University of Groningen
Valorization strategies for pyrolytic lignin
Bernardes Figueiredo, Monique
DOI:
10.33612/diss.111703614
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2020
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Bernardes Figueiredo, M. (2020). Valorization strategies for pyrolytic lignin. University of Groningen.
https://doi.org/10.33612/diss.111703614
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Summary
The continuous increase in global energy demand, predicted depletion of fossil re-sources and pressing environmental concerns have encouraged research towards the development of sustainable alternatives for the current petroleum-based industry. In this context, lignocellulosic biomass is expected to play an important role in reducing CO2 emissions due to its high availability, renewable character and rich chemical structure. Biomass is mainly comprised of carbohydrates (cel-lulose and hemicel(cel-lulose) and aromatic biopolymers (lignin). Due to its chemical heterogeneity and structural complexity, full conversion into valuable chemicals, materials and energy, i.e. the so-called biorefinery, remains a major challenge.
Within the biorefinery concept, the well-established fast pyrolysis technology stands out as an attractive primary process to liquefy biomass due to its oper-ational flexibility, relatively low costs and high yields of up to 75 % of pyrolysis liquid. This liquid can be easily fractionated into a water-soluble sugar phase and a lignin phase (pyrolytic lignin, PL). While biobased sugars are used in various processes, lignin has been overlooked due to its complex structural features and is typically treated as a residue for low-value energy generation. Nonetheless, after proper upgrading it has great potential as a source of biofuels and biobased chemicals with a wide range of applications (see figure below).
This thesis presents characterization studies and the experimental evaluation of oxidative and reductive strategies for PL depolymerization. While oxidation further functionalizes the PL structure by adding oxygen, reduction promotes the formation of hydrocarbons by removing oxygen instead. A combined oxi-dative-reductive strategy for enhanced depolymerization towards valuable mo-nomeric building blocks and biobased fuels is also demonstrated and extended to other lignin types.
In Chapter 1, the state of the art on the formation pathways of PL and its structural features is reviewed together with reductive, oxidative and multistep (catalytic) approaches for PL upgrading.
In Chapter 2, a typical PL was characterized in detail by advanced chromato-graphic and spectroscopic techniques in order to get a more accurate overview
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of its chemical structure. Qualitative and quantitative analyses elucidated the main monomers (15% of PL) and motifs present in the oligomeric fragments (85 % of PL). Furthermore, 72 % of the oxygen content in PL was successfully assigned to specific functional groups, and based on this combined information, updated structural models are proposed. Contrasting with literature, native lignin linkages (i.e. β-O-4, β-β, β-5) were not identified, and it was shown that the amount of carbonyl and acid groups in the PL is substantial and therefore cannot be neglected.
In Chapter 3, a catalyst screening study is described for the catalytic hydrotreat-ment of neat PL (batch set-up) in order to evaluate the direct reductive upgrading. Carbon-supported noble metal catalysts were used (Ru/C, Pd/C, Pt/C, Rh/C), as well as sulphided catalysts typically used in the hydroprocessing of petro-based feedstocks (NiMo/Al2O3, CoMo/Al2O3). Reaction temperatures ranging from
350–400 oC were evaluated, and the main reaction pathways were proposed.
Pd/C showed the best results, i.e. the highest carbon yield in the organic phase and monomer yields of up to 33 % based on PL intake.
In Chapter 4, six PLs obtained from the fast pyrolysis of different biomass sources were characterized in detail and hydrotreated with Pd/C (batch set-up) in order to evaluate the general applicability of the direct reductive upgrading. A range of reaction times (1–4 h) and temperatures (350–435 °C) were applied to assess their effects on product composition. The use of PLs from pine and sunflower seed peel led to the highest monomer yields (up to 39 % based on PL intake). Statistical modelling of the experimental dataset revealed relevant feed-product relations. For instance, the Mw (from GPC analysis) and amounts
of aromatic C-C and C-O linkages (from 13C-NMR analysis) in the parent PL
were shown to be excellent predictors for the combined yield of aromatics and phenolics in the hydrotreated organic products.
In Chapter 5, experiments aiming the valorization of PL by a non-catalytic oxidative approach using ozone are described. Experiments with PL were per-formed in a semi-batch set-up at 0 °C with methanol as the solvent, and ozonation times ranging from 15–240 minutes were evaluated. Extensive depolymerization and the formation of low molecular weight (di)carboxylic acids and esters (up to 45 %), along with oligomeric structures consisting of a highly oxygenated aliphatic backbone were observed. The ozonation of thirteen representative lignin model compounds and a biosynthetic lignin aided further elucidation on the most re-active chemical functionalities (phenolic OH and aliphatic unsaturations). Based on the results, main pathways involved in the ozonation process are proposed, i.e. heterolytic cleavage of aromatic rings and cleavage of inter-aromatic bonds with high electronic density followed by secondary oxidation and esterification reactions.
Following the observed reactivity of ozone towards PL in Chapter 5, the ozo-nation of PL in a continuous flow microreactor with methanol under ambient conditions is described in Chapter 6. Advantages of the continuous set-up com-pared to batch, i.e. improved mass transfer, safe handling, efficient use of ozone and less over-oxidation were demonstrated using vanillin as model compound. In addition, rapid depolymerization (seconds timescale) of a representative PL
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was achieved (Mw decrease of 29 %). The depolymerization potential of ozone was also demonstrated with two organosolv lignins (Mw decrease of 70 %). Fur-thermore, the ozonated PL was shown to yield higher levels of depolymerization (25–30 % lower Mw) upon a catalytic hydrotreatment with Pd/C, as well as higher amounts of identified monomers in the product oil (2.5-fold increase) in com-parison to the direct catalytic hydrotreatment of PL (without prior ozonation).
In Chapter 7, an experimental study is provided in which the ozonation meth-odology was extended to other technical lignins (Kraft and Organosolv), which are more complex regarding chemical structure and nearly insoluble in alcohols. Semi-batch experiments were performed under ambient conditions with ethanol. Ozonation times ranging from 20–120 minutes led to the solvolysis of a large portion of the lignin feedstocks (up to 87 %) and to the formation of depolym-erized lignin oils (40–75 % lower Mw). Lower particle sizes favored higher yields due to increased contact areas and better dispersion of the lignin particles in the ethanol medium. Furthermore, the prior degradation of the lignin structure was shown to be beneficial for the ozone-mediated solvolysis due to the increased proportions of highly reactive functionalities.
Finally, in Chapter 8, a two-step oxidative-reductive approach for the improved depolymerization of technical lignins (Kraft lignin, PL and Fabiola Organosolv lignin) in a larger (batch) scale using methanol and ethanol is provided. The hydrotreated organic products from the two-step approach showed improved properties compared to the products from a direct hydrotreatment, i.e. equivalent yields of organic product with a significantly lower Mw (up to 43 % lower), higher volatility, improved calorific value (up to 45.3 MJ/kg) and higher monomer yields (10–12 wt% higher). Apart from methanol, it was shown that also ethanol was suitable for the process, being highly advantageous due to its biobased character and low toxicity. While ozonation led to oxygen incorporation in the lignin fragments, which is not necessarily desired in hydroprocessing feeds, this oxygen was readily removed by the subsequent hydrotreatment step. The overall synergy between the two steps comes from the ability of ozone to break otherwise unreac-tive C-C double bonds and improve depolymerization, and thus the accessibility of the lignin structure for further processing. The results highlight the potential of this combined strategy for the valorization of recalcitrant technical lignins.
Overall, we expect that the promising results reported in this thesis will con-tribute to the development of (pyrolysis-based) biorefineries, whose realization ultimately depends on the development of cost-effective ways to maximize the value of the lignin fraction.
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Samenvatting
Het toenemende wereldwijde energieverbruik, de voorspelde uitputting van fossiele brandstoffen en ongerustheid over het milieu drijven de ontwikkeling van duurzame alternatieven voor de huidige op olie gebaseerde industrie. Voor de reductie van de CO2 uitstoot wordt een belangrijke rol aan lignocellulosische biomassa toegedicht vanwege haar omvangrijke beschikbaarheid, hernieuw-baarheid en haar rijke chemische structuur. Biomassa bestaat voornamelijk uit koolhydraten (cellulose en hemicellulose) en aromatische biopolymeren (lignine). Vanwege de complexheid en variaties in de chemische structuur blijft het een enorme uitdaging om biomassa volledig om te zetten naar waardevolle chemicaliën, materialen en energie (de zogenoemde bioraffinage).
Binnen het concept van bioraffinage springt de doorontwikkelde snelle pyrolyse technologie eruit als een aantrekkelijke eerste bewerkingsstap om biomassa vloeibaar te maken vanwege de goede controle over de reactie condities, relatief lage kosten en opbrengsten tot 75 % gepyrolyseerde vloeistof. Deze vloeistof kan gemakkelijk gescheiden worden in een wateroplosbare suiker fractie en een lignine fractie (pyrolytische lignine, PL). Terwijl de suikers afkomstig van biomassa in meerdere processen wordt toegepast, wordt lignine over het hoofd gezien vanwege de complexe chemische samenstelling en alleen toegepast als laagwaardige brandstof. Desalniettemin heeft lignine veel potentie als bron voor biobrandstof en biobased chemicaliën met ruime toepassingsmogelijkheden, mits er goede opwaarderingsprocessen op lignine worden toegepast.
Dit proefschrift presenteert zowel de karakterisering en de experimentele eva-luatie van oxidatieve en reductieve strategieën voor de depolymerisatie van PL. Waar oxidatie van PL meer functionaliteit geeft door zuurstof in de structuur te implementeren, verwijdert reductie juist zuurstof hetgeen de formatie van kool-waterstoffen in de hand werkt. Een gecombineerde oxidatie-reductie strategie voor verbeterde depolymerisatie richting waardevolle monomere bouwstenen en bio-brandstof wordt ook aangetoond en verder uitgebreid naar meerdere types lignine. In Hoofdstuk 1 worden de meest recente routes naar de vorming van PL en de structurele eigenschappen hiervan geëvalueerd samen met de reductieve, oxidatieve en meerstaps (katalytische) methodes voor de opwaardering van PL.
In Hoofdstuk 2 wordt een representatieve PL tot in detail gekarakteriseerd door middel van chromatografische en spectroscopische technieken om een nauwkeuriger beeld te krijgen van de chemische structuur. Kwalitatieve en kwantitatieve verhelderde de structuur van PL en toonde de meest voorkomende monomeren (15% van de PL) en verbindingen in de oligomeren (85% van de PL). Verder kon 72% van het totale zuurstofgehalte toegekend worden aan specifieke functionele groepen en op basis van deze gecombineerde resultaten kon er een verbeterd modelstructuur opgesteld worden. In tegenstelling tot de literatuur werden originele lignine verbindingen (β-O-4, β-β, β-5) niet geïdentificeerd worden en werd er aangetoond dat de hoeveelheid carbonyl en zuur groepen in de PL aanzienlijk is en daarom niet verwaarloosd kan worden.
In Hoofdstuk 3 wordt een screening van katalysatoren beschreven voor de gekatalyseerde hydrobewerking van puur PL (in batch) om de reductieve
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opwaardering goed te kunnen vergelijken. Edelmetalen op koolstof werden gebruikt (Ru/C, Pd/C, Pt/C, Rh/C) en sulfide katalysatoren die in het algemeen worden toegepast voor de hydrobewerking van petrochemische grondstoffen (NiMO/Al2O3,CoMo/Al2O3). Reactietemperaturen van 350–400 °C werden getest en de belangrijkste reactieroutes werden voorgesteld. Pd/C liet de beste resultaten zien, in dit geval de hoogste koolstof opbrengst in de organische fractie en een monomeer opbrengsten van maximaal 33% gebaseerd op de PL opname. In Hoofdstuk 4 worden zes PLs verkregen door middel van snelle pyrolyse van verschillende soorten biomassa tot in detail gekarakteriseerd en werd er hydrobewerking met Pd/C (in batch) toegepast om de algemene toepasbaarheid van de directe reductieve opwaardering goed in kaart te brengen. Er werden verscheidene reactietijden (1–4 uur) en temperaturen (350–435 °C) toegepast om het effect op de product compositie te beoordelen. Het gebruik van PL van pijnboom en schil van zonnebloempitten gaven de hoogste monomeer opbrengst (maximaal 39 % gebaseerd op de PL opname). Statistische modellering van de verkregen experimentele data ontwaarde relevante grondstof/product samen-hang. Zo kan aan de hand van de Mw (verkregen via GPC analyse) en het aantal aromatische C-C en C-O bindingen (verkregen via 13C-NMR analyse) in de oorspronkelijke PL de gecombineerde opbrengst van aromaten en fenolen in de organische producten (na hydrobewerking) uitstekend voorspeld worden.
In Hoofdstuk 5 worden niet gekatalyseerde oxidatie experimenten met ozon die gericht zijn de valorisatie van PL behandeld. Deze experimenten met PL werden in een semi-batch opstelling uitgevoerd op 0 °C met methanol als oplosmiddel, waarbij de invloed van ozonisatie tijden van 15–240 minuten werd bestudeerd. Verregaande depolymerization en de formatie van (di)carbonbonzuur en esters met een laag molecuulgewicht (tot maximaal 4 5% opbrengst) en oligomeren met een hoge mate van zuurstofhoudende alifatische hoofdketens. De ozonisatie van dertien representatieve lignine model verbindingen en een biosynthetische lignine hielpen met het verdere opheldering van de meeste reactieve functionele groepen (fenolische OH en onverzadigde alifatische groepen). Aan de hand van deze resultaten konden de belangrijkste reactieroutes die betrokken zijn bij ozonisatie ontwaard worden, o.a. heterolytische doorklieving van de aromatische ring structuur en het breken van de binding tussen aromatische structuren met een hoge elektrondichtheid gevolgd door oxidatie en esterificatie reacties.
Als een gevolg van de geobserveerde reactiviteit van ozon met PL in hoofd-stuk 5, wordt de ozonisatie van PL in continue doorstroomde microreactoren met methanol onder omgevingscondities is beschreven in Hoofdstuk 6. De voor-delen van een continue installaties, ten opzichte van batch, zijn een verbeterde stofoverdracht, verbeterde veiligheid, efficiënter gebruik van ozon en minder over oxidatie, hetgeen werd gedemonstreerd op vanilline. Verder werd er snelle depolymerisatie (enkele secondes) van een representatieve PL behaald (een afname van 29 % van de Mw). De grote potentie van ozon op het gebied van de-polymerisatie werd verder aangetoond op twee organosolv lignines (een afname van 70 % van de Mw). Verder werd er aangetoond dat er op PL na ozonisatie nog verdere depolymerisatie gedaan kan worden door katalytisch hydrobehandeling met Pd/C (25–30 % afname van Mw). Ook was er na deze behandeling een
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grotere hoeveelheid (2.5-voudig) identificeerbare monomeren in de olie fractie vergeleken met de directe katalytisch hydrobehandeling (zonder ozonisatie stap). In Hoofdstuk 7 wordt experimenteel onderzoek getoond waarbij de ozonisatie procedure wordt toegepast op andere technische lignines (Kraft en Organosolv), welke complexer zijn qua chemische structuur en bijna onoplosbaar in alcoholen. Semi-batch experimenten werden uitgevoerd onder omgevingscondities waarbij ethanol werd gebruikt als oplosmiddel. Ozonisatie tijden van 20–120 minuten leidden tot solvolyse van een groot gedeelte van het lignine startmateriaal (maxi-maal 87 %) en de formatie van een olie van gedepolymeriseerde lignine (een afname van 40–75 % van de Mw). Kleinere deeltjesgrootte zorgde voor hogere opbrengst vanwege de toename in contactoppervlak en een betere verspreiding van de lignine deeltjes in de oplossing. Verder werd duidelijk dat een eerdere afbraakstap van de lignine structuur bevorderlijk was voor de solvolyse met ozon, dankzij een toename van reactieve functionaliteiten.
Ten slotte wordt in Hoofdstuk 8 een tweetraps oxidatieve-reductieve benader-ing toegepast voor de verdere verbeterbenader-ing voor de depolymerisatie van technische lignines (Kraft lignine en Fabiola organosolv lignine) op grotere (batch) schaal met methanol en ethanol als oplosmiddel. De verkregen organische producten van deze tweetraps hydrobehandeling had betere eigenschappen vergeleken met de producten verkregen door directe hydrobehandeling. Zo was de opbrengst van organische producten vergelijkbaar maar was de Mw aanmerkelijk lager (maximaal 43 % lager), hogere vluchtigheid, een verbeterde verbrandingswaarde (maximaal 45.3 MJ/kg) en hogere opbrengst van monomeren (10–12 % hoger). Behalve methanol is ook ethanol geschikt om toe te passen in dit proces, met als bijkomende voordelen het groene karakter en lagere giftigheid. Hoewel ozonisatie leidde tot een toename van de hoeveelheid zuurstof in de lignine fragmenten, iets wat niet per se gewenst is voor hydrobewerking, kon de zuurstof weer weggehaald worden in de volgende bewerkingsstap. Het synergetisch effect van de twee stappen is het vermogen van ozon tot het breken van de normaliter onreactieve, C-C dubbele bindingen (verbeterde depolymerisatie) en hierbij de lignine beter beschikbaar te maken voor verdere bewerking. The resultaten benadrukken de grote potentie voor deze gecombineerde aanpak voor de valo-risatie van de moeilijk bewerkbare technische lignines.
Wij verwachten dat de veelbelovende resultaten die behandeld worden in dit proefschrift willen bijdragen tot de verdere ontwikkeling van de (op pyrolyse gebaseerde) bioraffinage, wiens totstandkoming zal afhangen van de ontwikkeling van rendabele manieren om de waarde van lignine fractie verder te verhogen.
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Resumo
A crescente demanda energética global, o esgotamento previsto de recursos fósseis e as pressões ambientais têm encorajado a pesquisa no sentido de desenvolver al-ternativas sustentáveis para a atual indústria baseada em petróleo. Neste contexto, espera-se que a biomassa lignocelulósica desempenhe um papel importante na redução das emissões de CO2 devido à sua alta disponibilidade, caráter renovável e rica estrutura química. A biomassa lignocelulósica é composta principalmente por carboidratos (celulose e hemicelulose) e biopolímeros aromáticos (lignina). Devido à heterogeneidade química e complexidade estrutural, sua conversão completa em químicos de alto valor agregado, materiais e energia (a chamada biorefinaria) constitui um grande desafio.
Dentro do conceito de biorefinaria, a pirólise rápida é uma tecnologia bem estabelecida que se destaca como um processo primário para liquefazer biomassa devido à sua flexibilidade operacional, baixo custo e altos rendimentos de até 75 % de líquido de pirólise. Este líquido pode ser facilmente separado em uma fase aquosa (contendo açúcares derivados dos carboidratos) e uma fase insolúvel em água derivada da lignina (denominada lignina pirolítica, LP). Enquanto os açúcares de biomassa são largamente utilizados em vários processos, a lignina tem sido negligenciada e é tipicamente tratada como resíduo para geração de energia de baixo valor. No entanto, após passar por um processo de despolimerização adequado, a lignina tem enorme potencial como fonte de biocombustíveis e compostos químicos com uma vasta gama de possíveis aplicações.
Esta tese apresenta estudos de caracterização e avaliação experimental de estratégias oxidativas e redutoras para a despolimerização de LP. Enquanto a oxidação funcionaliza ainda mais a estrutura da LP ao adicionar oxigênio, a redução leva à formação de hidrocarbonetos por meio da remoção de oxigênio. Uma estratégia oxidativa-redutora combinada visando maior despolimerização e, portanto, maior produção de monômeros de alto valor agregado também é demonstrada e estendida para outros tipos de lignina.
No Capítulo 1, o estado da arte relativo à formação da LP e suas caracterís-ticas estruturais é revisado, juntamente com abordagens (catalícaracterís-ticas) redutoras, oxidativas e combinadas para a valorização da LP.
No Capítulo 2, uma LP típica é caracterizada em detalhe por técnicas espectros-cópicas e cromatográficas avançadas com o intuito de obter uma visão geral mais precisa de sua estrutura química. Análises qualitativas e quantitativas elucidaram os principais monômeros (15 % da LP) e as principais funcionalidades químicas presentes nos fragmentos oligoméricos (85 % da LP). Ademais, 72 % do oxigênio contido na LP foi atribuído com sucesso a grupos funcionais específicos e, com base nas informações obtidas, modelos estruturais atualizados são propostos. Contrastando com a literatura, ligações químicas presentes na lignina nativa (β-O-4, β-β, β-5) não foram identificadas na LP. Também foi demonstrado que a quantidade de grupos carbonila e ácidos carboxílicos na LP é substancial, não podendo ser negligenciada.
No Capítulo 3, é descrito um estudo de triagem de catalisadores para o hidro-tratamento catalítico da LP (reator batelada pressurizado com hidrogênio), a fim
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de avaliar esta rota promissora de valorização. Foram utilizados catalisadores de metais nobres suportados em carbono (Ru/C, Pd/C, Pt/C, Rh/C), bem como catalisadores sulfurados normalmente utilizados no hidroprocessamento de matérias-primas originadas do petróleo (NiMo/Al2O3, CoMo/Al2O3). Foram avaliadas temperaturas de reação entre 350–400 °C, e as principais rotas rea-cionais são propostas. O catalisador Pd/C apresentou os melhores resultados, ou seja, o maior rendimento de carbono na fase orgânica e um rendimento de monômeros de até 33 % (baseado na quantidade inicial de LP).
No Capítulo 4, seis LPs provenientes da pirólise rápida de diferentes fontes de biomassa foram caracterizadas em detalhe e hidrogenadas com Pd/C (reator batelada pressurizado com hidrogênio) com o intuito de avaliar a aplicabilidade geral da valorização redutiva. Vários tempos de reação (1–4 h) e temperaturas (350–435 °C) foram testados para avaliar os efeitos na composição do produto orgânico. O uso de LPs derivadas do pinus e da casca da semente de girassol produziu rendimentos superiores de monômeros (até 39 % com base na quan-tidade inicial de LP). Uma modelagem estatística dos dados experimentais ob-tidos revelou relações significativas entre as características estruturais da LP e os produtos orgânicos obtidos após hidroprocessamento. Por exemplo, o peso molecular médio (obtido via GPC) e as quantidades relativas de ligações C-C e C-O aromáticas (obtidas via 13C-NMR) na LP inicial mostraram-se excelentes parâmetros para predizer o rendimento combinado de aromáticos e fenólicos nos produtos orgânicos hidroprocessados.
No Capítulo 5, a valorização da LP por meio de uma abordagem oxidativa não-catalítica usando ozônio é avaliada experimentalmente. Os experimentos foram realizados a 0 °C utilizando metanol como solvente, e tempos de reação variando entre 15–240 minutos foram avaliados (reator semi-batelada). Uma despolimerização extensa foi observada, levando à formação de ácidos (di)car-boxílicos e (di)ésteres de baixo peso molecular (rendimentos de até 45 % com base no produto oxidado), além de estruturas oligoméricas alifáticas altamente oxigenadas. A ozonização de treze compostos químicos representativos da lignina e de uma lignina bio-sintética ajudaram a elucidar as funcionalidades químicas mais reativas (OH fenólico e ligações alifáticas insaturadas). Com base nos resultados, as principais rotas reacionais envolvidas no processo de ozonização são propostas, consistindo na quebra heterolítica de anéis aromáticos e quebra de ligações inter-aromáticas com alta densidade eletrônica, além de reações secundárias de oxidação e esterificação.
Tendo como base a reatividade do ozônio em relação à LP observada no Capí-tulo 5, a ozonização da LP em um microreator de fluxo contínuo com metanol em condições ambientais é descrita no Capítulo 6. Vantagens da configuração contínua em relação à batelada (transferência de massa aprimorada, manuseio seguro, uso eficiente do ozônio) foram demonstradas usando vanilina (com-posto representativo da LP). Além disso, foi observada uma rápida despolime-rização (escala de tempo de segundos) da LP, com diminuição de 29 % no peso molecular médio. O potencial do ozônio também foi demonstrado com duas ligninas do tipo organosolv (diminuição de 70 % no peso molecular médio). Além disso, demonstrou-se que um subsequente hidrotratamento (catalisado
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por Pd/C, reator batelada em pequena escala) da LP ozonizada leva a um in-cremento na despolimerização (peso molecular médio 25–30 % menor), além de quantidades de monômeros no produto orgânico significativamente maiores (2.5 vezes) em comparação ao hidrotratamento catalítico direto da LP (ou seja, sem ozonização prévia).
No Capítulo 7, a metodologia de ozonização é estendida para outras ligninas técnicas (do tipo Kraft e Organosolv), estas mais complexas estruturalmente e praticamente insolúveis em álcoois. Experimentos em um reator semi-batelada foram realizados em condições ambiente com etanol. Tempos de reação variando entre 20–120 minutos levaram à solvólise de uma grande parte da lignina (até 87 %) e à formação de óleos de lignina despolimerizados (peso molecular médio 40–75 % mais baixo). Partículas de lignina menores favoreceram maiores ren-dimentos devido ao aumento da área de contato e melhor dispersão no meio etanólico. Além disso, a degradação prévia da estrutura da lignina demonstrou ser benéfica para a solvólise mediada por ozônio devido às maiores proporções de funcionalidades químicas reativas.
Finalmente, no Capítulo 8, uma abordagem oxidativa-redutora é proposta para a despolimerização de ligninas técnicas usando metanol e etanol. Os produtos orgânicos após hidrotratamento (reator batelada pressurizado com hidrogê-nio e catalisado por Pd/C) usando a abordagem em duas etapas apresentaram propriedades aprimoradas comparados aos produtos obtidos por meio do hi-drotratamento direto das ligninas. Por exemplo, rendimentos equivalentes de produto com peso molecular médio significativamente mais baixo (até 43 % menor), além de maior volatilidade, maior valor calorífico (até 45.3 MJ/kg) e maiores proporções de monômeros foram observados ao realizar a ozoniza-ção antes do hidrotratamento. Além de metanol, foi demonstrado que etanol também pode ser utilizado com sucesso na etapa oxidativa do processo, sendo altamente vantajoso devido à sua baixa toxicidade e possibilidade de obtenção a partir da biomassa. Enquanto a ozonização levou à incorporação de oxigênio nos fragmentos de lignina, o que não é necessariamente desejado nas matérias primas de hidroprocessamento, este oxigênio foi prontamente removido na etapa subsequente. A sinergia entre as duas etapas vem da capacidade do ozônio de quebrar ligações alifáticas insaturadas, aprimorando a despolimerização e, por-tanto, a acessibilidade da estrutura da lignina no processamento subsequente. Os resultados destacam o potencial desta estratégia combinada para a valorização de ligninas técnicas complexas e tipicamente recalcitrantes.
No geral, esperamos que os resultados promissores relatados nesta tese con-tribuam para o desenvolvimento de biorefinarias baseadas na pirólise rápida de biomassa lignocelulósica, visto que a sua realização depende diretamente do desenvolvimento de processos para maximizar o valor da fração de lignina.
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El continuo aumento en la demanda energética global, la alta utilización de com-bustibles fósiles y las urgentes preocupaciones medioambientales han motivado la investigación de alternativas sostenibles en la actual industria basada en el petróleo. En este contexto, se espera que la biomasa lignocelulósica sea de gran importancia para reducir las emisiones de CO2, debido a su alta disponibilidad, compleja estructura química y siendo un recurso natural renovable. La biomasa está compuesta principalmente por carbohidratos (celulosa y hemicelulosa) y biopolímeros aromáticos (lignina). Debido a su heterogeneidad química y complejidad estructural, la conversión total en productos químicos, materiales y energía (i.e. biorrefinería) es todavía un gran reto.
Dentro del concepto de biorrefinería, la tecnología de pirólisis rápida está bien establecida como un atractivo proceso para licuar biomasa debido a su alta flexibilidad operacional, relativamente bajo costo y un rendimiento de hasta 75 % de líquido pirolítico. Este líquido puede ser fácilmente fraccionado en dos fases: azúcares solubles en agua y lignina (lignina pirolítica, LP). A pesar de que estos azúcares son utilizados en numerosos procesos, la lignina no es comúnmente considerada debido a su compleja estructura y generalmente es tratada como residuo de bajo valor para generación energética. Sin embargo, tras un correcto procesamiento, tiene un gran potencial como fuente de biocombustibles y quími-cos, con una gran variedad de aplicaciones.
Esta tesis presenta los estudios de caracterización y evaluación experimental de estrategias oxidativas y reductivas para la depolimerización de LP. La oxidación funcionaliza la estructura de la LP añadiendo oxígeno, y la reducción promueve la formación de hidrocarburos removiendo oxígeno. Además, se evaluó una nueva estrategia utilizando oxidación y reducción en conjunto para aumentar la depolimerización de LP y otras ligninas técnicas.
En el Capítulo 1, los últimos avances en la formación de LP y sus características estructurales son analizados, junto con las técnicas (catalíticas y no catalíticas) de valorización reductivas, oxidativas y combinadas para PL.
En el Capítulo 2, una típica LP es caracterizada detalladamente utilizando técni-cas cromatográfitécni-cas y espectroscópitécni-cas para la precisa obtención de su estructura química. Los análisis cuantitativo y cualitativo esclareció los monómeros princi-pales (15 % de la LP) y los motivos presentes en los fragmentos oligoméricos (85 % de la LP). Adicionalmente, 72 % del oxígeno contenido en LP fue satisfactoria-mente asignado as grupos funcionales específicos, y basado en esta información se proponen modelos estructurales actualizados. Comparado con la literatura, no fue posible identificar los enlaces nativos de la lignina (i.e. β-O-4, β-β, β-5), y se muestra que la cantidad de carbonilos y grupos ácidos en la LP es substancial y por tanto no deben ser ignorados.
En el Capítulo 3, se describe un estudio para el hidrotratamiento catalítico de la LP para evaluar la actualización reductiva directa en un reactor batch. Se utilizaron metales nobles soportados sobre carbono como catalizadores (Ru/C, Pd/C, Pt/C, Rh/C), así como catalizadores sulfurados utilizados típicamente en el hidroprocesamiento de materias primas provenientes de la industria del petróleo
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(NiMo/Al2O3, CoMo/Al2O3). Las temperaturas de reacción entre 350–400 oC son
evaluadas, y se proponen las vías de reacción principales. El uso de Pd/C produce los mejores resultados, i.e. el mayor rendimiento de carbono en la fase orgánica y rendimiento de monómeros hasta un 33 % de la LP original.
En el Capítulo 4, seis LPs obtenidas mediante pirólisis rápida son caracter-izadas en detalle e hidrotratadas con Pd/C para evaluar la aplicación general del reformado reductivo directo en un reactor batch. Se estudiaron tiempos de reacción (1–4 h) y temperaturas (350–435 °C) sobre la composición de los productos. El uso de LPs procedentes de pino y cáscaras de semillas de girasol produce el mayor rendimiento de monómeros (hasta un 39 % de la LP original). El análisis estadístico de los datos experimentales muestra las relaciones entre materia prima y productos. Por ejemplo, el peso molecular promedio (Mw) procedente del análisis de GPC y la cantidad de enlaces aromáticos C-C y C-O proveniente del análisis de 13C-NMR pueden predecir de excelente forma el rendimiento combinado de aromáticos y fenólicos en la fase orgánica después del hidrotratamiento.
En el Capítulo 5, se describen experimentos enfocados a la valorización de la LP mediante un procedimiento oxidativo no catalítico utilizando ozono (re-actor semi-batch). Se realizan experimentos a 0 °C utilizando metanol como solvente, con tiempos de ozonización entre 15–240 minutos. Se observa una amplia depolimerización y formación de ácidos y ésteres (di)carboxílicos (hasta un 45 %), junto con estructuras oligoméricas alifáticas altamente oxigenadas. La ozonización de trece compuestos representativos de lignina y una lignina biosintética permiten dilucidar las funciones químicas más reactivas (OH fenólico y alifáticos insaturados). Basado en estos resultados, se proponen las vías de reacción principales para los procesos de ozonización, i.e. escisión heterolítica de anillos aromáticos y escisión de enlaces inter-aromáticos con alta densidad electrónica, seguida de reacciones secundarias de oxidación y esterificación.
Continuando con la reactividad observada del ozono hacia la LP en el Capítulo 5, la ozonización de la LP in un micro reactor de flujo continuo utilizando metanol se describe en el Capítulo 6. Se demuestran múltiples ventajas de un proceso continuo utilizando vanilina como compuesto modelo, i.e. mejor transferencia de masa, manejo seguro, uso eficiente del ozono y menor sobre-oxidación. Adi-cionalmente, se consigue una rápida depolimerización de una LP representativa (reducción del Mw de un 29 %). También se demuestra la depolimerización de dos ligninas organosolv (reducción del Mw de un 70 %) con el uso de ozono. La LP ozonizada muestra mayor rendimiento de depolimerización (25–30 % menor Mw) tras un hidrotratamiento catalítico con Pd/C, así como un mayor número de monómeros identificados en el producto (2.5 veces mayor) comparado con el hidrotratamiento directo de la LP (sin ozonización).
En el Capítulo 7, se propone un estudio experimental donde la metodología de ozonización es extendida a otras ligninas técnicas (Kraft y Organosolv), que son más complejas con respecto a su estructura química y son prácticamente insolubles en alcoholes. Los experimentos fueron realizados a temperatura am-biente utilizando ethanol en un reactor semi-batch. Los tiempos de ozonización de 20–120 minutos llevan a la solvolisis de una larga porción de la lignina inicial
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(hasta 87 %) y a la formación de aceites de lignina depolimerizados (40–75 % menor Mw). El menor tamaño de las partículas de lignina favorece un mayor rendimiento debido a un aumento del área de contacto y una mejor dispersión en etanol. Adicionalmente, se muestra como la degradación de la estructura de lignina es beneficiosa para la solvolisis con ozono debido a un incremento de las funcionalidades altamente reactivas.
Finalmente, en el Capítulo 8, se propone un método oxidativo-reductivo en dos pasos para una depolimerización mejorada de ligninas técnicas (Kraft, PL y Fabiola organosolv) mediante el uso de metanol y etanol en un reactor batch. Comparado con el hidrotratamiento directo, los productos orgánicos provenien-tes del método oxidativo-reductivo tienen mejores propiedades, i.e. equivalente rendimiento de productos orgánicos con un Mw significativamente menor (hasta 43 % menor), alta volatilidad, un incremento de valor calorífico (hasta 45.3 MJ/kg) y mayores rendimientos de monómeros (10–12 wt% mayor). Además del metanol, se muestra como el uso de etanol es aplicable a este proceso, con la ventaja de ser menos tóxico. A pesar de que la ozonización causa la incorporación de oxígeno en los fragmentos de lignina, este puede ser eliminado en el siguiente paso de hidrotratamiento. La sinergia general entre los dos pasos proviene de la habil-idad del ozono para romper enlaces dobles C-C y mejorar la depolimerización y consecuentemente la accesibilidad de la estructura de la lignina para futuros procesos. Los resultados muestran el alto potencial de esta estrategia combinada para la valorización de ligninas técnicas recalcitrantes.
En resumen, esperamos que los prometedores resultados que aparecen es esta tesis puedan contribuir en el desarrollo de biorefinerías basadas en pirólisis, cuya realización depende del desarrollo de formas económicas y efectivas de maximizar el valor de las fracciones de lignina.
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Acknowledgments
Vier zomers lang... They went fast and it’s almost hard to believe that this journey
is coming to an end! Here I would like to express my sincere gratitude to every-one who contributed and gave me support during my PhD, and believe me, it’s a really difficult task to put it into words.
I have to start by going back to 2013, two years before my PhD started. Robbie, being able to do an internship at BTG was paramount for standing here today, and I’m really grateful for the opportunity you gave me back then (I learned so much in so little time!). Fast-forwarding to 2015, some people probably heard me talking about how lucky I was with my PhD supervisors, and this couldn’t be more true. Prof. Erik Heeres: first of all, thank you for giving me the opportunity to work in your group. These four years were extremely important for my professional and personal development and I have learned so much from our discussions and from your feedback and advice. Since day one you were kind, easygoing and gave me all the guidance I needed, but also the freedom to be independent and decide which direction to take on my research. Furthermore, you and Peter were able to put me back on track and keep my motivation alive on the
“better-to-burn-lignin-indeed” moments, which is truly remarkable... Dr. Peter Deuss, having
you as my co-supervisor made me go farther than I expected with this thesis. I cannot thank you enough for the support, encouragement and for being always available for a (unplanned) discussion - sorry for the several interruptions in your office! You’re admirable and I’m sure that your academic career will continue to be very successful. I must also thank both of you for the great, fun non-research conversations and willingness to help me on my next professional steps.
Next, I’d like to thank the members of the assessment committee, Prof. Francesco Picchioni, Prof. Paolo Pescarmona and Prof. Pieter Bruijnincx, for taking the time and effort to read and evaluate my PhD thesis. Francesco and Paolo, while we (unfortunately) did not have the chance to collaborate, you’ve been always supportive and open for a nice discussion, thank you so much, it really makes a difference. Pieter, your work with lignin is inspiring and I am really happy to have my thesis evaluated by you.
A big thank you to all the professors and technicians at the chemical engineering department and to our great secretaries Kim and Geraldine. Together you are responsible for a friendly and welcoming work environment (I feel quite lucky for that too, vide proposition 14) that translates in always fun borrels, labuitjes and dinners. Prof. Jun Yue and Arne, thank you for joining forces on the very nice ozone-microreactor collaboration! Douwe, Dian, Gabriel, Prof. Carlos Pires and Yin, thank you for the fruitful research collaborations, these side projects have broadened my knowledge and I’m glad that I could contribute to them. Talking about scientific output would never be complete without acknowledging the hard work of Zorica Jotic and Folkert Keij, the Master students who contributed substantially to this thesis. Supervising your projects was an important learning experience for me, and I’m really glad to be chosen as your daily supervisor! I wish you lots of success in your future endeavors. Hanwen Gu, it was nice to supervise your Bachelor project as well and I wish you all the success! Robbie
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Venderbosch (also Hans Heeres and the whole BTG team), thank you for the always great meetings, fruitful (and fun) discussions and for providing the pyro-lytic feedstocks used in my experimental work. Erwin Wilbers, Marcel de Vries and Anne Apeldoorn, thank you for the technical support with the sometimes moody high pressure reactor (or moody me, but blame the reactor…). Jan Henk Marsman and Léon Rohrbach, thank you so much for the support with the lignin chromatographic madness and all the other analytical techniques needed for my projects. I started my PhD knowing little about them and you were true life saviors. Arjan Kloekhorst and Yin Wang, you helped me tremendously with the set-up and analyses in the beginning of my PhD, I am really grateful for that. I thank Thomas and the software engineering team for the excellent work towards building a new open source platform for GCxGC-FID data processing, I enjoyed very much to be part of this project! Thanks also to the former “lignin team”, now extended to “valuable chemicals from renewable resources team” - I enjoy very much our Friday meetings (or group therapy sessions?) and always appreciate your valuable help. To my lab mates in the 5118.0264 playground: Yin, Idoia, Jessi, Bala, Gabriel, Dian, Huaizhou, Xi, Qingqing, among others – handling (and smelling) all those lignin products was not exactly pleasant, but at least we were not alone in pain (and to be fair, we shared quite some joy as well).
So far I’ve talked about work a lot, but we all know that a PhD goes far beyond that… And I owe the amazing memories I have since my arrival in Groningen to the equally amazing friends and colleagues that this lovely city gave me. Ale, my paranymph (and witness of my wedding!), our friendship was one of the best surprises of my PhD. Estefanía, my paranymph, I’m so glad that the PhD Day brought us together as such good friends. Thanks to both of you for helping me with the preparation of my PhD defense! Will, you were the first friend I made in my very first day in Groningen. All our nice conversations and your commit-ment to make this world a better place are inspiring. Ana, it was such a great coincidence meeting you again in Groningen after being in the same exchange program in Eindhoven. Now I’m looking forward to visiting you in Spain! To my (previous and current) officemates Ria, Yin, Ionela, Henk, Homer, Savitha, Xiang, Douwe and Jordi: days are much more pleasant with you around and I’m so glad for our conversations and fun moments together.
During my PhD, there was a special group of people able to cheer up even the worst days. Coincidence or not, they are directly related to some really funny stories (as well as deadly hangovers), and I’ll try to be brief here otherwise this section will become a second book… Pablito (toilet narcoleptic and selfie
master) & Magda, Laurens (the most enthusiastic) & Liselotte, Patrizio (also known as Vin Diesel), Nicola (father of the Nicolian dialect, now being updated in a field trip around the world), Jessi (catlover and beerlover just like me), Idoia
(great taste in music and tortilla skills), Arne (top 30 mastermind), Douwe (proud
member of our fully international office, best beer buddy ever), Bala (globetrotter/ globeclimber), Martijn (owner of the funniest t-shirts and enemy of silence), Léon
(karaoke superstar), Gui (keeping Brazil well represented), Homer (always
cheer-ful), Maryam (always sweet), Ale (“a bit”), Arjen, Alice, Arjan & Zheng, Ionela,
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Aldo, Claudia, Pedro, Myriam, Felipe, Tatiana, Giovanni, Alexander, Matteo, Jordi.. Thank you so much for the uncountable (and often unspeakable) borrels, BBQ’s in the park, boat trips and great evenings together! It’s impossible not to acknowledge G.T.D. Bernoulli for organizing so many awesome events (Top 30, Woktober and Xmas dinner to name a few) – I won’t dare to list names as my memory would certainly fail me, but in short a big thank you to all Bernoullians! I would also like to thank Frita, Susanti, Angela, Prima and Ria (all very sweet
and very much missed), Henk (always helping everybody), Okan, Ciaran, Dian,
Wen, Huaizhou, Zhenlei, Qingqing, Shilpa, Rowie, Khaled, Wenze, Songbo, Yifei, Gabriel, Zhenchen, Li He, Cui, Shun, Yanfei, Jing, Daili, Xi, Yanyan, Yehan, Zahra, Yasser, Bauwan, Afshin, Dina, Aleksander, Tuhin, Nihat and many others that I might have forgotten to mention (sorry for that!).
In the past years I also got involved in extracurricular activities that brought me even more good friends (!). Being part of the program committee of the PhD Day 2016 was a great, fun experience shared with Estefanía, Ionela, Kumar, Marleen, Yingqiu, Musty and Steven. My years as a member of the GSSE PhD Council were shared with Daniel, Christian, Sabrina, Vincent, Frita, Carmem, Alka, Saurabh, Yvonne, Renate, Qingqing, Daphne, Taichi, among others. I am grateful for all the events we organized together, the many PhD-related discussions and loads of fun times. I wish you all the best in your PhD and future career and I’m so glad I met you along the way! I also thank Marc van der Maarel, Marco Koopman and Ika Neven for the nice discussions and support.
Besides this amazing network of people in Groningen, I got an incredible amount of support during my PhD from the ones directly responsible for who I am, my foundation, my family. I dedicate this book to my grandmothers Isabel, Luisa and Olga as are they are the biggest examples of resilience, wisdom, love and unshakable happiness I know. To my loving parents, Dinah and Genebaldo: Mom, you’ve always been so supportive and I admire you so much, thank you for everything you did and still do for me. Dad, we are so coordinated that we even started a PhD together (spoiler: he finished first)! I couldn’t be more grateful for our amazing friendship, you always motivated me to do my best, be independent and dream big. Tia Giovana, thank you so much for your always caring words and support. Dinda, I wish I was there with you especially now, but soon we will be having fun together. Iago, my brother and lifetime friend, I admire and miss you every single day. Leca, my lovely sister (and now mother of Marcela and Caetano!), I can’t wait to be there with you and I’m so happy to see your family growing. To all my aunts, uncles and cousins spread around Bahia, Minas, Rio and São Paulo, thank you for the nice time we spend together when I’m there. In particular, Tia Mariana, Débora, Flávia and Lívia, our everlasting friendship is one of the most precious things I got. To Horacio, Mari Carmen, Maribel and all my family from Yecla, thanks for making me feel so loved and for the great times we spent together in Spain and in the Netherlands. Iarinha, having you, Dani and André nearby makes me so happy. To my “chosen family” Clarissa, Fernanda, Isadora, Maíra and Michelle: our sisterhood is the biggest luck of my life. Knowing that we will be always together (regardless of distance) gives me courage, comfort and lift my spirits. Livinha, I have the best memories
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of our adventures in Europe and I look forward to the next ones! Kika and Dudu, I can’t wait to have you here and add more funny stories to our portfolio. I love and miss you all so much! To Alex, my wonderful husband: you make me a better person every day and I am so grateful for everything you have done for me – from moving to Groningen to all the support and care throughout this journey. When I think about our beautiful story, genuine love and friendship, I feel the luckiest person in the world.
Finally, (I have the impression that I write “a bit” too much…) this is the end of my thesis! Thank you for reading it and for your interest in my work!
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List of publications
1. Figueirêdo, M.B., Jotic, Z., Deuss, P.J., Venderbosch, R.H. and Heeres, H.J., 2019. Hydrotreatment of pyrolytic lignins to aromatics and phenolics using heterogeneous catalysts. Fuel processing technology, 189, pp.28–38.
2. Figueirêdo, M.B., Deuss, P.J., Venderbosch, R.H. and Heeres, H.J., 2019. Valorization of pyrolysis liquids: Ozonation of the pyrolytic lignin fraction
and model components. ACS Sustainable Chemistry & Engineering, 7(5), pp.4755–4765.
3. Figueirêdo, M.B., Deuss, P.J., Venderbosch, R.H. and Heeres, H.J. Cata-lytic hydrotreatment of pyroCata-lytic lignins from different sources to biobased chemicals: Identification of feed-product relations (Submitted to Biomass &
Bioenergy in 2019).
4. Figueirêdo, M.B., Keij, F.W., Hommes, A., Deuss, P.J., Venderbosch, R.H., Yue, J. and Heeres, H.J., 2019 Efficient depolymerization of lignin to biobased
chemicals using a two-step approach involving ozonation in a continuous flow microreactor followed by catalytic hydrotreatment. ACS Sustainable
Chemistry & Engineering, 7(22), pp.18384-18394.
5. Figueirêdo, M.B., Heeres, H.J. and Deuss, P.J., 2019 Ozone mediated de-polymerization and solvolysis of technical lignins at ambient conditions in ethanol. Sustainable Energy & Fuels.
6. Figueirêdo, M.B., Venderbosch, R.H., Heeres, H.J. and Deuss, P.J. In-depth structural characterization of the lignin fraction of pine-derived pyrolysis oil (Submitted to Journal of Analytical and Applied Pyrolysis in 2019). 7. Figueirêdo, M.B., Deuss, P.J., Venderbosch, R.H. and Heeres, H.J. A two-step
approach for the conversion of technical lignins to biofuels. (Manuscript in preparation, to be submitted to Advanced Sustainable Systems).
8. Yin, W., Venderbosch, R.H., Alekseeva, M.V., Figueirêdo, M.B., Heeres, H., Khromova, S.A., Yakovlev, V.A., Cannilla, C., Bonura, G., Frusteri, F. and Heeres, H.J., 2018. Hydrotreatment of the carbohydrate-rich fraction of pyrolysis liquids using bimetallic Ni based catalyst: Catalyst activity and product property relations. Fuel Processing Technology, 169, pp.258–268. 9. Jambeiro, T.A., Silva, M.F.S., Pereira, L.G.G., da Silva Vasconcelos, D., Batalha
Silva, G., Figueirêdo, M.B., Lima, S.B. and Pires, C.A.M., 2018. Fast pyrol-ysis of sisal residue in a pilot fluidized bed reactor. Energy & fuels, 32(9), pp.9478–9492.
10. Zijlstra, D.S., Lahive, C.W., Analbers, C.A., Figueirêdo, M.B., Lancefield, C.S. and Deuss, P.J. Mild lignin extraction with alcohols; the influence of benzylic alkoxylation on the extraction and lignin characteristics (Submitted to ACS
Sustainable Chemistry & Engineering in 2019).
11. Pereira, L.G.G., Figueirêdo, M.B., Santosa, D., Lima, S.B., Heeres, H.J. and Pires, C.A.M. Catalytic hydrotreatment of pyrolysis oil from sisal residue using Ni-Cu catalysts on a Al-MCM-41 support (Manuscript in preparation).
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List of attended conferences
Oral presentations
1. Figueirêdo, M.B., Jotic, Z., Deuss, P.J., Venderbosch, R.H. and Heeres, H.J.
Oxidative and reductive strategies for pyrolytic lignin valorization, 4th
Interna-tional Congress on Catalysis for Biorefineries (CatBioR), 2017, Lyon, France. 2. Figueirêdo, M.B., Jotic, Z., Deuss, P.J., Venderbosch, R.H. and Heeres, H.J.
Experimental studies on the hydrotreatment of pyrolytic lignin using hetero-geneous catalysts, 19th Netherlands Conference on Chemistry and Catalysis
(N3C XIX), 2018, Noordwijkerhout, the Netherlands.
3. Figueirêdo, M.B., Deuss, P.J., Venderbosch, R.H. and Heeres, H.J.
Depolym-erization of technical lignins and model compounds at room conditions with ozone, Chemistry as Innovating Science (CHAINS), 2018, Veldhoven, the
Netherlands.
4. Figueirêdo, M.B., Deuss, P.J., Venderbosch, R.H. and Heeres, H.J.
Depolym-erization of technical lignins and model compounds at room conditions with ozone, 4th ENTEG annual meeting, 2018, Haren, the Netherlands.
5. Figueirêdo, M.B., Deuss, P.J., Venderbosch, R.H. and Heeres, H.J.
Valori-zation of technical lignins: oxidative and reductive strategies, 2nd Groningen
Engineering Center (GEC) annual scientific meeting, 2019, Groningen, the Netherlands.
Poster presentations
1. Figueirêdo, M.B. and Heeres, H.J. Pyrolysis oil upgrading through oxidation
followed by catalytic hydrotreatment. 1st ENTEG annual meeting, 2015, Haren,
the Netherlands.
2. Figueirêdo, M.B., Venderbosch, R.H. and Heeres, H.J. Pyrolysis oil
upgrad-ing by mild oxidation followed by catalytic hydrotreatment, 17th Netherlands
Conference on Chemistry and Catalysis (N3C XVII), 2016, Noordwijkerhout, the Netherlands.
3. Figueirêdo, M.B., Venderbosch, R.H. and Heeres, H.J. Insights on the
ozo-nation of pyrolytic lignin. 2nd ENTEG annual meeting, 2016, Haren, the
Netherlands.
4. Figueirêdo, M.B., Venderbosch, R.H. and Heeres, H.J. Pyrolytic lignin
upgrad-ing via ozonolysis, 18th Netherlands Conference on Chemistry and Catalysis
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