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Conversion of Biomass to Renewable Liquid Feedstocks in Pyrolysis-based Applications
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.ORCID iD: 0000-0002-2373-4950
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 [en]
Pyrolysis; Biomass; Pre-treatment; Stepwise Pyrolysis; Catalytic Pyrolysis
Keywords [sv]
Pyrolys; Biomassa; Förbehandling; Stegvis Pyrolys; Katalytisk Pyrolys
National Category
Chemical Process Engineering Materials Engineering
Research subject
Materials Science and Engineering
Identifiers
URN: urn:nbn:se:kth:diva-259564ISBN: 978-91-7873-314-9 (print)OAI: oai:DiVA.org:kth-259564DiVA, id: diva2:1352178
Public defence
2019-10-18, Kollegiesalen, Brinellvägen 8, Stockholm, 10:00 (English)
Opponent
Supervisors
Funder
Swedish Energy Agency, 33284-2Available from: 2019-09-26 Created: 2019-09-17 Last updated: 2019-09-26Bibliographically approved
List of papers
1. Wood-derived acid leaching of biomass for enhanced production of sugars and sugar derivatives during pyrolysis: Influence of acidity and treatment time
Open this publication in new window or tab >>Wood-derived acid leaching of biomass for enhanced production of sugars and sugar derivatives during pyrolysis: Influence of acidity and treatment time
2017 (English)In: Journal of Analytical and Applied Pyrolysis, ISSN 0165-2370, E-ISSN 1873-250X, Vol. 127, p. 329-334Article in journal (Refereed) Published
Abstract [en]

Inorganic matter in biomass (especially alkali and alkaline earth metals) acts like intrinsic catalysts during pyrolysis and influences the composition of derived liquids. In this work, the influence of acidity and time on leaching of inorganics with wood pyrolysis-derived acids was investigated in order to understand their effect on the biomass characteristics and the composition of pyrolysis products, as well as to study the mechanism of leaching of different inorganic elements. Aqueous solutions of 5 and 10. wt% acetic acid (main acid in pyrolysis products and in similar concentrations) were used for demineralizing softwood at 85. °C for 30-90. min. Biomass characteristics, composition of intrinsic inorganics and primary pyrolytic vapors from different pretreatment cases are presented. Results show that removal of inorganics was in all cases enhanced by higher acidity; time of treatment was only seen to have a positive effect at lower acidity. The volatile matter of biomass was not affected by the pretreatment, confirming the conditions investigated being relatively mild. Results from Py-GC/MS of leached biomass show an increased selectivity towards sugars and sugar derivatives and simultaneous suppression of the relative composition of carbonyls and phenolic compounds in derived vapors. Sugars and sugar derivatives was enhanced by increasing the leaching time at higher acidity, without seeing a clear correlation to removal of alkali and alkaline earth metals. It is therefore suggested that other factors might influence the pathway of formation of primary pyrolysis products than what has previously been suggested by others. Because of the enhanced production of sugars and sugar derivatives from pyrolysis of leached biomass, this procedure might serve as a pathway to be enable the utilization of pyrolytic liquids as feedstock for existing fermentation-based biorefineries.

Place, publisher, year, edition, pages
Elsevier, 2017
Keywords
Leaching, Pretreatment, Pyrolysis, Organic acid, Softwood, Sugars
National Category
Chemical Process Engineering
Identifiers
urn:nbn:se:kth:diva-212067 (URN)10.1016/j.jaap.2017.07.018 (DOI)000413284000038 ()2-s2.0-85026403684 (Scopus ID)
Funder
Swedish Energy Agency, 33284-2
Note

QC 20171102

Available from: 2017-08-16 Created: 2017-08-16 Last updated: 2019-09-17Bibliographically approved
2. Fractionation of liquid products from pyrolysis of lignocellulosic biomass by stepwise thermal treatment
Open this publication in new window or tab >>Fractionation of liquid products from pyrolysis of lignocellulosic biomass by stepwise thermal treatment
Show others...
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
Keywords
Pyrolysis Biomass Bio-oil Stepwise Fractionation
National Category
Engineering and Technology
Research subject
Chemical Engineering; Chemistry; Energy Technology; Fibre and Polymer Science
Identifiers
urn:nbn:se:kth:diva-227249 (URN)10.1016/j.energy.2018.04.150 (DOI)000436886200033 ()2-s2.0-85046167007 (Scopus ID)
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
3. Catalytic pyrolysis over transition metal-modified zeolites: a comparative study between catalyst activity and deactivation
Open this publication in new window or tab >>Catalytic pyrolysis over transition metal-modified zeolites: a comparative study between catalyst activity and deactivation
Show others...
2019 (English)In: Journal of Analytical and Applied Pyrolysis, ISSN 0165-2370, E-ISSN 1873-250X, Vol. 138, p. 54-61Article in journal (Refereed) Published
Abstract [en]

The utilization of metal-doped zeolites in catalytic pyrolysis of biomass is a well-known approach to promote the formation of certain compounds. One major technical issue of using zeolites in biomass pyrolysis processes is their rapid deactivation due to coke formation. However, little is known about how metal-doping influences the characteristics of coking, such as coking rate and its composition.

In this study, four different materials were experimentally evaluated based on their catalytic activity and coking characteristics: HZSM-5, Fe/ZSM-5, Ni/ZSM-5 and FeNi/ZSM-5. The materials were prepared and characterized followed by screening in a bench-scale setup for in-situ catalytic pyrolysis. The mass balance and composition of pyrolysis products including catalyst coke were analyzed.

It was found that metal-doping increases the concentration of aromatic hydrocarbons in the liquid product from 59.0 to 82.8 % of GC/MS peak area, especially monoaromatic hydrocarbons (MAHs) and naphthalenes. Fe mainly promotes MAHs whereas Ni additionally promotes naphthalenes. FeNi/ZSM-5 enhances the production of both compound groups as well as further reducing the total acid number (TAN). Regarding the catalyst coke, metal-doped catalysts present an increased concentration of aromatic hydrocarbons in terms of MAHs, naphthalenes and polyaromatic hydrocarbons. For each catalyst, the chemical composition of catalyst coke reflects the catalyst’s activity seen in vapor upgrading. A reaction pathway based on the observed catalyst activities of metal-doped ZSM-5 and HZSM-5 is proposed.

The results also show that metal-doping of catalysts increases the formation of catalyst coke, mainly due to a higher concentration of strong acid sites. Also, the rate of coking is dependent on the strength of acid sites, where the strength correlates with the severity of coking. The coke yield was seen to increase from 3.5 wt% in the case of HZSM-5 to maximum 7.2 wt% over Fe/ZSM-5. However, the metal-doping of catalysts reduces the temperature of catalyst regeneration and catalyzes the oxidation of coke. Overall, this work presents a comparative study between catalyst activity and deactivation during thermochemical conversion of biomass.

Place, publisher, year, edition, pages
Elsevier, 2019
National Category
Engineering and Technology
Research subject
Chemical Engineering
Identifiers
urn:nbn:se:kth:diva-239877 (URN)10.1016/j.jaap.2018.12.005 (DOI)000457854800006 ()2-s2.0-85059121054 (Scopus ID)
Note

QC 20181206

Available from: 2018-12-04 Created: 2018-12-04 Last updated: 2019-09-17Bibliographically approved
4. Catalytic pyrolysis of demineralized lignocellulosic biomass
Open this publication in new window or tab >>Catalytic pyrolysis of demineralized lignocellulosic biomass
2019 (English)In: Fuel, ISSN 0016-2361, E-ISSN 1873-7153, Vol. 252, p. 200-209Article in journal (Refereed) Published
Abstract [en]

The effect of ash removal pre-treatment of lignocellulosic biomass prior to catalytic pyrolysis for producingbiofuels was investigated. Non-catalytic and catalytic pyrolysis of demineralized and raw biomass was performedin Py-GC/MS and bench-scale experiments to study the performance of in-bed and ex-bed upgrading. Pretreatedbiomass shows a significant increase in the organic liquid yield in experiments performed at 600 °C: from31 to 42 wt% compared to raw biomass, as well as a significant reduction of char yield. The performance of inbedcatalytic pyrolysis of pre-treated biomass over HZSM-5 is limited compared to the corresponding raw material.However, ex-bed catalytic pyrolysis of pre-treated biomass at 600 °C results in an overall increased yield ofBTX compounds. Pyrolysis vapors from pre-treated biomass present a suitable composition for catalytic upgradingafter secondary vapor-phase reactions. Additionally, demineralization reduces the total acid number ofderived liquids in catalytic and non-catalytic pyrolysis.

Keywords
Biomass Pyrolysis pre-treatment demineralization catalyst hzsm-5
National Category
Chemical Engineering
Research subject
Chemical Engineering
Identifiers
urn:nbn:se:kth:diva-250262 (URN)10.1016/j.fuel.2019.04.087 (DOI)000470113800020 ()2-s2.0-85064520274 (Scopus ID)
Funder
Swedish Energy Agency, 47971-1
Note

QC 20190516

Available from: 2019-04-26 Created: 2019-04-26 Last updated: 2019-09-17Bibliographically approved
5. Production of renewable aromatic hydrocarbons by ex-situ catalytic fast pyrolysis of biomass in a combined fluidized bed and fixed bed reactor system
Open this publication in new window or tab >>Production of renewable aromatic hydrocarbons by ex-situ catalytic fast pyrolysis of biomass in a combined fluidized bed and fixed bed reactor system
(English)Manuscript (preprint) (Other academic)
Abstract [en]

An ex-situ catalytic fast pyrolysis lab-scale setup consisting of a fluidized bed pyrolyzer and a fixed bed catalytic reactor was experimentally evaluated. The effect of weight hourly space velocity was investigated in the range of 0.35-0.77 h-1 during 260 min of operation. A lower biomass feed rate over a fixed amount of catalyst results in a higher degree of vapor deoxygenation (from 71 to 79.5 wt%) as well as higher concentrations of aromatic hydrocarbons. The carbon conversion from biomass to upgraded liquids is negatively correlated with the aromatic concentrations. Online gas analysis present no significant changes in the catalytic performance during the operational time. The results of this study indicate that the difference in liquid deoxygenation observed when varying the biomass feed rate is dependent on the vapor concentration in the gas stream over the catalytic bed rather than being significantly affected by catalyst deactivation during operation.

Keywords
Catalytic pyrolysis; HZSM-5; fluidized bed; fixed bed; WHSV
National Category
Chemical Engineering
Identifiers
urn:nbn:se:kth:diva-259563 (URN)
Note

QC 20190918

Available from: 2019-09-17 Created: 2019-09-17 Last updated: 2019-09-18Bibliographically approved

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