CFD simulation of a mixing-sensitive reaction in unbaffled vessels

Stirred tanks are widely used in the process industry, often to carry out complex chemical reactions. In many of such cases the perfect mixing hypothesis is not applicable for modelling purposes, and more detailed modelling approaches are required in order to accurately describe the reactor behaviour. In this work a fully predictive modelling approach, based on Computational Fluid Dynamics, is developed. Model predictions are compared with original experimental data obtained in un unbaffled stirred vessel with a parallel-competitive, mixing sensitive reaction scheme. Notably, satisfactory results are obtained at all injection rates with no recourse to micro-mixing model, thus confirming the major role played by macro-mixing in the investigated system

Supercritical water gasification of waste oils as a source of syngas

A huge amount of waste oil is produced worldwide. Also substantial amount of virgin oils is available that are interesting candidates for upgrading into syngas. Supercritical water gasification (SCWG) can be considered as an aqueous phase reforming process to produce syngas from oils. In this work, a variety of waste and virgin oils were gasified in a continuous down-flow autoclave reactor at supercritical conditions. Experiments were carried out at 430 °C and 660 °C, 25 MPa, with a residence time in the range 103-170 s, in order to investigate gasification and carbon efficiency, hydrogen yield and composition of the produced gas. All the analysed feedstocks were suspended in water at various concentrations before gasification. Pyrolysis bio-oil showed a gasification efficiency of 74 % and 86 % for mixtures with 3 and 10 oil/water wt ratio, respectively. Waste motor oil, suspended in water at a concentration of 1 % wt thanks to the use of surfactants, was successfully gasified with a gasification efficiency of 73 %. Virgin motor oil gasification efficiency higher than 60% had been obtained for both analysed concentrations (5 % wt and 10 % wt of oil). Gasification of rapeseed oil at 5 % wt showed a gasification efficiency close to 88 %. On the contrary, the gasification of sunflower oil at 430 °C showed that this temperature is not high enough to obtain acceptable gasification efficiencies that varied from 20 % to 15 % for concentrations of oil from 2 % wt to 8 % wt, respectively. The analysis of the gas composition, in all the studied cases, showed that the obtained gas stream was rich in H2, CH4 and CO2, with variable quantities of light hydrocarbons (C2H4, C2H6 and C3H8)

Pollutants removal from municipal sewage by means of microalgae

Microalgae are microorganisms able to photosynthesize, namely transforming inorganic substrates and sun light into organic compounds and chemical energy. The industry of microalgae has expanded in the last decades and several applications are now developed, making their biomass interesting under an economic perspective. Nannochlopsis gaditana is one of the most interesting species already employed in industry because of its high content in lipids that could be employed as source for biodiesel synthesis but also in other fields such as cosmetic and pharmaceutic. One of the most promising application is the exploitation of microalgal grow for bioremediating wastewaters polluted with inorganic nutrients such as nitrates and phosphates that microalgae are able to employ as nutrients. Bio-treatment of wastewaters by using microalgae has the advantage to reclassify the water and preserve it from wasting while producing a valuable biomass. In this work, a microalgal strain, Nannochloropsis gaditana, was employed for testing its performance in the bioremediation of municipal sewages. The wastewater was taken from a municipal plant, after the primary treatment, and the algae processing was aimed at replacing the secondary treatment. Algal growth in its growth medium and in the sewage was compared and algal biomass was characterized. Biochemical Oxygen Demand (BOD), Chemical Oxygen Demand (COD), total nitrogen and total phosphorous levels of the sewage before and after algae treatment were also determined in order to evaluate the efficiency of this microalgal strain on wastewater bioremediation. Our results showed that N. gaditana grows better in wastewater than in the control growth medium and it is able to efficiently remove nutrients from the sewage. However, COD and BOD values did not decrease after algal treatment. These results suggest that the use of selected bacteria and/or yeast strains (together with microalgae) could improve the efficiency of wastewater treatments decreasing BOD and COD values

Comparison of Agitators Performance for Particle Suspension in Top-Covered Unbaffled Vessels

Power savings is a problem of crucial importance nowadays. In process industry, suspension of solid particles into liquids is usually obtained by employing stirred tanks, which often are very power demanding. Notwithstanding tanks provided with baffles are traditionally adopted for this task, recent studies have shown that power reductions can be obtained in top-covered unbaffled vessels. In the present work experiments were carried out in a top-covered unbaffled vessel with a diameter T=0.19m and filled with distilled water and silica particles. Two different turbines were tested: a standard six-bladed Rushton Turbine (RT) and a 45\ub0 four bladed Pitched Blade Turbine (PBT). For the case of the PBT both the up-pumping (PBT-Up) and the downpumping (PBT-Down) operation mode were tested. Two different impeller sizes D (T/3 and T/2) and clearances C (T/3 and T/10) were investigated. The effects of particle size and concentration were also assessed. Investigations concern the assessment of the minimum impeller speed for complete suspension (Njs) along with the measurement of the relevant power consumption (Pjs) aiming at identifying the most efficient tank-turbine configuration among those investigated here. Results were also compared with corresponding ones pertaining to baffled tanks (obtained via correlations available in the literature). Results have shown that the RT with D=T/3 and C=T/3 and the PBT-Up with D=T/2 and C=T/10 appear to be the most convenient (least power demanding) options. Finally, a significant power saving with respect to the most efficient baffled configurations was observed thus confirming the convenience of operating solid-liquid suspensions in an unbaffled system for all those processes where the mixing time is not a limiting factor

Antisense Transcription Controls Cell Fate in Saccharomyces cerevisiae

SummaryEntry into meiosis is a key developmental decision. We show here that meiotic entry in Saccharomyces cerevisiae is controlled by antisense-mediated regulation of IME4, a gene required for initiating meiosis. In MAT a/α diploids the antisense IME4 transcript is repressed by binding of the a1/α2 heterodimer at a conserved site located downstream of the IME4 coding sequence. MAT a/α diploids that produce IME4 antisense transcript have diminished sense transcription and fail to initiate meiosis. Haploids that produce the sense transcript have diminished antisense transcription and manifest several diploid phenotypes. Our data are consistent with transcription interference as a regulatory mechanism at the IME4 locus that determines cell fate

Apparatus for synthesizing and separating synthesis products e.g. gaseous and liquid phases on bed, maintains heavier liquid phase at lower portion of first meatus due to gravity and lighter liquid phase at upper portion of meatus

NOVELTY - The apparatus has header that is set to make the heavier and lighter liquid phases flow along outer side surface of a third tube (8) as far as first closure element (13). The third tube is provided with second side openings for directly connecting the first and second meatus. The heavier liquid phase is maintained at lower portion of the first meatus due to gravity and lighter liquid phase is maintained at upper portion of the first meatus until the liquid phases fall into a fourth tube (9). The heavier liquid phase is collectible through a collection hole (12). USE - Apparatus e.g. reactor/separator for synthesizing and separating synthesis products e.g. gaseous phase and heavier and lighter liquid phases on catalytic bed, used in production of biodiesel. ADVANTAGE - Since heavier liquid phase is maintained at lower portion of the first meatus due to gravity and lighter liquid phase is maintained at upper portion of the first meatus, sedimentation separation of the liquid phases is improved. The structure of the apparatus is simplified and the apparatus is constructed easily. The efficacy and use of catalyst are maximized. DETAILED DESCRIPTION - The apparatus has synthesis module (M1) that is set with a first tube (1) which is provided with an opening at one end and closed at second end by a mesh (7). The first tube is adapted to contain a catalytic bed (6). A separation module (M2) is set to separate heavier and lighter liquid phases and gaseous phase originating from the synthesis module. A second tube (1') is arranged adjacent to second end of the first tube. A first closure element is provided with a through hole for sole passage of the second liquid and of the gaseous phase. A third tube is affixed to first end of second tube. A first meatus is set between second tube and the third tube. The fourth tube is set inside the third tube so as to define a second meatus between the third tube and the fourth tube. A separation zone is set between the heavier and lighter liquid phases. A collection hole is set in the second tube to collect the heavier liquid phase. The third tube is set with first side openings at first end, and is set with a header for collecting the liquid phases originating from the synthesis module. The first meatus is directly inserted into the third tube and subsequently into the fourth tube. A control system is set between the liquid phases, to check and maintain interface level below the upper end of the first side openings. The control system has interface level indicator that is connected to the second tube by second side holes envisaged in side surface of the second tube. One of the second side holes is arranged in proximity of the first closure element and other is positioned above the upper end of the first side openings. The protrusions are arranged along cylindrical side surface of the third tube, and are separated by spaces for passage of the liquid phases from the header to the first meatus. A redistribution module (M3) is set to redistribute the lighter liquid phase and gaseous phase originating from the fourth tube. A fifth tube (1") is arranged adjacent to second end of the second tube. The closure element is set with a central perforated area. A sixth tube (14) is set to descent and release of the gaseous phase. The central perforated area is provided with several holes for homogeneous distribution of lighter liquid phase downstream of the redistribution module. The sixth tube is affixed to a second closure element (15). The mesh is provided with a passage area. The synthesis module, separation module and redistribution module are vertically-stacked. An INDEPENDENT CLAIM is included for a method for synthesizing and separating synthesis products e.g. gaseous phase and heavier and lighter liquid phases on catalytic bed, involves synthesizing on a catalytic bed and producing the synthesis products. The liquid phases and gaseous phase are separated in the separation module

Hydrogel scaffolds based on k-Carrageenan/xyloglucan blends to host spheroids from human adipose stem cells

Hydrogels are water-swollen networks of hydrophilic polymer. They can be fabricated in various shapes and swell in water or aqueous solutions maintaining their original shape or undergo progressive erosion; can exibit large volume phase transitions with the change of one environmental parameter (stimuli-responsivness), shock absorption and low sliding friction properties (1). The morphology and mechanical properties of hydrogels are strongly affected by the network composition, the nature and degree of crosslinking and the degree of swelling. Indeed, when hydrogels are designed as scaffolds for human tissues remodeling, they must have sufficient mechanical integrity to provide support to the cells from the time of implantation to the completion of the process. The large amount of water present in the hydrogels and its microscopic pores interconnectivity allows transportation of nutrients, oxygen and metabolites, that ensures cells viability, and permits cells migration and scaffold colonization. The polymeric network can immobilize biomolecules that may affect cells growth or differentiation, control drug release profiles and enzymatic degradation (2,3). The combination of two hydrogelforming polymers with different chemistries and crosslinking densities can be used to tailor the morphology, mechanical strength and toughness of the scaffold to meet specific requirements (1). This work investigates the physico-chemical, morphological and mechanical properties of hydrogels formed by the blend of two polysaccharides, k-Carrageenan (k-C) and Degalactosylated Xyloglucan (Deg-XG) undergoing salt-induced and temperature-induced solgel transition, respectively. It also studies the compatibility of the two biopolymers with spheroids from adipose-derived stem cells (S-ASCs) in the prospect of developing instructive scaffolds for use in regenerative medicine

Atomic-scale representation and statistical learning of tensorial properties

This chapter discusses the importance of incorporating three-dimensional symmetries in the context of statistical learning models geared towards the interpolation of the tensorial properties of atomic-scale structures. We focus on Gaussian process regression, and in particular on the construction of structural representations, and the associated kernel functions, that are endowed with the geometric covariance properties compatible with those of the learning targets. We summarize the general formulation of such a symmetry-adapted Gaussian process regression model, and how it can be implemented based on a scheme that generalizes the popular smooth overlap of atomic positions representation. We give examples of the performance of this framework when learning the polarizability and the ground-state electron density of a molecule

Hydrogel scaffolds blends to host Spheroids from human adipose stem cells

INTRODUCTION Adipose stem cells represent a reliable source of stem cells for their widely demonstrated potential in regenerative medicine and tissue engineering applications. New recent insights show that 3D models may properly mimic the native tissue properties; in fact Spheroids from Adipose derived Stem Cells (S-ASCs) displayed enhanced regenerative abilities if compared to 2D models. Stem cell therapy success is determined by "cell-quality" thus the involvement of stress signals and cellular aging need to be deeply investigated. The development of 3D cell-laden hydrogels has enabled to mimic the peculiar scenario of a native tissue. We studied SASCs-cell quality and tested their viability and differentiation abilities in new hydrogels. METHODS S-ASCs were obtained from liposuction of healthy patients. Analysis of aging, telomeric length and stress-oxidative genes was performed through Real-Time PCR. Physico-chemical, morphological and mechanical properties of k-Carrageenan (k-C, 2%w) and degalactosylated xyloglucan (Deg-XG, 2%w) hydrogels were defined. S-ASCs compatibility with hydrogels was evaluated by viability test and mesenchymal differentiation abilities. RESULTS Gene expression of genes linked with stemness, senescence and stress-oxidative was evaluated and correlated with SASCs-cell quality. Indeed, aging-related p16INK4a mRNA is downregulated while anti-aging Sirtuin1 is upregulated in 3D-SASCs. Furthermore, vegetal-origin hydrogels have guaranteed an optimal environment for S-ASCs in stemness and mesenchymal differentiation conditions. CONCLUSION Bio-instructive scaffolds are critical for exploiting stem cells therapeutic potential in tissue engineering. This study provides a versatile approach to investigate the interactions between cells in controlled settings, opening up novel 3D in vitro approaches to mimic the tissues complexity

Predictors of Mortality and Cardiovascular Outcome at 6 Months after Hospitalization for COVID-19

Clinical outcome data of patients discharged after Coronavirus disease 2019 (COVID-19) are limited and no study has evaluated predictors of cardiovascular prognosis in this setting. Our aim was to assess short-term mortality and cardiovascular outcome after hospitalization for COVID-19. A prospective cohort of 296 consecutive patients discharged after COVID-19 from two Italian institutions during the first wave of the pandemic and followed up to 6 months was included. The primary endpoint was all-cause mortality. The co-primary endpoint was the incidence of the composite outcome of major adverse cardiac and cerebrovascular events (MACCE: cardiovascular death, myocardial infarction, stroke, pulmonary embolism, acute heart failure, or hospitalization for cardiovascular causes). The mean follow-up duration was 6 ± 2 months. The incidence of all-cause death was 4.7%. At multivariate analysis, age was the only independent predictor of mortality (aHR 1.08, 95% CI 1.01–1.16). MACCE occurred in 7.2% of patients. After adjustment, female sex (aHR 2.6, 95% CI 1.05–6.52), in-hospital acute heart failure during index hospitalization (aHR 3.45, 95% CI 1.19–10), and prevalent atrial fibrillation (aHR 3.05, 95% CI 1.13–8.24) significantly predicted the incident risk of MACCE. These findings may help to identify patients for whom a closer and more accurate surveillance after discharge for COVID-19 should be considered