Mechanistic investigations on a homogeneous ruthenium Guerbet catalyst in a flow reactor

A mechanistic investigation on the ethanol self-condensation reaction (Guerbet reaction) catalyzed by a bis(pyridylimino)isoindolate Ru(ii) catalyst was performed using a specifically designed continuously-stirred tank reactor (CSTR).

Over-Equilibrium as a Result of Conservatively-Perturbed Equilibrium (Acyclic and Cyclic Mechanisms)

The effect of over-equilibrium, i. e., the effect at which the concentration of some substance is higher than the corresponding equilibrium value, is demonstrated for two types of ideal chemical reactors, continuously stirred tank reactor (CSTR) and plug-flow reactor (PFR), respectively, under conditions of conservatively perturbed-equilibrium (CPE). Two types of complex chemical mechanisms are analyzed, acyclic and cyclic ones. Using numerical experiments and the same residence times, it is shown that for the steady-state PFR this effect is more pronounced that for the steady-state CSTR, and it is true both for acyclic and cyclic reactions. In the studied mechanisms, cyclic and acyclic, the initial concentration of some substance is taken as the equilibrium one, and two other concentrations are the nonequilibrium ones. The greater the difference between the two initially nonequilibrium concentrations, the greater the concentration of the third substance, which was taken initially as the equilibrium one. At the specific values of kinetic parameters considered here, the sensitivity of the occurrence time of the B-concentration extremum for the different reactors (PFR and CSTR) at the fixed mechanism is small, but for the different mechanisms (acyclic and cyclic) at the fixed reactor is significant.

pH-Based Control Strategies for the Nitrification of High-Ammonium Wastewaters

Aquatic nitrogen pollution is one of the most urgent environmental issues requiring prevention and mitigation. Large quantities of high-ammonium wastewaters are generated by several industrial sectors, such as fertilizer and anaerobic-digestion plants. Nitrification of these wastewaters is commonly carried out, either to remove nitrogen or produce liquid fertilizers. Standard control methodologies for the efficient nitrification of high-ammonium wastewaters to produce liquid fertilizers have not yet been established and are still within their early stages of development. In this paper, novel pH-based control algorithms are presented that maintain operation at the microbial maximum reaction rate (υmax) in batch and continuous reactors. Complete conversion of ammonium to nitrate was achieved in a batch setup, and a conversion of 93% (±1%) was achieved in a continuously-stirred-tank-reactor. The unparalleled performance and affordability of the control schemes proposed offer a steppingstone to the future of sustainable fertilizer production.

Methods for Oxygenation of Continuous Cultures of Brewer’s Yeast, Saccharomyces cerevisiae

Maintaining steady-state, aerobic cultures of yeast in a bioreactor depends on the configuration of the bioreactor system as well as the growth medium used. In this paper, we compare several conventional aeration methods with newer filter methods using a novel optical sensor array to monitor dissolved oxygen, pH, and biomass. With conventional methods, only a continuously stirred tank reactor configuration gave high aeration rates for cultures in yeast extract peptone dextrose (YPD) medium. For filters technologies, only a polydimethylsiloxan filter provided sufficient aeration of yeast cultures. Further, using the polydimethylsiloxan filter, the YPD medium gave inferior oxygenation rates of yeast compared to superior results with Synthetic Complete medium. It was found that the YPD medium itself, not the yeast cells, interfered with the filter giving the low oxygen transfer rates based on the volumetric transfer coefficient (KLa). The results are discussed for implications of miniaturized bioreactors in low-gravity environments.

Development of an Iron-Based Fischer–Tropsch Catalyst with High Attrition Resistance and Stability for Industrial Application

In order to develop an iron-based catalyst with high attrition resistance and stability for Fischer–Tropsch synthesis (FTS), a series of experiments were carried out to investigate the effects of SiO2 and its hydroxyl content and a boron promoter on the attrition resistance and catalytic behavior of spray-dried precipitated Fe/Cu/K/SiO2 catalysts. The catalysts were characterized by means of N2 physisorption, nuclear magnetic resonance (NMR), X-ray diffraction (XRD), Raman spectrum, X-ray photoelectron spectroscopy (XPS), H2-thermogravimetric analysis (H2-TGA), temperature-programmed reduction and hydrogenation (TPR and TPH), and scanning and transmission electron microscopy (SEM and TEM). The FTS performance of the catalysts was tested in a slurry-phase continuously stirred tank reactor (CSTR), while the attrition resistance study included a physical test with the standard method and a chemical attrition test under simulated reaction conditions. The results indicated that the increase in SiO2 content enhances catalysts’ attrition resistance and FTS stability, but decreases activity due to the suppression of further reduction of the catalysts. Moreover, the attrition resistance of the catalysts with the same silica content was greatly improved with an increase in hydroxyl number within silica sources, as well as the FTS activity and stability to some degree. Furthermore, the boron element was found to show remarkable promotion of FTS stability, and the promotion mechanism was discussed with regard to probable interactions between Fe and B, K and B, and SiO2 and B, etc. An optimized catalyst based on the results of this study was finalized, scaled up, and successfully applied in a megaton industrial slurry bubble FTS unit, exhibiting excellent FTS performance.

Markov Chain Monte Carlo Analysis of the Variable-Volume Exothermic Model for a Continuously Stirred Tank Reactor

In this paper, a variable-volume Continuously Stirred Tank Reactor (CSTR) deterministic exothermic model has been formulated based on the Reynold Transport Theorem. The numerical analysis of the formulated model and the identifiability of its physical parameters are done by using the least squares and the Delayed-Rejection Adaptive Metropolis (DRAM) method. The least square estimates provide the prior information for the DRAM method. The overall numerical results show that the model gives an insight in describing the dynamics of CSTR processes, and 14 parameters of the CSTR are well identified through DRAM convergence diagnostic tests, such as trace, scatter, autocorrelation, histograms, and marginal density plots. Global sensitivity analysis was further performed, by using the partial rank correlation coefficients obtained from the Latin hypercube sampling method, in order to study and quantify the impact of estimated parameters, uncertainties on the model outputs. The results showed that 7 among the 14 estimated model parameters are very sensitive to the model outcomes and so those parameters need to be handled and treated carefully.

Energetic Valorization of Cereal and Exhausted Coffee Wastes Through Anaerobic Co-digestion With Pig Slurry

In the past years, there has been steady growth in work relating to improve resource efficiency through waste minimization and bioenergy recovery to mitigate climate change. Agro-food industries produce large amounts of bio-waste, challenging innovative energetic valorization strategies in the framework of circular economy principles. Anaerobic digestion (AD) technology is an interesting route to stabilize organic matter and produce biogas as a renewable energy source. This study involves continuous co-digestion of pig slurry (PS), cereal and exhausted coffee wastes (CECW) performed in a continuously stirred tank reactor, with a hydraulic retention time (HRT) of 16 days under at mesophilic conditions (36.9 ± 0.3°C). The experimental trials, were designed to include different cereal and exhausted coffee liquor (CECL) shares in the feeding mixture, corresponding to different PS to CECL ratios (PS:CECL), respectively: 100:0 (T0), 90:10 (T1), 80:20 (T2), and 70:30 (T3), in terms of percentage of inlet feeding rate (v:v). The results obtained for the feeding rate (70:30) yield to the highest specific methane production (SMP = 341 ml.gVS−1) led to a 3.5-fold improvement in comparison with the reference scenario. The synergetic effect between the microbial consortia of PS and the high carbon to nitrogen ratio (C/N) of CECL explain the improvements achieved. The maximum soluble chemical oxygen demand (SCOD) reduction (84.0%) due to the high content and soluble chemical oxygen demand to total chemical oxygen demand ratio (SCOD/TCOD) corroborate the results achieved. The digester stability, evaluated by specific energetic loading rate, was below the limit (0.4 d−1). Results from ANOVA showed a significant effect of CECL on the resulting GPR and SMP values. Additionally, Tukey's “Honest Significant Difference” method, confirmed statistically significant differences between the trials T3-T0, T3-T1, T3-T2, and T2-T0. Thus, co-digestion of PS and of CECL seems to be a promising approach for bioenergy recovery and promoting biowastes circularity.