Catalytic pyrolysis conversion of lignin from different sources to phenols

Naron, David Rangnaan (2019-04)

Thesis (PhD)--Stellenbosch University, 2019.


ENGLISH ABSTRACT: Lignin is a by-product of the paper and pulp industry and the emerging cellulosic ethanol production technologies. Both industries only considered lignin a source of energy to complement the energy needs of their processes. However, the phenolic nature of lignin makes it a valuable renewable resource for sustainable production of chemical products. In the current study, prior to lignin conversion to phenolic chemical products, physico-chemical characterisation of several lignins were conducted using conventional methods namely, wet chemical, gel permeation chromatography (GPC), and Fourier transform infra-red spectroscopy (FTIR). In addition to these methods, a novel analytical pyrolysis method was developed combining thermogravimetric analysis (TGA), thermal desorption (TD), and gas chromatography coupled to mass spectrometry (GC-MS), named as TGA-TD-GC-MS. It was used to analyse and estimate the monomeric phenolic products namely, syringol (S), guaiacol (G) and phenol (H) from lignins. The phenolic monomeric proportions (S/G/H), obtained using the TGA-TD-GC-MS was compared with the ones obtained by thioacidolysis (wet chemical method). The lignin monomeric products obtained by pyrolysis, based on internal calibration, was in the range of 5.5-12.9 wt.%. The ability of the TGA-TD-GC-MS to break several types of bonds gave it the advantage over thioacidolysis, resulting in the production of monomeric phenolic compositions that were more representative of the lignin. A comparison of phenols production from catalytic pyrolysis of lignins of different biomass origin, namely eucalyptus (hardwood) lignin, pine (softwood) lignin, and sugarcane bagasse (herbaceous) lignin was studied using the TGA-TD-GC-MS. The lignins were impregnated with two hydroxides (NaOH and KOH) and two metal oxides (ZnO, and Al2O3), with amounts equivalent to 1 wt.% of the lignin mass, and pyrolysed at the temperature of 600 °C using a heating rate of 10 °C/min. KOH produced the most catalytic effect on the yield of total phenols from sugarcane bagasse (S-S) lignin, leading to the highest increase of +26%, and likewise NaOH for eucalyptus (E-K) lignin (+40%). Syringol yield being the major syringol-type (S-type) phenols reached a record high of 1.8 wt.%, equivalent to 90% increase from E-K lignin, catalysed by NaOH. Additionally, NaOH increased the yield of 4-vinylguaicol-the guaiacol-type (G-type) phenol from E-K lignin up to 2.8 wt.%, equivalent to 39% increase, as compared to the non-catalytic yield. A catalyst screening study was conducted in which twelve catalysts, namely Al2O3, Fe2O3, MoO3, TiO2, Ni/Al2O3-SiO2, CaO, ZnO, MgO, NaOH, CuO, KOH and NiO were each impregnated on three different types of sugarcane bagasse lignins with amounts equivalent to 1 wt.% of the lignin mass. KOH, CaO, and Fe2O3 recorded the highest effects on the total yield of phenols from soda (SD), soda-anthraquinone (SAQ), and steam explosion combined with enzymatic hydrolysis lignins respectively. The increases were 11.2 wt.%, 8.2 wt.%, and 8.6 wt.%, equivalent to + 26%, + 60% and + 43% respectively. Syringol, guaiacol, and 4-vinylguaiacol were the most improved with yield increases ranging from 0.6 to 2.8 wt.%, equivalent to 32-121% from the lignins. Optimisation of phenols was investigated. Pyrolysis was first conducted at analytical scale and then applied in the second stage at bench scale. The results at analytical scale showed that the amounts of KOH required to maximise the yield of phenols (15.3-16.0 wt.%) were in the range of 5-7 wt.%. Analysis of the bio-oil showed that the yields of syringol and guaiacol had their maximum values at 450 °C and 4.5 wt.% KOH content with yield increases of 0.70 wt.% and 0.6 wt.%, which represent 106% and 83% respectively, compared with that of pyrolysis without catalyst. Phenol (the P-type phenol) achieved a maximum at 450 °C and 8.5 wt.% KOH content, with a yield of 0.96 wt.%, corresponding to 141% increase.

AFRIKAANSE OPSOMMING: Lignien is ’n byproduk van die papier- en pulpindustrie en die opkomende sellulosiese etanolproduksie-tegnologieë. Beide industrieë beskou lignien slegs as ’n bron van energie om die energiebenodigdhede van hul prosesse te komplimenteer. Die fenoliese natuur van lignien maak dit egter ’n waardevolle herwinbare hulpbron vir volhoubare produksie van chemiese produkte. In die huidige studie, voor die lignien omskakeling na fenoliese chemiese produkte, is fisikochemiese karakterisering van verskeie ligniene verrig deur konvensionele metodes te gebruik, naamlik nat chemiese, jel deurlating chromatografie (GPC), en Fourier transform infrarooi spektroskopie (FTIR). Buiten hierdie metodes is ’n nuwe analitiese pirolise metode ontwikkel wat termogravimetriese analise (TGA), termodesorpsie (TD), en gaschromatografie gekoppel aan massa spektrometrie (GC- MS) kombineer, genaamd TGA-TD-GC-MS. Dit is gebruik om die monomeriese fenoliese produkte, syringol (S), guajakol (G) en fenol (H) van ligniene, te analiseer en beraam. Die fenoliese monomeriese proporsies (S/G/H), verkry deur die TGA-TD-GC-MS te gebruik, is vergelyk met dié verkry deur thioacidolysis (nat chemiese metode). Die lignien monomeriese produkte verkry deur piroliese, gebaseer op interne kalibrering, was in die bestek van 5.5–12.9 wt.%. Die vermoë van die TGA-TD-GC-MS om verskeie tipes bindings te breek, gee dit die voordeel oor thioacidolysis, wat die produksie van monomeriese fenoliese komposisies wat meer verteenwoordigend is van die lignien, tot gevolg het. ’n Vergelyking van fenolproduksie van katalitiese pirolise van ligniene van verskillende biomassa oorsprong, naamlik eukaliptus- (hardehout) lignien, den- (sagtehout) lignien, en suikerriet bagasse- (kruidagtig) lignien is bestudeer deur die TGA-TD-GC-MS te gebruik. Die ligniene is geïmpregneer met twee hidroksiedes (NaOH en KOH) en twee metaaloksiedes (ZnO en Al2O3) met hoeveelhede ekwivalent aan 1 wt.% van die lignien massa, en gepiroliseer by ’n temperatuur van 600 °C deur ’n verhittingstempo van 10 °C/min te gebruik. KOH het die grootste katalitiese effek op die opbrengs van totale fenol uit suikerriet bagasse (S-S) lignien gehad, wat tot die hoogste verhoging van +26% gelei het, en ook NaOH vir eukaliptus- (E-K) lignien (+40%). Syringol-obrengs, wat die grootste syringol-tipe (S-tipe) fenol is, het ’n rekord hoogte van 1.8 wt.%, ekwivalent aan 90% verhoging van E-K-lignien gehad, gekataliseer deur NaOH. Boonop het die NaOH die opbrengs van 4-vinielguajakol-tipe (G-tipe) fenol van E-K-lignien verhoog tot en met 2.8 wt.%, ekwivalent tot 39% verhoging, in vergelyking met die nie-katalitiese opbrengs. ʼn Katalis siftingstudie is uitgevoer waarin twaalf kataliste, genaamd Al2O3, Fe2O3, MoO3, TiO2, Ni/Al2O3-SiO2, CaO, ZnO, MgO, NaOH, CuO, KOH en NiO elk geïmpregneer is op drie verskillende tipes suikerriet bagasse ligniene met hoeveelhede ekwivalent aan 1 wt.% van die lignien massa. KOH, CaO en Fe2O3 het die hoogste effek op die totale opbrengs van fenol uit soda (SD), soda-antrakinoon (SAQ), en stoomontploffing gekombineerd met ensimatiese hidrolise ligiene, onderskeidelik, aangeteken. Die verhogings was 1.2 wt%, 8.2 wt.% en 8.6 wt.%, ekwivalent aan +26%, +60% en +43%, onderskeidelik. Syringol, guajakol en 4-vinielguajakol het die grootste verbetering getoon met opbrengsverhogings met ’n bestek van 0.6 tot 2.8 wt.%, ekwivalent aan 32–121% van die ligniene. Optimering van fenol is ondersoek. Pirolise is eers uitgevoer op analitiese skaal en toe toegepas in die tweede fase by banktoetskaal. Die resultate op analitiese skaal het gewys dat die hoeveelhede KOH benodig om die opbrengs van fenol (15.3 – 16.0) te maksimeer, is in die bestek van 5–7 wt.%. Analise van die bio-olie het gewys dat die opbrengs van syringol en guajakol hul maksimum waardes het by 450 °C en 4.5 wt.% KOH inhoud met opbrengsverhogings van 0.70 wt.% en 0.6 wt.%, wat 106% en 83% onderskeidelik, verteenwoordig, in vergelyking met dié van pirolise sonder katalis. Fenol (die P-tipe fenol) het ’n maksimum bereik by 450 °C en 8.5 wt.% KOH inhoud, met ’n opbrengs van 0.96 wt.%, ooreenstemmend met 141% verhoging.

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