This paper details an investigation into the separation of Hexamethylenediamine (HMD) from dilute aqueous solutions by exploiting phase separation. HMD is a monomer used in the production of ...Nylon-6,6 and as such this separation is potentially useful in extracting purifying HMD produced from biological sources or reclaimed from waste made by the production of nylon. An investigation was undertaken into the effect of using sodium hydroxide (NaOH) to promote the phase separation, and a model was derived to predict this behaviour. Furthermore, the effect of various salts on this phase separation was investigated, and it was found that sodium sulphate and sodium carbonate promote the phase separation, but are unable to cause phase separation without the presence of sodium hydroxide.
•Hexamethylenediamine and sodium hydroxide are each individually soluble in water, but when both are present phase separation can occur.•The amount of sodium hydroxide required to cause phase separation decreases with increasing concentration of hexamethylenediamine.•A mathematical model was developed for the concentrations of each species in samples which undergo phase separation.•Various salts were shown to have a shown to have positive or negative effect on the formation of the secondary phase.•No salt was able to cause the formation of a secondary phase in the absence of any sodium hydroxide.
In this study, attapulgite (ATP) was modified by Zr-based metal organic framework (UiO-66-NH2) and poly(hexamethylenediamine-tannic acid) (HTA), an amino material named UiO-66-NH2/HTA/ATP (UHA) was ...prepared to efficiently remove Cr(VI). The morphology and structure of UHA were analyzed through various characterization methods. The conditions and influencing factors of UHA preparation and Cr(VI) adsorption were studied. The material had a maximum adsorption capacity of 270.3 mg/g for Cr(VI) when pH was 2.0, temperature was 298 K, adsorption time was 300 min, and ionic strength was 0.01 mol/L, which was obtained by the Langmuir fitting model. The adsorption process conforms to the pseudo-second-order kinetic and Langmuir isothermal models, indicating that the adsorption process is mainly based on the chemical adsorption of monolayers. X-ray photoelectron spectroscopy analysis shows that UHA mainly removes Cr(VI) by hydrogen bonding, electrostatic attraction, reduction, and complexation. Thermodynamic investigation suggested a disordered, endothermic and spontaneous adsorption process. After UHA treatment, the simulated wastewater containing Cr(VI) met the discharge standard, and the results of cycling experiments showed that UHA has good renewable performance and offers potential prospects for Cr(VI) removal in water.
The graphical abstract shows the preparation process of UHA composite material and the adsorption removal mechanism of Cr(Ⅵ) by UHA. As shown in the Graphical abstract, UHA composite materials was prepared by a two-step process. And UHA can remove Cr(Ⅵ) by adsorption through electrostatic interaction, hydrogen bonding as well as reduction and coordination. Display omitted
•Amounts of Cr(Ⅵ) adsorbed onto UHA were highly enhanced by HTA and MOFs.•UHA has excellent adsorption performance and high selectivity for Cr(VI).•UHA has good regenerative properties.•UHA can not only adsorb fixed Cr(Ⅵ), but also partially reduce it to low-toxicity Cr(Ⅲ).
In this investigation, a novel aqueous Hexamethylenediamine (HMDA) and 2-Dimethylaminoethanol (DMAE) amine blend was made to capture CO2, which would strongly contribute towards net-zero emission. ...The capability of the novel amine blend was investigated by conducting CO2 absorption and desorption experiments. The major research findings were equilibrium CO2 loading (α), cyclic capacity, heat duty, regeneration efficiency, CO2 absorption and desorption rate, pH, density, 13C NMR and FTIR characterization, process optimization, and toxicity assessment. CO2 absorption experimental operating conditions: temperature (T) = 298.15–333.15 K, CO2 partial pressure (PCO2) = 10.13–25.33 kPa, mole fraction of HMDA (mHMDA) = 0.05–0.20, and solution concentration (C) = 1–3 mol/L. The optimum equilibrium CO2 loading was found to be 1.2174 mol CO2/mol amine at T = 298.15 K, PCO2 = 25.33 kPa, mHMDA = 0.20, and C = 1 mol/L. Similarly, desorption experiments were performed at constant T = 393.15 K and PCO2 = 25.33 kPa. For C = 3 mol/L, cyclic capacity was 1.5951 mol CO2/L solution, which was 61.77 % higher than the benchmark 30 wt% monoethanolamine (MEA). The heat duty and regeneration efficiency for 3 mol/L solution were calculated to be 131.24 kJ/mol CO2 and 60.47 %, respectively. The novel amine blend's heat of CO2 absorption was calculated to be −75.50 kJ/mol. Response surface methodology (RSM) was used for modeling and optimization: αoptimum = 1.04583 mol CO2/mol amine at T = 306.90 K, PCO2 = 21.53 kPa, mHMDA = 0.16 and C = 1.5 mol/L.
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•Novel aqueous HMDA + DMAE amine blend yielded, αmax = 1.2174 mol CO2/mol amine.•13C NMR and FTIR techniques characterized various HMDA + DMAE amine blend samples.•Heatdutyblend: 70.83 % < 30 wt% MEA and regeneration efficiency = 60.47 %.•Modeling and optimization of equilibrium CO2 loading was done by RSM–CCD approach.•Based on LD50 value, novel aqueous amine of HMDA + DMAE is slightly toxic.
•Butanol is suitable for extracting hexamethylenediamine from dilute aqueous solution.•Addition of sodium hydroxide resulted in improved separation.•Model derived to predict partitioning of HMD ...between aqueous and organic phases.•Extraction of HMD produced biologically or reclaimed from nylon recycling.
This paper details an investigation into the separation of hexamethylenediamine (HMD) from dilute aqueous solutions by solvent extraction. This separation is potentially useful in (i) reclaiming HMD from waste generated in the production of nylon, (ii) for extracting HMD produced by fermentation, or (iii) reclaiming it from waste emanating from the depolymerization of nylon during recycling. Butanol was identified as a suitable solvent for the preferential dissolution of HMD from an aqueous solution, and it was found that the addition of sodium hydroxide resulted in improved separation. It was deduced that HMD has a bridging effect on the partial miscibility of water and butanol, and approximately 10 wt% of HMD was sufficient to allow for complete miscibility and the avoidance of phase separation. However, the addition of NaOH to the system reversed this bridging effect and reduced the solubility of butanol in the aqueous phase whilst also increasing the partitioning of HMD between the organic and aqueous phase.
A model for an equilibrium mixer-settler unit was developed with three important findings emerging. Firstly, the amount of water which could be dissolved in the organic phase was found to increase with the amount of HMD present, although this effect was neutralised by the presence of sufficient NaOH. Secondly, the amount of butanol which could be dissolved in the aqueous phase was found to decrease as the amount of NaOH present increased but was largely independent of the amount of HMD. Lastly, the partitioning coefficient of HMD was found to decrease as the amount of HMD increased but increased as the molar ratio of NaOH to HMD was raised. Fitted equations for these three findings allowed closure to be achieved. This model predicted a set of operating conditions giving 99.95% extraction of a very dilute aqueous HMD solution (1 wt%), including a doubling of the HMD concentration in the organic product.
•We have synthesized a novel molecule by a green method.•The calculated bond distances and bond angles showed good agreement with the literature.•The IR vibrational frequencies are calculated, and ...the fundamental bands are assigned and compared with the experimental data.•The GIAO 1H and 13CNMR chemical shift values correlated well with the experimental data.•The conformational analysis shows some important facts about this Schiff base.
The study focuses on the green synthesis of a novel bis-Schiff base (EE) derived from 4-N, N-dimethylaminobenzaldehyde, and hexamethylenediamine. The structural properties of the bis-Schiff base were investigated using experimental methods such as IR, 1HNMR, 13CNMR, and elemental analyses (CHN). Computer simulation using Gaussian03 software at DFT/B3LYP/6–311 G (d, p) level of theory was also used to identify the structural parameters, geometrical isomers, conformational analysis, Mulliken charges, optical properties, frontier orbitals, electrostatic potential map and chemical reactivity descriptors of the bis-Schiff base. The formation mechanism of EE and its geometrical isomers were studied. The study compares theoretical and experimental IR, 1HNMR, and 13CNMR spectra, highlighting the importance of green chemistry in reducing toxic organic solvents and chemicals.
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•Measurement of physico-chemical properties of ternary (HMDA + SG + H2O) solvent.•Experimental measurement and modelling of CO2 solubility in aqueous (HMDA + SG).•Investigation of CO2 absorption ...kinetics in aqueous (HMDA + SG).•Development of rate model based on the zwitterion mechanism.
Equilibrium solubility and absorption kinetics of CO2 in hexamethylenediamine (HMDA) activated aqueous sodium glycinate (SG) solvent are measured in the temperature range of 313–333 K. For the experimental investigation, HMDA concentration in the solvent is varied in the range of 5–15 mass% keeping total amine concentration at 30 mass%. Solubility data is presented in the form CO2 loading (mole CO2 absorbed per mole of total amine). Kinetics of CO2 absorption is evaluated assuming pseudo first order reaction condition. Both solubility and kinetics of CO2 absorption are found to enhance significantly due to addition of small amount of HMDA in the aqueous SG solvent. CO2 loading data is correlated using modified Kent-Eisenberg model. For developing kinetic model, overall rate is assumed to be the combined rate contribution of CO2-HMDA and CO2-SG reaction system. Based on this concept, a kinetic model is proposed using zwitterion mechanism for both the component reaction system. Kinetic and solubility models developed in this work are in good agreement with the experimental data with average absolute deviation of 7.4% and 4.5% respectively.
Biocidal disinfectants (BDs) that kill microorganisms or pathogens are widely used in hospitals and other healthcare fields. Recently, the use of BDs has rapidly increased as personal hygiene has ...become more apparent owing to the pandemic, namely the coronavirus outbreak. Despite frequent exposure to BDs, toxicity data of their potential neurotoxicity (NT) are lacking. In this study, a human-derived SH-SY5Y/astrocyte was used as a co-culture model to evaluate the chemical effects of BDs. Automated high-content screening was used to evaluate the potential NT of BDs through neurite growth analysis. A set of 12 BD substances classified from previous reports were tested. Our study confirms the potential NT of benzalkonium chloride (BKC) and provides the first evidence of the potential NT of poly(hexamethylenebicyanoguanide-hexamethylenediamine) hydrochloride (PHMB). BKC and PHMB showed significant NT at concentrations without cytotoxicity. This test system for analyzing the potential NT of BDs may be useful in early screening studies for NT prior to starting in vivo studies.
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•SH-SY5Y and astrocyte co-culture model may be useful for in vitro evaluation of neurotoxicity.•BKC and PHMB induced neurotoxicity at non-cytotoxic concentrations.•Provides new insights into the neurotoxicity of BKC and PHMB.
An innovative approach for immobilizing α-amylase was used in this investigation. The acrylic fabric was first treated with hexamethylene diamine (HMDA) and then coated with copper ions that were ...later reduced to copper nanoparticles (CuNPs). The corresponding materials obtained, Cu(II)@HMDA-TA and CuNPs@HMDA-TA, were employed as carriers for α-amylase, respectively. The structural and morphological characteristics of the produced support matrices before and after immobilization were assessed using various techniques, including FTIR, SEM, EDX, TG/DTG, DSC, and zeta potential. The immobilized α-amylase exhibited the highest level of activity at pH 7.0, with immobilization yields observed for CuNPs@HMDA-TA (81.7 %) (60 unit/g support) followed by Cu(II)@HMDA-TA (71.7 %) (49 unit/g support) and 75 % and 61 % of activity yields, and 91.7 % and 85 % of immobilization efficiency, respectively. Meanwhile, biochemical characterizations of the activity of the soluble and immobilized enzymes were carried out and compared. Optimal temperature, pH, kinetics, storage stability, and reusability parameters were optimized for immobilized enzyme activity. The optimal pH and temperature were recorded as 6.0 and 50 °C for soluble α-amylase while the two forms of immobilized α-amylase exhibit a broad pH of 6.0–7.0 and optimal temperature at 60 °C. After recycling 15 times, the immobilized α-amylase on CuNPs@HMDA-TA and Cu(II)@HMDA-TA preserved 63 % and 52 % of their activities, respectively. The two forms of immobilized α-amylase displayed high stability when stored for 6 weeks and preserved 85 % and 76 % of their activities, respectively. Km values were calculated as 1.22, 1.39, and 1.84 mg/mL for soluble, immobilized enzymes on CuNPs@HMDA-TA, and Cu(II)@HMDA-TA, and Vmax values were calculated as 36.25, 29.68, and 21.57 μmol/mL/min, respectively. The total phenolic contents of maize kernels improved 1.4 ± 0.01 fold after treatment by two immobilized α-amylases.
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•α-Amylase was immobilized on CuNPs@HMDA-TA with high efficiency.•The immobilized enzyme was characterized by FTIR, SEM, TG/DTG, DSC, and zeta potential.•Immobilization improved reusability and storage stability.•Immobilization of α-amylase on CuNPs@HMDA-TA opens new opportunities for food industries.
Renewable chemicals, which could potentially replace crude oil-derived chemicals, have been receiving increased interest due to their environment-friendliness (i.e., carbon neutrality). Nylon 66 and ...nylon 6 are synthetic polymers that are widely used in daily life, synthesized by polycondensation of adipic acid and hexamethylenediamine (HMDA) and by ring-opening polymerization of ε-caprolactam, respectively. This review assesses catalytic productions of these three monomers from food waste. The food waste-based routes to the target compounds are analyzed separately and compared to conventional petroleum-based routes. Even though no commercially available methods to directly convert food waste into the target molecules exist, we have suggested emerging and promising catalytic routes via combined processes. The proposed pathways for the renewable production of adipic acid, HMDA, and ε-caprolactam are not yet fully competitive with petrochemical pathways due to higher costs and lower process efficiencies. However, considering that the renewable food waste-based routes are still being developed, their commercialization should happen soon.
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•Renewable routes from food waste to monomeric precursors of Nylon are proposed.•Ways to convert food waste into the monomeric compounds for manufacturing nylon are discussed.•Current challenges and prospects for the renewable chemical production are highlighted.
