Valorisation of Orange Peel Residues: Waste to Biochemicals and Nanoporous Materials
Valorisation of Orange Peel Residues: Waste to Biochemicals and Nanoporous Materials
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DOI：
10.1002/cssc.201200381
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发表时间：
2012-09-01
期刊：
影响因子：
8.4
通讯作者：
Clark, James H.
中科院分区：
文献类型：
--
作者：
Mariana Balu, Alina;Budarin, Vitaliy;Clark, James H.
柑橘皮是地球上最未充分利用和地理上最多样化的生物废物残留物之一。在榨汁后，残留的果皮占水果的50重量%，存在环境问题。[1]利用这种资源是一个真实的挑战，每年3120万公吨加工柑橘类水果产生1560万公吨废物。[2]废橙子皮（WOP）由20%干物质（糖、纤维素、半纤维素、果胶和D-柠檬烯）和80%水组成。[3]然而，对柑橘废物价值的研究几乎总是集中在单一成分的生产上，如D-柠檬烯，[4]果胶，[5]或生物乙醇。[6]洛佩斯等人强调了WOP生物精炼厂的巨大潜力。[7]不幸的是，Pourbafrani报道了柑橘废物综合增值的唯一例子，[8]用于生物乙醇，沼气和D-柠檬烯的联合生产。纤维素和半纤维素的低价值应用和高干燥成本[9]，加上资源密集型的两步酸催化果胶提取工艺[10]，使得目前对单个产品的价值评估策略只能获得少量利润。微波技术正逐渐被接受为促进化学反应的方法[11]，因为微波通常比传统加热更可控[12]以及能量[13]和成本效益[14]。此外，微波处理已被证明在中试规模[15]和工业规模下对于生产具有出色稳定性和纯度的植物材料提取物是有效的。[16]微波处理对于提取单独的植物化学物质是有效的，包括橙皮苷[17]和柠檬烯，[18，19]具有提高的果胶提取产率。[20]这些工艺仍然使用HCl，产生大量酸性废水。例如，在Kratchanova的[20]和Zhongdong的工作[21]中，微波被简单地用作预处理步骤，然后在pH 1.5-2下提取果胶。Langrish重点比较了索氏提取和微波提取，表明微波辅助提取果胶更快。[22]然而，所有这些方法都专门利用微波加热作为预处理步骤，特别针对WOP的单一组分。最近，我们发现生物质中多糖的低温特异性微波活化发生在2008 ℃以下[23，24]，因此可以帮助建立一种新型的WOP生物精炼厂，而无需预处理，使公司能够降低成本，提高竞争力，并产生额外的利润。在本文中，我们报告了一种新的级联型增值方法，通过使用单步低温水热微波处理（方案1）将整个WOP转化为高价值的生物衍生化学品和材料。产物包括D-柠檬烯、果胶（一种不常见的介孔纤维素），并首次报道了D-柠檬烯原位转化为α-松油醇。[23]为了鉴定这些结构变化，采用了调制差示扫描量热法（MDSC）。1808 ℃和2008 ℃的两个主要热事件被确定为对随后的研究至关重要。因此，所有的微波实验都是在1808 ℃和2008 ℃之间的温度下进行的。作为微波处理和标准分离程序的结果，获得四个主要级分（生物油、果胶、纤维素和糖）（参见方案1和实验部分）。
Citrus peel is one of the most underutilized and most geographically diverse biowaste residues on the planet. After juice extraction the residual peel accounts for 50 wt% of the fruit, presenting an environmental problem.[1] There is a real challenge to utilize this resource, with 15.6 million metric tonnes of waste produced from 31.2 million metric tonnes of processed citrus fruit annually.[2] Waste orange peel (WOP) is composed of 20% dry matter (sugars, cellulose, hemicellulose, pectin, and D-limonene) and 80% water.[3] However, research carried out on citrus waste valorization has nearly always focused on production of a single component, such as D-limonene,[4] pectin,[5] or bioethanol.[6] Lopez et al. highlighted the remarkable potential of a WOP biorefinery.[7] Unfortunately, the only example of integrated valorization of citrus waste was reported by Pourbafrani,[8] for the combined production of bioethanol, biogas, and D-limonene. Low-value applications for cellulose and hemicellulose and high drying costs,[9] together with a resource intensive two-step acid-catalyzed pectin extraction process,[10] make current valorization strategies to individual products only marginally profitable. Microwave technology is becoming accepted as a method for promoting chemical reactions [11] as microwaves are often more controllable [12] as well as energy-[13] and cost-efficient [14] than conventional heating. Furthermore, microwave processing has been shown to be effective at both pilot scale [15] and at industrial scale for the production of plant material extracts of outstanding stability and purity.[16] Microwave treatments have been effective for extraction of individual phytochemicals including hesperidin [17] and limonene,[18, 19] with improved extraction yields of pectin.[20] These processes still use HCl, resulting in large quantities of acidic wastewater. For example, in Kratchanova’s [20] and Zhongdong’s work [21] microwaves were simply utilized as a pretreatment step followed by pectin extraction at pH 1.5–2. Langrish focused on comparing Soxhlet and microwave extractions, suggesting that microwave-assisted extraction of pectin is faster.[22] Nevertheless, all these methods exclusively utilized microwave heating as pretreatment step, specifically targeting a single component of WOP. Recently we have found that lowtemperature specific microwave activation of polysaccharides within biomass takes place below 2008C [23, 24] and as such could help to establish a novel type of WOP biorefinery without pretreatment, allowing companies to reduce costs, increase competitiveness, and generate additional profits. Herein, we report a novel cascade-type valorization approach to convert whole WOP into high-value, bioderived chemicals and materials by using a single-step, low-temperature hydrothermal microwave treatment (Scheme 1). Products obtained include D-limonene, pectin, an unusual form of mesoporous cellulose, and for the first time, the in situ conversion of D-limonene into α-terpineol is reported.Microwave irradiation was previously demonstrated to interact with biomass at specific temperatures where there is a structural changes within the biomass.[23] To identify these structural changes modulated differential scanning calorimetry (MDSC) was employed. Two major thermal events at 1808C and 2008C were identified as being critical for subsequent investigations. Therefore, all microwave experiments were carried out at temperatures between 1808C and 2008C. As a result of microwave treatment and standard separation procedures, four major fractions (bio-oil, pectin, cellulose and sugars) were obtained (see Scheme1 and the Experimental Section).