STUDIA CHEMIA - Issue no.4 / 2020 - Table of contents

Hydrogen is foreseen as a promising energy vector for the future on the road to develop a low carbon economy. In this respect, developing energy-efficient improved hydrogen production systems with low CO2 emissions is an important aspect. This study is evaluating the most relevant economic and environmental impact elements for hydrogen production based on catalytic natural gas steam reforming. As an illustrative example, an industrial-relevant hydrogen production plant with an output of 50000 Nm3/h was investigated. In addition, a pre-combustion carbon capture feature, based on reactive gas-liquid absorption using alkanolamines (Methyl-DiEthanol- Amine - MDEA), was considered to reduce the CO2 emissions. The overall carbon capture rate was 70%. Similar natural gas reforming plant without decarbonization feature is also discussed to quantify the efficiency and economic penalties for CO2 capture. As assessment methods, computational tools, thermal integration analysis and an in-depth techno-economic and environmental procedure were used. For instance, to quantify the overall environmental impact, Life Cycle Assessment (LCA) was used. Various relevant technical, economic and environmental indicators are calculated and discussed in the present work.

Keywords: Hydrogen production; Natural gas steam reforming; Carbon capture by chemical scrubbing; Techno-economic and environmental assessment.

The aim of this work is to assess the energy vector polygeneration capabilities of gasification plants equipped with carbon capture and utilization (CCU) features. As evaluated energy carriers, various total or partial decarbonized vectors were investigated (e.g., power, hydrogen, synthetic natural gas, methanol, Fischer-Tropsch fuel). As illustrative examples, the gasification concepts with 100 MW net energy output were considered having an overall plant decarbonization rate of 90%. As decarbonization technologies, the gas – liquid absorption based on chemical and physical scrubbing was assessed. A broad range of process system engineering tools were used (e.g., modeling and simulation, process integration, plant flexibility elements, technical and environmental evaluation). As results show, the application of carbon capture and utilization technologies for gasification-based polygeneration has promising results in term of increasing the overall energy efficiency (up to 68%), reducing CO2 emissions (down to 7 kg/MWh) and improving cycling capabilities.

Keywords: Carbon capture and utilization (CCU) technologies, Gasification, Energy vectors poly-generation, Technical and environmental assessment.

Electrochemical sensors have been prepared using pristine and activated multi-walled carbon nanotubes on glassy carbon electrode. The detection of dopamine in the presence of ascorbic acid was tested by square wave voltammetry and cyclic voltammetry. Best results were obtained for glassy carbon modified with activated carbon nanotubes electrodes. A linear dependence between current intensities and dopamine concentrations is found in both the absence/presence of ascorbic acid, in the range of 4-100 μM / 6-100 μM, with detection and quantification limits of 0.44 / 0.64 and 1.45 / 2.14 μM, respectively and high sensitivity. The developed electrodes also showed very good performance in separating the oxidation potentials of ascorbic acid, dopamine and uric acid, with peak potential differences of 200 and 170 mV. Dopamine detection in synthetic solutions in the presence of both ascorbic and uric acid gave recovery rates of 98%, indicating that the method is reliable.

Keywords: electrochemical sensor, carbon nanotubes, dopamine, ascorbic acid, square wave voltammetry

Crude oil processing often requires the extraction of large amounts of water. Crude oil often mixes with water to form water-in-crude oil emulsions as a result of exposure such as high shear at the wellhead and natural surfactants in crude oil. These emulsions are undesirable and require demulsification to remove dispersed water and associated inorganic salts in order to meet production and shipping specifications. In addition, demulsifying these crude oil emulsions reduces corrosion and catalyst and consistently maximizes the overall profitability of crude oil production. The article looks into the results of tests on the selection of a demulsifier for the breakdown of waterin- oil emulsion mixtures at different settling times and temperatures depending on the specific consumption of the chemical agent, the effect of various demulsifiers on emulsions breakdown. The process of oil desalination with and without the addition of demulsifiers is considered. Desalination is carried out stepwise. Research results have shown that proxanol 305/50 is the most effective demulsifier.

Keywords: oil-water emulsion; demulsifier; demulsification; residual water; dewatering.

Polymers represent a novel alternative in bone regeneration. Polydioxanone combined with Pluronic was used as a carrier for Oxytocin in form of an interfacial deposition obtained scaffold. The low rate of resorption of the scaffold follow the bone regeneration sequence assuring a constant and continuous release of Oxytocin. The Oxytocin release was monitored by RP-HPLC method. The separation was performed on a Phenomenex Luna 5μm C18 100A, 250x4.6mm, using isocratic elution with acetonitrile: phosphate buffer pH 7 (30:70 v/v) mobile phase. Flow rate 1 ml / min, column temperature 30°C, DAD, λ= 220nm. The surface morphology of polydioxanone - pluronic 127 - Oxytocin impregnated mesh was characterized by SEM. The preliminary results show that the Polydioxanone combined with Pluronic is a promising polymer for bone regeneration engineering.

Keywords: polydioxanone, Oxytocin, bone reconstruction, biodegradable scaffolds, RP-HPLC, SEM

Processing calcium and phosphor-rich natural resources, such as marble and seashells, and bovine and fish bones, envelops an environmentally friendly and eco-sustainable promising alternative for developing biomimetic products for various orthopaedic applications. In this regard, convenient, efficient, facile and completely reproducible technologies were involved in the fabrication process of biogenic calcium phosphates-based products through the conversion of the proposed resources. The aim of this research was to comparatively evaluate the morpho-compositional, structural and mechanical features of the developed products, subjected in advance to an air sintering program. The results revealed that the high temperature affects differently the morphological characteristics of the samples and facilitates the conservation of several elements, traced from their natural marine or terrestrial habitat. Moreover, the nature of the initial precursors clearly influenced the final composition of the samples: biphasic configuration for calcium carbonate derived products versus single phase for the calcium phosphate ones. The mechanical features are also a composed result of the resources type and sintering process, with significant recorded differences. Therefore, this study unveils the prospect for suitable strategies in terms of adequate natural precursor, fabrication technology and final properties of the biogenic products destined for a certain application in the biomedicine field.

Keywords: marble, seashells, bovine bone, fish bone, biogenic hydroxyapatite, compact products, comparative assessment

In the present study, dielectric spectroscopy was used to assess the influence of ELF (1-200 Hz) electromagnetic fields over protein relaxation from activated sludge (approx. 99% water content), sampled from the biological tank of a domestic wastewater treatment plant. Dielectric loss (tgδ) was determined for both activated sludge samples and autoclaved samples. Experimental data analysis shows that biological samples (activated sludge) have different dielectric behavior than the sterile samples (sterilized sludge). Unlike sterile samples in which the function tgδ vs. frequency is continuous, in the activated sludge samples, this function presents two discontinuities specific to electrical resonances around the frequencies of 26.5 Hz and 50.1 Hz. This behavior indicates that under the influence of the measuring signal of 26.5 Hz and 50.1 Hz, biochemical processes are stimulated in activated sludge. Also, the significant changes in the number of charge carriers suggest that, at these frequencies, changes occur in the mechanism and kinetics of biochemical processes.

Keywords: wastewater, activated sludge, dielectric spectroscopy, dielectric loss, electromagnetic fields, ELF

In this study referring to the surface sediments quality of Strâmtori-Firiza reservoir, a series of heavy metals like arsenic, cadmium, copper, lead and zinc were investigated from 2017 to 2019. The samples analysis and interpretation of the results for 18 samples taken from surface sediments indicated that the correlation coefficients calculated for the metallic elements showed a significant correlation between them. Thus, highlighting their same origin in the composition of the studied surface sediments, only the value of the coefficient between As and Pb implies a statistically significant correlation. Pollution indices, calculated for each sampling site, indicated anthropogenic unpolluted surface sediments. The potential ecological risk (RI), calculated for assessing the toxicity risk related to surface benthic biomass, showed that the potential ecological risk for biological life in surface sediments was low.

Keywords: surface sediment, heavy metals, risk, pollution indices

The adsorption of malachite green (MG) by the use of an ecofriendly adsorbent Urtica dioica (U. dioica) has been reported in the present study. The effects of different parameters were tested on MG adsorption and optimization of the effective parameters (pH, temperature and initial dye concentration) were performed by response surface methodology (RSM). Maximal adsorption yield of 91.67% was achieved at pH 6.5 and 50 °C with 200 mgL-1 initial dye concentration. The isotherm and kinetic studies were employed to describe the adsorption process. The experimental data fitted better on the Freundlich model and the adsorption process followed by the pseudo-second order model.

Keywords: Urtica dioica, Malachite Green, Adsorption, Response Surface Methodology

This study focused on the comparative analyses between the alum synthesized from aluminum can and natural coagulant synthesized from watermelon seed in water treatment. It also involved the identification of phytochemical groups of watermelon seed cake. The two different synthesized coagulants were used in jar test analysis; the result obtained showed a good elimination of turbidity and suspended solid particles. The pH of the natural coagulant of the treated water falls within the range of 6.9 to 7.2. Alkaloid tannins, saponin, anthracene and flavonoid were found present in the watermelon seed cake. Moreover, the result from the research showed that both the natural coagulant synthesized from watermelon seed and the one synthesized from aluminum cans could be used as good flocculant in surface water treatment.

Keywords: Watermelon seed cake, Alum, Aluminum can, Coagulation, Phytochemical

Structure-property relationship is one of the most important research areas in the liquid crystals. Therefore, in the present work, we studied a new series of rod-like heterocyclic liquid crystals, 6-methyl-2-[4-(4- alkoxybenzoyloxy)benzylideneamino]benzothiazoles. The rod-like molecules having heterocyclic and two phenyl rings as core system, imine and ester as linking units, long alkoxy chain at the terminal position. There are six members in the series with different length of alkoxy chain (CnH2n+1O-, where n = 6, 8, 10, 12, 14, 16). The structures of the compounds were elucidated using spectroscopic techniques. Their mesomorphic behaviours were determined by differential scanning calorimetry, polarizing optical microscopic and powder X-ray diffraction techniques. Members with shorter alkoxy chain (n = 6, 8, 10) exhibited single mesophase (nematic). As the alkoxy chain increased to n = 12, 14, 16, the nematic phase appeared together with an additional mesophase (smectic). The phase width was dependent on the alkoxy chain length. The incorporation of the methyl substituent at the sixth position (lateral) of the benzothiazole able to increase the clearing point and widen the mesophase width of the compounds.

Keywords: benzothiazole, Schiff base, nematic, smectic A

The article presents the AMS (accelerator mass spectrometry) radiocarbon dating results of the Giant of Bevoay, which is a very large Grandidier baobab (Adansonia grandidieri Baill.) of Madagascar. The investigation of this baobab shows that it has a cluster structure, which consists of 3 perfectly fused stems. The calculated wood volume of the tree is 520 m3, which makes it the third largest Grandidier baobab and also the third largest individual of all Adansonia species. Two samples were collected from the outer part of the stems. The oldest dated sample segment had a radiocarbon date of 525 ± 23 BP, which corresponds to a calibrated age of 585 ± 10 years. According to this value, the Giant of Bevoay is 825 ± 50 years old.

Keywords: AMS radiocarbon dating, Adansonia grandidieri, tropical trees, age determination

Bovine milk is a product with high consumption rate across the world and therefore its evaluation in terms of consumers’ safety and public health is of extreme relevance. In this study, the occurrence of residues of polychlorinated biphenyls (PCBs), organochlorine pesticides and heavy metals was monitored in environmental samples (soil, grassland grass, water) and bovine milk collected from seven locations in Romania, for the assessment of their potential health risk. PCBs were detected in almost all the environmental and milk samples; it highlighted in soil values higher than the normal limit set by the national legislation, but below the alert thresholds and intervention levels. Dichlorodiphenyltrichloroethane (DDT) and its metabolites were found in consistently higher amounts in environmental samples and bovine milk at all sites. Increased values of hexachlorocyclohexane (HCH) were also found in milk samples but without exceeding the maximum admissible levels set by the Romanian legislation. High concentration of cadmium, copper and zinc were found in soil, grass and water samples from the industrial area. Lead exceeded the maximum admissible level in samples from the urban area. The results obtained confirmed the importance of surveilling persistent pollutants in raw milk as part of the healthcare system.

Keywords: PCBs, organochlorine pesticides, heavy metals

In this study, isotherm, kinetic and thermodynamic studies of corrosion inhibitory properties of Oryza Glaberrima husk extract (OGHE) on aluminium in 1.5 M H2SO4 solution was investigated via mass loss measurement. Aluminium coupon and OGHE were characterized using SEM, EDS, FTIR and AAS. Increase in Al corrosion rate in H2SO4 solution was observed as exposure period (24 - 120 hrs) and temperature (293 - 333K) were increased but decreased with pH (2 - 6). Corrosion inhibition efficiency of OGHE is a function of its concentration and ability to be easily absorbed on Al surface to form thick protective films against H2SO4 attack. Adsorption of OGHE molecule on Al surface in 1.5 M H2SO4 solution agrees excellently well with Langmuir isotherm. Thermodynamic study revealed the adsorption process to be spontaneous, endothermic and physisorption in nature. Kinetic study affirmed adsorption of OGHE molecule on Al surface to obey second order reaction. Appropriate corrosion mechanisms of Al dissolution in H2SO4 and in the presence of OGHE were proposed. This study proved positive prospects of OGHE as effective corrosion inhibitor for Al in acidic medium.

Keywords: Aluminium, Sulphuric acid, Oryza Glaberrima, Corrosion, Inhibition

Lipidomics is an advanced analytical technology applying techniques like Gas- or Liquid Chromatography coupled with Mass Spectrometry or Magnetic Resonance Spectrometry to find the lipid biomarkers in tissues, blood or urine. This review selected significant results which show the impact of lipidomic investigations for discriminating the metabolic profiles and dysregulation of metabolic pathways in CRC patient’s comparative to healthy controls. It focuses on the description of best methods and procedures to separate and identify hydrophobic molecules with molecular weights under 1000 Daltons, especially using high pressure liquid chromatography coupled with mass spectrometry. The main lipid classes involved in the onset and progression of CRC are presented, as well the alterations of lipid-related cellular pathways during tumorigenesis. Especially lipid profile changes (of cerotic acid, hydroxylated, polyunsaturated fatty acids, free fatty acids, oxylipins, glycerophospholipids, di- and triglycerides, sphingomyelins and ceramides) showed significant differences and can be considered reliable biomarkers to discriminate between early and advanced stages of CTC malignancy, prognosis or survival prediction.

Keywords: metabolomics, lipidomics, colorectal cancer, biomarkers