Abstract
Microwave-assisted depolymerization of black-liquor lignin in formic acid was studied, concentrating on the yield of liquid fractions as bio-oil 1 (mainly aromatic monomers) and bio-oil 2 (mainly aromatic oligomers) and the distribution of the specific compositions. Bio-oil 1 (9.69%) and bio-oil 2 (54.39%) achieved their maximum yields under 160 °C with the reaction time of 30 min. The chemical compositions of bio-oil 1 and bio-oil 2 were respectively identified by means of Gas Chromatography-Mass Spectrometer (GC-MS) and Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). Ethanone, 1-(4-hydroxy-3-methoxyphenyl) and Ethanone, 1-(4-hydrox-3,5-dimethoxyphenyl) were evidenced to be the two prominent compounds in bio-oil 1. Production of aromatic oligomers with the molecular weight of 328, 342, 358, 378, 394, 424 and 454 identified by MALDI-TOF MS was substantially tuned with the reaction temperature. A two-separate-stage kinetic model was proposed to describe the acidic solvolysis of lignin assisted by microwave heating, where the first stage is dominated by the depolyerization of lignin to monomers and oligomers with the activation energy of 40.27 kJ·mol−1, and the second stage with the activation energy of 49.18 kJ·mol−1 is mainly ascribed to the repolymerization of first-stage produced compounds.
Highlights
Rich in the natural plant cell-wall (15–35 wt %), has a three-dimensional (3D) chemical structure polymerized by three kinds of phenyl propane units through ether bonds or carbon-carbon linkages [1,2,3]
Phenol and methyl phenol were observed as the primary liquid products from the degradation of alkali lignin in supercritical water [8]
The amount of four monophenols (4-ethylphenol, guaiacol, 4-vinylphenol, 4-vinylguaiacol, and 4-ethylguaiacol) was up to 30% of all identified compounds from degradation organosolv lignin in ethanol [10], stating that the lignin depolymerization were subjected to the cleavage of aryl–O ether bonds and decarbonylation reaction
Summary
Rich in the natural plant cell-wall (15–35 wt %), has a three-dimensional (3D) chemical structure polymerized by three kinds of phenyl propane units through ether bonds or carbon-carbon linkages [1,2,3]. Solvolysis (thermal degradation of solid in the specific solvent) is one of the applicable methods for producing value-added chemicals. Similar products (such as guaiacol, vanillin and vanillic acid) were identified by Pinkowsk et al, finding that both depolymerization of lignin and repolymerization of the produced fragments were enhanced with the increased temperature [9]. 2017, 18, 2082 lignin is concentrated on the effect of solvent, reaction time, temperature, and the addition of catalyst species, but rarely on that of heating method. Heating is still ambiguous, limiting its application for efficient production of value-Ianddoreddecrhteomficilallst.he knowledge gap, depolymerization of lignin in formic acid assisted by micrIonwoardveerhtoeafitlilntghewkansowinlvedesgteiggaatped, d, ecpoonlcyemrneirnizgattihoen yoifellidgnoinf ilniqfuoirdmpicraocdiducatsssiasntedddbiystmriibcurotiwonavoef haeraotminagticwams oinnovmesetirgsataendd, coolnigceormnienrgs. Tnhoet dacetpoaslyamesoriuzracteionof phryodcersosgepnro-dcoenedoerdinseqthueenttriaanllsyfevriarefaocrtmioynlsa,tiobnu,t eplirmominoatteiodn,thaendelhimydinroaltyiosnis. rFeaocrtmioinc atchirdoudgidh ntohte aacnt aayslyassisouorfcedoenf shiytydrfougnecnti-odnoanlotrhienortyhe(DtrFanTs)fesrturdeyact[i1o6n].s,Tbhuet mpreocmhaonteisdmthoenelsiomlvinoalytisoins roefalcitgionnin tuhrnoduegrhmthiceraonwaayvlyesihseoaftidnegnsisitystfiullnacmtiobnigalutohueso,rylim(DitFinTg) sittusdayp[p16li]c.aTtihoenmfoercheafnfiicsimenot npsrooldvuoclytisoins ooff livganluine-uandddeerdmchicermowicaavlse. heating is still ambiguous, limiting its application for efficient production of value-Ianddoreddecrhteomficilallst.he knowledge gap, depolymerization of lignin in formic acid assisted by micrIonwoardveerhtoeafitlilntghewkansowinlvedesgteiggaatped, d, ecpoonlcyemrneirnizgattihoen yoifellidgnoinf ilniqfuoirdmpicraocdiducatsssiasntedddbiystmriibcurotiwonavoef haeraotminagticwams oinnovmesetirgsataendd, coolnigceormnienrgs. thTeheyieplodssoibf lleiqumiedchparnoidsumctsofanldigndiinstridbeugtriaodnatoifonaroamgaaitnicst mteomnpomeraetrusraenadnodlitgimome ewrsil.l Tbheedpisocsussisbeled mreegcahradninisgmthoef floigrnminatidoengroafdsapteiocinficagpahiennstoltiecmcpomerpatouurnedasn. dA ttimwoe-wseipllabreatdei-ssctuagsseekdinreegtiacrdmiondgetlhiesfporrompaotsioedn ofofrspdeecsicfircibpinhgenlioglnicincodmeppooluynmdesr. iAzattwioon-saenpdarsaetceo-nstdaagrey krienpeotilcymmoerdiezlaitsiopnroinpofosremd ifcoracdiedsucrnibdienrgmliigcnroinwdaevpeohlyeamtienrgiz.ation and secondary repolymerization in formic acid under microwave heating
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