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Advancing Lignocellulosic Biorefineries through Co-Production of Hemicellulosic Biopolymers and Bioenergy
Thesis (PhD)--Stellenbosch University, 2022.
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| Format: | Thesis |
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Stellenbosch : Stellenbosch University
2022
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| _version_ | 1867613972661796864 |
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| access_status_str | Open Access |
| author | Mihiretu, Gezahegn Teklu |
| author2 | Görgens, Johann Ferdinand |
| author_browse | Görgens, Johann Ferdinand Mihiretu, Gezahegn Teklu |
| author_facet | Görgens, Johann Ferdinand Mihiretu, Gezahegn Teklu |
| author_sort | Mihiretu, Gezahegn Teklu |
| collection | Thesis |
| dc_rights_str_mv | Stellenbosch University |
| description | Thesis (PhD)--Stellenbosch University, 2022. |
| format | Thesis |
| id | oai:scholar.sun.ac.za:10019.1/124968 |
| institution | Stellenbosch University (South Africa) |
| language | en_ZA |
| last_indexed | 2026-06-10T12:44:38.662Z |
| license_str | Other — see source repository |
| provenance_str_mv | Harvested via OAI-PMH from SUNScholar — Stellenbosch University Repository |
| publishDate | 2022 |
| publishDateRange | 2022 |
| publishDateSort | 2022 |
| publisher | Stellenbosch : Stellenbosch University |
| publisherStr | Stellenbosch : Stellenbosch University |
| record_format | dspace |
| source_str | SUNScholar — Stellenbosch University Repository |
| spelling | oai:scholar.sun.ac.za:10019.1/124968 Advancing Lignocellulosic Biorefineries through Co-Production of Hemicellulosic Biopolymers and Bioenergy Mihiretu, Gezahegn Teklu Görgens, Johann Ferdinand Chimphango, Annie Fabian Abel Stellenbosch University. Faculty of Engineering. Dept. of Process Engineering. Lignocellulosic biorefineries Lignocellulose Biopolymers Hemicellulosic biopolymers Xylans Biomass energy Thesis (PhD)--Stellenbosch University, 2022. ENGLISH SUMMARY: This research project was conceived in the context of advancing a lignocellulosic biorefinery for co-production of xylan biopolymers, bioethanol and electricity from two agro-industrial materials, namely sugarcane residues (SCT) and aspen wood (AW). The research was primarily designed to include two full-fledged experimental studies and one techno-economic case study. Accordingly, two biomass pretreatment approaches, namely: microwave-assisted pressurised hot water (MWA-PHW) and alkalinised steam explosion pretreatment (ASEPT) methods were experimentally investigated for their effect on the extraction of xylan from SCT and AW. Extraction experiments (via MWAPHW and ASEPT) were conducted by varying temperatures between 165 – 205 ℃ and retention times 3 - 22 min at test points identified using Central Composite Design (CCD) as response surface methodology (RSM). Pretreatment conditions were intended for a dual purpose: maximizing xylan extraction yield while simultaneously enhancing cellulose digestibility. Experimental results on xylan yield and cellulose digestibility were analysed using ANOVA method to establish optimal conditions for significantly enhanced values. Accordingly, under the MWA-PHW method, maximum xylan yields of 66 and 50%, and highest cellulose digestibility of 78 and 74%, were respectively attained for AW at (195℃, 20 min) and SCT at (195 ℃, 15 min). Whereas maximum xylan yields of 51 and 24%, and highest cellulose digestibility of 92 and 81%, were attained for SCT and AW respectively, following their pretreatment under ASEPT at (204 ℃, 10 min). Under both methods, the xylan extracts were predominantly non-monomeric with insignificant formation of degradation products. This strongly suggested both MWA-PHW and ASEPT were viable approaches for xylan extraction purposes. ANOVA results also revealed that temperature was the dominant factor influencing the xylan yield and cellulose digestibility. The techno-economic case study was aimed at evaluating the economic viability of the biorefinery for co-production of xylan biopolymers, bioethanol and electricity (i.e. main-case scenario, MCS) against two benchmark processes, i.e. Base-case (BCS) and Intermediate-case (ICS) scenarios, where only bioethanol and electricity are produced from sugarcane residues (Basis: daily capacity of 1000 tons of dry biomass subjected to ASEPT condition of 204 ℃ and 10 min). The study results showed that co-production of xylan biopolymers substantially improved the economic performance of the main biorefinery case (i.e. MCS) by lowering the selling price of ethanol against higher values under the benchmark processes. A minimum hemicellulose selling price (MHSP) of 809 USD/ton of xylan co-product was determined by fixing ethanol selling price at 0.70 USD/L (market price of ethanol in 2019); higher MHSP values certainly lead to further lower prices. Minimum ethanol selling prices (MESP) under the MCS, BCS and ICS were respectively estimated at 0.61, 0.95 and 0.81 USD/L, where the xylan price was assumed at 1000 USD/ton (=> MCS). Even though the economic viability of the main biorefinery case was significantly enhanced with co-production of xylan than without, this multiproduct biorefinery complex was rendered rather energy-intensive as a result of such coproduction scheme where the recovery of xylan biopolymers necessitated substantial thermal and electrical energy demands. From environmental point of view, the coproduction of xylan biopolymers along with bioethanol and electricity was shown to have a positive contribution towards mitigating GHG emissions from fossil sources. The GHG emissions savings under the MCS, BCS and ICS were estimated around 69, 64 and 65% against gasoline as fossil baseline of 90 gCO2eq/MJ (RSB-Global), but there was only marginal difference between the savings under the main biorefinery case and that under the benchmark processes. AFRIKAANS OPSOMMING: Hierdie navorsingsprojek is ontwikkel in die konteks van die bevordering van ’n lignosellulosiese bioraffinadery vir ko-produksie van xilaanbiopolimere, bio-etanol en elektrisiteit uit twee agri-industriële materiale, naamlik suikerrietresidu’s (SCT) en espenhout (AW). Die navorsing is ontwerp rondom twee volledige eksperimentele studies en een tegno-ekonomiese gevallestudie. Dienooreenkomstig, is twee biomassa voorbehandelingbenaderings, naamlik mikrogolf-geassisteerde warm water onder druk (MWA-PHW) en gealkaliseerde stoomontploffing voorbehandeling (ASEPT) metodes eksperimenteel ondersoek vir hul effek op die ekstrahering van xilaan uit SCT en AW. Ekstraksie-ekperimente (via MWA-PHW en ASEPT) is uitgevoer deur temperature te varieer tussen 165 – 205 °C en retensietye tussen 3 – 22 min by toetspunte geïdentifiseer deur Sentrale Samestelling Ontwerp (CCD) as responsoppervlakmetodologie (RSM) te gebruik. Voorbehandelingskondisies is bedoel vir ’n tweeledige doel: maksimering van xilaanekstraksie-opbrengs terwyl sellulose verteerbaarheid gelyktydig verbeter word. Eksperimentele resultate op xilaanopbrengs en selluloseverteerbaarheid is geanaliseer deur ANOVA-metode te gebruik om optimale kondisie/s vir beduidende verbeteringswaardes te bepaal. Dienooreenkomstig, onder die MWA-PHW-metode, is maksimum xilaanopbrengs van 66 en 50%, en hoogste selluloseverteerbaarheid van 78 en 74%, onderskeidelik, verkry vir AW by (195 °C, 20 min) en SCT by (195 °C, 15 min). Maksimum xilaanopbrengste van 51 en 24%, en hoogste selluloseverteerbaarheid van 92 en 81%, is verkry vir SCT en AW onderskeidelik, na hul voorbehandeling onder ASEPT by (204 °C, 10 min). Onder beide metodes, was die xilaanekstraksies oorwegend niemonomeries met onbeduidende formasie van degradasie produkte daarvan. Hierdie stel sterk voor dat beide MWA-PHW en ASEPT lewensvatbare benaderings vir xilaanekstraksie doeleindes is. ANOVA-resultate het ook gewys dat temperatuur die hooffaktor is wat xilaanopbrengs en selluloseverteerbaarheid beïnvloed. Die tegno-ekonomiese gevallestudie het beoog om die ekonomiese lewensvatbaarheid van die bioraffinadery vir ko-produksie van xilaanbiopolimere, bioetanol en elektrisiteit (i.e. hoofgeval scenario, MCS) te evalueer teenoor twee standaardprosesse, i.e. Basis-geval (BCS) en Intermediêre-geval (ICS) scenario’s, waar slegs bio-etanol en elektrisiteit geproduseer word uit suikerrietresidu’s (Basis: daaglikse kapasiteit van 1000 ton droë biomassa onderwerp aan ASEPT-kondisie van 204 °C en 10 min). Die studie se resultate het getoon dat ko-produksie van xilaanbiopolimere die ekonomiese prestasie van die hoof-bioraffinaderygeval (i.e. MCS) substansieel verbeter, deur die verkoopsprys van etanol (teenoor hoër waardes onder die standaardprosesse) te verlaag. ’n Minimum hemisellulose-verkoopsprys (MHSP) van 809 USD/ton xilaan koproduk is vasgestel deur etanol se verkoopsprys teen 0.70 USD/L (markprys van etanol in 2019) vas te maak; hoër MHSP-waardes het verseker tot verdere laer pryse gelei. Minimum etanol verkoopspryse (MESP) onder die MCS, BCS en ICS is onderskeidelik beraam teen 0.61, 0.95 en 0.81 USD/L, waar die xilaanprys aangeneem is teen 1000 USD/ton (=> MCS). Selfs al is die ekonomiese lewensvatbaarheid van die hoofbioraffinadery beduidend verbeter met ko-produksie van xilaan as daarsonder, is hierdie multi-produk bioraffinaderykompleks bewys om energie-intensief te wees as ’n resultaat van so ’n ko-produksieskema waar die herwinning van xilaanbiopolimere substansiële termiese en elektriese energievereistes genoodsaak het. Uit omgewingsoogpunt, het die ko-produksie van xilaanbiopolimere saam met bio-etanol en elektrisiteit ’n positiewe bydrae gelewer tot die versagting van GHG-emissies uit fossielhulpbronne. Die GHG-emissiebesparing onder die MCS, BCS en ICS is beraam rondom 69, 64 en 65% teenoor petrol as fossielbasislyn van 90 gCO2eq/MJ (RSB-Global), maar daar was slegs ’n marginale verskil tussen die besparing onder die hoofbioraffinaderygeval en die onder die standaard prosesse. Masters 2022-03-09T09:00:45Z 2022-04-29T09:44:02Z 2022-03-09T09:00:45Z 2022-04-29T09:44:02Z 2022-04 Thesis http://hdl.handle.net/10019.1/124968 en_ZA Stellenbosch University xxiii, 312, 1 pages : illustrations application/pdf Stellenbosch : Stellenbosch University |
| spellingShingle | Lignocellulosic biorefineries Lignocellulose Biopolymers Hemicellulosic biopolymers Xylans Biomass energy Mihiretu, Gezahegn Teklu Advancing Lignocellulosic Biorefineries through Co-Production of Hemicellulosic Biopolymers and Bioenergy |
| title | Advancing Lignocellulosic Biorefineries through Co-Production of Hemicellulosic Biopolymers and Bioenergy |
| title_full | Advancing Lignocellulosic Biorefineries through Co-Production of Hemicellulosic Biopolymers and Bioenergy |
| title_fullStr | Advancing Lignocellulosic Biorefineries through Co-Production of Hemicellulosic Biopolymers and Bioenergy |
| title_full_unstemmed | Advancing Lignocellulosic Biorefineries through Co-Production of Hemicellulosic Biopolymers and Bioenergy |
| title_short | Advancing Lignocellulosic Biorefineries through Co-Production of Hemicellulosic Biopolymers and Bioenergy |
| title_sort | advancing lignocellulosic biorefineries through co production of hemicellulosic biopolymers and bioenergy |
| topic | Lignocellulosic biorefineries Lignocellulose Biopolymers Hemicellulosic biopolymers Xylans Biomass energy |
| url | http://hdl.handle.net/10019.1/124968 |
| work_keys_str_mv | AT mihiretugezahegnteklu advancinglignocellulosicbiorefineriesthroughcoproductionofhemicellulosicbiopolymersandbioenergy |