Georg Schaub

Microalgae and terrestrial biomass as source for fuels - A process view

Due to increasing oil prices and climate change concerns, biofuels have become more important as potential alternative energy sources. It is an open question which kind of biofuels with which yield potentials, characteristic properties and environmental consequences should give the largest contributions. Microalgae offer novel aquatic biomass systems with higher fuel yield potential and lower water demand than terrestrial biomass. They allow the direct generation of desired end products like biooil, hydrogen, or of materials to be processed afterwards (like starch, biomass). Research and development activities at present include fundamentals of algae strain improvement, reactor design and process integration, with auxiliary power requirements and specific reactor cost being addressed as most critical issues.

Fischer–Tropsch on Iron with H2/CO and H2/CO2 as Synthesis Gases: The Episodes of Formation of the Fischer–Tropsch Regime and Construction of the Catalyst

Fischer–Tropsch synthesis experiments have been performed with reduced precipitated Fe-Al-Cu-K2O catalysts, using a H2/CO and a H2/CO2 synthesis gas. Samples of the reaction products and of the catalyst were taken at distinct run lengths. The product samples were analyzed in detail and from their composition the kinetic data of elemental reaction steps (growth, branching, desorption as olefin or paraffin) calculated, applying the extended model of “nontrivial surface polymerization”. The catalyst samples were characterized by BET, XRD, Mössbauer spectroscopy, XPS and TPD in hydrogen and thus specifically phase changes of e.g. alpha iron, iron oxides, and iron carbides observed.It has been measured how the product composition changed with time, up to the steady state of synthesis. Several episodes with their own kinetic regimes were identified. These were then correlated with compositional and structural changes of the catalyst. This is addressed as “construction of the true iron Fischer–Tropsch catalyst”.

Transient initial kinetic regimes of Fischer–Tropsch synthesis

Transient kinetic regimes of Fischer–Tropsch (FT) synthesis with a potassium-promoted iron catalyst have been observed and characterized by time-resolved conversion and selectivity studies using H2/CO and a H2/CO2 synthesis gases. Up to six episodes relating to catalyst transformations/reconstructions could be distinguished. Amazingly, with the H2/CO2 synthesis gas a Fischer–Tropsch product of nearly the same composition as that with the H2/CO synthesis gas was finally obtained at the steady state. However, the transient episodes lasted for a long time. Selectivity has been related to steps of elemental reactions by use of a kinetic model. As intrinsic FT feature, the principle of selective inhibition is established from the detailed selectivity results. Spatial constraints at the FT sites appear also to control selectivity. The iron catalyst exhibits fundamental differences in how generating FT sites, as compared with cobalt catalysts. FT sites on iron are stable, whereas FT sites on cobalt are of dynamic nature.

Modeling microalgae cultivation productivities in different geographic locations – estimation method for idealized photobioreactors

Microalgae can be used to produce versatile high‐value fuels, such as methane, biodiesel, ethanol, or hydrogen gas. One of the most important factors that influence the economics of microalgae cultivation is the primary production of biomass per unit area. This is determined by productivity rates during cultivation, which are influenced by the local climate conditions (solar irradiation, temperature). To compare locations in different climate regions for microalgae cultivation, a mathematical model for an idealized closed photobioreactor was developed. The applied growth kinetics were based on theoretical maximum photon‐conversion efficiencies (for the conversion of solar energy to chemical energy in the form of biomass). Known or estimated temperature effects for different algal strains were incorporated. The model was used to calculate hourly average areal productivity rates as well as annual primary production values under local conditions at seven example locations. Here, hourly weather data (solar irradiance and air temperature) were taken into account. According to these model calculations, maximum annual yields were achieved in regions with high irradiation and temperature patterns in or near the optimum range of the specific algal strain (here, desert and equatorial humid climates). The developed model can be used as a tool to assess and compare individual locations for microalgae cultivation.

Effects of flue gas composition on the catalytic destruction of chlorinated aromatic compounds with a V-oxide catalyst

When using catalytic flue gas cleaning, several flue gas compounds may influence oxidation reactions of hazardous volatile organic compounds, possibly leading to lower reaction rates and, thus, to an incomplete destruction. Experimental investigations were performed with regard to the influence of selected flue gas compounds, like hydrogen chloride, sulfur dioxide, oxygen, and water vapour, on the catalytic destruction behavior of chlorobenzenes under flue gas cleaning conditions of an incineration plant. For this purpose, a metal oxide catalyst was operated at different temperatures at a space velocity of 3600 h-1 in a laboratory-scale fixed bed reactor with model flue gases, and with real flue gases generated from the TAMARA waste incineration plant. The results obtained from the studies with model flue gas were analyzed with respect to reaction kinetics. These kinetics were applied for comparison with the experimental data gained in the real flue gas.

Hydrocarbons via CO2 Hydrogenation Over Iron Catalysts: The Effect of Potassium on Structure and Performance

We present a study in which the suitability of potassium promoted iron-based Fischer–Tropsch (FT) catalysts for the generation of synthetic natural gas additives via the hydrogenation of carbon dioxide through a combined reverse water gas shift (WGS) and FT reaction is studied. Using novel in situ instrumentation based on XRD and magnetometry techniques the reversible conversion of metallic iron to Hägg carbide under reaction conditions and its decomposition in hydrogen could be monitored. The facilitating effect of potassium in the formation of iron carbide could be exposed as function of time on stream. While the FT reaction was reduced in the presence of high potassium loadings the reverse WGS reaction seemed to be unperturbed. A faster activation of an iron phase obtained via the decomposition of iron carbide, compared to the initial activation of a pristine iron phase obtained via the reduction of iron oxide was witnessed.Graphical Abstract

Combining Fischer-Tropsch (FT) and Hydrocarbon Reactions under FT Reaction Conditions: Model Compound and Combined-Catalyst Studies

The main objectives of the further downstream operations (product upgrading) of Fischer-Tropsch products are to i) improve yields and selectivities of the desired fractions, and ii) improve fuel properties to meet the fuel product specifications. The present study addresses the combination of low-temperature Fischer-Tropsch (FT) synthesis (with Co or Fe catalysts) and hydrocarbon modification reactions (hydroprocessing) in one reactor.In addition to earlier results with Pt/ZSM-5 in a dual-layer configuration in a fixed-bed reactor (Mena et al. 2007), the objective of the present investigation was to study the influence of CO during hydroprocessing and oligomerisation reactions of hydrocarbon model compounds (1-octene, ethene/propene) on two different bifunctional catalysts (Pt/ZSM-5, Pt/Beta). In addition, the influence of the catalyst-bed configuration for the combination FT synthesis and hydrocarbon reactions was investigated (dual layer/physical mixture).The achieved results indicate a potential of combining FT and hydrocarbons reactions in one reactor. Hydrogenation, isomerisation, cracking and oligomerisation reactions take place on a Pt/zeolite catalyst at FTS temperatures and in the presence of CO and H2O. The most critical point of this combination seems to be the deleterious effect of CO on the cracking reactions of isomers. For that reason, the wax fraction (C21+) was only partially cracked. The experimental results also indicate that the type of zeolite and the catalyst-bed configuration have an influence on the diesel/gasoline ratio obtained. It seems that the final fuel products will be a mixture of gasoline and diesel fuel and C1 to C5 compounds, as long as no diesel-selective hydroprocessing catalyst is found.

Energy flows, material cycles and global development

This book starts by discussing the global flows of energy and materials and changes caused by human activities. It then examines the limitations of anthropogenic energy and material flows and the consequences for the development of human society. Different scenarios for lifestyle patterns are correlated with the future development of the global energy supply and climate. As it provides a process engineering approach to the Earth system and global development, readers should have a basic understanding of mathematics, physics, chemistry and biology. This second edition also reflects new developments since the original publication: increases in anthropogenic energy and material flows due to significant economic growth in certain parts of the world, and recent changes in energy policy and technological development countries, such as Germany (the Energiewende, or transition to renewable energy sources), where goals have been defined and measures initiated for a future energy supply without fossil and nuclear sources. As such, it offers a valuable resource for undergraduate and graduate students as well as practicing experts alike.

Fuels and petrochemicals from CO2 via Fischer-Tropsch synthesis — steady state catalyst activity and selectivity

The behaviour of CO2 in Fischer-Tropsch synthesis was investigated using a promoted iron and a promoted cobalt catalyst. The decrease in yield of hydrocarbons is more pronounced on cobalt than on iron. The product distribution on iron remains nearly constant with increasing CO2 concentration, however on cobalt the selectivity to methane increases dramatically.

Initial transient rates and selectivities of Fischer-Tropsch synthesis with CO2 as carbon source

Initial transient changes of conversion and selectivity during Fischer-Tropsch synthesis with a potassium-promoted iron catalyst with H 2 /CO 2 and H 2 /CO syngases were determined and several episodes of catalyst transformation distinguished. Selectivity changes are related to changes in elemental reaction steps probabilities using the model of “non trivial surface polymerization”. With the H 2 /CO 2 syngas the catalyst transformation episodes are extended to about one week. Transient episodes are discussed as for compositional and structural catalyst changes and related Fischer-Tropsch surface chemistry.