Exploiting diluted bioethanol solutions for the production of ethylene: Preliminary process design and heat integration

Several activity tests on a zeolite-based catalyst for the ethanol to ethylene dehydration reaction are used to outline the stoichiometry of 4 reactions describing the observed outcome. The heat and mass balances of a reactor were calculated. The thermal input was mainly sustained with a standard product-to-feed heat exchange. Upstream, two possible strategies of ethanol-water beer concentration were compared, namely a single stage flash and a small column, yielding respectively a 3:1 water:ethanol mixture and a slightly diluted azeotrope. The external heat input needed for the separation unit, the feed heating up to the reaction temperature and the reaction upkeep are compared. A flow diagram for the hot utility is then designed, converting part of the water of the beer into superheated steam that gives also electric power. The conceptual design of an ethanol to ethylene plant is therefore available to exploit bioethanol solution with different water/ethanol ratios, with different ethanol purification routes with variable heat input and energy recovery

Process simulation for the design and scale up of heterogeneous catalytic process: Kinetic modelling issues

Process simulation represents an important tool for plant design and optimization, either applied to well established or to newly developed processes. Suitable thermodynamic packages should be selected in order to properly describe the behavior of reactors and unit operations and to precisely define phase equilibria. Moreover, a detailed and representative kinetic scheme should be available to predict correctly the dependence of the process on its main variables. This review points out some models and methods for kinetic analysis specifically applied to the simulation of catalytic processes, as a basis for process design and optimization. Attention is paid also to microkinetic modelling and to the methods based on first principles, to elucidate mechanisms and independently calculate thermodynamic and kinetic parameters. Different case studies support the discussion. At first, we have selected two basic examples from the industrial chemistry practice, e.g., ammonia and methanol synthesis, which may be described through a relatively simple reaction pathway and the relative available kinetic scheme. Then, a more complex reaction network is deeply discussed to define the conversion of bioethanol into syngas/hydrogen or into building blocks, such as ethylene. In this case, lumped kinetic schemes completely fail the description of process behavior. Thus, in this case, more detailed\ue2\u80\u94e.g., microkinetic\ue2\u80\u94schemes should be available to implement into the simulator. However, the correct definition of all the kinetic data when complex microkinetic mechanisms are used, often leads to unreliable, highly correlated parameters. In such cases, greater effort to independently estimate some relevant kinetic/thermodynamic data through Density Functional Theory (DFT)/ab initio methods may be helpful to improve process description

Photocatalytic Reduction of Nitrates and Combined Photodegradation with Ammonium

Bare titania and metal-promoted TiO2 catalysts were employed in the treatment of nitrates, which are ubiquitous pollutants of wastewater. The results show that the process can be carried out under visible light (from a white light LED lamp) and, in the best case, 23.5% conversion of nitrate was obtained over 4 h with full selectivity towards N2 by employing 0.1 mol% Ag/TiO2 prepared by flame spray pyrolysis. Moreover, the performance was worse when testing the same catalysts with tap water (11.3% conversion), due to the more complex composition of the matrix. Finally, it was found that photoreduction of nitrate can be effectively performed in combination with photo-oxidation of ammonium without loss in the activity, opening up the possibility of treating highly polluted wastewater with a single process. The latter treatment employs the two contaminants simultaneously as electron and holes scavengers, with very good selectivity, in a completely new process that we may call Photo-Selective Catalytic Reduction (Photo-SCR)

Pure and Fe-doped mesoporous titania catalyse the oxidation of acid orange 7 by H2O2 under different illumination conditions: Fe doping improves photocatalytic activity under simulated solar light

A sample of mesoporous TiO2 (MT, specific surface area = 150 m2\uc2\ub7g\ue2\u88\u921) and two samples of MT containing 2.5 wt.% Fe were prepared by either direct synthesis doping (Fe2.5-MTd) or impregnation (Fe2.5-MTi). Commercial TiO2 (Degussa P25, specific surface area = 56 m2\uc2\ub7g\ue2\u88\u921) was used both as a benchmark and as a support for impregnation with either 0.8 or 2.5 wt.% Fe (Fe0.80-IT and Fe2.5-IT). The powders were characterized by X-ray diffraction, N2 isotherms at \ue2\u88\u92196\ue2\u97\ua6C, Energy Dispersive X-ray (EDX) Spectroscopy, X-ray Photoelectron Spectroscopy (XPS), Diffuse Reflectance (DR) ultra-violet (UV)-Vis and M\uc3\ub6ssbauer spectroscopies. Degradation of Acid Orange 7 (AO7) by H2O2 was the test reaction: effects of dark-conditions versus both UV and simulated solar light irradiation were considered. In dark conditions, AO7 conversion was higher with MT than with Degussa P25, whereas Fe-containing samples were active in a (slow) Fenton-like reaction. Under UV light, MT was as active as Degussa P25, and Fe doping enhanced the photocatalytic activity of Fe2.5-MTd; Fe-impregnated samples were also active, likely due to the occurrence of a photo-Fenton process. Interestingly, the Fe2.5-MTd sample showed the best performance under solar light, confirming the positive effect of Fe doping by direct synthesis with respect to impregnation

Photoreforming of Glucose over CuO/TiO2

Hydrogen production has been investigated through the photoreforming of glucose, as model molecule representative for biomass hydrolysis. Different copper-or nickel-loaded titania photocatalysts have been compared. The samples were prepared starting from three titania samples, prepared by precipitation and characterized by pure Anatase with high surface area, or prepared through flame synthesis, i.e., flame pyrolysis and the commercial P25, leading to mixed Rutile and Anatase phases with lower surface area. The metal was added in different loading up to 1 wt % following three procedures that induced different dispersion and reducibility to the catalyst. The highest activity among the bare semiconductors was exhibited by the commercial P25 titania, while the addition of 1 wt % CuO through precipitation with complexes led to the best hydrogen productivity, i.e., 9.7 mol H2/h kgcat. Finally, a basic economic analysis considering only the costs of the catalyst and testing was performed, suggesting CuO promoted samples as promising and almost feasible for this application

Surface probing by spectroscopy on titania-supported gold nanoparticles for a photoreductive application

The continuous increase in scientific reports concerning photocatalysis and in particular CO2 photoreduction in recent years reveals the high degree of interest around the topic. However, the adsorption and activation mechanisms of CO2 on TiO2, the most used photocatalyst, are poorly understood and investigated. Gold nanoparticles were prepared by a modified deposition-precipitation method using urea and a chemical reductant. Bare P25 was used as reference. Combined spectroscopic investigations of fresh and spent samples with photoactivity studies reported in this article provide new insights to the role of CO2 adsorption and carbonate formation on Au/TiO2 during CO2 photocatalytic reduction. The key intermediates’ and products’ adsorption (CO, methanol, ethanol) was studied, coupled with X-ray photoelectron microscopy (XPS) and UV-Visible spectroscopy. The adsorption of CO2 on fresh and spent catalysts changes radically considering the carbonate formation and the gold surface presence. Methanol and ethanol revealed new adsorbed species on Au with respect to bare titania. The characterisation of the spent catalysts revealed the good stability of these sample

Quantification of \u201cdelivered\u201d H2 by a volumetric method to test H2 storage materials

We set up and validated a volumetric method to quantify the amount of hydrogen \u201cdelivered\u201d after saturation of a solid material as adsorber at different pressures (up to 100 kgf/cm 2) and temperatures (down to 77 K). This is the practically most relevant datum to quantify the effectiveness of an adsorbent for the present application. A complementary dynamic method has been also developed to take into account the reversibility of adsorption and to assess in at least a semi-quantitative way the strength of interaction between H2and the adsorbent. The method has been applied to compare the hydrogen storage capacity of some significant different carbon-based materials (two active carbons and one graphite), as supplied or after thermal treatments under oxidising or reducing conditions. The best results,ca.7 wt% H2 \u201cdelivered\u201d, were achieved after saturation at 77 K, 20 kgf/cm2 with an active carbon withca.3000 m2/g of apparent specific surface area. The thermal treatments, almost always inducing a drop in surface area, showed effective only for saturation at 273 K, in particular the oxidising procedure. This was correlated to the formation of surface oxidised species, likely carboxylic groups, which improved the interaction strength between H2and the adsorbent

Catalytic, Photocatalytic and Electrocatalytic Processes for the Valorisation of CO2

Increasing attention is being paid to the development of effective technologies for the sequestration of CO2 and its storage. Hopefully, this will result in processes that can lead to its valorisation as a chemical, e.g., for the regeneration of fuels, but also for the production of intermediates. These are usually energy demands and rather slow processes, requiring energy input and catalysts. Some examples are the innovative strategies for the hydrogenation, photoconversion, or electroreduction of carbon dioxide. This book collects original research papers, reviews, and commentaries focused on the challenges related to the valorisation and conversion of CO2

Carbon Nitride-Based Catalysts for High Pressure CO2 Photoreduction

In this work we focus on carbon nitride materials to improve the conversion and productivity of the photoreduction of CO2, developing a coupled strategy to optimize materials and operating conditions. The metal-free polymeric catalyst, graphitic carbon nitride (g-C3N4), is a relatively novel material, characterized by a wide absorbance in the visible region and demonstrating a superior performance compared to the commercial titania P25 benchmark, the most used photocatalyst for this application. We used an innovative photoreactor operating at high pressures of up to 20 bar, which is unprecedented in photocatalytic applications where transparent windows are needed. This enabled a boost in the solubility of CO2 in water when operating the reactor as a tri-phase liquid/gas/solid device and improved the surface adsorption over the catalyst. The best productivity for HCOOH so far achieved with these catalysts at 8 bar, pH = 14 and by using Na2SO3 as a hole scavenger was ca. 370 g/h kgcat. Such productivity is several orders of magnitude higher than the literature values