High-Performance Magnetic Activated Carbon from Solid Waste from

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High-performance magnetic activated carbon from solid waste from lignin conversion processes. Part II: Their use as NiMo catalyst supports for lignin conversion. Mikel Oregui-Bengeochea, Nemanja Mileti#, Wenming Hao, Fredrik Björnerbäck, Mali Husby Rosnes, Jose Javier Saiz Garitaonandia, Niklas Hedin, Pedro L. Arias, and Tanja Barth ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.6b02796 • Publication Date (Web): 13 Oct 2017 Downloaded from http://pubs.acs.org on October 20, 2017

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ACS Sustainable Chemistry & Engineering

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High-performance magnetic activated carbon from

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solid waste from lignin conversion processes. Part II:

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Their use as NiMo catalyst supports for lignin

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conversion.

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Mikel Oregui-Bengoechea*a ([email protected]), Nemanja Miletićb,c

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([email protected]), Wenming Haod,e ([email protected]), Fredrik Björnerbäckd,e

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([email protected]), Mali H. Rosnesa ([email protected]), J. S. Garitaonandiaf

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([email protected]), Niklas Hedind,e ([email protected]), Pedro L. Ariasb

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([email protected]) and Tanja Bartha ([email protected])

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a

Department of Chemistry, University of Bergen, Allégaten 41, 5007 Bergen, Norway

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b

Department of Chemical and Environmental Engineering, School of Engineering, University of

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the Basque Country (EHU/UPV), C/Alameda Urquijo s/n,48013 Bilbao, Spain

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c

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34, 32000 Čačak, Serbia

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d

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University, SE-106 91 Stockholm, Sweden

Department of Food Technology, Faculty of Agronomy, University of Kragujevac, Cara Dušana

Department of Materials and Environmental Chemistry, Arrhenius Laboratory, Stockholm

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e

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SE-106 91 Stockholm, Sweden

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f

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Keywords: Lignin catalytic conversion, formic acid, hydrodeoxygenation (HDO), magnetic activated carbons, NiFe

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Berzelii Center EXSELENT on Porous Materials, Arrhenius Laboratory, Stockholm University,

Fisika Aplikatua II Saila, Euskal Herriko Unibertsitatea, 644 P. K. 48080 Bilbao, Spain


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SYNOPSIS

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Large quantities of low-value hydrochar are typically produced in lignin conversion processes. In

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this paper, hydrochar is valorized into activated carbon and re-used as catalyst support in the

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same process.

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ABSTRACT

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Lignin conversion processes produce carbon rich residues1,2 that can be converted into valuable

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materials such as magnetic activated carbons (MACs). Such lignin-derived MACs can be further

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used as functional substrates for hydrotreating NiMo catalysts. In this work, we studied the

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activity of different NiMo-MACs for the catalytic conversion of lignin in a formic acid/ethanol

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media (LtL process). Two KOH-activated LtL hydrochars from Eucalyptus (MACE) and

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Norwegian Spruce (MACS) lignins were used as catalyst supports. In addition, the activity of the

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resulting NiMo-MACs, namely C-MACE and C-MACS, was compared with a NiMo catalyst

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supported on a commercial activated carbon (AC). At reaction conditions of 340 °C and 6 h, the

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best result was obtained for the NiMo-MACS with a yield of 72.2 wt.% of oil and 21.1 wt.% of

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organic solids. At 300 °C and 10 h, both NiMo-MAC catalysts displayed higher HDO activities

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than their commercial counterpart, yielding considerably higher oil yields. The higher HDO

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activities are tentatively assigned to the formation of NiFe species on the catalytic surfaces of the

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NiMo-MAC catalysts. In addition, the magnetism exhibited by the C-MACS made it easy to

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recover the catalyst. However, a considerable loss of activity was observed upon recycling due to

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a chemical modification of the catalyst surface.

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INTRODUCTION

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In a biorefinery, biomass conversion processes and technologies are integrated to produce fuels

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and value-added chemicals and products2,3. When developing sustainable and economically

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efficient bio-refinery concepts, it is especially interesting to study unexploited biomass resources

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and wastes, and their conversion into bio-oils and/or value-added products4. Lignin is a major

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byproduct from the pulp-and-paper industry and from biomass pretreatment processes for bio-

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ethanol production5,6. This natural amorphous polymer can be thermochemically converted into

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bio-oil and fine chemicals7,8, although in most cases there are side reactions that convert a

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considerable amount of the biopolymer into organic solids or hydrochar2,9–11.

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A promising and relatively new approach to convert lignin, known as lignin-to-liquid

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(LtL), involves the use of formic acid (FA) together with a solvent, either ethanol or water. High

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oil yields, with high H/C and low O/C ratios, are obtained, whilst retaining the phenol-type

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structure of the bio-oil components. Nevertheless, high temperatures (typically 350-400 °C) and

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long reactions times (typically 8-16 h) are needed to convert the lignin feedstock into bio-oil in

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high yields12,13. Thus, in order to produce fuels and chemicals that can compete with traditional

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petroleum based products, two main issues need to be addressed: lowering the process severity

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(temperature and reaction time), and valorizing the low-value side streams. Such side streams

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include solid residues/hydrochars that can be further processed into value-added products.

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Two different strategies can be used to enhance the competitiveness of the LtL process.

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The reaction rates can be increased by using a catalyst and/or the hydrochar byproducts can be

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further processed into valuable products. With a suitable catalyst, the lignin de-polymerization

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and hydrodeoxygenation (HDO) rates for producing the target aromatic compounds could be

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improved. In this context, several combinations of traditional hydrotreating catalysts have been 4 ACS Paragon Plus Environment

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extensively studied, and their activities for thermo-catalytic conversion of lignin into bio-oil have

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been proven. Typical examples of such catalysts are NiMo-based sulfided catalysts and noble

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metals (Rh, Ru, Pd, Pt) over a wide variety of supports (i.e. alumina, silica, zeolites, activated

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carbon and zirconia)2,14–16. However, sulfided catalysts require a continuous addition of H2S to

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remain stable and active, making them less suited for lignin HDO due to the risk of sulfur

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incorporation in the bio-oil products17. Noble metals are not the preferred choice as their large

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ring hydrogenation selectivity decreases the content of aromatic products of the bio-oil increasing

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the amount of saturated alcohols instead. Furthermore, their cost may make them less relevant

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for industrial production of lignin-derived aromatics18. Regarding the support, HDO catalyst

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supported on activated carbons (ACs) are promising alternatives to traditional metal oxide

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supported catalysts due to (i) less coking19,20 (ii) low cost and (iii) the possibility of recovering

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the active metals from spent catalysts by burning off the carbon. Moreover, the textural and

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surface chemical properties of ACs might be tailored by varying the activation procedure21.

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The second approach to increase the competitiveness of the LtL process is to convert the

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solid organic residues to functional carbon materials. Several groups have studied the conversion

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of lignin and other biomass sources into renewable ACs for various purposes7,22–28. To our

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knowledge, except for a previous joint study29, no previous research been performed to convert

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solid organic residues of LtL processes (or other lignin processing related solid residues) into

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functional carbon materials such as ACs. In that study, we activated such residues into magnetic

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activated carbons (MACs) with high surface areas and studied their potential use in CO2

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separation.

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Here, we studied these lignin-derived and iron-containing MACs as catalyst supports for non-sulfided NiMo catalysts in the LtL conversion process. The activity of these NiMo-MACs 5 ACS Paragon Plus Environment


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was studied and compared with a NiMo catalyst supported on a conventional AC. The observed

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increases in the oil yields and decreases in the solid yields were compared to the non-catalyzed

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system (NC) and used as the primary evaluation parameters. The catalytic effect of the supports

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alone and the influence of pre-reducing the catalysts on the LtL conversion yields were also

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investigated. The promoting effects of Fe on the NiMo/MACs catalysts were also evaluated and

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discussed. Finally, the stability of the C-MACS catalyst upon recycling was determined.

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EXPERIMENTAL SECTION

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Chemicals

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Formic acid (>98%), tetrahydrofuran (THF) (>99.9%), ethyl acetate (EtAc) (99.8%), hexadecane (>99.8

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%) and anhydrous sodium sulphate (>99.0 %) were purchased from Sigma Aldrich and used as supplied.

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Nickel(II) nitrate hexahydrate (99.9+% Ni), ammonium molybdate tetrahydrate (99.98% Mo) and a

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commercial AC were purchased from Strem Chemicals Inc.

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Rice straw lignin from strong acid carbohydrate dissolution pre-treatment was received from

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Technical College of Bergen. The lignin was ground, and sieved (

High-Performance Magnetic Activated Carbon from Solid Waste from

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