Mesoporous silica core shell particles are materials of high interest especially due to pharmaceutical and catalytic applications. In the current work we presented the synthesis of uniformly porous and solid core porous particles by aerosol spray pyrolysis route according to the principles of EISA, by a one step process. The particles are evaluated morphologically by TEM and by nitrogen adsorption and desorption isotherms for pore size distribution and pore connectivity, validating the effect of synthesis parameters on the core size, surface area and porosity of the uniformly porous and core-shell structures. Three different surfactants Brij-58, CTAB, P123 at various concentrations and combinations as well as three different core type compositions of NaCl, CeO2 and, Ce0.8Zr0.2O2 have been evaluated for the controlled synthesis of silica core-shell particles by a scalable synthesis method.

Hydrothermal liquefaction (HTL) technology could potentially be utilized for the conversion of non-recyclable plastics emanating from process streams into added value products, exploiting the feedstock moisture. Although solar heat and HTL coupling is a promising prospect for reducing the high energy requirements of the process, it is not sufficiently developed. The present study aims to investigate the product properties and biocrude yield resulting from HTL of plastic waste mix and polypropylene at the lab scale by conventional heating and solar energy-aided. Two different units were used and heating was provided by an electric heater and an in-house solar simulator respectively. Temperatures tested ranged from 350 to 450 °C with an initial pressure of 1 and 20 bar for a retention time of 30 min. A solar setup was designed and constructed including ceramic insulation and a stainless steel support shell for testing in a solar simulator. The arrangement has an 80 mm front aperture from which light rays from 4 Xenon arc lamps reached the reactor and contributed to its heating. The lamps intensity was adjusted based on the process needs through a computer interface, temperature and pressure were monitored via 4 thermocouples and a pressure transducer respectively and the whole system was monitored remotely. Biocrude yield achieved exceeded 50% in the case of polypropylene and it was increased by 5–10% when treated under the solar simulator. Higher heating values of products were increased by 30–45% compared to the feedstock for the plastic waste mix, while for the resulting PP biocrude further treatment would be needed to reach a similar increase.

In this study a historical perspective of the mass continuity equation for fully developed laminar flow in the lumen side of a hollow-fiber membrane contactor is presented with respect to the lumen-wall boundary condition (BC). It is shown that the constant wall concentration case (Dirichlet boundary condition) imposed by the Graetz-Lévêque postulations is a sub-case of the mixed Neumann-Dirichlet linear BC largely overestimating the performance of such contactors. For the linear BC the analytical solution derived by the separation of variables method is revisited proving that it is very accurate and practical even in the region very close to the entrance of the computational domain. The analysis is extended by incorporating and solving nonlinear lumen-wall BCs with the method-of-lines approach by discretizing the radial domain using the Gauss-Jacobi orthogonal collocation and integrating the resulting initial-value differential-algebraic system. The analytical solution, the derivation of the collocation matrices and the numerical solution are presented with the aid of the open-source SageMath and the commercial package Maple.

Cement production is one of the most energy intensive industrial processes, accounting for approximately 5% of the total CO2 emissions worldwide; about 2/3 of such emissions are due to limestone calcination. The SOLCEMENT process pertains to the use of concentrated solar radiation for limestone calcination in cement plants. The process employs also a thennochemical storage reactor (TSR) integrated into the conventional solids preheating system, to partially compensate for the intermittent nature of sunlight, by enabling the transfer of stored solar energy to night operation thereby reducing the use of fossil fuels. In addition to fossil fuels replacement during daytime, the partial solarization of limestone calcination has the potential of CO2 recovery produced by the chemical reaction in pure form. A first detailed Ilowsheet of the integrated process is presented and reveals the possibility to transfer daily 28-52 MWh of solar energy between day and night operations for a 2.4 kt/day limestone calcination capacity cement plant. The study adopts a Process Systems Engineering approach which involves process modeling and optimization of design and operating parameters, towards maximization of solids' temperature (up to 850 degrees C) after preheating, as well as optimal loading and use of the TSR (up to 6 MW). Four operating scenarios were considered, and show that the process perfonnance scales with the temperature of the calciner flue gases, saving 52 IVIA,Vh for 1000 degrees C, which accounts for 6% of the total required energy during non-solar operation (-856 MWh).

Stringent regulation is endorsed to restrict global gaseous and particulate vehicle emissions by adapting advanced catalytic systems on the exhaust, incorporating costly platinum group metals (PGM) for oxidation catalysis. Porous silica and alumina particles are synthesized in the present work via a one-step aerosol spray route. The particles are doped with Pt, Ce and Na and are evaluated with respect to their pore size distribution, exhibiting surface areas between 6-269 m2/gr. The particles have been evaluated in a packed bed reactor with respect to NO oxidation in presence or absence of hydrocarbons (C2H4) in order to study the hydrocarbon inhibition effect on oxidation kinetics, showing higher conversion curves for higher surface area samples. The current work studies also the correlation between reactant accessibility to the in-pore Pt nanoparticles and catalytic activity by reaction kinetic model. (c) 2021 Published by Elsevier Ltd.

It is well-known that the structural properties of soot aggregates determine their behavior in the atmosphere and depend on their morphology. Previous work on the field has been focused on examining the impact of the critical features such as size, polydispersity, or overlap between primary particles separately. However, aggregates formed in real processes have complex, irregular shapes and they usually consist of monomers of variable size and overlap. In this study, fractal aggregates of different sizes and/or overlap extent are computationally generated using fractal properties relevant to soot and the proposed expressions include the effect of both phenomena. It is shown that both the mobility diameter and the effective density are increasing proportionally with the level of polydispersity, while the mobility diameter is reduced as overlap coefficient augments, leading to higher effective densities. The mobility diameter is taken as the projected area-equivalent diameter for the free molecular regime and an expression is suggested for its dependence from the aggregate’s structural properties. Furthermore, a universal effective density equation as proposed taking into account the effect of variable primary particle sizes and the existence of penetration between adjacent monomers.

To prove the usefulness and achieve penetration of microporous ceramic membranes in gas separation applications of industrial interest, their behavior needs to be validated and predicted at relatively realistic conditions. In this respect, the present study employed hybrid silica (HybSi) membranes, modified by chemical vapor infiltration (CVI) in order to render them more selective to hydrogen in hydrogen/carbon dioxide binary mixtures, which are representative to effluent streams of methane or biogas steam reforming/water gas shift processes. Experimental studies with a single modified membrane exhibited high hydrogen permeance (1.5.10-7 mol.m(-2).s(-1).Pa-1, at 250 degrees C) and H-2/CO2 permselectivity (H-2/CO2 = 61.3, at 250 degrees C). Gas separation tests with binary gas mixtures revealed that high hydrogen purity values (>99%) can be reached at different process conditions. The mathematical model, also developed in this study in order to interpret the experimental results, can reliably predict hydrogen separation process performance over a wide range of operating conditions and also serve as a tool for subsequent optimum process engineering purposes.

Solar Hydrothermal Liquefaction technology is a relatively novel and less developed area of solar fuels category. It enhances the circular economy by promoting both the environmental sustainability and the production of added value products, since its feedstock is comprised of organic waste and their water content that takes over the double role as reactant and catalyst. The present study focuses on the lab-scale screening of different organic waste in terms of their bio-oil production yield, with an immediate next step being the HTL system coupling with Concentrating Solar Technologies (CST). The relative lab-scale solar experiments will be carried out in APTL/CERTH's high flux solar simulator and solar furnace with the use of a dedicated batch reactor, while pilot-scale experiments will be performed in using a reactor coupled with a parabolic trough system. The feedstocks examined in the current work were peach stones, food waste and dairy waste processed in two different temperatures (300 and 350 degrees C) and two initial pressures (1 and 20 bar) for a retention time of 30 minutes. Based on the findings, GC/MS analysis has shown that the main compounds of the bio-oil consisted of fatty acids, phenols and long-chain alkanes, whereas the primary gas-phase products (GC analysis) were CO2, CO, CH4, C2H4, C2H6, C3H8 and C3H6. Dairy waste had the highest bio-oil yield efficiency (up to 22 wt%), by employing dichloromethane as a solvent at a reaction temperature of 300 degrees C and 1 bar initial N-2 pressure. An increase of water/feedstock ratio by adding surplus water had a significantly positive effect on the bio-oil yield with an up to 98% increase.

Solid particle number vehicle exhaust measurements necessitate an aerosol conditioning system that removes efficiently volatile particles, does not create artifacts, and minimizes solid nucleation particle losses. Here, we present the development and evaluation of a catalytic stripper (CS) based on a unique dual-function monolithic reactor that oxidizes hydrocarbons and stores sulfur material. The CS was tested for its tetracontane particle removal efficiency, sulfur adsorption capacity with sulfur dioxide, and particle penetration with solid CAST-generated particles. The optimal operation conditions were examined including different aerosol flows and configurations, i.e., as a stand-alone device and as part of a volatile removal system with a hot and a cold dilution stage upstream and downstream of the CS, respectively. The CS managed to comply with current legislation requirements for solid particle number measurements down to 23 nm as a stand-alone device and showed great potential as part of a volatile particle removal (VPR) system for measurements at least down to 10 nm. Finally, we compared the performance of two VPR systems that use the developed CS (VPR-CS) and an evaporation tube (VPR-ET), respectively. Our results suggest that the VPR-CS exhibits higher volatile removal efficiency without creating artifacts while the particle losses are lower with the VPR-ET. Nevertheless, when measuring solid nucleation particles generated by a diesel engine with the VPR-CS, the measurement uncertainty was very low due to its high particle penetration fractions. Copyright (c) 2020 American Association for Aerosol Research

Improved understanding and compact descriptions of the pressure drop evolution of Particulate Filters (both for diesel and gasoline powered vehicles) are always in demand for intelligent implementations of exhaust emission system monitoring and control. In the present paper we revisit the loading process of a particulate filter focusing on a parametric description of the deep bed-to-cake transition in the light of recent progress in the understanding of soot deposit structure, growth dynamics and evolution. Combining experimental data, simulation models and information theoretic concepts we provide a closed-form representation of the entire evolution of pressure drop (from the initial clean state up to the evolving linear cake growth regime) parameterized in terms of the physical parameters of the system (filter and particle structure/geometry and flow properties). The representation is shown to be in excellent agreement with the available experimental data and it opens the door for improved on-board monitoring/control of particulate filter systems.

This work focuses on the investigation of the relationship between structure and oxidation behavior of particulate matter (PM) emitted from different diesel combustion systems. Commercially available graphite and carbon black materials were also studied as representing the soot with the lowest reactivity. An interpretation of the differences of soot oxidation between these materials is attempted based on the carbon morphology and microstructure; thus, various structural parameters, such as the average particle size, specific surface area, degree of nanostructural organization, average crystallite stacking height, fringe length, fringe tortuosity, and surface functional groups, have been opposed to the reactivity of the carbonaceous materials. Small structural differences were observed in between the carbonaceous samples which seem to directly affect the soot reactivity in terms of oxidation. Particulate matter composition (hydrogen-to-carbon ratio, ash content, and volatile matter) appears to have an impact on the soot reactivity.

The measurement of vehicle particle number emissions and, therefore, regulation, necessitates a rigorous sampling and conditioning technology able to deliver solid emitted particles with minimum particle losses. European legislation follows a solid particle number measurement method with cutoff size at 23 nm proposed by the Particle Measurement Programme (PMP). Accordingly, the raw exhaust is sampled with constant volume, subsequently passes through a volatile particle remover (VPR), and finally is measured with a particle counter. Lowering the 23 nm cutoff size with current VPR technologies introduces measurement uncertainties mainly due to the high particle losses and possible creation of artefacts. This study describes the development and evaluation of a sampling and conditioning particle system, the SCPS, specially designed for sub-23 nm solid particles measurement. The dilution process is achieved in two stages; the primary dilution is done with a porous tube while the secondary with an ejector diluter that also acts as a pump for the sampling flow. The SCPS offers flexibility in terms of dilution ratio (DR) which is real-time calculated with an algorithm based on a differential pressure measurement across an orifice. Between the two dilution stages, a catalytic stripper removes volatile material with high efficiency. The SCPS evaluation includes the DR calculation algorithm testing, the stability of DR during transient engine conditions, the volatile particle removal efficiency with tetracontane particles, the solid particle penetration efficiency with polydisperse CAST-generated soot particles, and the measurement of sub-23 nm particles emitted by a diesel engine. The high stability of the DR in combination with >99% volatile particle removal and a cutoff size (d50) at 7.5 nm suggest that the SCPS may deliver solid emitted particles for robust particle number measurements down to at least 10 nm.

Being a relatively new but quite promising field in CSP, thermochemical energy storage could be the next generation solution towards the implementation of baseload cost-effective solar thermal plants. The present work, taking place within the framework of EU-funded project PEGASUS, aims at synthesizing, shaping and experimentally evaluating the catalytic activity and main physicochemical attributes of Fe2O3-based particles. These particles can be exploited as both heat transfer fluid of the CSP plant and highly active catalysts for the key step of the SO3 dissociation reaction to produce SO2 and O-2 in the framework of a solid sulfur thermochemical energy storage cycle. The experimental campaign takes place in a purpose-built setup used to evaluate the materials in a fixed bed reactor formulation at a temperature of 850 degrees C and ambient pressure while concentrated liquid sulfuric acid (H2SO4) was used as feedstock. Based on the findings, pure Fe2O3 particles sintered at 950 degrees C offered the most promising compromise between high SO3 conversion on the one hand and crushing strength value (i.e. a preliminary measure of thermomechanical stability) and particles' color before and after exposure at reaction conditions on the other hand.

The present study provides a viable route to solar syngas production and conversion to fine chemicals using renewable energy sources and rendering CO2 a valuable reactant instead of a waste. It uses existing facilities and on-going breakthrough technological advancements from CO2 transportation to H2O/CO2 solar co-splitting for syngas formation to further conversion to either methanol or Fischer-Tropsch (FT) products. A full scale simulation of the overall chemical process is established, considering its subsections with respect to all relevant cost elements and operating expenses using appropriate cost correlations. Eight spanning routes of the CO2 superstructure are assessed for a real case of transporting compressed pure or mixtures of CO2 with a 130 kg/s capacity over a distance of 120 km from a power plant in Ptolemaida, Greece, operating with either natural gas or coal, and combining with water from an existing wastewater treatment facility in Thessaloniki, Greece. It is estimated that the choice of producing methanol requires an investment of (sic)7B and (sic)430 M/y to operate, while for FT-related plants it would cost >(sic)3B to build and (sic)190 M/y to operate. Applying a standard feed-in tariff (FIT) value in terms of subsidization of the energy consumed by renewable sources boosts the expenditure resulting for the best case to a yearly net profit of (sic)500M or (sic)100 M, for methanol or FT products, respectively. Other scenarios are also considered, including the best spanning route for the minimum FIT revenues by the break-even method, or the required carbon price without any subsidization of the proposed schemes.

Diesel and gasoline direct injection engines emit nucleation mode particles either under special conditions or as part of their normally emitted size distribution, respectively. Currently, European legislation excludes nucleation mode particles as particle number vehicle emission measurements are limited down to 23 nm. The rationale behind such a cut-off size is based on the avoidance of significant uncertainties inherent in the sampling and measuring of sub-23 nm solid particles. However, the sub-23 nm particles have drawn increased attention since a large fraction of particles emitted by modern vehicles lies in this size range. In this study we investigate the possibility of accurate nucleation mode particles detection by using the Advanced Half Mini Differential Mobility Analyzer (HM-DMA). The Advanced HM-DMA system is able to classify aerosol particles in the mobility size range 5 - 30 nm with high resolution and fast spectrum acquisition that can accommodate a sample flow maintained at up to 200°C. The unique ability to classify particles at high temperatures permits engine exhaust measurements without the need for aerosol conditioning. Initially, the Advanced HM-DMA hot operation mode accuracy is tested with reference aerosols against State-of-the-Art instruments. Thereafter, the Advanced HM-DMA is employed for measuring nucleation mode particles generated by a diesel engine using a single hot dilution step. Advanced HM-DMA measurements are compared to measurements performed with PMP protocol-compliant volatile particle removal system. The excellent agreement between the two measurements confirms the reliability of the Advanced HM-DMA hot operation mode and indicates the possibility of using a simplified conditioning setup for solid nucleation-mode particles measurement.

Car brakes appear to be a significant atmospheric pollutant source, with a contribution to total non-exhaust traffic-related PM 10 emissions being estimated at approximately 55% in big cities and urban environments (Bukowiecki et al., 2009 ). Brake wear particle emissions of a minivan running on a chassis dynamometer were measured using a custom sampling system, positioned close to the braking system, under different initial speeds (30 km/h and 50 km/h), deceleration rates (0.5 m/s 2 , 1.5 m/s 2 , 2.5 m/s 2 ), and ambient temperatures (0 °C, 15 °C and 25 °C). Braking from 50 km/h to full stop, results in 40–100% more particles compared to 30 km/h, depending on the deceleration rate. It was also found that only 9–50% of the total particles emitted, are released during the braking phase and therefore the most significant amount is released on the following acceleration phase. High brake pad temperature results in a bimodal distribution with the first peak being at 1 μm and the second falling at the nanometer scale at 200 nm. The ambient temperature appears to have a negligible effect on the particle generation.