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Processing Lignocellulosic Biomass into Ethanol - Implications of High Solid Loadings

Palmqvist, Benny LU (2014)
Abstract (Swedish)
Popular Abstract in Swedish

Ansträngningen att framställa nya förnyelsebara drivmedel har under de senaste årtionden ökat markant. Anledningarna har varit flera, dels oron för klimatpåverkan vid användningen av fossila bränslen, dels från ett nationellt energisäkerhetsperspektiv då lokal produktion skulle kunna stabilisera tillgången. Bioetanol är ett av de största biobränslena i världen och produceras idag framförallt från sockerrör och majsstärkelse. När man betraktar totala växthusgasutsläpp är i synnerhet majsstärkelse i längden nödvändigtvis inte hållbart. Analyser visar att ett mer hållbart alternativ är att använda hela växtmaterial och inte bara frö-delen som det görs idag. Omvandlingen av växtmaterial är dock en... (More)
Popular Abstract in Swedish

Ansträngningen att framställa nya förnyelsebara drivmedel har under de senaste årtionden ökat markant. Anledningarna har varit flera, dels oron för klimatpåverkan vid användningen av fossila bränslen, dels från ett nationellt energisäkerhetsperspektiv då lokal produktion skulle kunna stabilisera tillgången. Bioetanol är ett av de största biobränslena i världen och produceras idag framförallt från sockerrör och majsstärkelse. När man betraktar totala växthusgasutsläpp är i synnerhet majsstärkelse i längden nödvändigtvis inte hållbart. Analyser visar att ett mer hållbart alternativ är att använda hela växtmaterial och inte bara frö-delen som det görs idag. Omvandlingen av växtmaterial är dock en mycket mer komplicerad process där materialet först måste brytas ned enzymatiskt till fria sockermolekyler som sedan jäses till etanol. Vidare består växtmaterial generellt av flera olika sockerarter. Den mest förekommande sockerarten är glukos, som kan jäsas till etanol naturlig av vanlig bagerijäst, Saccharomyces cerevisiae, vilken traditionellt används inom etanolindustrin. För att jäsa xylos, den näst mest förekommande sockerarten i många växtyper, krävs däremot genmodifiering av jästen.

Forskningen har nu kommit så långt att de första kommersiella anläggningarna har börjat tas i drift. För dessa anläggningar är vikten av att kunna arbeta vid höga torrhalter stor, då detta förutspås ge stora ekonomiska fördelar i form av lägre investerings- och driftskostnader. Att arbeta vid höga torrhalter är dock en stor processteknisk utmaning, bland annat på grund av hög viskositet samt höga koncentrationer av fermentationsinhibitorer.

Arbetet i denna avhandling har syftat till att förstå den komplexa reologin, dvs. flödesegenskaperna, hos förbehandlat granmaterial. Dessutom kopplas dessa till hur omblandning påverkar den enzymatiska nedbrytningen av materialet till socker. Flödesegenskaperna visade sig vara starkt kopplade till mängden torrmaterial samt till fördelningen av fiberstorlek i materialet. Vidare påvisades en stark inverkan av omrörning på den enzymatiska hydrolysen av förbehandlad gran, vilket kunde kopplas till flödesbetingelserna i reaktorn. För mer gräslika material kunde dock ingen påverkan av omrörning påvisas. Detta var säkerligen kopplat till den mycket snabbare förvätskning som skedde under den enzymatiska hydrolysen.

Nya processtrategier utvecklades dessutom för att med hjälp av genmodifierade jäststammar effektivare omvandla både glukos och xylos till etanol. Genom att mata reaktorn med både material och enzymer så kunde xylosupptaget i processen ökas med 25 %, vilket gav en 10 %-tig ökning av den slutliga etanolkoncentrationen. Vid höga koncentrationer av ättiksyra kunde dessutom xylosupptaget ökas markant genom en ökning av pH. (Less)
Abstract
Fuel ethanol from lignocellulosic biomass has the potential to provide a sustainable replacement for traditional oil-based fuels. This dissertation assesses the processing of three different lignocellulosic materials – spruce, wheat straw and giant reed – at industrially relevant solid loadings. The work is divided into two main parts. The first part deals with the degradation of biomass to sugars, focusing on the complex rheological behavior of biomass slurries and the connection to mixing during high solids hydrolysis. The second part deals with the process design of combined hydrolysis and fermentation processes, focusing on efficient xylose co-consumption at high solids loadings.

Rheological characterization of steam... (More)
Fuel ethanol from lignocellulosic biomass has the potential to provide a sustainable replacement for traditional oil-based fuels. This dissertation assesses the processing of three different lignocellulosic materials – spruce, wheat straw and giant reed – at industrially relevant solid loadings. The work is divided into two main parts. The first part deals with the degradation of biomass to sugars, focusing on the complex rheological behavior of biomass slurries and the connection to mixing during high solids hydrolysis. The second part deals with the process design of combined hydrolysis and fermentation processes, focusing on efficient xylose co-consumption at high solids loadings.

Rheological characterization of steam pretreated spruce revealed strong non-Newtonian flow behavior with rapidly increasing viscosities and yield stress at high solid loadings, for instance the yield stress more than doubled when increasing the WIS content from 10 to 12 % (from 10 Pa to 24.5 Pa). Moreover, a strong effect of particle size distribution was found on both the viscosity and the yield stress. High viscosities create a need for efficient mixing during enzymatic hydrolysis of pretreated spruce. The hydrolysis rate was significantly influenced by both the amount and type of agitation. For pretreated spruce, for example, an increased agitation rate from 75 rpm to 500 rpm doubled the hydrolysis yield after 96 hours (an increase in yield from 35 to 72 %). The positive effect remained during scale-up to cubic meter scale and could be correlated to the flow conditions in the reactor. However, large discrepancies were found between different pretreated materials, and it became evident that the hydrolysis rate of giant reed was not affected by mixing. This was likely due to the much more rapid liquefaction achieved during the hydrolysis of giant reed.

In addition to glucose, many potential raw materials contain considerable amounts of the pentose sugar xylose. Xylose metabolism has today been successfully implemented in Saccharomyces cerevisiae through genetic engineering, although glucose is still the preferred substrate. In this work, xylose co-consumption was significantly enhanced by applying different process design strategies. By using a dual feed strategy, xylose consumption could be increased by 25 %, which resulted in a 10 % increase in final ethanol titer. It was also found that, in the presence of high acetic acid concentrations, xylose uptake could be significantly enhanced by increasing the pH. Whether or not this was beneficial for ethanol production, however, was found to be dependent on the specific process design. (Less)
Please use this url to cite or link to this publication:
author
supervisor
opponent
  • Felby, Claus, Department of Geosciences and Natural Resource Management, University of Copenhagen, Denmark
organization
publishing date
type
Thesis
publication status
published
subject
keywords
Lignocellulose, Bioethanol, High solid loadings, Biomass rheology, Enzymatic hydrolysis, Simultaneous Saccharification and co-Fermentation
pages
205 pages
publisher
Department of Chemical Engineering, Lund University
defense location
Kårhusets Hörsal (Kårhör), John Ericssons väg 3, Lund University Faculty of Engineering
defense date
2014-05-23 13:15
ISBN
978-91-7422-351-4
language
English
LU publication?
yes
id
bcd2be6c-bb42-4156-bdd3-4027204fa9bf (old id 4407249)
date added to LUP
2014-04-28 12:10:31
date last changed
2016-09-19 08:45:06
@misc{bcd2be6c-bb42-4156-bdd3-4027204fa9bf,
  abstract     = {Fuel ethanol from lignocellulosic biomass has the potential to provide a sustainable replacement for traditional oil-based fuels. This dissertation assesses the processing of three different lignocellulosic materials – spruce, wheat straw and giant reed – at industrially relevant solid loadings. The work is divided into two main parts. The first part deals with the degradation of biomass to sugars, focusing on the complex rheological behavior of biomass slurries and the connection to mixing during high solids hydrolysis. The second part deals with the process design of combined hydrolysis and fermentation processes, focusing on efficient xylose co-consumption at high solids loadings.<br/><br>
Rheological characterization of steam pretreated spruce revealed strong non-Newtonian flow behavior with rapidly increasing viscosities and yield stress at high solid loadings, for instance the yield stress more than doubled when increasing the WIS content from 10 to 12 % (from 10 Pa to 24.5 Pa). Moreover, a strong effect of particle size distribution was found on both the viscosity and the yield stress. High viscosities create a need for efficient mixing during enzymatic hydrolysis of pretreated spruce. The hydrolysis rate was significantly influenced by both the amount and type of agitation. For pretreated spruce, for example, an increased agitation rate from 75 rpm to 500 rpm doubled the hydrolysis yield after 96 hours (an increase in yield from 35 to 72 %). The positive effect remained during scale-up to cubic meter scale and could be correlated to the flow conditions in the reactor. However, large discrepancies were found between different pretreated materials, and it became evident that the hydrolysis rate of giant reed was not affected by mixing. This was likely due to the much more rapid liquefaction achieved during the hydrolysis of giant reed.<br/><br>
In addition to glucose, many potential raw materials contain considerable amounts of the pentose sugar xylose. Xylose metabolism has today been successfully implemented in Saccharomyces cerevisiae through genetic engineering, although glucose is still the preferred substrate. In this work, xylose co-consumption was significantly enhanced by applying different process design strategies. By using a dual feed strategy, xylose consumption could be increased by 25 %, which resulted in a 10 % increase in final ethanol titer. It was also found that, in the presence of high acetic acid concentrations, xylose uptake could be significantly enhanced by increasing the pH. Whether or not this was beneficial for ethanol production, however, was found to be dependent on the specific process design.},
  author       = {Palmqvist, Benny},
  isbn         = {978-91-7422-351-4},
  keyword      = {Lignocellulose,Bioethanol,High solid loadings,Biomass rheology,Enzymatic hydrolysis,Simultaneous Saccharification and co-Fermentation},
  language     = {eng},
  pages        = {205},
  publisher    = {ARRAY(0x87de960)},
  title        = {Processing Lignocellulosic Biomass into Ethanol - Implications of High Solid Loadings},
  year         = {2014},
}