulosic biofuels.
Pentenoic acid pathways for cellulosic biofuels.
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DOI：
10.1002/anie.201002061
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发表时间：
2010-06
影响因子：
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通讯作者：
R. Palkovits
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文献类型：
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作者：
R. Palkovits
化石燃料的枯竭、气候变化、不断增长的世界人口以及未来的能源供应，无疑是当今需要应对的重要挑战。虽然有几种选择可以覆盖未来的能源供应，包括太阳能、风能和水力发电，但个人机动性、航空和重型车辆在一段时间内仍将需要高能量密度的燃料，以保证足够的驾驶能力和巡航里程。生物乙醇和生物柴油是最早的生物燃料，在发展生物燃料市场方面肯定很有价值。然而，它们从糖、淀粉和植物油中生产出来，导致与粮食生产的竞争，因此很难提供全球运输所需的大量货物。目前的预期集中在木质纤维素上，这种纤维可以大量获得，可能不会与食物链竞争，可以作为燃料和化学品的替代原料。生物质气化与费托技术或将生物质热解为生物油将提供碳氢化合物，这些碳氢化合物在今天的S炼油厂很容易集成，但对能源的需求相当高，主要需要氢气，并且不使用木质纤维素的定义化学结构。化学催化合成确定的目标分子作为燃料和化学品的基石是一种替代方法，可以在生物精炼概念中实现，以整合完整的价值链。潜在的生物燃料应该非常适合今天的S发动机，表现出高能量密度，生产过程中需要的能源很少，无毒，并减少燃烧过程中的排放。基于葡萄糖、5-羟甲基呋喃(5HMF)和乙酰丙酸(LA)的燃料平台已在以前的文献中描述。后两种燃料可以通过将己糖脱水成5-HMF，然后再水合生成LA和甲酸来获得(方案1)。5-HMF与丙酮的羟醛缩合反应生成C9或C15烷烃，而葡萄糖加氢生成山梨醇，然后加氢脱氧可生成己烷。然而，这两条路线都需要大量的外部氢，而这些氢在很大程度上是以水的形式“损失”的。在真正的“生物”燃料方面，LA的酯与g-戊内酯(GVL)和甲基四氢呋喃(MTHF)一起被考虑，后者可以通过LA加氢得到。利用单一的多功能分子催化剂，通过控制LA和衣康酸的转化，可以得到内酯、二元醇和环醚。虽然在燃烧性能和能量含量方面是合适的，但它们的极性和高膨胀和溶解传统的聚合物材料使它们在今天的S燃烧系统中的应用变得复杂。最近，提出了两个新的方向，都是建立基于戊烯酸的价值链。6]该酸可以通过将LA加氢生成GVL，然后在固体酸催化下开环得到。生产GVL所需的氢气可以通过甲酸转移氢化来提供。8]Dumesic和他的同事报告了一种基于GVL的综合方法，用于合成燃料用C8+烯烃，而不需要外部氢(方案2)。GVL转化为戊烯酸，方案1。己糖脱水成5-羟甲基呋喃，再水合生成甲酸和乙酰丙酸。
The depletion of fossil fuels, climate change, growing world population, and future energy supplies are certainly important challenges to tackle these days. While several options exist to cover energy supplies of the future, including solar, wind, and water power, individual mobility, aviation, and heavy duty vehicles will for some time continue to require fuels of high energy density to guarantee sufficient drive capacity and cruising range. Bioethanol and biodiesel were the first biofuels and have certainly been valuable in developing the biofuel market. However, their production from sugars, starches, and vegetable oils induces competition with food production and can thus hardly deliver the large volumes required for worldwide transportation. Current expectations concentrate on lignocellulose, which is available in large amounts, potentially not in competition with the food chain, and could serve as an alternative feedstock for fuels and chemicals. Biomass gasification along with Fischer–Tropsch technology or pyrolysis of biomass to bio-oils would deliver hydrocarbons which could be integrated easily in today s refineries, but have rather high energy demands, mostly require hydrogen, and do not use the defined chemical structures of lignocellulose. The chemocatalytic synthesis of defined target molecules as building blocks for fuels and chemicals is an alternative approach and could be realized in a biorefinery concept to integrate complete value chains. Potential biofuels should ideally be suited to today s engines, exhibit a high energy density, require little energy in their production, be nontoxic, and result in reduced emissions during combustion. Fuel platforms based on glucose, 5-hydroxymethylfurfural (5HMF), and levulinic acid (LA) were described in previous publications. The latter two fuels may be derived by dehydration of hexoses to 5-HMF, followed by rehydration to yield LA along with formic acid (Scheme 1). Aldol condensation of 5-HMF with acetone and subsequent hydrogenation produces C9 or C15 alkanes, while hydrogenation of glucose to sorbitol followed by hydrodeoxygenation could yield hexane. 2] Both routes, however, require lots of external hydrogen, which is to a large extent “lost” as water. With regard to real “bio”fuels, esters of LA have been considered along with g-valerolactone (gVl) and methyltetrahydrofuran (mTHF), which can be obtained by hydrogenation of LA. Lactones, diols, and cyclic ethers could be thus obtained by controlled transformation of LA and itaconic acid by utilizing a single multifunctional molecular catalyst. Although suitable in terms of combustion properties and energy content, their polarity and high tendency to swell and dissolve conventional polymer materials complicate their application in today s combustion systems. Recently, two new directions have been proposed, both establishing a value chain based on pentenoic acid. 6] This acid can be obtained by hydrogenation of LA to gVl and subsequent ring opening catalyzed by solid acids. The hydrogen required for the production of gVl can be supplied by transfer hydrogenation from formic acid. 8] Dumesic and co-workers reported an integrated approach based on gVl for the synthesis of C8+ alkenes for fuel application without the need for external hydrogen (Scheme 2). gVl is converted into pentenoic acid, which Scheme 1. Dehydration of hexoses to 5-hydroxymethylfurfural and rehydration to yield formic and levulinic acid.