Lignin Dotaz Zobrazit nápovědu
Na Zemi vznikne každoročně procesem fotosyntézy přibližně 180 × 1011 tun lignocelulosové biomasy44, ze kterých představuje přibližně 15 až 30 % suché hmotnosti lignin45. Přestože se jedná o zásadní zdroj aromatických sloučenin, není, až na pár výjimek, zavedeno jeho průmyslové využití na výrobu produktů s přidanou hodnotou. Největší množství ligninu vzniká jako vedlejší produkt papírenského průmyslu, jehož zisky budou pravděpodobně vlivem rostoucí oblíbenosti on -line komunikace a postupnému snižování závislosti firem na papíru meziročně klesat. Zavedením nových aplikací ligninu by se podařilo zvýšit jeho tržní cenu a tím i zisk firem produkujících lignin. Tento efekt by byl rovněž žádoucí pro biorafinerie druhé generace a nepřímo by podpořil výzkum v oblasti biopaliv a dalších hodnotných chemikálií z obnovitelných zdrojů. Jedna z možností, jak tento odpadní biopolymer využít, je v přípravě kovových nanočástic, které patří mezi komerčně nejvíce používané nanomateriály. Proto tato práce shrnuje nedávné úspěchy v této oblasti včetně možností aplikace připravených nanočástic.
The annual production of lignocellulosic biomass by the photosynthesis process on Earth is estimated at 180 × 1011 tonnes44, of which approximately 15 to 30 % of the dry weight is lignin45. Although it is an essential source of aromatic compounds, its industrial use to produce value -added products, with a few exceptions, is not established. The largest amount of lignin arises as a by -product of the paper industry, whose profits will probably decrease year after year due to the growing popularity of online communication and lower dependence of companies on paper. With the introduction of new applications of lignin, it would be possible to increase its market price and thus the profit of companies producing lignin. This effect would be also desirable for second -generation biorefineries and indirectly support research dealing with biofuels and other valuable chemicals from renewable sources. One of the ways to use this waste biopolymer is in the preparation of metal nanoparticles, which are among the most commercially used nanomaterials. Therefore, this work summarizes recent successes in this area, including the possibility of applying prepared nanoparticles.
Lignin, the term commonly used in literature, represents a group of heterogeneous aromatic compounds of plant origin. Protolignin or lignin in the cell wall is entirely different from the commercially available technical lignin due to changes during the delignification process. In this paper, we assess the status of lignin valorization in terms of commercial products. We start with existing knowledge of the lignin/protolignin structure in its native form and move to the technical lignin from various sources. Special attention is given to the patents and lignin-based commercial products. We observed that the technical lignin-based commercial products utilize coarse properties of the technical lignin in marketed formulations. Additionally, the general principles of polymers chemistry and self-assembly are difficult to apply in lignin-based nanotechnology, and lignin-centric investigations must be carried out. The alternate upcoming approach is to develop lignin-centric or lignin first bio-refineries for high-value applications; however, that brings its own technological challenges. The assessment of the gap between lab-scale applications and lignin-based commercial products delineates the challenges lignin nanoparticles-based technologies must meet to be a commercially viable alternative.
Lignins are the most abundant biopolymers that consist of aromatic units. Lignins are obtained by fractionation of lignocellulose in the form of "technical lignins". The depolymerization (conversion) of lignin and the treatment of depolymerized lignin are challenging processes due to the complexity and resistance of lignins. Progress toward mild work-up of lignins has been discussed in numerous reviews. The next step in the valorization of lignin is the conversion of lignin-based monomers, which are limited in number, into a wider range of bulk and fine chemicals. These reactions may need chemicals, catalysts, solvents, or energy from fossil resources. This is counterintuitive to green, sustainable chemistry. Therefore, in this review, we focus on biocatalyzed reactions of lignin monomers, e.g., vanillin, vanillic acid, syringaldehyde, guaiacols, (iso)eugenol, ferulic acid, p-coumaric acid, and alkylphenols. For each monomer, its production from lignin or lignocellulose is summarized, and, mainly, its biotransformations that provide useful chemicals are discussed. The technological maturity of these processes is characterized based on, e.g., scale, volumetric productivities, or isolated yields. The biocatalyzed reactions are compared with their chemically catalyzed counterparts if the latter are available.
Methods in enzymology ; Vol. 161
574 s. : il.
- Konspekt
- Biochemie. Molekulární biologie. Biofyzika
- NLK Obory
- biochemie
The objective of the study was to investigate alkali lignin polymerization/depolymerization pathways in subcritical water (SW) without additives. Following a SW treatment at 200, 250, 275 and 300 °C, the products were subjected to a comprehensive suite of analyses addressing the product speciation and molecular weight (MW) distribution. The MW reduction (1.4 times) in the solid products following the SW treatment indicated a surprisingly reduced impact of cross-linking/repolymerization at 300 °C and lower temperatures. This was further confirmed by thermal carbon analysis (TCA) showing a reduction in pyrolytic charring after the SW treatment. The TD-Py gas chromatography analysis of the SW treated lignin indicated that the solid residue is less oxygenated than the initial lignin (23 vs. 29% as confirmed by elemental analysis). Thus, deoxygenation rather than re-polymerization appears to be the main process route in the absence of catalysts within the temperature range considered.
Laccases have been widely explored for their ligninolytic capability in bioethanol production and bioremediation of industrial effluents. However, low reaction rates have posed a major challenge to commercialization of such processes. This study reports the first evidence of laccase inhibition by two types of lignin degradation intermediates - fungal-solubilized lignin and alkali-treated lignin - thus offering a highly plausible explanation for low reaction rates due to buildup of inhibitors during the actual process. Reversed-phase high-performance liquid chromatography revealed the presence of similar polar compounds in both lignin samples. A detailed kinetic study on laccase, using 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS) as the substrate, was used to calculate the Michaelis constant (Km) and maximum reaction rate (Vmax). With an increase in the concentration of lignin degradation intermediates, Vmax remained nearly constant, while Km increased from 1.3 to 4.0 times that of pure laccase, revealing that the inhibition was competitive in nature. The kinetic studies reported here and the insight gained into the nature of inhibition can help design process strategies to mitigate this effect and improve overall process efficiency. This work is applicable to processes that employ laccase for delignification of biomass, such as second-generation biofuels processes, as well as for industrial effluent treatment in paper and pulp industries.
- MeSH
- biodegradace MeSH
- biokatalýza MeSH
- fungální proteiny chemie MeSH
- kinetika MeSH
- lakasa chemie MeSH
- lignin chemie MeSH
- Trametes chemie enzymologie genetika MeSH
- Publikační typ
- časopisecké články MeSH
