Modeling of the permeate flux decline during MF and UF cross-flow filtration of soy sauce lees

Cross-flow ultrafiltration and microfiltration have been used to recover refined soy sauce from soy sauce lees for over 25 years. The precise mechanism which dominated the permeate flux during batch cross-flow filtration has not been clarified. In the present study, we proposed a modified analytical method incorporated with the concept of deadend filtration to determine the initial flux of cross-flow filtration and carried out the permeate recycle and batch cross-flow filtration experiments using soy sauce lees. We used UF and MF flat membrane (0.006 m² polysulfone) module under different transmembrane pressures (TMP) and cross-flow velocities. The modified analysis provided an accurate prediction of permeate flux during the filtration of soy sauce lees, because this model can consider the change in J₀ at initial stage of filtration which was caused by the pore constriction and plugging inside membrane, and these changes may not proceed when the cake was formed on the membrane surface. Mean specific resistance of the cake increased with TMP due to the compaction of the cake and decreased with cross-flow velocity due to the change of deposited particle size, but less depended on the membrane in the present study. These results indicate that the value of J₀ determined by modified method was relevant to exclude the effects of the initial membrane fouling by pore constriction due to protein adsorption and plugging with small particles. The modified analytical method for the cake filtration developed in the present study was considered to be capable of selecting an appropriate operating conditions for many cross-flow filtration systems with UF, MF membranes.     

A combined osmotic pressure and cake filtration model for crossflow nanofiltration of natural organic matter

A combined osmotic pressure and cake filtration model for crossflow nanofiltration of natural organic matter (NOM) was developed and successfully used to determine model parameters (i.e. permeability reduction factor (η) and specific cake resistance (α_cake)) for salt concentrations, NOM concentrations, and ionic strength of salt species (Na⁺ and Ca⁺⁺). In the absence of NOM, with increasing salt concentration from 0.004 to 0.1 M, permeability reduction factor (η)) decreased from 0.99 to 0.72 and 0.94 to 0.44 for monovalent cation (Na⁺) and divalent cation (Ca⁺⁺), respectively. This reduced membrane permeability was due to salt concentrations and salt species. In the presence of NOM, specific cake resistance tended to increase with increasing NOM concentration and ionic strength in the range of 0.85 × 10¹⁵–3.66 × 10¹⁵ m kg⁻¹. Solutions containing divalent cation exhibited higher normalized flux decline (J_v/J_vo = 0.685–0.632) and specific cake resistance (α_cake = 2.89 × 10¹⁵–6.24 × 10¹⁵ m kg⁻¹) than those containing monovalent cation, indicating a highly compacted NOM accumulation, thus increased permeate flow resistance during NF filtration experiments. After membrane cleaning, divalent cation exhibited lower water flux recovery than monovalent cation, suggesting higher non-recoverable (R_non-rec) resistance than monovalent cation.     

Trilinearity deviation ratio: A new metric for chemometric analysis of comprehensive two-dimensional gas chromatography time-of-flight mass spectrometry data

Comprehensive two-dimensional gas chromatography coupled with time-of-flight mass spectrometry (GC × GC–TOFMS) is a well-established instrumental platform for complex samples. However, chemometric data analysis is often required to fully extract useful information from the data. We demonstrate that retention time shifting from one modulation to the next, Δ²t_R, is not sufficient alone to quantitatively describe the trilinearity of a single GC × GC–TOFMS run for the purpose of predicting the performance of the chemometric method parallel factor analysis (PARAFAC). We hypothesize that analyte peak width on second dimension separations, ²W_b, also impacts trilinearity, along with Δ²t_R. The term trilinearity deviation ratio, TDR, which is Δ²t_R normalized by ²W_b, is introduced as a quantitative metric to assess accuracy for PARAFAC of a GC × GC–TOFMS data cube. We explore how modulation ratio, M_R, modulation period, P_M, temperature programming rate, T_ramp, sampling phase (in-phase and out-of-phase), and signal-to-noise ratio, S/N, all play a role in PARAFAC performance in the context of TDR. Use of a P_M in the 1–2 s range provides an optimized peak capacity for the first dimension separation (500–600) for a 30 min run, with an adequate peak capacity for the second dimension separation (12–15), concurrent with an optimized two-dimensional peak capacity (6000–7500), combined with sufficiently low TDR values (0–0.05) to facilitate low quantitative errors with PARAFAC (0–0.5%). In contrast, use of a P_M in the 5 s or greater range provides a higher peak capacity on the second dimension (30–35), concurrent with a lower peak capacity on the first dimension (100–150) for a 30 min run, and a slightly reduced two-dimensional peak capacity (3000–4500), and furthermore, the data are not sufficiently trilinear for the more retained second dimension peaks in order to directly use PARAFAC with confidence.     

Multiwavelength spectrophotometric determination of protolytic constants of 4-(2-pyridylazo) resorcinol (PAR) in binary DMF-water mixtures

A multiwavelength spectrophotometric titration method was applied to study the protolytic constants of 4-(2-pyridylazo) resorcinol(PAR), in binary DMF + water mixtures. UV-vis absorption spectra of PAR solution were recorded in the course of pH-metric titration of acidic solutions of PAR with standard base solution. The protolytic equilibrium constants, spectral profiles, concentration diagrams and also the number of components have been calculated from the fitting of the pH-spectral titration data with appropriate mass balance equations by a home written program according to an established target factor analysis. To precise determination of number of absorptive components a recently developed statistical indicator function (IND function) was used. A glass electrode calibration procedure based on a four-parameter equation pH=α+SpcH+JH⁺[H⁺]+JOH⁻Kw/[H⁺] based on the Gran's plots was used to obtain pH readings in the concentration scale (p_cH). It has been observed that there is an inverse relationship between second and third protolytic constants and mole fraction of DMF. The effect of the solvent on the protolytic constants was discussed.     

Are closed clusters expected from the (n + 1) skeletal electron pairs rule in alanes and gallanes? A DFT structural study of AnHn + 2 (A = Al, Ga, and n = 4-6)

It has been suggested recently that the alanes Al_nH_n + 2 can be treated by the polyhedral skeletal electron pair theory (PSEPT) of Wade and Mingos (W-M) as it was successful for their borane congeners such as B_nH_n + 2, well known as the deprotonated B_nH_n²⁻. To do so, the neutral Al_nH_n + 2 have been considered as Al_nH_n²⁻ + 2H⁺. The additional hydrogens donate their electrons to the Al_nH_n polyhedral framework and according to the n + 1 electron pairs rule; these clusters should have closo-polyhedral structures. In this work the homologous gallanes, the structures and stabilities of Ga_nH_n + 2 are studied at high levels of calculational theory and we investigated the applicability of the W-M rule to the alanes and gallanes A_nH_n + 2 (n = 4-6; A = Al, Ga). It will be shown that the presence of bridging hydrogen atoms reduces the compactness of the corresponding polyhedron and so these species do not have the closed structures. The computations were performed at B3LYP/6-311+G(d,p), BPW91/6-311G(d,p) and B3LYP/6-311+G(3df,2p) levels of theory. Our interest in these compounds includes their potential use as hydrogen storage species and future clean sources of energy.     

Effect of phase behavior, density, and isothermal compressibility on the constant-volume heat capacity of ethane + n-pentane mixed fluids in different phase regions

The phase behavior, density, and constant-volume molar heat capacity (C_v,m) of ethane + n-pentane binary mixtures have been measured in the supercritical region and subcritical region at T=309.45 K. In addition, the isothermal compressibility (κ_T) has been calculated using the density data determined. For a mixed fluid with a composition close to the critical composition, C_v,m and κ_T increase sharply as the pressure approaches the critical point (CP), the dew point (DP), or the bubble point (BP). However, C_v,m is not sensitive to pressure in the entire pressure range if the composition of the mixed fluid is far from the critical composition. To tune the properties of the binary mixtures effectively by pressure, both the composition and the pressure should be close to the critical point of the mixture. The intermolecular interactions in the mixture are also discussed on the basis of the experimental results.     

Nano TiO2/SO4 as a heterogeneous solid acid catalyst for the synthesis of 5-substited-1H-tetrazoles

An efficient and economical protocol for the synthesis of 5-substituted-1H-tetrazoles from various nitriles and sodium azide is reported using nano TiO₂/SO₄²⁻ as an effective heterogeneous catalyst. A wide variety of aryl nitriles underwent [3 + 2] cycloaddition to afford tetrazoles in good to excellent yields.     

Structural Insights and Docking Analysis of Adamantane-Linked 1,2,4-Triazole Derivatives as Potential 11β-HSD1 Inhibitors

The solid-state structural analysis and docking studies of three adamantane-linked 1,2,4-triazole derivatives are presented. Crystal structure analyses revealed that compound 2 crystallizes in the triclinic P-1 space group, while compounds 1 and 3 crystallize in the same monoclinic P2₁/c space group. Since the only difference between them is the para substitution on the aryl group, the electronic nature of these NO₂ and halogen groups seems to have no influence over the formation of the solid. However, a probable correlation with the size of the groups is not discarded due to the similar intermolecular disposition between the NO₂/Cl substituted molecules. Despite the similarities, CE-B3LYP energy model calculations show that pairwise interaction energies vary between them, and therefore the total packing energy is affected. HOMO-LUMO calculated energies show that the NO₂ group influences the reactivity properties characterizing the molecule as soft and with the best disposition to accept electrons. Further, in silico studies predicted that the compounds might be able to inhibit the 11β-HSD1 enzyme, which is implicated in obesity and diabetes. Self- and cross-docking experiments revealed that a number of non-native 11β-HSD1 inhibitors were able to accurately dock within the 11β-HSD1 X-ray structure 4C7J. The molecular docking of the adamantane-linked 1,2,4-triazoles have similar predicted binding affinity scores compared to the 4C7J native ligand 4YQ. However, they were unable to form interactions with key active site residues. Based on these docking results, a series of potentially improved compounds were designed using computer aided drug design tools. The docking results of the new compounds showed similar predicted 11β-HSD1 binding affinity scores as well as interactions to a known potent 11β-HSD1 inhibitor.     

A tetranuclear complex from the employment of pyridine-2,6-dimethanol in copper(II) nitrate chemistry: Synthetic,structural and magnetic studies

The use of pyridine-2,6-dimethanol (pdmH₂) in copper(II) nitrate chemistry is reported. The reaction of Cu(NO₃)₂·3H₂O with one equivalent of pdmH₂ in MeCN affords the known mononuclear complex [Cu(pdmH₂)₂](NO₃)₂ (1) in high-yield. The reaction of 1 and NaOMe in an 1:1 ratio, as well as the reaction between Cu(NO₃)₂·3H₂O, pdmH₂ and NaOMe in an 1:1:1 ratio, in MeOH gives the tetranuclear complex [Cu₄(NO₃)₂(pdmH)₄(H₂O)(MeOH)](NO₃)₂ (2) in moderate yields. The cation of 2 possesses a slightly distorted tetrahedral Cu₄ topology with a [Cu₄(μ₂-OR)₄]⁴⁺ core. The pdmH⁻ ions behave as η¹:η¹:η²:μ₂ ligands. Strong intramolecular hydrogen bonds and π–π stacking interactions provide thermodynamic stability on compound 2. Variable-temperature, solid-state dc magnetic studies were carried out on complex 2 in the 2.0–300 K range. The data indicate predominant antiferromagnetic exchange interactions and a resulting S = 0 ground state, which is expected for a solely, μ₂-alkoxide-bridged system with obtuse Cu–O–Cu bond angles that magnetically behaves as a Cu₄ ring. A simplified 1 − J model was found to be adequate to describe the variable-temperature dc susceptibility data. The data were fitted to the appropriate equation derived from the Hamiltonian H = −J₁(S₁ · S₂ + S₂ · S₄ + S₃ · S₄ + S₁ · S₃), giving the parameters J₁ = −99.5 cm⁻¹ and g = 2.11(4). The combined work demonstrates the ligating flexibility of the pdmH₂ chelate and its usefulness in the synthesis of oligo- and polynuclear Cu^II_x clusters with interesting structural and magnetic properties, without requiring the co-presence of carboxylate ligands.     

NMR investigation and theoretical studies on the tautomerism of β,β′-tricarbonyl compounds

The behaviour on keto–enol tautomeric equilibration of ethyl 2-benzoyl-5-(2-furyl)-3-hydroxy-penta-2,4-dienoate (1) and ethyl 2-acetyl-3-hydroxy-5-phenyl-penta-2,4-dienoate (2) was investigated by ¹H and ¹³C NMR spectroscopy in different solvents and BP86/TZVP density functional theory computations. The spectral assignment to enol and keto tautomers was performed with one- and two-dimensional techniques. The percentage of the keto form in the tautomeric equilibrium depends on solvents and rises by increasing solvent polarity. The enol–enol tautomerism is also discussed on the basis of the coupling constants ²J_C,OH, ³J_C,OH and ⁴J_H,OH, respectively.     

Formation of appropriate sites on nanofiltration membrane surface for binding TiO2 photo-catalyst: Performance, characterization and fouling-resistant capability

Titanium dioxide (TiO₂) nanoparticles were assembled on the surface of nanofiltration blend membrane. For settling TiO₂ on the membrane surface, two membrane categories were used: (i) unmodified polyethersulfone (PES)/polyimide (PI) blend membrane, and (ii) –OH functionalized PES/PI blend membrane with different concentrations of diethanolamine (DEA). These membranes were radiated by UV light after TiO₂ depositing with different concentrations. 15 min immersion in colloidal suspension and 15 min UV irradiation with 160 W lamps were used for modification. The modification resulted in the formation of a photo-catalytic property with enhanced membrane hydrophilicity. The self-assembly of TiO₂ nanoparticles was established through coordinance bonds with –OH functional groups on the membrane surface. A comparison between the UV irradiated TiO₂ deposited blend membrane and deposited-functionalized blend membranes showed that –OH groups originate excellent adhesion of TiO₂ nanoparticles on the membrane surface, increase reversible deposition, and diminish irreversible fouling. The membranes were characterized using SEM, FTIR, EDX, contact angle, cross flow filtration, and antifouling measurements. SEM images show that the presence of –OH groups on the DEA-modified membrane surface is the main parameter for extra uniformly settlement of TiO₂ nanoparticles on the membrane surface. This procedure is a superior technique for modification of PES/PI nanofiltration membranes to enhance water flux and minimization membrane fouling.     

Characterization of lignin using multi-angle laser light scattering and atomic force microscopy

Small differences in the isolation techniques of lignin can result in significant changes in its molecular structure and configuration. Light scattering (evaluated at 18 different angles in a plane), Atomic Force Microscopy (AFM) and Near Infrared Spectroscopy (NIR) proved very effective for evaluating the characteristics of lignin. Zimm plots were generated using Zimm, Debye and Berry formalisms to evaluate the weight average molecular weight (MW), radius of gyration (r_g), hydrodynamic radius (r_h) and second virial coefficient (A₂). Two types of lignin and nine different solvents were used for the study, to analyze the conformation of lignin molecules in different solvents expected to be used in lignin degradation and subsequent analysis. Absolute MW and r_g decreased and the dn/dc increased when the solvent used for lignin was changed from water to sodium hydroxide. The two types of lignin also exhibited different values for all the above estimated parameters. This study also highlighted the differences between the unlyophilized and lyophilized lignin in terms of aggregation, pH dependence and stability over time. This aggregation has never been seen on a ultraviolet (UV) or refractive index (RI) detector that has been used so far for liquid chromatography (LC) reducing the reliability of lignin depolymerization data obtained without light scattering.     

Addition-type polynorbornene with Si(CH3)3 side groups: Detailed study of gas permeation and thermodynamic properties

Polymerization of norbornene bearing Si(CH₃)₃ groups in the five position with the opening of double bonds was performed. By accurate selection of the ratios catalyst/co-catalyst and monomer/catalyst the samples with increased molecular mass (about 400,000) were obtained. Transport parameters of this, addition type poly(trimethylsilyl norbornene) (PTMSN) were measured using the gas chromatographic and mass spectrometric methods for different gases (H₂, He, O₂, N₂, CO₂, CH₄, C₂H₆, C₃H₈ and n-C₄H₁₀). Temperature dependence of the permeability coefficients (P) indicated that low activation energies of permeation (E_P) and diffusion (E_D) are characteristic for PTMSN. In some cases (CO₂, C₂H₆) negative E_P values were observed. Thermodynamics of vapor sorption in this polymer was studied using the inverse gas chromatography method. It was shown that PTMSN is characterized by very large solubility coefficients S similar to those of poly(trimethylsilyl propyne) (PTMSP). The comparison of the P, D, and S values of these highly permeable polymers showed that the greater permeability of PTMSP is determined by the larger D values. Application of different approaches for the determination of the size of microcavities in PTMSN indicated that this polymer is characterized by large size of microcavity (800–1200 ?³).     

Excess enthalpies and (vapour + liquid) equilibrium data for the binary mixtures of dimethylsulphoxide with ketones

Excess enthalpies (H^E), at ambient pressure and T = 298.15 K, have been measured by using a solution calorimeter for the binary liquid mixtures of dimethyl sulphoxide (DMSO) with ketones, as a function of composition. The ketones chosen in the present investigation were methyl ethyl ketone (MEK), methyl isobutyl ketone (MIBK), and cyclohexanone (CH). The H^E values are positive over the entire composition range for the three binary mixtures. Furthermore, the (vapour + liquid) equilibrium (VLE) was measured at 715 Torr for these mixtures, of different compositions, with the help of Swietoslawski-ebulliometer. The experimental temperature-mole fraction (t-x) data were used to compute Wilson parameters and then used to calculate the equilibrium vapour-phase compositions as well as the theoretical points for these binary mixtures. These Wilson parameters are used to calculate activity coefficients (γ) and these in turn to calculate excess Gibbs free energy (G^E). The intermolecular interactions and structural effects were analyzed on the basis of the measured and derived properties.     

Characterization of new types of stationary phases for fast and ultra-fast liquid chromatography by signal processing based on AutoCovariance Function: A case study of application to Passiflora incarnata L. extract separations

In this study, a comparative investigation was performed of HPLC Ascentis^® (2.7 μm particles) columns based on fused-core particle technology and Acquity^® (1.7 μm particles) columns requiring UPLC instruments, in comparison with Chromolith™ RP-18e columns. The study was carried out on mother and vegetal tinctures of Passiflora incarnata L. on one single or two coupled columns. The fundamental attributions of the chromatographic profiles are evaluated using a chemometric procedure, based on the AutoCovariance Function (ACVF). Different chromatographic systems are compared in terms of their separation parameters, i.e., number of total chemical components (m_tot), separation efficiency (σ), peak capacity (n_c), overlap degree of peaks and peak purity. The obtained results show the improvements achieved by HPLC columns with narrow size particles in terms of total analysis time and chromatographic efficiency: comparable performance are achieved by Ascentis^® (2.7 μm particle) column and Acquity^® (1.7 μm particle) column requiring UPLC instruments. The ACVF plot is proposed as a simplified tool describing the chromatographic fingerprint to be used for evaluating and comparing chemical composition of plant extracts by using the parameters D% – relative abundance of the deterministic component – and c_EACF – similarity index computed on ACVF.     

(p, ρ, T) properties, and apparent molar volumes V? of ZnBr2 in methanol at T = (298.15 to 398.15) K and pressures up to p = 40 MPa

The (p, ρ, T) properties of pure methanol, the (p, ρ, T) properties and apparent molar volumes V_? of ZnBr₂ in methanol at T = (298.15 to 398.15) K and pressures up to p = 40 MPa are reported, and apparent molar volumes have been evaluated. The experimental (p, ρ, T, m) values were described by an equation of state. For the solutions the experiments were carried out at molalities m = (0.05772, 0.37852, 0.71585 and 1.95061) mol · kg⁻¹ of zinc bromide.     

Improvement of the analysis of the biochemical oxygen demand (BOD) of Mediterranean seawater by seeding control

Biochemical oxygen demand (BOD) is a useful parameter for assessing the biodegradability of dissolved organic matter in water. At the same time, this parameter is used to evaluate the efficiency with which certain processes remove biodegradable natural organic matter (NOM). However, the values of BOD in seawater are very low (around 2 mg O₂ L⁻¹) and the methods used for its analysis are poorly developed. The increasing attention given to seawater desalination in the Mediterranean environment, and related phenomena such as reverse osmosis membrane biofouling, have stimulated interest in seawater BOD close to the Spanish coast. In this study the BOD analysis protocol was refined by introduction of a new step in which a critical quantity of autochthonous microorganisms, measured as adenosine triphosphate, is added. For the samples analyzed, this improvement allowed us to obtain reliable and replicable BOD measurements, standardized with solutions of glucose-glutamic acid and acetate. After 7 days of analysis duration, more than 80% of ultimate BOD is achieved, which in the case of easily biodegradable compounds represents nearly a 60% of the theoretical oxygen demand. BOD₇ obtained from the Mediterranean Sea found to be 2.0 ± 0.3 mg O₂ L⁻¹ but this value decreased with seawater storage time due to the rapid consumption of labile compounds. No significant differences were found between two samples points located on the Spanish coast, since their organic matter content was similar. Finally, the determination of seawater BOD without the use of inoculum may lead to an underestimation of BOD.     

Comparison of physico-chemical pretreatment methods to seawater reverse osmosis: Detailed analyses of molecular weight distribution of organic matter in initial stage

In desalination, effective pretreatment is the key to reduce membrane fouling that occurs during the seawater reverse osmosis (SWRO) process. However, it is difficult to compare the flux decline after different pretreatments using a small-scale reverse osmosis filtration unit. In this study, we successfully evaluated the effect of pretreatment on SWRO in terms of molecular weight distribution (MWD) of seawater organic matter (SWOM) after 20 h of SWRO operation. Microfiltration (MF), ultrafiltration (UF), ferric chloride (FeCl₃) flocculation and powdered activated carbon (PAC) adsorption, were used as pretreatment. The effluents and the retentates after each pretreatment and 20 h of SWRO operation were characterized in terms of MWD.Although the normalized flux of SWRO showed similar flux decline (J/J₀ = 0.17) with/without pretreatment, SWOM concentration in the retentates after different pretreatments was different in quantity and it increased linearly with time. The slope of the SWOM increase was 0.110, 0.096, 0.077 and 0.059 after MF, FeCl₃ flocculation, UF and PAC adsorption pretreatments, respectively. MW peaks for the seawater used in this study consisted of 1200 Da (biopolymers), 950 Da (fulvic acids), 650 Da (hydrolysates of humic substances), 250 Da (low MW acids) and 90 Da (low MW neutrals and amphiphilics). FeCl₃ flocculation preferentially removed 1200 Da (biopolymers), while PAC adsorption mostly removed 950 Da (fulvic acids). UF and NF removed only a marginal amount of relatively large organics, while RO removed the majority of organics. The intensity of 1200, 950, 650 and 250 Da MW in the RO retentates increased with the RO operation time. The organics of MW around 1200 Da (biopolymers) had a relatively low rate of increase with time compared with those of lower MW. This suggests that the SWOM of 1200 Da MW was preferentially retained on the membrane surface.     

Determination of Activation Energies and the Optimum Temperatures of Hydrolysis of Starch by α-Amylase from Porcine Pancreas

The present paper reports the determination of the activation energies and the optimum temperatures of starch hydrolysis by porcine pancreas α-amylase. The parameters were estimated based on the literature data on the activity curves versus temperature for starch hydrolysis by α-amylase from porcine pancreas. It was assumed that both the hydrolysis reaction process and the deactivation process of α-amylase were first-order reactions by the enzyme concentration. A mathematical model describing the effect of temperature on porcine pancreas α-amylase activity was used. The determine deactivation energies E_a were from 19.82 ± 7.22 kJ/mol to 128.80 ± 9.27 kJ/mol, the obtained optimum temperatures T_opt were in the range from 311.06 ± 1.10 K to 326.52 ± 1.75 K. In turn, the values of deactivation energies E_d has been noted in the range from 123.57 ± 14.17 kJ/mol to 209.37 ± 5.17 kJ/mol. The present study is related to the starch hydrolysis by α-amylase. In the industry, the obtained results the values E_a, E_d, T_opt can be used to design and optimize starch hydrolysis by α-amylase porcine pancreas. The obtained results might also find application in research on the pharmaceutical preparations used to treat pancreatic insufficiency or prognosis of pancreatic cancer.