Production of syndiotactic polystyrene powder for part manufacturing through SLS

Selective laser sintering (SLS) is a well-established additive manufacturing (AM) process. While AM originally found its use as rapid prototyping technique, it is nowadays more and more considered for the production of actual end-use parts. A widely acknowledged hindrance in the evolution of this technology is the limited range of materials available for processing with SLS, making the application window rather small. Introducing new materials with the correct morphology and thermal requirements for SLS could broaden this window and give rise to new products. This research aims at identifying such promising materials, considering the relevant requirements for selecting and processing a new material. Considered foremost within this manuscript is the processability of syndiotactic polystyrene from pellet form into spherical particles of 50-90 μm without significantly changing their properties. Regarding processing methods, the focus of this work is on solution based techniques (single phase precipitation, emulsion precipitation) instead of more conventional mechanical processing methods (ball milling) as these are believed to be more accessible and more suitable as a precursor step for a wide range of processing technique

Review of catalytic systems and thermodynamics for the Guerbet condensation reaction and challenges for biomass valorization

The Guerbet condensation reaction is an alcohol coupling reaction that has been known for more than a century. Because of the increasing availability of bio-based alcohol feedstock, this reaction is of growing importance and interest in terms of value chains of renewable chemical and biofuel production. Due to the specific branching pattern of the alcohol products, the Guerbet reaction has many interesting applications. In comparison to their linear isomers, branched-chain Guerbet alcohols have extremely low melting points and excellent fluidity. This review provides thermodynamic insights and unravels the various mechanistic steps involved. A comprehensive overview of the homogeneous, heterogeneous and combined homogeneous and heterogeneous catalytic systems described in published reports and patents is also given. Technological considerations, challenges and perspectives for the Guerbet chemistry are discussed

Influence of spray drying suspension on the morphology of Fe-based oxygen carriers for chemical looping

Chemical looping reforming (CLR) and chemical looping combustion (CLC) are promising technologies with inherent CO2 capture for transforming fuels into syngas and energy respectively. Circulating oxygen carriers (OC) are used to transfer oxygen from mostly air to the fuel inside the process. Over the past years a variety of materials have been proposed for the role of oxygen carriers, ranging from bulk mineral powders to oxygen carrier particles engineered for shape, size and composition. Iron based materials are very promising and cost effective candidates with minor impact on the environment as compared to the toxic Ni-based OCs. Granulation by the industrial spray-drying technique is suitable for producing oxygen carrier particles with high sphericity and dimensions fit for the fluidized-bed reactors of the CL-process. The lifetime of the oxygen carriers in these reactors however strongly depends on their mechanical properties (as measured by the crushing strength and the attrition resistance) which is related with their morphology and porosity. As this morphology depends on the spray drying suspension, the relation between the additives used in the iron-based suspension and the morphology of the spray-dried particles is investigated in this work [1]. The influence of the concentration of the binder, dispersing agent and solids in the spray-drying suspensions and the intensity of the milling procedure on the morphology and microstructure of the resulting particles is studied by Hg-porosimetry, tapped density, optical microscopy and SEM. A controlled sintering treatment is used during post-processing of these spray-dried particles in order to further improve their mechanical properties before investigating their performance as oxygen carriers in the chemical looping process

Study of n-butanol conversion to butenes : effect of Si/Al ratio on activity, selectivity and kinetics

As bio-butanol is gaining more and more interest as a commercially available bioresource, the dehydration of this alcohol towards butenes and higher carbons gains more of interest. In general HZSM-5 has shown to be the most promising catalyst for this conversion. The role of the zeolite’s Si/Al ratio in the butanol dehydration reaction is still not fully understood. Experimental data obtained for a series of HZSM-5 with decreasing Si/Al ratio revealed an increase in activity of the catalyst per active site without affecting the selectivity profile. To understand the underlying effects, a microkinetic model was constructed for H-ZSM-5 with a Si/Al ratio of 25, based on literature DFT calculations, and the model was further modified by fitting the key parameters to the measured data at the four different temperatures studied in this work. This resulted in an adequate model for the dehydration of butanol across the evaluated temperature range of 503K to 533K. Investigation of the occurring mechanisms indicated a inhibiting effect due to the strong adsorption of di-n-butylether. This ‘poisoning’ of the catalyst surface resulted in a peculiar S-like curve for the conversion site time relation, which was also experimentally observed. This newly fitted base model was used to obtain more insight in the effect of the Si/Al ratio by implementing an additional H parameter, which is related to the adsorption strength of n-butanol in the base model. H varies between -4.8 to +11.3 kJ/mol and provides a good fit for Si/Al ratios ranging from 15 to 140. The higher dehydration rates observed with decreasing Si/Al can be traced back to an increase in adsorption strength resulting in an overall increase in surface coverage. The constant selectivity-conversion profile can be explained by a similar dependency of all elementary steps on the adsorption strength. The model developed in this study enables to simulate and understand the experimentally observed effects of temperature and Si/Al ratio on the n-butanol dehydration