Chemicals, biomass lactic acid

Beyond the transportation sector, biomass is also a promising feedstock for the chemical industry. This industry accounts for 5-10% of today s oil and gas consumption. It may require an even larger fraction in the future as the demand for chemicals has outpaced that for energy in the last few decades. Recently, the chemical industry has indeed showed a significant interest in converting agricultural feedstock into chemical intermediates such lactic acid or propene-l,3-diol. 

Different routes for converting biomass into chemicals are possible. Fermentation of starches or sugars yields ethanol, which can be converted into ethylene. Other chemicals that can be produced from ethanol are acetaldehyde and butadiene. Other fermentation routes yield acetone/butanol (e.g., in South Africa). Submerged aerobic fermentation leads to citric acid, gluconic acid and special polysaccharides, giving access to new biopolymers such as polyester from poly-lactic acid, or polyester with a bio-based polyol and fossil acid, e.g., biopolymers . 

Even though the yields obtained in yeast are not yet comparable with those obtained with LAB, S. cerevisiae has great potential for the development of a cost-competitive process, leading to the conclusion that this eukaryotic host can represent an alternative production platform to LAB. The production of lactic acid from biomass with LAB has already been the object of investigation [153] nevertheless, the advances obtained with S. cerevisiae in using raw biomass as substrate represent important drivers for exploiting this yeast for chemicals production. 

The production of multiple products is generally seen as necessary to increase the economic viability of biomass conversion. This is encapsulated in the concept of a biorefmery , which according to the National Renewable Energy Laboratory (NREL) is a facility that integrates conversion processes and equipment to produce fuels, power and chemicals from biomass [23], Examples of chemicals that can be produced from biomass include ethanol, methanol, furfural, paper, lignin, vanillin, lactic acid, dimethylsulfoxide and xylitol. In many cases, using biomass as a feedstock for chemical production requires an initial step to separate or fractionate the three main components into usable fractions [20, 22], This also maximises the usage of the different biomass components. 

Lactic acid is a major end product from fermentation of a carbohydrate by lactic acid bacteria (Tormo and Izco, 2004). However, lactic acid can be produced commercially by either chemical synthesis or fermentation. The chemical synthesis results in a racemic mixture of the two isomers whereas during fermentation an optically pure form of lactic acid is produced. However, this may depend on the microorganisms, fermentation substrates, and fermentation conditions. Lactic acid can be produced from renewable materials by various species of the fungus Rhizopus. This has many advantages as opposed to bacterial production because of amylolytic characteristics, low nutrient requirements, and the fungal biomass, which is a valuable fermentation by-product (Zhan, Jin, and Kelly, 2007). 

Lactic acid is an important additive and preservative agent in the chemical, cosmetics, pharmaceutical, and food industries. It is also used as the base for the production of biodegradable polymers like polylactates [4.12]. Its current worldwide production is estimated to be 40,000 tons per year. The results reported by Olmos-Dichara and coworkers [4.13] are typical of the results reported in many of the prior studies of this reaction system. They carried out a study comparing the performance of a batch reactor and a MBR for the production of lactic acid using L. cassei sp. rhamnosus as a biocatalyst. The MBR consists of the batch bioreactor coupled with a cross-flow mineral membrane filtration unit. MBR productivity was eight times that of the batch reactor, while the biomass concentration (77g f ) in the MBR was 19 times that found in the batch culture. 

The third approach of using a large proportion of biomass to produce so-called platform molecules is worth close consideration. Here, we need to learn how to make best use of a number of medium-sized, usually multifunctional, organic molecules that can be obtained relatively easily by controlled enzymatic fermentation or chemical hydrolysis. The simplest of these is (bio) ethanol others include levu-linic acid, vanillin, and lactic acid. These are chemically interesting molecules in the sense that they can be used themselves or can quite easily be converted into other useful molecules - building on rather than removing funcHonahty - as can be seen, for example, with lactic acid (Scheme 1.1-6). 

A biocatalytic system for converting biomass to industrial chemicals is not only applicable to enzymatic conversions but also to fermentative conversion using cellulose. We report here three examples of fermentative conversion of cellulose to chemicals namely 1,3 propanediol, lactic acid, and succinic acid. 

Keywords Biomass-to-chemicals Catalysis Cellulose Renewables Lactic acid Vinyl glycolic acid Biodegradable polymers... 

Lactic acid is thus a perfectly suited chemical target to produce from biomass carbohydrates and no petrochemical routes for its formation are likely to take over. Once a proper chemical target molecule is selected, a fundamental understanding of the reaction network is crucial in order to tackle its selective formation from... 

The next two sections of this review chapter will introduce the reader to the world of lactic acid. The acid is both a key platform chemical of the biorefinery concept, from which other interesting molecules may be formed (Sect. 2), and a monomer for commercial bioplastic polylactic acid (PLA) (Sect. 3). In the platform approach, the assessment from Chap. 1 in this volume [23] proves its value, as it is an equally useful tool to seek out the most desired routes for transforming a biomass-derived platform molecule as it is to select the most relevant carbohydrate-based chemicals from a chemist s point of view. In what follows, the desired catalytic cascade from cellulose to lactic acid will be described (Sect. 4) as well as the specific catalytic data reported for different feedstock (Sects. 5 and 6). Section 7 will introduce the reader to recent synthesis routes for other useful AHA compounds such as furyl and vinyl glycolic acid, as well as others shown in Fig. 1. Before concluding this chapter, Sect. 8 will provide a note on the stereochemistry of the chemically produced AHAs. 

The utilization of cellulose as the raw material for production of monomers and polymers is reviewed and discussed. As the most abundant nonfood biomass resource on Earth, cellulose can be catalytically depolymerized to glucose, while glucose is a versatile starting material for a large variety of platform chemicals including ethanol, lactic acid, HMF, levulinic acid, sorbitol, succinic acid, aspartic acid, glutamic acid, itaconic acid, glucaric acid, and so oti. These platforms can be used as monomers directly or further converted to polymerizable monomers for polymer synthesis. 

Lactic acid is currently produced by fermentation of carbohydrates and is rme of the high potential and versatile biomass-derived platform chemicals, leading to various useful polymer products. PLA is produced by ROP of lactide (derived from lactic acid) and exhibits mechanical properties similar to poly(ethylene terephthal-ate) and polypropylene. Representative examples discussed herein included the synthesis of highly stereo-controlled PLAs, such as isotactic, heterotactic, and syndiotactic PLA materials, rendered by different catalyst/initiator systems. 

Vaccari et al. also applied NIR to the control of the lactic acid fermentation process (20). To get a chemical parameter such as the concentrations of the substrate, nutrients, and biomass, an on-line NIR system has been introduced to the quantitative determination of glucose, lactic acid, and biomass in real time during fermentation. The spectrophotometer, InfraAlyzer 450 (Bran-Luebbe Co., Germany) equipped with a cuvette for liquid was used. Lactic acid and glucose concentrations in the broth were measured with HPLC as a conventional method. The cell (biomass) concentration was measured conventionally by a drying method. A set of 45 samples of broth was used as the calibration sample set to create the calibration equation. Lactobacillus easel was cultivated in a fermentor with working volume of 3 1. The calibration equations... 

In addition to the extractable functional molecules found in biomass, we can also make additional useful functional molecules or platform molecules , such as succinic acid, lactic acid and levoglucosenone, by biochemical or thermochemical processing of the bulk cellulosic components of many types of biomass. A biorefinery is an analogue to the current petro-refinery in the sense that it produces energy and chemicals. The major differences lies in the raw material it will use, ranging from biomass to waste (Figure 1.2). 

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