Catalytic Hydrogenation for Biomass Valorization: Volume 13 (Energy and Environment Series) - Hardcover

Hardcover

ISBN 10: 1849738017 ISBN 13: 9781849738019

Publisher: Royal Society of Chemistry, 2014

Synopsis

As the biorefinery industry expands to meet the latest discoveries in biomass conversion, this book provides a thorough grounding in the subject.

About this title

About the Author

Dmitry Murzin is Chair of Chemical Technology at Åbo Akademi University. He serves on the editorial boards of several journals in the catalysis and chemical engineering fields, and is an elected member of the Societas Scientiarum Fennica and Svenska Tekniska Vetenskapsakademien i Finland science academies.

From the Back Cover

The efficient conversion of biomass to value-added products has become a major research area in the pursuit of alternatives to petroleum-based feedstocks; hydrogenation and hydrogenolysis are important tools to achieving this aim. This book presents comprehensive coverage of the different catalysts for these reactions, targeting the efficient conversion of bio-based molecules and biopolymers.

The editor, Roberto Rinaldi, is an acknowledged leader in the field of biomass conversion, and has brought together experts from across the globe to examine all aspects of the process, including the solvents, catalysts and feedstocks used in modern biorefineries. Consideration is also given to the fundamentals of running a plant, such as equipment and safety issues.

As the biorefinery industry expands to meet the latest discoveries in biomass conversion, this book provides a thorough grounding in the subject and is an essential reference to researchers at the forefront of discovering new products, companies wishing to scale-up biomass conversion, and postgraduate students of sustainable chemistry and chemical engineering.

Excerpt. © Reprinted by permission. All rights reserved.

Catalytic Hydrogenation for Biomass Valorization

By Roberto Rinaldi

The Royal Society of Chemistry

Copyright © 2015 The Royal Society of Chemistry
All rights reserved.

ISBN: 978-1-84973-801-9

Contents

Chapter 1 Hydrogen: Economics and its Role in Biorefining Ferdi Schüth, 1, 
Chapter 2 General Reaction Mechanisms in Hydrogenation and Hydrogenolysis for Biorefining Ning Li, Wentao Wang, Mingyuan Zheng and Tao Zhang, 22, 
Chapter 3 Noble-Metal Catalysts for Conversion of Lignocellulose under Hydrogen Pressure Hirokazu Kobayashi, Hidetoshi Ohta and Atsushi Fukuoka, 52, 
Chapter 4 Solvents and Solvent Effects in Biomass Conversion Roberto Rinaldi, 74, 
Chapter 5 Hydrogenolysis of Cellulose and Sugars Peter J. C. Hausoul, Jens U. Oltmanns and Regina Palkovits, 99, 
Chapter 6 Hydrodeoxygenation of Lignocellulose-Derived Platform Molecules Konstantin Hengst, Martin Schubert, Wolfgang Kleist and Jan-Dierk Grunwaldt, 125, 
Chapter 7 Catalytic Hydrotreatment of Fast Pyrolysis Oils Using Supported Metal Catalysts Agnes Retno Ardiyanti, Robertus Hendrikus Venderbosch, Wang Yin and Hero Jan Heeres, 151, 
Chapter 8 Hydrodeoxygenation of Biomass-Derived Liquids over Transition-Metal-Sulfide Catalysts Barbara Pawelec and Jose Luis Garcia Fierro, 174, 
Chapter 9 Biofuels Generation via Hydroconversion of Vegetable Oils and Animal Fats Jefferson Roberto Gomes, Stella Bezergianni, José Luiz Zotin and Eduardo Falabella Sousa-Aguiar, 204, 
Chapter 10 Catalytic Hydrogenation of Vegetable Oils An Philippaerts, Pierre Jacobs and Bert Sels, 223, 
Chapter 11 Hydrogenolysis of Lignocellulosic Biomass with Carbon Monoxide or Formate in Pressurized Hot Water Ulf Schuchardt and Jean Marcel R. Gallo, 242, 
Chapter 12 Reactor Technology and Modeling Aspects for the Hydrogenation of Components from Biomass Teuvo Kilpiö, Victor Sifontes, Kari Eränen, Dmitry Yu. Murzin and Tapio Salmi, 253, 
Chapter 13 Safety and Practical Aspects of Liquid-Phase Hydrogenation Marco Kennema and Nils Theyssen, 282, 
Subject Index, 299, 

CHAPTER 1

Hydrogen: Economics and its Role in Biorefining

FERDI SCHÜTH

1.1 Introduction

Hydrogen is perhaps one of the most promising energy carriers of the future. In renewable energy systems with high fractions of intermittent supply (e.g. wind power and solar thermal energy), potential surplus electricity could be converted into hydrogen through water electrolysis. This hydrogen can be used in a wide variety of applications. The most often discussed option, the reconversion of hydrogen into electricity, be it by gas turbines or by fuel cells, appears to be rather unattractive, due to the low round-trip efficiencies. Electrolysis – based on the process scale – can be estimated to have an efficiency of about 60% (if higher efficiencies are given, they are typically relative to the cell level). A recent NREL analysis, based on questionnaires given to manufacturers, indicate a mean efficiency value of 53% for the system. Considering that the fuel-cell efficiency on the systems' level and gas turbines (not available for hydrogen yet) is estimated at about 50–60%, the overall round-trip efficiency is thus reduced to slightly above 30%. It will certainly be possible to improve this figure to some extent, but substantial losses in the round trip from electricity to electricity will invariably always be present. Therefore, the use of "renewable" hydrogen – not for the reconversion into electricity, but rather as a feedstock for the chemical industry, in oil refineries, or in biorefineries – appears to be promising. For biomass upgrading, a substantial need for hydrogen undoubtedly exists due to the high oxygen content present in biogenic molecules.

Figure 1.1 plots the chemical composition of different energy carriers in an O/C vs. H/C diagram. The typical biomass constituents contain much more oxygen than potential target molecules. In addition, the hydrogen content often needs to be increased. Decarboxylation and decarbonylation pathways are one of the possibilities for the reduction of the O/C ratio, but they alone are insufficient for this purpose. Accordingly, for further oxygen removal, hydrogen is often required as a reducing agent in order to convert biogenic molecules into less -oxygenated target compounds. In order to increase the H/C ratio, hydrogen is needed directly either in the hydrogenation and hydrogenolysis pathways, or indirectly after dehydration, since the dehydration leads to unsaturated compounds that are often undesired intermediates, as they are very reactive, and thus may undergo side reactions, decreasing overall product yields. The various process options that hydrogen is used for in order to convert biomass into chemical intermediates and end products will be briefly discussed at the end of this chapter.

1.2 Conventional Routes for Hydrogen Production and Corresponding Costs

The vast majority of hydrogen is currently produced from fossil fuels (estimated at 49% from natural gas, 29% from liquid hydrocarbons, either directly from naphtha or related feedstocks, or indirectly by converting residues in refineries or as off-gases from chemical or refinery processes, 18% from coal, and 4% from electrolysis). Most of today's production is intended for further processing in the chemical and refinery industries, and is thus not traded on the market. It is estimated that only ca. 10% of the produced hydrogen is traded (i.e. merchant hydrogen); the rest is produced and directly used onsite (i.e. captive hydrogen). Due to this fact, there are various figures available, as the production levels are difficult to assess. From the estimates published for different years and projected growth, current global production is about 60 million metric tons per year, with wide margins of error.

For the purposes of this chapter, we will consider processes rendering hydrogen as the main product (i.e. hydrogen made on purpose). Thus, typical refinery processes (e.g. coking and visbreaking) are not further discussed. Also disregarded are petrochemical processes, such as steam cracking for lower olefins production, since here the olefin is the main product, although the hydrogen produced contributes to the overall profitability of the process. Some processes can be considered as borderline cases, such as cracking, in which the amount of produced hydrogen can be adjusted by the processes conditions, and can thus be tuned to the hydrogen requirements of the refineries.

1.2.1 Steam Reforming/Autothermal Reforming/Partial Oxidation of Fossil Feedstocks

There are three main processes for the production of hydrogen from carbon-containing feedstocks: catalytic steam reforming (SR), autothermal reforming (AR) and partial oxidation (PO), as well as other configurations, which contain various aspects of any of the aforementioned processes. The selection of the reforming technology depends on many factors, such as the intended use of the hydrogen, acceptable impurity level, pressure level of downstream processes, price and availability of hydrocarbon and fuel, investment and operational costs, catalyst price, and several others secondary factors. Overall, the reforming technologies are intimately connected to the chemical reaction networks that govern hydrogen formation, making them perhaps best to be discussed altogether.

The basic reaction of steam reforming is given as eqn (1.1) for the example of methane,

CH4 + H2O [??] 3 H2 + CO ΔHR0 = 206 kJ mol-1 (1.1)

however, any other carbon-containing feedstock can be converted by a similar process, although this may require changes in process technology. Moreover, the syngas composition is dependent on the elemental composition (i.e. H/C/O ratios) of the feedstock.

Partial oxidation can be described by eqn (1.2), again formulated for methane as feed:

2CH4+O2 [??] 2CO+4 H2 ΔHR0=-36 kJ mol-1 (1.2)

However, it is difficult to achieve full selectivity to syngas as expressed in eqn (1.2), since partial oxidation is always competing against total oxidation:

CH4 + 2 O2 [??] CO2 + 2H2O ΔHR0 = -802 kJ mol-1 (water in gas phase) (1.3)

Moreover, several other equilibria are relevant in all of these systems, such as:

CO + H2O [??] CO2 + H2 ΔHR = -90 kJ mol-1 (1.4)

C + O2 [??] 2CO ΔHR0 = -222 kJ mol-1 (1.5)

C + H2O [??] CO + H2 ΔHR0 = 131 kJ mol-1 (1.6)

In addition, methane can be cracked into hydrogen and carbon; for higher hydrocarbons, cracking reactions also come into play, and heteroatoms, which are almost invariably present in the feedstocks, react as well under the conditions of the hydrogen-generating reactions. While all of these reactions can occur in all of the systems, it is helpful to conceptually separate them, and discuss the three processes as prototypes. SR is described by eqn (1.1) and PO by eqn (1.2). As the overall reaction network contains exothermic and endothermic reactions, the feed can be composed in such a manner that the resulting enthalpy becomes nearly zero. This option is called autothermal reforming (AR).

In SR, the hydrocarbon, methane for the majority of the produced hydrogen, and steam react over a nickel/γ-Al2 O3 catalyst at 1073–1173 K under a pressure of 1.5 to 3 MPa in a tubular reactor, producing syngas. One of the key problems is the supply of the heat to the reactor, since the reaction is highly endothermic (206 kJ mol-1). Typically, the heat is integrated into the system via a firebox, in which part of the feed gas is combusted. Methane and other fuel gases can be used in the firebox. The product gas after the steam-reforming reactor has the equilibrium composition at the exit temperature of the reformer, containing H2, CO, CO2, and CH4 in the case of natural gas and naphtha as feedstock; in turn, with oil or coal, nitrogen and sulfur compounds can be present, as well. In order to maximize hydrogen yields, the product gas is first exposed to a high temperature shift reaction (1.4) over iron-based catalysts at 623–723 K. Depending on the plant configuration, the final hydrogen product is obtained after purification via pressure swing adsorption (standard in modern plants) or by a low-temperature shift stage at 493 K over Cu/ZnO/Al2O3 catalysts, followed by CO2 scrubbing, with a final removal of COx by catalytic methanation. Instead of providing heat for the reforming reaction by an external heating of the reformer tubes, the required energy can be supplied to the process by partial combustion of the feed gas (autothermal reforming). In this case, the feed is mixed with oxygen before it enters the catalyst bed. In sequence, the gas is combusted in the entrance section of the bed, thus providing the heat for the reforming reaction in the later section of the unit. Such designs are advantageous if high temperatures are desired in order to minimize methane concentration, to allow high pressures, or to directly provide nitrogen for ammonia synthesis (in which air is thus used instead of oxygen).

Conventional partial oxidation processes for hydrogen production are used for heavy feeds (e.g. heavy residues or oil fractions with high sulfur or metal contents). The PO reaction takes place in a flame in an empty furnace with substoichiometric amounts of oxygen. For the production of hydrogen, CO needs to be shifted to hydrogen, which is advantageously carried out in the presence of a catalyst at temperatures below 773 K after the steam addition to the feed. The purification of hydrogen proceeds by one of the many available scrubbing processes. Partial oxidation has also been reported to be suitable for syngas production from methane with very high selectivity and yields. At residence times of milliseconds, methane can be partially oxidized with oxygen rendering ca. 90% yields of CO and H2. Key for this development is the very short contact time with noble-metal catalysts supported on ceramic foam monoliths. Despite the promising results, this technology does not seem to have been commercially implemented, probably due to the potential hazards of the gas mixture that is in the middle of the explosion regime.

1.2.2 Cost Analysis for Hydrogen Production

Cost analysis for hydrogen production is not a simple task, and data provided in the literature have to be interpreted with caution. Should just production costs be analyzed, centralized facilities have clear advantages over distributed production, as the former can provide significant economies of scale. However, this advantage can be easily lost upon including the cost for delivery (i.e. liquefaction/pressurization and transport). An analysis for specific boundary conditions gave a cost for the dispensed hydrogen of 3.3 $/kg H2 for a distributed production. Costs were only half of that in a centralized plant, but liquefaction and delivery cost of 3.5 $/kg H2 have to be added to the pure production costs. However, in other studies, the additional cost for transportation has been estimated at only 1.02 $/kg H2. Transportation costs are obviously dependent on the mode of hydrogen transportation (pressurized, liquefied, truck, pipeline, etc.). In the following, if no other information is given, the hydrogen cost is referred to as the production costs alone. The studies quoted are also from different years, and thus for a direct comparison, inflation would need to be taken into account. However, most of the studies quoted are from the last five to ten years, and thus the error in neglecting inflation is minor when compared to strongly fluctuating prices of raw materials. Finally, the differences in exchange rates will also affect the figures. For the purpose of this contribution, the values are given in the currency that had been used in the original publication; when currencies are converted, an exchange rate of 1.38 $/[euro] is utilized.

Due to the broad range of feedstocks that can be used for production of hydrogen and the different process options available, the production costs greatly depend on local conditions. A detailed analysis from 1983 is available for hydrogen production in Germany. The situation, especially with respect to feedstock prices, has changed significantly since then, but some of the features, especially the split between feedstock and investment costs, are probably still valid. On the one hand, in the case of methane as a feedstock, investment costs for the reformer are the lowest, while feed/fuel costs are intermediate. On the other hand, a reformer operating on lignite shows the highest investment costs; however, due to the low price of lignite, the lowest feed cost. Most unfavorable are naphtha- and fuel-oil-based reformers. In the case of fuel oil, the feed cost is much higher than the investment costs so that the overall cost is one of the highest (Figure 1.2). Altogether, the pathway starting with natural gas is currently the most favored, as it is associated with the lowest overall costs.

In a centralized methane reforming, the natural gas price dominates the cost for hydrogen production. Natural gas prices are influenced by regional economic conjunctures, since it is traded globally only to a limited extent, despite the availability of liquefied natural gas terminals in addition to the steady expansion of their capacity over the last decades. Considering the natural gas price at 5 $/GJ, the cost for hydrogen has been estimated at approximately 1 $/kg H2 gate price for a large-scale plant with a production capacity of 427 tons per day. In the United States, due to the shale gas boom, natural gas prices are currently below 5 $/GJ (4.3 $/MMBTU, corresponding to about 4.1 $/GJ). Accordingly, the cost for hydrogen should be ca. 0.9 $/kg H2 or 0.65 [euro]/kg. In Europe, natural gas prices are about 22.5 [euro]/MWh (i.e. corresponding to approximately 8.5 $/GJ) at the European Energy Exchange (March 24th 2014). The EU feed cost leads to a hydrogen production cost of about 1.2 [euro]/kg H2 (calculation based on the figures given in Ref. 13). Nonetheless, with the increasing supply of natural gas traded globally, it can be expected that also the European price of natural gas will eventually fall within the next few years, and thus hydrogen production costs at around 1 [euro]/kg H2 may also be estimated as a base-case scenario, against which other hydrogen production technologies will have to compete. In addition to the raw materials costs, it is worth mentioning that such estimates are dependent on other boundary conditions, e.g. the process scale (hydrogen production is at substantially higher cost on small-scale plants), price of possible coproducts (e.g. oxygen in electrolyzers), to mention just a few.

(Continues...)

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Edition details

• Publisher: Royal Society of Chemistry
• Publication date: 2014
• Language: English
• ISBN 10: 1849738017
• ISBN 13: 9781849738019
• Binding: Hardcover
• Number of pages: 324
• Editor: Roberto Rinaldi