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Fractionation of liquid products from pyrolysis of lignocellulosic biomass by stepwise thermal treatment
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.ORCID iD: 0000-0002-2373-4950
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.ORCID iD: 0000-0002-9949-6274
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2018 (English)In: Energy, ISSN 0360-5442, E-ISSN 1873-6785, Vol. 154, p. 346-351Article in journal (Refereed) Published
Abstract [en]

The thermal properties of cellulose, hemicellulose and lignin can be utilized to improve the characteristics of pyrolysis liquids. In this study, a concept of stepwise pyrolysis to fractionate the liquid based on the thermal properties of the biomass constituents was investigated. Lignocellulosic biomass was thermally treated in two steps: 200–300 °C followed by 550 °C. Derived liquids were studied for GC/MS analysis, water content, acid concentration and a solvent extraction method. Pyrolytic liquid derived from 550 °C after treatment at lower temperatures have a higher relative composition of phenolic compounds compared to one-step pyrolysis (increased from 58 to 90% of GC/MS peak area). Also, compounds known to promote aging, such as acids and carbonyl compounds, are derived at lower temperatures which may suppress aging in the liquid derived downstream at 550 °C. For liquids derived at 550 °C, the total acid number was reduced from 125 in one-step treatment to 14 in two-step treatment. Overall, no significant difference in the total liquid yield (sum of the liquids derived in separated treatments) nor any variations in their collective composition compared to one-step treatment at 550 °C was observed, i.e. stepwise pyrolysis can be utilized for direct fractionation of pyrolytic vapors.

Place, publisher, year, edition, pages
Elsevier, 2018. Vol. 154, p. 346-351
Keywords [en]
Pyrolysis Biomass Bio-oil Stepwise Fractionation
National Category
Engineering and Technology
Research subject
Chemical Engineering; Chemistry; Energy Technology; Fibre and Polymer Science
Identifiers
URN: urn:nbn:se:kth:diva-227249DOI: 10.1016/j.energy.2018.04.150ISI: 000436886200033Scopus ID: 2-s2.0-85046167007OAI: oai:DiVA.org:kth-227249DiVA, id: diva2:1203928
Funder
Swedish Energy Agency, 33284-2Swedish Energy Agency, 39449-1
Note

QC 20180522

Available from: 2018-05-04 Created: 2018-05-04 Last updated: 2019-09-17Bibliographically approved
In thesis
1. Conversion of Biomass to Renewable Liquid Feedstocks in Pyrolysis-based Applications
Open this publication in new window or tab >>Conversion of Biomass to Renewable Liquid Feedstocks in Pyrolysis-based Applications
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The production of chemicals and fuels currently rely on fossil resources which are associated with global warming as well as economic and political instabilities. The demand for renewable alternatives is increasing as legislations on greenhouse gas emissions are becoming more stringent. Biomass is the main renewable carbonaceous feedstock that can be converted into chemicals and fuels. Pyrolysis allows the conversion of biomass to liquid feedstocks that could substitute the reliance on fossil crude. However, liquids originating from pyrolysis of biomass have unfavourable characteristics with respect to technical requirements from end-users. Therefore, further research and development of the biomass-to-liquid conversion is needed to enhance the quality of derived liquids. By developing liquefaction processes based on the influence of the biomass characteristics on the derived products, the conversion routes can be optimized to produce targeted precursors. In this dissertation, the selective conversion of lignocellulosic biomass into renewable liquid feedstocks by combining pyrolysis with upstream and downstream process modifications was experimentally investigated. Pre-treatment of biomass in aqueous solutions of organic acids found in the pyrolysis liquid was investigated to reduce the ash content in biomass, known for catalyzing the cracking of pyrolysis vapors. Results show that the major fraction of ash can be removed without affecting the volatile matter of biomass. The composition of pyrolysis liquids derived from pre-treated biomass is significantly different to raw biomass, with increased selectivity of anhydrosugars and suppression of low molecular weight compounds such as carbonyls. Stepwise pyrolysis was investigated to produce multiple fractionated liquids with compositions based on the thermal stability of the biomass polymers. A process concept of two pyrolysis units connected in-series, operating at 200 to 300 C and 550C, respectively, was investigated. The results show that stepwise pyrolysis can be used to concentrate chemical compounds into fractionated liquids without reducing the total amount of liquid derived from biomass. However, complete separation of chemicals in a two-step pyrolysis setup faces technical difficulties due to the overlap in thermal decomposition temperatures of the biomass polymers. Catalytic pyrolysis was studied for the production of aromatic hydrocarbons from biomass. Metal-doped zeolitic catalysts were prepared and studied based on the catalyst activity and the deactivation characteristics. Fe and Ni were impregnated into HZSM-5 followed by catalytic pyrolysis and investigation of the liquid and coke properties. The coke composition reflects the catalytic activity observed for upgraded liquids. Metal-doping promotes the conversion of vapors into aromatic hydrocarbons, increases the catalyst deactivation rate, and alters the catalyst regeneration conditions. The influence of the vapor composition fed for catalytic upgrading was studied by comparing the differences when using the pre-treated demineralized biomass mentioned above and raw biomass in catalytic pyrolysis. For ex-bed catalytic pyrolysis at 600C using HZSM-5, pre-treated biomass results in higher conversion of biomass to aromatic hydrocarbons compared to raw biomass. This could be explained by a favorable composition of secondary pyrolysis vapors from pre-treated biomass for catalytic upgrading over HZSM-5. Lastly, a continuous ex-situ catalytic fast pyrolysis process was experimentally investigated. The performance of HZSM-5 for continuous upgrading of pyrolysis vapors was evaluated by varying the biomass feeding rate to the pyrolyzer followed by upgrading over a fixed amount of catalyst. The results indicate the significance of the biomass-to-catalyst ratio in the design of large-scale processes in terms of the magnitude of catalytic conversion of pyrolysis vapors.

Abstract [sv]

Dagens framställning av kemikalier och flytande bränslen är starkt beroende av tillgången på fossila råvaror. Detta bidrar till global uppvärmning samt ekonomiska och politiska osäkerheter. Efterfrågan på förnybara alternativ ökar i takt med att utsläppskraven gällande växthusgaser blir allt hårdare. Biomassa utgör den huvudsakliga tillgången på förnybart kolbaserat material som kan omvandlas till kemikalier och bränslen. Pyrolys är en metod som kan omvandla biomassa till en olja som kan ersätta dagens behov av fossil råolja. Olja från pyrolys har dock flertalet ofördelaktiga egenskaper för direkt tillämpning i industrin. Därför behövs ytterligare forskning och utveckling av omvandlingsprocessen för att förbättra egenskaperna hos pyrolysoljan. Genom att utveckla omvandlingsprocesser baserat på hur biomassans egenskaper påverkar sammansättningen på den framställda produkten kan omvandlingen av biomassa till pyrolysolja optimeras för produktion av olja för specifika ändamål. I denna avhandling utvärderas flertalet olika tekniska tillvägagångssätt experimentellt för att selektivt kunna omvandla lignocellulosisk biomassa till förnybara oljor genom att kombinera pyrolys med process-modifieringar placerade uppströms och nedströms pyrolysören. Förbehandling av biomassa i en vattenbaserad vätska innehållande organiska syror som förekommer i pyrolysoljan undersöktes för att minska halten aska i biomassa. Aska bidrar till katalytisk krackning av pyrolysångor. Resultaten visar att en majoritet av askan kan separareras från biomassa utan att påverka dess innehåll av flyktiga komponenter. Sammansättningen av pyrolysolja från förbehandlad biomassa skiljer sig från rå biomassa, med en ökad andel anhydrosocker och en minskning av lågmolekylära föreningar såsom karbonyler. Stegvis pyrolys undersöktes som en metod för att framställa flertalet fraktionerade oljor vars sammansättning beror av biomassapolymerernas termiska egenskaperna. En konceptuell process av två seriekopplade pyrolysörer värmda till 200-300C respektive 550C undersöktes. Resultaten visar att stegvis pyrolys kan användas för att koncentrera kemikalier i olika vätskefraktioner utan att minska den totala mängden olja som utvinns ur biomassa. Dock är det svårt att i en process om två pyrolysörer nå fullständig separation av kemikalier. Detta tros bero på överlappande temperaturer för termisk nedbrytning hos de olika biomassa-polymererna. Katalytisk pyrolys undersöktes för framställning av aromatiska kolväten från biomassa. Metall-impregnerade zeolitiska katalysatorer framställdes och utvärderades utifrån sina katalytiska egenskaper såsom aktivitet samt deaktivering. Fe och Ni impregnerades i HZSM-5 följt av katalytisk pyrolys och analys av uppgraderad olja samt bildat koks. Kokssammansättningen hos en katalysator speglar dess aktivitet för uppgradering av olja. Metallimpregnering av en katalysator bidrar till en ökad omvandling av pyrolysångor till aromatiska kolväten, ökar katalysatordeaktivering genom koksning, samt ändrar dess egenskaper vid regenering. Påverkan av sammansättningen på pyrolysångor som passerar genom en katalysatorbädd undersöktes genom att jämföra skillnader mellan användning av den förbehandlade biomassa som nämnts ovan med rå biomassa. Katalytisk pyrolys vid 600C i en ex-bäddsuppsättning med HZSM-5 ger en högre omvandling av biomassa till aromatiska kolväten med förbehandlad biomassa jämfört med rå biomassa. Detta kan förklaras genom en fördelaktig sammansättning hos pyrolysångorna som passerar genom katalysatorbädden efter att ha genomgått sekundära pyrolys-reaktioner. Slutligen undersöktes en kontinuerlig process för ex-situ katalytisk snabbpyrolys genom experimentella försök. HZSM-5:s prestanda för att kontinuerligt uppgradera pyrolysångor utvärderades genom att variera flödet av biomassa följt av katalytisk uppgradering över en konstant mängd katalysator. Resultaten indikerar vikten av den signifikanta påverkan som förhållandet mellan biomassa och katalysator har i processen för katalytisk omvandling av pyrolysångor till aromatiska kolväten.

Place, publisher, year, edition, pages
KTH Royal Institute of Technology, 2019. p. 117
Series
TRITA-ITM-AVL ; 2019:29
Keywords
Pyrolysis; Biomass; Pre-treatment; Stepwise Pyrolysis; Catalytic Pyrolysis, Pyrolys; Biomassa; Förbehandling; Stegvis Pyrolys; Katalytisk Pyrolys
National Category
Chemical Process Engineering Materials Engineering
Research subject
Materials Science and Engineering
Identifiers
urn:nbn:se:kth:diva-259564 (URN)978-91-7873-314-9 (ISBN)
Public defence
2019-10-18, Kollegiesalen, Brinellvägen 8, Stockholm, 10:00 (English)
Opponent
Supervisors
Funder
Swedish Energy Agency, 33284-2
Available from: 2019-09-26 Created: 2019-09-17 Last updated: 2019-09-26Bibliographically approved

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