Steen Brummerstedt Iversen - Academia.edu (original) (raw)

Papers by Steen Brummerstedt Iversen

Chemistry of Materials, Jan 14, 2010

ABSTRACT In situ synchrotron powder X-ray diffraction (PXRD) measurements have been conducted to ... more ABSTRACT In situ synchrotron powder X-ray diffraction (PXRD) measurements have been conducted to follow the nucleation and growth of crystalline CexZr1−xO2 nanoparticles synthesized in supercritical water with a full substitution variation (x = 0, 0.2, 0.5, 0.8, and 1.0). Direction-dependent growth curves are determined and described using reaction kinetic models. A distinct change in growth kinetics is observed with increasing cerium content. For x = 0.8 and 1.0 (high cerium content), the growth is initially limited by the surface reaction kinetics; however, at a size of 6 nm, the growth changes and becomes limited by the diffusion of monomers toward the surface. For x = 0 and 0.2, the opposite behavior is observed with the growth initially being limited by diffusion (up to 3.5 nm) and later by the surface reaction kinetics. Thus, although a continuous solid solution can be obtained for the ceria−zirconia system, the growth of ceria and zirconia nanoparticles is fundamentally different under supercritical water conditions. For comparison, ex situ synthesis has also been performed using an in-house supercritical flow reactor. The resulting samples were analyzed using PXRD, small-angle X-ray scattering (SAXS), and transmission electron microscopy (TEM). The nanoparticles with x = 0, 0.2, and 0.5 have very low polydispersities. The sizes range from 4 nm to 7 nm, and the particles exhibit a reversibly pH-dependent agglomeration.

European Biomass Conference and Exhibition Proceedings, 2013

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Journal of Solid State Chemistry, Aug 1, 2006

Highly crystalline anatase TiO2 nanoparticles have been synthesised in less than 1min in a superc... more Highly crystalline anatase TiO2 nanoparticles have been synthesised in less than 1min in a supercritical propanol–water mixture using a continuous flow reactor. The synthesis parameter space (T, P, concentration) has been explored and the average particle size can be accurately controlled within 10–18nm with narrow size distributions (2–3nm). At subcritical conditions amorphous products are obtained, whereas a broad range of

Elsevier eBooks, 2018

Abstract Hydrofaction™ targets the lack of renewable fuel alternatives for heavy transportation b... more Abstract Hydrofaction™ targets the lack of renewable fuel alternatives for heavy transportation by converting forestry residues into drop-in renewable diesel and marine fuel, by supercritical HTL, and by subsequent hydrotreating. A process block diagram of the Hydrofaction™ process is presented, subprocesses are described, and experimental data on both the HTL and hydrotreating stages are summarised. A comparison of six renewable Hydrofaction™ crude oils produced by continuous and supercritical HTL from different pine, spruce, birch, and bark mixtures shows similar quality independent of the woody feedstock. Two continuous hydrotreating campaigns were successfully carried out on a presulphided NiMo/Al2O3 catalyst for 300 and 700 h. The characteristic low sulphur content (100–200 ppm S) of the renewable crude oil was shown to inhibit catalyst activity, relative to an oil that was spiked to 1 wt% S. Nonsulphided catalysts (NiW/SiO2/Al2O3 and Pd/Al2O3) were screened in batch reactors to simulate a two-zone deoxygenation and hydrogenation reactor system, where H2S in the gaseous upgrading products may be avoided. The initial screening of this upgrading approach shows complete deoxygenation and improved devolatilisation relative to the sulphided catalysts. Finally, a life-cycle GHG emission analysis estimates that drop-in renewable diesel and marine Hydrofaction™ fuels can be associated with GHG emission reductions of 77%–108% depending on the Hydrofaction™ process configuration.

International Journal of Photoenergy, 2012

Pure phase anatase TiO 2 nanoparticles with sizes of 5-8 nm and varying crystallinity were synthe... more Pure phase anatase TiO 2 nanoparticles with sizes of 5-8 nm and varying crystallinity were synthesized in supercritical isopropanol/water using a continuous flow reactor. Their photodegradation of rhodamine B (RhB) was evaluated under visible light irradiation. The as-prepared TiO 2 nanoparticles show much higher photodegradation efficiencies than commercial Degussa P25 TiO 2. Moreover, the photodegradation of RhB on the as-prepared TiO 2 follows a different process from that on P25 TiO 2 , quicker N-deethylation and slower cleavage of conjugated chromophore structure. Based on PXRD, TEM, and BET measurements, these two photodegradation properties have been explained by the physicochemical properties of TiO 2 .

Journal of Membrane Science, Jul 1, 1997

Methods of selecting applicable membranes for use in membrane contactors for flue gas desulfuriza... more Methods of selecting applicable membranes for use in membrane contactors for flue gas desulfurization are proposed in this paper. The mass transfer mechanism for SO2 diffusion through gas filled pores is explored by simple measurements in order to identify suitable membrane structures for use in contactors for flue gas cleaning. It is attempted to correlate the experimentally determined membrane mass transfer coefficient to intrinsic physical properties of the membrane by applying theoretical and empirical correlations for the porosity-tortuosity relationship of the porous structure. Thereby limiting fluxes can be predicted with good accuracy from data quoted in the manufactures catalogue.

Journal of Solid State Chemistry, Oct 1, 2008

Nickel nanoparticles have been produced by combining two well-tested methods: (i) the continuous ... more Nickel nanoparticles have been produced by combining two well-tested methods: (i) the continuous flow supercritical reactor and (ii) the reduction of a nickel salt with hydrazine. The normal precipitation of a nickel–hydrazine complex, which would complicate pumping and mixing of the precursor, was controlled by the addition of ammonia to the precursor solution, and production of nickel nanoparticles with average

Biomass & Bioenergy, Oct 1, 2015

ABSTRACT Feedstock pretreatment is a prerequisite step for continuous processing of lignocellulos... more ABSTRACT Feedstock pretreatment is a prerequisite step for continuous processing of lignocellulosic biomass through HTL, in order to facilitate the pumpability of biomass aqueous slurries. Until now, HTL feedstock pumpability could only be achieved at solid mass content below 15%. In this work, two pretreatment methods to obtain wood-based slurries with more than 20% solid mass content, for continuous processing in HTL systems, are proposed. The effect of biomass particle size and pretreatment method on the feedstock pumpability is analyzed. The experimental results show that pumpable wood-based slurries containing 20% solids can be prepared using recycle HTL biocrude as carrier fluid, if particles smaller than 0.125 mm are used. The recycle biocrude concentration used for slurry make-up is strongly affected by the sawdust size distribution. A second pretreatment option is feedstock thermal treatment with alkalis. This method is less sensitive to particle size or wood type. 1 mm particles of either softwood or hardwood could be converted into pumpable liquid feedstock by thermal treatment with NaOH at 180 °C. Wood-water-biocrude slurries viscosity is reduced from 100 to 1000 Pa s to about 1 Pa s, when thermal treatment is applied.

Journal of Experimental Nanoscience, Sep 1, 2006

Crystallite size distributions and particle size distributions were determined by transmissions e... more Crystallite size distributions and particle size distributions were determined by transmissions electron microscopy (TEM), X-ray powder diffraction (XRD), and small-angle X-ray scattering (SAXS) for three commercially available TiO 2 powders (P25, UV100, and TiO2_5 nm) and one SSEC produced powder (SSEC78). The theoretical Guinier model was fitted to the experimental obtained XRD data and compared to analytical expressions. Modeling of the XRD spectra showed a difference between the analytical size dependent expressions and the theoretical Guinier model. Primary particle size distributions were extracted from SAXS measurements by the hard sphere model including an interparticle interference factor. The sizes obtained from SAXS were smaller than the sizes obtained from the XRD experiments; however, a good agreement was obtained between the two techniques. Electron microscopy confirmed the primary particle sizes and the shapes obtained by XRD and SAXS. The SSEC78 powder and the commercially available powders showed different morphologies, but SSEC78, UV100, and TiO2_5 nm all consisted of both primary particles as well as a secondary structure comprised of nanosized primary particles agglomeration into larger clusters. P25 showed the largest primary particle size, but did not show a secondary structure.

TechConnect Briefs, May 20, 2007

In this study the world's first real time in-situ simultaneous small angle x-ray scattering (SAXS... more In this study the world's first real time in-situ simultaneous small angle x-ray scattering (SAXS) and wide angle x-ray scattering (WAXS) characterization of supercritical nanoparticle formation was performed. In previous supercritical studies the reaction is treated as a 'black box' and the final product has been used to understand the process. In this study we open up the black box and directly reveal the mechanism behind sol-gel reactions in supercritical CO 2. The brilliance of the APS source and the design of the supercritical reaction chambers played a critical role in successfully exploring the key parameters in the formation of high quality nanoparticles in supercritical fluids. By the current setup the supercritical sol-gel nanoparticle formation can be controlled and altered by changing the process parameters. This means that the particle properties can be tailor-made by fine-tuning the process parameters.

Energy & Fuels, Nov 16, 2022

Organic solid wastes such as sewage sludge are potential feedstocks for the production of drop-in... more Organic solid wastes such as sewage sludge are potential feedstocks for the production of drop-in biofuels. Hydrothermal liquefaction (HTL) is a process that converts the wet sewage sludge into an organic biocrude. To fulfill industrial fuel standards, the considerable heteroatom content of the biocrude needs to be lowered by downstream processes. Nitrogen (N) contained in several compounds poses a challenge and yet, the complex chemical composition of HTL-biocrude samples has hindered detailed analysis and understanding. In particular, N-containing aromatic substances appear very persistent in biocrude. In the present work, two alkaline (NaHCO 3 and NaOH) and one acidic (HCL) aqueous solutions were subsequently applied to extract and recover polar N-containing compounds from the biocrude matrix with an N-content of 3.8 wt %. Gas chromatography−mass spectrometry, atmospheric pressure chemical ionization in positive mode, and Fourier transform ion cyclotron resonance mass spectrometry were applied for their characterization and results show that a large share of N-compounds with an aromatic, pyridinic structure was found in the acidic extracted fraction with an N-content of 9.5 wt %. Aliphatic N-compounds were less affected by the separation and ended in the residual fraction. N-compounds with multiple oxygen functionalizations are enriched in the alkaline extracted fractions. This showed that N-compounds with an aromatic structure are strongly affected by polar groups and can potentially be extracted by downstream processes with appropriate solvents.