Laser induced breakdown spectroscopy for monitoring the molten phase desulfurization process of blister copper.

The development of real-time monitoring sensors for pyro-metallurgical processes is an analytical challenge, mainly due to adverse environmental conditions, high spectral interferences and multiphase (molten and gas) reactions. This work demonstrates the suitability of stand-off LIBS (ST-LIBS) for real time monitoring of the desulfurization of blister copper which is carried out in molten phase. Here sulfur is removed by the formation of SO2 by supplying oxygen in molten phase. Using ST-LIBS the relative emission intensities of Cu(I) at 351.06 nm, O at 777.34 nm and S at 921.29 nm in both molten and gaseous phase were considered simultaneously during the process. This was possible only by the use high energy laser pulse over up to 270 mJ per pulse. In the case of copper, the selection of emission lines was assessed considering non-linear behavior, which is caused by self-absorption. For the first time, real time determination of sulfur in ppm range is reported by ST-LIBS using low sensitive lines from the NIR region. These results were validated with differential optical absorption spectroscopy (DOAS) as gold standard method. The analytical information obtained by LIBS can precisely determine the critical end-point of the desulfurization where the removal of sulfur is finished, and copper started to oxidize.

A Radiometric Technique for Monitoring the Desulfurization Process of Blister Copper.

In this paper, a novel optical technique for following the progress of the blister copper desulfurization process is presented. The technique is based on the changes observed in the continuous spectrum of the visible-near-infrared (VIS-NIR) radiation that the blister melt emits while the chemical reactions of the sulfur elimination process are taking place. Specifically, the proposed technique uses an optical probe composed of an optical fiber, a collimating lens, and a quartz tube, which is immersed in the melt. This optical probe provides a field of view of the blowing zone where the desulfurization reaction occurs. The experimental results show that the melt VIS-NIR total irradiance evolves inversely to the SO2 concentration reported by a gas analyzer based on differential optical absorption spectroscopy. Furthermore, the blister copper spectral emissivity as well as the total emissivity observed throughout the process show strong correlation with the sulfur content during desulfurization reaction.

H2S oxidation coupled to nitrate reduction in a two-stage bioreactor: Targeting H2S-rich biogas desulfurization.

A two-stage bioreactor operated under anoxic denitrifying conditions was evaluated for desulfurization of synthetic biogas laden with H2S concentrations between 2500 and 10,000 ppmv. H2S removal efficiencies higher than 95% were achieved for H2S loads ranging from 16.2 to 51.9 gS mliquid-3h-1. Average H2S oxidation performance (fraction of S-SO42- produced per gram of S-H2S absorbed) ranged between 8.2 ± 1.2 and 18.7 ± 5.3% under continuous liquid operation. Nitrogen mass balance showed that only 2-6% of the N-NO3- consumed was directed to biomass growth and the rest was directed to denitrification. Significant changes in the bacterial community composition did not hinder the H2S removal efficiency. The bioreactor configuration proposed avoided clogging issues due to elemental sulfur accumulation as commonly occurs in packed bed bioreactors devoted to H2S-rich biogas desulfurization.

Probing mesoporous character, desulfurization capability and kinetic mechanism of synergistic stabilizing sorbent CaxCuyMnzOi/MAS-9 in hot coal gas.

Developing structurally stable sorbents for high-temperature H2S direct removal is recognized as a valuable energy-saving strategy for efficient utilization of hot coal gas (HCG), which depends upon their mesoporous features and desulfurization capabilities. Herein, tailored hierarchical CaxCuyMnzOi/MAS-9 sorbents were fabricated via a facile sol-gel method using high-activity phase CaxCuyMnzOi anchored onto versatile mesoporous MAS-9. After O/S-exchange procedure, noteworthy straight channels of MAS-9 (SBET = 808 m2 g-1) provided enough available spaces for the storage of generative large MeSy nanoparticles, which was better than other conventional zeolites. The probing of variables (i.e. support type, active ingredient, loadings, and sulfidation temperature) on H2S removal revealed that 50%Ca3Cu10Mn87Oi/MAS-9 shared an excellent breakthrough sulfur capacity (171.57 mg g-1) at 800 °C, even it experienced six reusable cycles, due to synergistic stabilizing effect of Ca-Cu-Mn and high-temperature tolerance of SiOAl framework of MAS-9. Especially, CaO dopant endowed the sorbent with superficial alkalinity and high-temperature resistance. The brilliant desulfurization behavior was also described by the fast H2S diffusion or component deactivation vs. duration time on stream according to the followed kinetic investigation. Thus, the refined Ca3Cu10Mn87Oi/MAS-9 possesses the expected representative desulfurization nature and great potentiality for raw HCG in practical applications.

PET-modified red mud as catalysts for oxidative desulfurization reactions.

This work describes the synthesis of catalysts based on red mud/polyethylene terephthalate (PET) composites and their subsequent heat treatment under N2 atmosphere. The materials were characterized by scanning electron microscopy (SEM), temperature programmed reduction (TPR), Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), thermogravimetric (TG) analysis and N2 adsorption/desorption. The catalysts were evaluated in the oxidative desulfurization reaction of dibenzothiophene (DBT) in a biphasic system. The results indicated that the PET impregnation on red mud increased the affinity of the catalyst with the nonpolar phase (fuel), in which the contaminant was dissolved, allowing a higher conversion (up to 80%) and selectivity to the corresponding dibenzothiophene sulfone. The sulfone compound is more polar than DBT and diffused into the polar solvent as indicated by the data obtained via gas chromatography-mass spectrometry (GC-MS).

A study of photosynthetic biogas upgrading based on a high rate algal pond under alkaline conditions: Influence of the illumination regime.

Microalgal-bacterial processes have emerged as environmental friendly systems for the cost-effective treatment of anaerobic effluents such as biogas and nutrients-laden digestates. Environmental parameters such as temperature, irradiation, nutrient concentration and pH effect the performance of the systems. In this paper, the potential of a microalgal-bacterial photobioreactor operated under high pH (≈9.5) and high alkalinity to convert biogas into biomethane was evaluated. The influence of the illumination regime (continuous light supply vs 12h/12h light/dark cycles) on the synthetic biogas upgrading efficiency, biomass productivity and nutrient removal efficiency was assessed in a High-Rate Algal Pond interconnected to a biogas absorption bubble column. No significant differences in the removal efficiency of CO2 and H2S (91.5±2% and 99.5%±0.5, respectively) were recorded regardless of the illumination regime. The high fluctuations of the dissolved oxygen concentration during operation under light/dark cycles allowed to evaluate the specific growth rate and the specific partial degradation rate of the microalgae biomass by photosynthesis and respiration, respectively. The respiration reduced the net microalgae biomass productivity under light/dark cycles compared with process operation under the continuous light supply.

Technical, Economical, and Microbiological Aspects of the Microaerobic Process on H2S Removal for Low Sulfate Concentration Wastewaters.

We studied the feasibility of the microaerobic process, in comparison with the traditional chemical absorption process (NaOH), on H2S removal in order to improve the biogas quality. The experiment consisted of two systems: R1, biogas from an anaerobic reactor was washed in a NaOH solution, and R2, headspace microaeration with atmospheric air in a former anaerobic reactor. The microaeration used for low sulfate concentration wastewater did not affect the anaerobic digestion, but even increased system stability. Methane production in the R2 was 14 % lower compared to R1, due to biogas dilution by the atmospheric air used. The presence of oxygen in the biogas reveals that not all the oxygen was consumed for sulfide oxidation in the liquid phase indicating mass transfer limitations. The reactor was able to rapidly recover its capacity on H2S removal after an operational failure. Bacterial and archaeal richness shifted due to changes in operational parameters, which match with the system functioning. Finally, the microaerobic system seems to be more advantageous for both technical and economical reasons, in which the payback of microaerobic process for H2S removal was 4.7 months.

Effective removal of sulfur components from Brazilian power-coals by ultrasonication (40kHz) in presence of H2O2.

The present investigation reports a preliminary attempt of using ultrasonic energy (40kHz) to clean some low rank high sulfur Brazilian power-coal samples in presence of H2O2 solution. All types of sulfur components (i.e. pyritic, sulfate and organic) could be removed from the coal samples by this process. The raw and ultrasonicated coal samples were characterized by chemical analysis, Fourier Transformation Infrared (FT-IR) spectroscopy, X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), focused ion beam (FIB), high-resolution transmission electron microscope (HR-TEM) with selected area electron diffraction (SAED) and/or microbeam diffraction (MBD), scanning transmission electron microscopy (STEM), energy-dispersive X-ray spectrometer (EDS), and Thermogravimetry (TG-DTG) techniques to evaluate the clean-coal quality. The FT-IR spectroscopic analysis demonstrated the formation of oxidized sulfur species (SO and -SO2) and their subsequent removals after ultrasonication. The XRD profiles supported the presence of mineral matters in the coals. The TG-DTG profiles of the beneficiated coals revealed their improved quality for using in thermal plants with better combustion efficiency.

An Evaluation of Kinetic Models in the Biodesulfurization of Synthetic Oil by Rhodococcus erythropolis ATCC 4277.

Biodesulfurization is an eco-friendly technology applied in the removal of sulfur from fossil fuels. This technology is based on the use of microorganisms as biocatalysts to convert the recalcitrant sulfur compounds into others easily treatable, as sulfides. Despite it has been studied during the last decades, there are some unsolved questions, as per example the kinetic model which appropriately describes the biodesulfurization globally. In this work, different kinetic models were tested to a batch desulfurization process using dibenzothiophene (DBT) as a model compound, n-dodecane as organic solvent, and Rhodococcus erythropolis ATCC 4277 as biocatalyst. The models were solved by ODE45 function in the MATLAB. Monod model was capable to describe the biodesulfurization process predicting all experimental data with a very good fitting. The coefficients of determination achieved to organic phase concentrations of 20, 80, and 100 % (v/v) were 0.988, 0.995, and 0.990, respectively. R. erythropolis ATCC 4277 presented a good affinity with the substrate (DBT) since the coefficients of saturation obtained to reaction medium containing 20, 80, and 100 % (v/v) were 0.034, 0.07, and 0.116, respectively. This kinetic evaluation provides an improvement in the development of biodesulfurization technology because it showed that a simple model is capable to describe the throughout process.

Harvesting microalgae cultures with superabsorbent polymers: desulfurization of Chlamydomonas reinhardtii for hydrogen production.

It is presented in this work a new methodology to harvest fresh water microalgae cultures by extracting the culture medium with superabsorbent polymers (SAPs). The microalgae Chlamydomonas reinhardtii were grown in the Sueoka culture medium, harvested with polyacrylic SAPs and re-suspended in the culture medium tris-acetate-potassium without sulfur (TAP-S) to generate hydrogen (H2 ) under anoxic conditions. The H2 production as an alternative fuel is relevant since this gas has high-energy recovery without involving carbon. Before microalgae harvesting, a number of range diameters (1-7 mm) for SAPs spherical particles were tested, and the initial rate (V0 ) and the maximal capacity (Qmax ) were determined for the Sueoka medium absorption. The SAP particles with the diameter range 2.0-2.5 mm performed the best and these were employed for the rest of the experiments. The Sueoka medium has a high salt content and the effect of the ionic strength was also studied for different medium concentrations (0-400%). The SAPs were reused in consecutive absorption/desorption cycles, maintaining their absorption capacity. Although the Sueoka medium reduces the SAPs absorption capacity to 40% compared with deionized water, the use of SAPs was very significant for the desulfurization process of C. reihardtii. The presence of C. reinhardtii at different concentrations does not affect the absorption capacity of the Sueoka culture medium by the SAPs. In order to reduce the time of the process, an increase of the SAPs concentration was tested, being 20 g of SAP per liter of medium, a condition to harvest the microalgae culture in 4 h. There were no evident cell ruptures during the harvesting process and the cells remained alive. Finally, the harvested biomass was re-suspended in TAP-S medium and kept under anaerobic conditions and illumination to produce H2 that was monitored by a PEM fuel cell. The use of SAPs for microalgae harvesting is a feasible non-invasive procedure to obtain high concentrations of functional biomass at low cost; it offers an attractive alternative due to its versatility and simplicity.