Efficient conversion of lignin to alkylphenols over highly stable inverse spinel MnFe2O4 catalysts
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The chemical amplification concept proposed in 1982 to support high resolution short wavelength lithographic technologies that demand highly sensitive advanced resist systems is based on acid-catalyzed crosslinking, deprotection, and depolymerization reactions. Each approach has shown a tremendous progress. In this paper is reviewed the depolymerization concept for the design of sensitive positive resist systems formulated with triarylsulfonium salt acid generators. Three modes of the initiation of acid-catalyzed depolymerization are discussed; (1) attack of acids onto backbone oxygens as exemplified by depolymerization of polyphthalaldehyde (PPA), (2) scission of pendant ester groups followed by depolymerization with poly(α-acetoxystyrene) (PACOST) as an example, and (3) unzipping from the polymer ends as demonstrated by depolymerization of cationically obtained poly(p-hydroxy-α-methylstyrene) (pPHOMS). The positive resist systems based on depolymerization of PPA derivatives include a thermally- evelopable O2 reactive ion etch (RIE) barrier resist for use in the bilayer scheme and the use of PPA as a polymeric dissolution inhibitor for novolac resins. The deesterification of PACOST results in formation of poly(phenylacetylene) (PPA) and simultaneous depolymerization to provide positive images upon development with xylenes, which is briefly discussed. Cationically prepared pPHOMS exhibits 80% thickness loss at ca. 1mJ/cm2 upon postbake at 130°C whereas anionic pPHOMS and cationic meta-PHOST are very stable toward acidolysis, indicating that the depolymerization propagates from the termination side of the chain.
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The research progress in recent years on the characteristics of lignin's chemical depolymerization products and the depolymerization mechanism were reviewed in this paper. Brief introduction was made of the lignin macromolecule formation process, structure unit, connecting way and the yield, composition, and of the characteristics in three-phase product(liquid phase, gas phase and solid phase) by hydrothermal depolymerization and hydrogenation depolymerization and catalytic oxygen depolymerization processes. The characteristics of liquidphase product by the process of different sources of lignin and different depolymerization methods were mainly discussed; the mechanism of chemical depolymerization was also reviewed. Finally, the existing problems in the current lignin's chemical depolymerization process were summarized, the forthcoming research direction for lignin depolymerization was put forward and the development of lignin utilization was prospected.
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a discussion about the opportunity and challenge for lignin valorization, especially for the aromatic chemicals preparation, is firstly provided (Chapter 4.1). Then, focusing on the topic of lignin (catalytic) depolymerization to aromatic monomers, the involved scientific questions are briefly summarized (Chapter 4.2) as follows: (1) promoting the lignin depolymerization via selective cleavage of the ubiquitous lignin C–O/C–C bonds, increasing the conversion; and (2) restraining the lignin fragments recondensation with more stable chemical bonds generation or multimers formation, increasing the selectivity and final monomer yield. Then, two different approaches for the foundation of lignin depolymerization strategies are introduced: (1) direct lignin conversion; and (2) the bottom-up approach (Chapter 4.3). To provide a macro understanding of the research field of lignin conversion, the classification of lignin conversion methods by reaction types is summarized (Chapter 4.4), during which the corresponding catalyst types are also briefly provided. Then, a brief list of some representative systems reported in the last 10 years for native/technical lignin conversion is provided (Chapter 4.5). Based on the brief introduction and summary of the lignin conversion research in this chapter, we hope to provide a basic understanding of the lignin conversion process, which can make the acceptance of the following mechanism discussion easier.
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Several metal oxides and their salts are used as catalysts to study the depolymerization of polyglyolic acid( PGA) oligomers. It is found that the temperature of depolymerization reaction decreases obviously under the catalysis of Zn( acac)2. At the same time,the coking is reduced in the process of preparing glycolide with the improved yield of glycolide. Zn( acac)2is also applied in the solution depolymerization of PGA,and thermal degradation of the azeotropic solvent is prevented at high temperature. It proves that Zn( acac)2can enhance the efficiency of depolymerization and the higher catalytic activity is thought to correlate to the coordination-insertion mechanism. The experimental results show that PGA oligomer is depolymerized at lower temperature( 200℃) under Zn( acac)2catalyst with a mass fraction of 0. 4%.The yield of glycolide reaches 95%. The activation energy value in process of oligomer depolymerization is lower in the presence of Zn( acac)2than the other catalysts,enhancing the efficiency of depolymerization.
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