Catalytic conversion of furfural and glucose over activated carbon-supported metal catalysts

Abstract Forest-based sectors such as sawmills and pulp and paper play an important role in Finnish industry. Lignocellulosic side stream fractions from these activities, such as wood sawdust and lignin, are primarily used for energy. However, these fractions could be used more efficiently in biorefinery concepts like the production of value-added bio-based materials and chemicals instead of energy production. In biorefinery concepts, catalysis is an important tool for creating more sustainable processes. Efforts to develop novel catalytic systems for biomass valorization to obtain platform chemicals from biomass feedstock are worth pursuing. In catalytic applications, novel bio-based activated carbon catalysts could be used to replace the non-renewable catalytic materials currently used. In this thesis, the application of lignocellulose-based side stream materials as a raw material for activated carbon catalysts and their use in catalytic applications are studied, and the physical and chemical characteristics of the activated carbon catalysts prepared using various methods are examined. Catalysts prepared for catalytic conversion reactions to produce value-added chemicals for biorefinery applications are investigated: specifically, the conversion of the biomass-based molecules furfural and glucose into 2-methylfuran, 5-hydroxymethylfurfural, lactic acid and its ester, ethyl lactate. This research provides new insights into the preparation of lignocellulose-based activated carbon catalysts and their suitability for catalytic conversion reactions to produce important value-added chemicals for industrial applications. The present study found that lignocellulosic side stream materials can be used in preparing high-quality activated carbon catalysts or supported catalysts. Prepared carbon-based catalysts showed promising results in the conversion reactions studied, indicating that tailored catalyst supports for specific applications are needed.Tiivistelmä Suomessa metsä- ja sahateollisuus sekä paperi- ja selluteollisuus ovat keskeisiä teollisen tuotannon toimialoja. Tuotannossa syntyvät arvokkaat sivuvirrat, kuten sahanpuru- sekä ligniinifraktiot hyödynnetään tänä päivänä suurelta osin energiantuotannossa polttamalla. Nämä arvokkaat sivuvirrat voidaan hyödyntää energiatuotannon sijaan biojalostamokonsepteissa korkeamman lisäarvon tuotteiksi, kuten uusiksi biomassapohjaisiksi biomateriaaleiksi ja -kemikaaleiksi. Biojalostamokonsepteissa katalyyttiset menetelmät ovat tärkeässä roolissa mahdollistaen energiatehokkaammat prosessit. Uusien katalyyttisten menetelmien kehittäminen biomassan konvertoimiseksi biokemikaaleiksi ja -materiaaleiksi on tavoiteltavaa. Biopohjaisilla aktiivihiilikatalyyteillä voidaan myös korvata nykyisiä ei-uusiutuvia katalyyttejä. Tässä väitöskirjatutkimuksessa on tutkittu lignoselluloosapohjaisten sivuvirtamateriaalien soveltuvuutta aktiivihiilipohjaisten katalyyttimateriaalien valmistukseen sekä näiden katalyyttien käyttöä sovelluksissa. Aktiivihiilten fysikaalisten ja kemiallisten ominaisuuksien vaikutusta katalyyttimateriaaleihin ja sovelluksiin on tutkittu. Valmistettujen katalyyttien soveltuvuutta konversioreaktioissa korkean lisäarvon tuotteiksi biojalostamosovelluksiin on tutkittu: erityisesti biomassapohjaisten molekyylien kuten furfuraalin ja glukoosin konversiota 2-metyylifuraaniksi, 5-hydroksimetyylifurfuraaliksi, maitohapoksi sekä maitohapon esteriksi etyylilaktaatiksi. Tutkimus tuo uutta tietoa lignoselluloosapohjaisten sivuvirtamateriaalien hyödyntämisestä ja soveltuvuudesta biopohjaisten aktiivihiilikatalyyttien valmistuksessa sekä käytöstä katalyyttisissä sovelluksissa korkean lisäarvon kemikaalien tuotannossa. Tutkimuksessa havaittiin, että lignoselluloosapohjaisia sivuvirtoja voidaan hyödyntää korkealaatuisten aktiivihiilikatalyyttimateriaalien valmistuksessa. Valmistetut hiilipohjaiset katalyytit osoittivat potentiaalia tutkituissa sovelluksissa ja tutkimus viittasi siihen, että hiilipohjaiset katalyyttitukiaineet tulee räätälöidä eri sovelluksiin

Lignin-based activated carbon-supported metal oxide catalysts in lactic acid production from glucose

Abstract In this study, heterogeneous biomass-based activated carbon-supported metal oxide catalysts were prepared and tested for lactic acid production from glucose in aqueous solution. Activated carbons were produced from hydrolysis lignin by chemical (ZnCl₂) or steam activation and modified with a nitric acid treatment and Sn, Al, and Cr chlorides to obtain carbon-based metal oxide catalysts. The modification of the carbon support by nitric acid treatment together with Sn and Al oxides led to an increase in lactic acid yield. The highest lactic acid yield (42 %) was obtained after 20 min at 180 °C with the Sn/Al (5/2.5 wt.%) catalyst on steam-activated carbon treated by nitric acid. Reusability of the catalyst was also studied with the conclusion that the deposition of carbonaceous byproducts and leaching of Al oxides led to a decrease in catalyst selectivity to lactic acid

Conversion of furfural to 2-methylfuran over CuNi catalysts supported on biobased carbon foams

Abstract In this study, carbon foams prepared from the by-products of the Finnish forest industry, such as tannic acid and pine bark extracts, were examined as supports for 5/5% Cu/Ni catalysts in the hydrotreatment of furfural to 2-methylfuran (MF). Experiments were conducted in a batch reactor at 503 K and 40 bar H₂. Prior to metal impregnation, the carbon foam from tannic acid was activated with steam (S1), and the carbon foam from pine bark extracts was activated with ZnCl₂ (S2) and washed with acids (HNO₃ or H₂SO₄). For comparison, a spruce-based activated carbon (AC) catalyst and two commercial AC catalysts as references were investigated. Compressive strength of the foam S2 was 30 times greater than that of S1. The highest MF selectivity of the foam-supported catalysts was 48 % (S2, washed with HNO₃) at a conversion of 91 %. According to the results, carbon foams prepared from pine bark extracts can be applied as catalyst supports

Production of ethyl lactate by activated carbon-supported Sn and Zn oxide catalysts utilizing lignocellulosic side streams

Abstract In this study, activated carbon-supported Sn and Zn oxide catalysts were prepared from hydrolysis lignin and used for the conversion of model solutions of trioses, hexoses, and lignocellulosic biomass hydrolysates to ethyl lactate. Both catalysts, SnO₂@AC and ZnO@AC, were able to produce ethyl lactate in high yields. SnO₂@AC was a more active and selective catalyst in triose (dihydroxyacetone) conversion, providing 99% yield to ethyl lactate. ZnO@AC, by contrast, was more selective in glucose and hydrolysate conversion, with a yield of 60% and 85%, respectively. The ethyl lactate yields were significantly higher than those from the optimized model solution experiments when using ZnO@AC catalyst. These findings indicate that milder acidity of the ZnO@AC catalyst together with Na⁺ and SO₄²⁻ in hydrolysate favored ethyl lactate production, preventing byproduct, furan derivatives and acetal, formation. Moreover, the catalysts were able to maintain their catalytic activity in recycling experiments

Conversion of xylose to furfural over lignin-based activated carbon-supported iron catalysts

Abstract In this study, conversion of xylose to furfural was studied using lignin-based activated carbon-supported iron catalysts. First, three activated carbon supports were prepared from hydrolysis lignin with different activation methods. The supports were modified with different metal precursors and metal concentrations into five iron catalysts. The prepared catalysts were studied in furfural production from xylose using different reaction temperatures and times. The best results were achieved with a 4 wt% iron-containing catalyst, 5Fe-ACs, which produced a 57% furfural yield, 92% xylose conversion and 65% reaction selectivity at 170 °C in 3 h. The amount of Fe in 5Fe-ACs was only 3.6 µmol and using this amount of homogeneous FeCl₃ as a catalyst, reduced the furfural yield, xylose conversion and selectivity. Good catalytic activity of 5Fe-ACs could be associated with iron oxide and hydroxyl groups on the catalyst surface. Based on the recycling experiments, the prepared catalyst needs some improvements to increase its stability but it is a feasible alternative to homogeneous FeCl₃

Performances of metals modified activated carbons for fluoride removal from aqueous solutions

Abstract The present research work focused on the activated carbon (AC) preparation from dates waste followed by its surface modification by incipient wetness impregnation using different metals: Ca, Co, Mg and Al. The obtained results showed that the AC-Al presented the best removal efficiency of the fluoride. The prepared activated carbons (AC) and (AC-Al) were characterized by several techniques. The optimization study of the AC-Al impregnation conditions was investigated by varying the impregnation time and the Al loading. Batch experiments were carried out to investigate the effect of certain operating parameters on the removal percentage. Several isotherm models were applied

Zinc adsorption by activated carbon prepared from lignocellulosic waste biomass

Abstract Sawdust was used as a precursor for the production of biomass-based activated carbon. Carbonization and activation are single-stage processes, and steam was used as a physical activation agent at 800 °C. The adsorption capacity towards zinc was tested, and the produced activated carbon proved effective and selectively adsorbent. The effects of pH, initial concentration, adsorbent dosage, time, temperature, and regeneration cycles were tested. The adsorption capacity obtained in this study was compared favorably to that of the materials reported in the literature. Several isotherms were applied to describe the experimental results, with the Sips isotherm having the best fit. Kinetic studies showed that the adsorption follows the Elovich kinetic model