Subcritical and Supercritical Water as a Cellulose Solvent

Lasse Tolonen

Subcritical and Supercritical Water as a Cellulose Solvent

Julkaisun otsikon käännös: Ali- ja ylikriittinen vesi selluloosan liuottimena

Lasse Tolonen

Biotuotteiden ja biotekniikan laitos

Tutkimustuotos: Doctoral Thesis › Collection of Articles

Abstrakti

Selluloosan liukenemattomuus yleisimpiin liuottimiin rajoittaa merkittävästi lignoselluloosan hyötykäyttöä polttoaineiden ja kemikaalien tuotannossa. Viimeisen kahden vuosikymmenen aikana ali- ja ylikriittiseen veteen pohjautuvat prosessit ovat herättäneet kiinnostusta mahdollisina ympäristöystävällisinä vaihtoehtoina selluloosan hydrolyysille. Aiemmat julkaisut viittaavat mahdollisuuteen, että selluloosan liukoisuus veteen kasvaa merkittävästi niin kutsutun kriittisen pisteen läheisyydessä. Tässä työssä tutkittiin mahdollisuutta liuottaa selluloosaa polymeerimuodossa käyttäen ali- tai ylikriittistä vettä, sekä mahdollisuutta ottaa talteen liuenneet polymeerit ilman merkittäviä hajoamisreaktioita. Työssä käytettiin kahta reaktorisysteemiä, joilla mikrokiteistä selluloosaa käsiteltiin 0,2 - 6,0 s ajan 245 - 380 °C lämpötilassa. Liukenematonta selluloosaa analysoitiin pyyhkäisyelektronimikroskoopilla, laajakulmaröntgensirontamenetelmällä sekä kiintoaine NMR menetelmällä. Selluloosapolymeerien depolymerisaatiota tutkittiin viskositeettianalyysillä ja kokoekskluusiokromatografialla; lisäksi depolymerisaatiokäyttäytymistä verrattiin satunnaispilkkutumis- ja päätepilkkoutumismalleihin. Dehydraatio ja fragmentaatio-reaktioita tutkittiin GC-MS, HPAEC-PAD-MS, and ESI-MS/MS menetelmillä. Lisäksi selluloosan liukenemisen Gibbsin energia 400 °C analysoitiin molekyylidynamiikkasimulaatioilla. Tulokset osoittavat, että alikriittinen vesi alle 300-320 °C on heikko liuotin selluloosalle. Tämä käy ilmi liuenneiden selluloosapolymeerien puutteesta sekä siitä ettei liukenemattomista selluloosapartikkeleista löydy merkkejä rakenteen turpoamisesta. Myös depolymerisaatio vaikuttaa rajoittuneen selluloosapartikkelien pinnalle. Selluloosan liukoisuus veteen lisääntyy kuitenkin lämpötilan ylittäessä 300-320 °C. Tällöin osa selluloosan rakenteesta muuttuu selluloosa II muotoon, mikä todennäköisesti aiheutuu veden liuotinominaisuuksien muutoksesta yhdessä samanaikaisen selluloosan depolymerisaation kanssa. Kohonnut liukoisuus liuottaa myös selluloosapolymeerejä, jotka saostuvat normaaliolosuhteissa; samanaikaiset depolymerisaatio-reaktiot kuitenkin rajoittavat merkittävästi saostuneen selluloosan polymerisaatioastetta. Saostuneen selluloosan saanto riippui suuresti lähtöaineena käytetyn mikroselluloosan ominaisuuksista ja vaihteli välillä 0-68%. Liuenneissa selluloosaketjuissa havaittiin huomattavia määriä levuglukosaani- ja erytroosipääteryhmiä. Molekyylidynamiikkasimulaatio osoittivat että selluloosan liukeneminen ylikriittisessä vedessä on termodynaamisesti mahdollista ja lisääntyy veden paineen tai tiheyden kasvaessa. Lisäksi simulaatiot osoittivat selluloosan liukenemisen veteen olevan normaaliolosuhteissa termodynaamisesti epäsuotuisaa.

Julkaisun otsikon käännös	Ali- ja ylikriittinen vesi selluloosan liuottimena
Alkuperäiskieli	Englanti
Pätevyys	Tohtorintutkinto
Myöntävä instituutio	Aalto-yliopisto
Valvoja/neuvonantaja	Sixta, Herbert, Vastuuprofessori Kruse, Andrea, Ohjaaja, Ulkoinen henkilö Wohlert, Jakob, Ohjaaja Bergenstråhle-Wohlert, Malin, Ohjaaja
Kustantaja	Aalto University
Painoksen ISBN	978-952-60-7024-7
Sähköinen ISBN	978-952-60-7025-4
Tila	Julkaistu - 2016
OKM-julkaisutyyppi	G5 Tohtorinväitöskirja (artikkeli)

Tutkimusalat

selluloosa
alikriittinen vesi
ylikriittinen vesi
hydrolyysi
liukoisuus

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http://urn.fi/URN:ISBN:978-952-60-7025-4Lisenssi: Määrittelemätön

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@phdthesis{23ad1e545a224101b7cc5dc53119421b,

title = "Subcritical and Supercritical Water as a Cellulose Solvent",

abstract = "Cellulose's recalcitrance to dissolve in common solvents is a major obstacle for the utilization of lignocellulose biomass into fuels and chemicals. As a promising answer to this challenge, subcritical and supercritical water have been proposed as a green medium for cellulose hydrolysis. Prior reports also indicate that the solubility of cellulose substantially increases near the critical point of water. This thesis investigated whether subcritical or supercritical water can dissolve cellulose as a polymer and whether the dissolved polymers can be recovered without extensive degradation. Two reactor systems were used to treat microcrystalline cellulose at 245-380 °C with treatment times between 0.2 and 6.0 s. Solid cellulose residue samples were investigated for evidence of swelling via scanning electron microscopy, wide angle X-ray, and solid-state NMR techniques. The depolymerization pattern of cellulose polymers was determined by viscosity analysis and size exclusion chromatography, and the results were compared to random chain cleavage and end-attack models. Dehydration and fragmentation reactions in dissolved polymers were analyzed by GC-MS, HPAEC-PAD-MS, and ESI-MS/MS techniques. In addition to the experimental work, the Gibbs energy of dissolution in supercritical water at 400 °C was analyzed via atomistic molecular dynamics simulations. The results showed that subcritical water below 300-320 °C is a poor cellulose solvent. This was demonstrated by the lack of polymeric dissolution products; also no evidence of cellulose swelling was found. The solubility of cellulose was enhanced when the temperature exceeded 300-320 °C. Then the structure of cellulose crystallites was transformed into cellulose II allomorph, likely caused by the enhanced solvent power and concomitant cellulose depolymerization. Increased solubility resulted in cellulose dissolution as a polymer of sufficiently high molar mass to precipitate at ambient temperature. At the same time the dissolved polymers were subjected to fast depolymerization which rendered the molar mass of precipitated cellulose low. The yield of cellulose precipitate depended on the characteristics of microcrystalline cellulose feedstock and spanned from 0 to 68 wt%. Significant amounts of levoglucosan and erythrose end-groups were detected in the dissolved cellulose chains. The molecular dynamics simulations indicated that the thermodynamics favor cellulose dissolution in supercritical water and an increasing water density or pressure decreases the Gibbs energy of dissolution while it predicted insolubility in ambient water.",

keywords = "cellulose, subcritical water, supercritical water, hydrolysis, solubility, selluloosa, alikriittinen vesi, ylikriittinen vesi, hydrolyysi, liukoisuus, cellulose, subcritical water, supercritical water, hydrolysis, solubility",

author = "Lasse Tolonen",

year = "2016",

language = "English",

isbn = "978-952-60-7024-7",

series = "Aalto University publication series DOCTORAL DISSERTATIONS",

publisher = "Aalto University",

number = "190",

address = "Finland",

school = "Aalto University",

}

TY - THES

T1 - Subcritical and Supercritical Water as a Cellulose Solvent

AU - Tolonen, Lasse

PY - 2016

Y1 - 2016

N2 - Cellulose's recalcitrance to dissolve in common solvents is a major obstacle for the utilization of lignocellulose biomass into fuels and chemicals. As a promising answer to this challenge, subcritical and supercritical water have been proposed as a green medium for cellulose hydrolysis. Prior reports also indicate that the solubility of cellulose substantially increases near the critical point of water. This thesis investigated whether subcritical or supercritical water can dissolve cellulose as a polymer and whether the dissolved polymers can be recovered without extensive degradation. Two reactor systems were used to treat microcrystalline cellulose at 245-380 °C with treatment times between 0.2 and 6.0 s. Solid cellulose residue samples were investigated for evidence of swelling via scanning electron microscopy, wide angle X-ray, and solid-state NMR techniques. The depolymerization pattern of cellulose polymers was determined by viscosity analysis and size exclusion chromatography, and the results were compared to random chain cleavage and end-attack models. Dehydration and fragmentation reactions in dissolved polymers were analyzed by GC-MS, HPAEC-PAD-MS, and ESI-MS/MS techniques. In addition to the experimental work, the Gibbs energy of dissolution in supercritical water at 400 °C was analyzed via atomistic molecular dynamics simulations. The results showed that subcritical water below 300-320 °C is a poor cellulose solvent. This was demonstrated by the lack of polymeric dissolution products; also no evidence of cellulose swelling was found. The solubility of cellulose was enhanced when the temperature exceeded 300-320 °C. Then the structure of cellulose crystallites was transformed into cellulose II allomorph, likely caused by the enhanced solvent power and concomitant cellulose depolymerization. Increased solubility resulted in cellulose dissolution as a polymer of sufficiently high molar mass to precipitate at ambient temperature. At the same time the dissolved polymers were subjected to fast depolymerization which rendered the molar mass of precipitated cellulose low. The yield of cellulose precipitate depended on the characteristics of microcrystalline cellulose feedstock and spanned from 0 to 68 wt%. Significant amounts of levoglucosan and erythrose end-groups were detected in the dissolved cellulose chains. The molecular dynamics simulations indicated that the thermodynamics favor cellulose dissolution in supercritical water and an increasing water density or pressure decreases the Gibbs energy of dissolution while it predicted insolubility in ambient water.

AB - Cellulose's recalcitrance to dissolve in common solvents is a major obstacle for the utilization of lignocellulose biomass into fuels and chemicals. As a promising answer to this challenge, subcritical and supercritical water have been proposed as a green medium for cellulose hydrolysis. Prior reports also indicate that the solubility of cellulose substantially increases near the critical point of water. This thesis investigated whether subcritical or supercritical water can dissolve cellulose as a polymer and whether the dissolved polymers can be recovered without extensive degradation. Two reactor systems were used to treat microcrystalline cellulose at 245-380 °C with treatment times between 0.2 and 6.0 s. Solid cellulose residue samples were investigated for evidence of swelling via scanning electron microscopy, wide angle X-ray, and solid-state NMR techniques. The depolymerization pattern of cellulose polymers was determined by viscosity analysis and size exclusion chromatography, and the results were compared to random chain cleavage and end-attack models. Dehydration and fragmentation reactions in dissolved polymers were analyzed by GC-MS, HPAEC-PAD-MS, and ESI-MS/MS techniques. In addition to the experimental work, the Gibbs energy of dissolution in supercritical water at 400 °C was analyzed via atomistic molecular dynamics simulations. The results showed that subcritical water below 300-320 °C is a poor cellulose solvent. This was demonstrated by the lack of polymeric dissolution products; also no evidence of cellulose swelling was found. The solubility of cellulose was enhanced when the temperature exceeded 300-320 °C. Then the structure of cellulose crystallites was transformed into cellulose II allomorph, likely caused by the enhanced solvent power and concomitant cellulose depolymerization. Increased solubility resulted in cellulose dissolution as a polymer of sufficiently high molar mass to precipitate at ambient temperature. At the same time the dissolved polymers were subjected to fast depolymerization which rendered the molar mass of precipitated cellulose low. The yield of cellulose precipitate depended on the characteristics of microcrystalline cellulose feedstock and spanned from 0 to 68 wt%. Significant amounts of levoglucosan and erythrose end-groups were detected in the dissolved cellulose chains. The molecular dynamics simulations indicated that the thermodynamics favor cellulose dissolution in supercritical water and an increasing water density or pressure decreases the Gibbs energy of dissolution while it predicted insolubility in ambient water.

KW - cellulose

KW - subcritical water

KW - supercritical water

KW - hydrolysis

KW - solubility

KW - selluloosa

KW - alikriittinen vesi

KW - ylikriittinen vesi

KW - hydrolyysi

KW - liukoisuus

KW - cellulose

KW - subcritical water

KW - supercritical water

KW - hydrolysis

KW - solubility

M3 - Doctoral Thesis

SN - 978-952-60-7024-7

T3 - Aalto University publication series DOCTORAL DISSERTATIONS

PB - Aalto University

ER -

Subcritical and Supercritical Water as a Cellulose Solvent

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