Philipp Rudolf von Rohr

Printability of calcium phosphate powders for three-dimensional printing of tissue engineering scaffolds.

Three-dimensional printing (3DP) is a versatile method to produce scaffolds for tissue engineering. In 3DP the solid is created by the reaction of a liquid selectively sprayed onto a powder bed. Despite the importance of the powder properties, there has to date been a relatively poor understanding of the relation between the powder properties and the printing outcome. This article aims at improving this understanding by looking at the link between key powder parameters (particle size, flowability, roughness, wettability) and printing accuracy. These powder parameters are determined as key factors with a predictive value for the final 3DP outcome. Promising results can be expected for mean particle size in the range of 20-35 μm, compaction rate in the range of 1.3-1.4, flowability in the range of 5-7 and powder bed surface roughness of 10-25 μm. Finally, possible steps and strategies in pushing the physical limits concerning improved quality in 3DP are addressed and discussed.

Oxidation of Lignin Using Aqueous Polyoxometalates in the Presence of Alcohols

A novel approach has been developed in order to use Kraft lignin as a renewable resource for the production of chemicals. The concept is based on the use of polyoxometalates as reversible oxidants and on the use of radical scavengers, which prevent lignin fragments from repolymerizing. The oxidation of Kraft lignin, which is a potential source of functionalized phenols, by H3PMo12O40 in water yields a relatively small amount of monomeric species detected by GC-MS. The addition of methanol to the reaction resulted in an increase in the yield of monomeric products by a factor of up to 15. Vanillin and methyl vanillate are the main products obtained, in a maximum yield of 5 wt % based on dry Kraft lignin. Methanol plays a decisive role in the prevention of repolymerization by reducing lignin-lignin condensation reactions. Furthermore, it is proposed that methanol generates small amounts of .CH3 and CH3O. radicals through the acid-catalyzed formation of dimethyl ether which couple with lignin fragments.

The mean oxidation number of carbon (MOC)—a useful concept for describing oxidation processes

Abstract When characterizing real waste waters and sludges, usually collective parameters like COD and TOC are used. Detailed protocols (USEPA, APHA, DIN) concerned with the analytical determination of these parameters exist. However, some difficulties may arise when interpreting the measured values. Waste waters may contain substances refractory to the COD determination, or high concentrations of easily oxidizable inorganic salts may be mistaken for organic matter. When treating waste waters and sludges using physical, chemical or biological processes, there may be unexpected phenomena apparently contributing to a reduction or even concentration of the dissolved substances: adsorption effects (on reactor walls, catalyst, biomass), stripping of volatile organics, sedimentation, complexation, precipitation, or evaporation of water. When monitoring only COD or TOC, one cannot conclude whether a change of these values is due to a chemical degradation process or to a purely physical elimination like stripping. In this paper the concept of the mean oxidation number of organic carbon (MOC) is presented. By combining TOC (or DOC) and COD measurements, one can obtain valuable additional information concerning the reaction development during waste water treatment processes, especially when oxidative transformations are involved. The applicability of the MOC concept is demonstrated using the wet oxidation of pyridine, stripping of toluene, decarboxylation of malonic acid, and wet oxidation of phenol as well as the wet oxidation of sewage sludge as an example of a real system.

Large-scale structures in a developed flow over a wavy wall

We address - motivated in part by the findings of Gong et al. and Miller the role of streamwise-oriented large-scale structures in a developed flow between a sinusoidal bottom wall and a flat top wall. Particle image velocimetry (PIV) is used to examine the spatial variation of the velocity in different planes of the flow through a water channel with an aspect ratio of 12:1. The wave amplitude is equal to one tenth of the wall wavelength, Λ, and Reynolds numbers between 500 and 7300, defined with the bulk velocity and the half-height of the channel, are considered. To examine streamwise-oriented structures, the spanwise variation of the velocity field is studied in a plane parallel to the top wall, and in one that intersects the wavy surface at an uphill location

Impact of K and Ba promoters on CO2 hydrogenation over Cu/Al2O3 catalysts at high pressure

CO2 hydrogenation over K and Ba promoted Cu/Al2O3 catalyst was systematically investigated to study the promoter effects in a wide range of pressure conditions. The catalysts prepared by the impregnation method were characterized by XRD, physisorption, N2O-pulse chemisorption, H2-TPR, and CO2-TPD techniques. The catalytic performance was evaluated using a fixed-bed microreactor for a pressure and temperature range of 0.40–36 MPa and 443–553 K. The influence of promoters on the formation of surface species present during the reaction was examined by in situ DRIFTS. As expected from thermodynamics, high pressure and low temperature are the favourable conditions to achieve high selectivity to methanol over the Cu/Al2O3 catalyst. Improved reaction performance towards methanol synthesis and reverse water-gas shift (RWGS) reaction was observed for the Ba and K promoted Cu/Al2O3 catalysts, respectively. Notably, with the Ba promotion the selectivity to methanol was enhanced to 62.2% compared to 46.6% of the unpromoted Cu/Al2O3 catalyst at 10 MPa and 473 K at the expense of a lowered CO2 conversion. In contrast, the K promoted catalyst exhibited high selectivity to CO (95.8%) under the same reaction conditions. Formation of dimethyl ether, significant over the unpromoted Cu/Al2O3 catalyst at 0.4–10 MPa, was strongly suppressed at 36 MPa. Ba and K promoters effectively suppressed the formation of dimethyl ether under all examined pressure conditions by weakening the acidity of the alumina support. The strong promotional effects of K was explained by the predominant coverage of both Cu and alumina surface sites, creating specific active sites stabilizing surface intermediate species and preferring the RWGS pathway. On the contrary, the Ba promoter covers the alumina surface exclusively and renders Cu accessible and more easily reducible, promoting methanol synthesis. The effects of promoters on the catalytic performance were found to be valid at low and at elevated pressures.

Acidic oxidation of kraft lignin into aromatic monomers catalyzed by transition metal salts

Abstract As one of the three main components in woody biomass, lignin is an abundant but underused renewable raw material and carbon source. Owing to its aromatic structure and large availability as a by-product of pulping, its conversion into chemicals is highly attractive. In the present work, the oxidation of a softwood kraft lignin in acidic media was investigated in the presence of a homogeneous catalyst. The objective was to find a cheap but efficient catalyst for the depolymerization of kraft lignin into aromatic monomers. Different transition metal salts were screened and compared to phosphomolybdic acid, which was investigated in previous studies, and to experiments in sulfuric acid without additional catalyst. Vanillin and methyl vanillate were the main monomeric products detected by gas chromatography/mass spectrometry but their formation was only slightly increased by using transition metal salts (up to 6.28 wt% yield). However, the presence of iron or copper chloride resulted in fast formation kinetics and significant amounts of other monomeric products. In addition, an efficient fragmentation of the lignin molecule from a weight-average molecular weight of 3500 g mol-1 down to 500 g mol-1 was observed by size-exclusion chromatography. The enhanced incorporation of oxygen into the reaction products in the presence of those catalysts was proven by Fourier transform infrared spectroscopy and the influence of the catalyst concentration was studied.

Microwave plasma characteristics of a circulating fluidized bed-plasma reactor for coating of powders

Abstract Coating of powders by Plasma-CVD is an adequate way to protect particles from environmental attack or to provide a large catalytic surface on carrier particles. The μ-SLAN® microwave plasma source is placed into the riser of a circulating fluidized bed, and its performance as a particle-coating reactor is evaluated for silicon oxide deposition on glass beads. Fluctuations of the particle concentration reduce the efficiency of MW coupling. The minimum MW input power for stable plasma generation is 4 times higher in the presence of particles and increases with oxygen partial pressure. The temperature of the entrained particles can be adjusted to very low values, but higher temperatures are achieved near the MW-coupling slots. The conversion ratio of HMDSO only depends on the specific power ( P / F ). It is slightly lower with particles and 5 W/sccm are required for 80% conversion.

Lignin repolymerisation in spruce autohydrolysis pretreatment increases cellulase deactivation

This study presents a modified autohydrolysis pretreatment which helps to overcome the recalcitrance of softwood for enzymatic hydrolysis of its cellulose. Autohydrolysis pretreatments of spruce wood were performed with 2-naphthol, which prevents lignin repolymerisation reactions, thereby increasing the enzymatic digestibility of cellulose by up to 64%. The negative influence of repolymerised lignin structures on enzymatic hydrolysis was confirmed by the addition of resorcinol in autohydrolysis, which is known to promote repolymerisation reactions and decreased the biomass digestibility. Several analyses were performed to study the underlying mechanism of this effect on hydrolysis, indicating that cellulolytic enzymes are adsorbed and deactivated especially by repolymerised lignin structures, which accounts for the high differences in biomass digestibility. It was shown that lignin repolymerisation significantly increases its specific surface area through modification of the lignin nanostructure, which is supposed to increase the unproductive binding of enzymes.

Wavy wall effects on turbulence production and large-scale modes

We describe how outer flow turbulence phenomena depend on the interaction with the wall. We quantify the influence of highly rough surfaces on turbulence statistics, eigenmodes and spectra of eigenvalues in the outer part of the wall shear layer of an isothermal turbulent flow. Surface geometries with different amplitude-to-wavelength ratios can be regarded as surfaces of defined wall roughness. The wavelength, Λ, and the wave amplitude, 2a, of a water channel are varied by changing the bottom wall in the test section. We consider three sinusoidal wall profiles defined by the amplitude-to-wavelength ratio α = 2a/Λ = 0.2 (Λ = 30 mm), α = 0.2 (Λ = 15 mm), and α = 0.1 (Λ = 30 mm). Digital particle image velocimetry is performed to examine the spatial variation of the streamwise, spanwise and wall-normal velocity components. Statistical quantities that are determined are the Reynolds stresses, turbulent kinetic energy, and turbulent energy production. Measurements are performed at a Reynolds number of 11200, defined by the half channel height and the bulk velocity. A characteristic length scale in the most dominant eigenmodes can be found that agrees for all wall profiles and is independent of the amplitude-to-wavelength ratio. The turbulence quantities compared at defined streamwise coordinates in wall-normal direction are independent of the wavy wall profile in the outer region when scaled with the friction velocity, u* w .

Plasma enhanced chemical vapor deposition on powders in a low temperature plasma fluidized bed

The main goal of this article is to coat a significant amount of particles in a fluidized bed under low temperature plasma conditions, using the PECVD (Plasma Enhanced Chemical Vapor Deposition) technique.