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Enhanced Enzymatic Hydrolysis of Lignocellulose in Bioethanol Production Substrate Interactions with Surfactants and Polymers

Börjesson, Johan LU (2007)
Abstract (Swedish)
Popular Abstract in Swedish

Ett av dagens stora miljöproblem är de höga halter av koldioxid som ackumuleras i atmosfären. En stor del av samhällets koldioxidutsläpp kommer från förbränning av fossila bränslen som kol, olja eller bensin. Ett av de mest lovande alternativa bränslen som kan ersätta dagens stora bensinförbrukning är bioetanol. Cellulosainnehållande restprodukter från skogsbruk (t.ex. grenar, toppar och rötter) och jordbruk (t.ex. halm) ger en riklig tillgång på råmaterial för tillverkning av bioetanol. Den största potentialen för att skapa en konkurrenskraftig industri och bioetanolprodukt ligger i att utveckla en bioteknikbaserad tillverkning. Produktionen av bioetanol sker då med hjälp av en blandning av... (More)
Popular Abstract in Swedish

Ett av dagens stora miljöproblem är de höga halter av koldioxid som ackumuleras i atmosfären. En stor del av samhällets koldioxidutsläpp kommer från förbränning av fossila bränslen som kol, olja eller bensin. Ett av de mest lovande alternativa bränslen som kan ersätta dagens stora bensinförbrukning är bioetanol. Cellulosainnehållande restprodukter från skogsbruk (t.ex. grenar, toppar och rötter) och jordbruk (t.ex. halm) ger en riklig tillgång på råmaterial för tillverkning av bioetanol. Den största potentialen för att skapa en konkurrenskraftig industri och bioetanolprodukt ligger i att utveckla en bioteknikbaserad tillverkning. Produktionen av bioetanol sker då med hjälp av en blandning av olika cellulosanedbrytande enzymer (cellulaser) som bryter ner cellulosapolymerer till socker (glukos), vilket sedan fermenteras (jäses) till etanol. Effektiva enzymproducenter är svampar som står för en stor del av den naturliga nedbrytningen av växtmaterial. I Sverige utgör rester från granskog (biomassa) den största delen av tillgängligt råmaterial. För att få högre utbyte vid hydrolys och fermentation förbehandlas biomassan så att endast lignin och cellulosa återstår (lignocellulosa). Den mest tidskrävande och kostsamma delprocessen är den enzymatiska hydrolysen av lignocellulosa. Ett av problemen består i förluster av dyra enzymer genom adsorption till lignindelen i lignocellulosa. De studier som presenteras i denna avhandling visar att tillsater av ytaktiva ämnen (detergenter eller polymerer) kan avsevärt öka hastigheten vid nedbrytningen samt utbytet av glukos. Detta sker genom att de ytaktiva ämnena konkurrerar ut enzymerna från ligninytor på lignocellulosan. En större mängd enzymer finns på det sättet tillgängligt för hydrolys av cellulosa. Tillsatser av detergenter har även undersökts i en processutformning med samtidig hydrolys och jäsning; även då med positiv effekt på processen. Genom förståelse av lignocellulosans interaktioner med enzymer och ytaktiva ämnen kan förändringar göras vid hydrolysprocessen samt enzymer utvecklas med förbättrade ytegenskaper. För att vidareuveckla de enzymblandningar som skall användas vid etanolproduktion behövs mer kunskap kring dessa. I denna studie har även ett nytt effektivt enzymsystem med intressanta egenskaper undersökts. Förekomsten av proteinnedbrytande enzymer (proteaser) i enzymblandningar är ett förekommande problem. En av de mest använda och studerade enzymblandningarna produceras av svampen Hypocrea jecorina. Ett tidigare okänt proteas från denna svamp har indentifierats och dess egenskaper undersökts. (Less)
Abstract
Ethanol produced from cellulose is a promising future alternative fuel. The production process has three main steps: (i) pretreatment of raw material to increase degradability; (ii) enzymatic hydrolysis of cellulose to produce glucose; (iii) fermentation of glucose into bioethanol. This thesis contains studies with the aim to improve the enzymatic hydrolysis of cellulose from steam pretreated spruce. Improvements have been made by additions of surface active additives such as non-ionic surfactants or poly(ethylene glycol) polymers (PEG). It was found that that these surface active additives increased the enzymatic hydrolysis by reduction of non-productive adsorption of cellulases on the lignin part of the substrate. As a result the enzyme... (More)
Ethanol produced from cellulose is a promising future alternative fuel. The production process has three main steps: (i) pretreatment of raw material to increase degradability; (ii) enzymatic hydrolysis of cellulose to produce glucose; (iii) fermentation of glucose into bioethanol. This thesis contains studies with the aim to improve the enzymatic hydrolysis of cellulose from steam pretreated spruce. Improvements have been made by additions of surface active additives such as non-ionic surfactants or poly(ethylene glycol) polymers (PEG). It was found that that these surface active additives increased the enzymatic hydrolysis by reduction of non-productive adsorption of cellulases on the lignin part of the substrate. As a result the enzyme consumption could be significantly lowered with retained cellulose conversion. With addition of PEG a higher hydrolysis temperature (50 C) could be used; reduced deactivation of enzymes is due to PEG adsorption on lignin surfaces. By increased temperature the conversion rate was significantly improved. PEG was found to interact with lignin by hydrophobic interaction. Lignin adsorbed PEG polymers excludes enzymes from the lignin surface, which will increase the amount enzymes available for cellulose hydrolysis. A study on the adsorption of cellulase modules showed difference in lignin affinity for the cellulose binding modules of the enzymes Cel7A and Cel7B. This was suggested to be caused by surface exposed hydrophobic aromatic residues. Simultaneous saccharification and fermentation of spruce lignocellulose with Tween 20 additions resulted in increased ethanol yields and shorter residence times.



Enzymes in a new efficient cellulase system from Penicillium brasilianum has been purified and characterised. Activity studies showed that these enzymes were two cellobiohydrolases, three endoglucanases and one xylanase. Two of the endoglucanase enzymes were found to belong to glycoside hydrolase family 5 and 12.



In production of cellulases, degradation of produced enzymes by proteases is not uncommon. An unidentified protease from the widely used cellulase producer Hypocrea jecorina has been purified and characterised. The new protease was found to be a trypsin-like serine protease. (Less)
Please use this url to cite or link to this publication:
author
supervisor
opponent
  • Prof. Viikari, Liisa, VTT Biotechnology
organization
publishing date
type
Thesis
publication status
published
subject
keywords
enzymologi, Penicillium brasilianum, SSF, Ethanol, Proteins, enzymology, Proteiner, Protease, Adsorption, PEG, Surfactant, Hydrolysis, Lignocellulose, Cellulase, Hypocrea jecorina, Trichoderma reesei, Cellulose
pages
140 pages
publisher
Center for Chemistry and Chemical Engineering
defense location
Kemicentrum, Sölvegatan 39, Lund. Hörsal B
defense date
2007-01-19 10:30
ISBN
978-91-7422-139-8
language
English
LU publication?
yes
id
667f98f0-e724-48e5-b10e-aa1e10440fcc (old id 547757)
date added to LUP
2007-10-09 09:45:59
date last changed
2016-09-19 08:45:01
@phdthesis{667f98f0-e724-48e5-b10e-aa1e10440fcc,
  abstract     = {Ethanol produced from cellulose is a promising future alternative fuel. The production process has three main steps: (i) pretreatment of raw material to increase degradability; (ii) enzymatic hydrolysis of cellulose to produce glucose; (iii) fermentation of glucose into bioethanol. This thesis contains studies with the aim to improve the enzymatic hydrolysis of cellulose from steam pretreated spruce. Improvements have been made by additions of surface active additives such as non-ionic surfactants or poly(ethylene glycol) polymers (PEG). It was found that that these surface active additives increased the enzymatic hydrolysis by reduction of non-productive adsorption of cellulases on the lignin part of the substrate. As a result the enzyme consumption could be significantly lowered with retained cellulose conversion. With addition of PEG a higher hydrolysis temperature (50 C) could be used; reduced deactivation of enzymes is due to PEG adsorption on lignin surfaces. By increased temperature the conversion rate was significantly improved. PEG was found to interact with lignin by hydrophobic interaction. Lignin adsorbed PEG polymers excludes enzymes from the lignin surface, which will increase the amount enzymes available for cellulose hydrolysis. A study on the adsorption of cellulase modules showed difference in lignin affinity for the cellulose binding modules of the enzymes Cel7A and Cel7B. This was suggested to be caused by surface exposed hydrophobic aromatic residues. Simultaneous saccharification and fermentation of spruce lignocellulose with Tween 20 additions resulted in increased ethanol yields and shorter residence times.<br/><br>
<br/><br>
Enzymes in a new efficient cellulase system from Penicillium brasilianum has been purified and characterised. Activity studies showed that these enzymes were two cellobiohydrolases, three endoglucanases and one xylanase. Two of the endoglucanase enzymes were found to belong to glycoside hydrolase family 5 and 12.<br/><br>
<br/><br>
In production of cellulases, degradation of produced enzymes by proteases is not uncommon. An unidentified protease from the widely used cellulase producer Hypocrea jecorina has been purified and characterised. The new protease was found to be a trypsin-like serine protease.},
  author       = {Börjesson, Johan},
  isbn         = {978-91-7422-139-8},
  keyword      = {enzymologi,Penicillium brasilianum,SSF,Ethanol,Proteins,enzymology,Proteiner,Protease,Adsorption,PEG,Surfactant,Hydrolysis,Lignocellulose,Cellulase,Hypocrea jecorina,Trichoderma reesei,Cellulose},
  language     = {eng},
  pages        = {140},
  publisher    = {Center for Chemistry and Chemical Engineering},
  school       = {Lund University},
  title        = {Enhanced Enzymatic Hydrolysis of Lignocellulose in Bioethanol Production Substrate Interactions with Surfactants and Polymers},
  year         = {2007},
}