Search Results (24)

Tertiary amines such as N,N-dimethyl-cyclohexylamine (DMCHA) are recently explored as candidate solvents for the extraction and separation of lipids from algal biomass. DMCHA exhibits the interesting property of polarity switching which is based on the interaction of DMCHA with CO₂, termed CO₂ switching. Although this approach exhibits certain advantages, various issues have to be improved to address for example the duration required for process optimization, the energy demand, or the low solvent recovery. The aim of this work is the examination of amine recovery from an oil extract, utilizing strong electrolytes (SE) such as HCl for protonation and NaOH for deprotonation of amine, instead of conventional CO₂ switching. It was found that the acid based hydrophobic-to-hydrophilic switching and the alkali based hydrophilic-to-hydrophobic back-switching carried out in the order of few minutes, a considerably shorter time compared to few hours required by gas switching, resulting in addition to higher amine recovery. In addition, the combined CO₂ switching with SE-back switching using NaOH proved to be a promising approach for large-scale applications, exhibiting several advantages related to technical, economic, environmental and safety issues. Full article

Chemical emergencies in transport are rare but operationally demanding. This study presents a framework that converts the timeline of a real intervention involving a cyclohexylamine leak after a tanker truck overturned into a Petri net and subsequently into an absorbing Markov model. This provides decision-oriented indicators for the intervention phases and enables what-if analysis. Application to a case study shows that the capacity of the decontamination line has a significant impact on the duration of the incident resolution, while introducing a small probability of returning from technical measures to decontamination slightly prolongs the course while leaving the certainty of successful completion unchanged. Mapping between activities, Petri net locations, and aggregated states promotes transparency and the repeatability of procedures and highlights activities with a high number of repeat visits. The outputs are useful for decision making related to personnel and material resources, post-review analyses, and exercise planning. The limitations lie in calibration to a single incident, the partial use of expertly estimated parameters, and the approximate conversion of “steps” to time. Future work will focus on multiple cases, finer-grained time handling, and explicit capacity modelling. Full article

A malignant leakage presents a significant challenge in drilling engineering, particularly within carbonate formations, where such a leakage is frequently encountered. Currently, there is no effective solution to this problem. In this study, a water-reactive polyurethane sealing agent was developed using multifunctional polypropylene glycol and 1,4-butanediol (BDO) as soft segments, diphenylmethane diisocyanate (MDI) as the hard segment, and a composite catalyst consisting of N, N-dimethyl cyclohexylamine (PC-8) and dibutyltin dilaurate (T-12). The material reacts rapidly with water to form a high-strength gel, with the reaction time being controllable. Through experimental optimization, it was determined that the BDO mass fraction was 1%, and the molar ratio of isocyanate group to hydroxyl group was 1.8. Additionally, the gelation time can be controlled by adjusting the mass fraction of the composite catalyst. Experimental results from sand-bed and fracture-plate tests indicated that the material could withstand pressures exceeding 3 MPa at 93 °C and exhibited resistance to saturated NaCl and CaCl₂ environments. The plugging mechanism was investigated using scanning electron microscopy (SEM), thermogravimetric analysis (TGA), and Fourier-transform infrared (FTIR) spectroscopy. The results demonstrated that the agent formed a compact, micron-scale porous structure upon reacting with water, exhibiting excellent thermal stability and dual plugging performance through both physical and chemical mechanisms. Due to its water-reactive characteristics, a multi-stage injection process was adopted for field application design. This material shows promising potential for mitigating large-fracture-type malignant leakages in drilling operations. Full article

Reductive amination of cyclohexanone with NH₃ and H₂ over Rh and Rh-Ni catalysts on SiO₂ has been studied. Research has focused on the catalytic efficiency of monometallic and bimetallic catalysts in the production of cyclohexylamine, a key intermediate in the synthesis of numerous fine chemicals. Through the wet impregnation method, Rh and Rh-Ni catalysts with varying nickel loadings (1, 2, 5, and 10 wt.%) were synthesized and characterized using techniques such as N₂ physisorption, TEM, HAADF-STEM, XRD, XPS, H₂-TPR, and NH₃-TPD. The catalytic reactions were conducted under controlled conditions using a glass-coated reactor, using ammonia as nitrogen source. Rh-Ni bimetallic catalysts exhibited the highest conversion rates on reductive amination, attributed to enhanced dispersion and advantageous surface properties. High metal dispersion and small particle sizes were confirmed by TEM, HAADF-STEM, and XRD. XPS analysis confirmed the reduced state of Rh and mainly oxidized state of Ni, while H₂-TPR and NH₃-TPD results indicated improved reducibility and acidity, respectively, which are critical for catalytic activity. Monometallic Rh/SiO₂ catalyst showed 83.4% of conversion after 300 min and selectivity of 99.1% toward the desired product cyclohexylamine. The addition of nickel, a cheap and easily available metal, increases the activity without compromising selectivity. At 300 min of the reaction, the 2 wt.% NiRh/SiO₂ catalyst exhibited the highest conversion, yield, and selectivity for the desired product cyclohexylamine, 99.8%, 96.4%, and 96.6% respectively. Additionally, this catalyst is recyclable after the fourth cycle, showing 99.5% selectivity and 74.0% yield for cyclohexylamine at 75.7% conversion. Recycling tests confirmed the stability of bimetallic catalysts, maintaining performance over multiple cycles without significant deactivation. Full article

Cyclohexylamines are important and valuable key intermediates in the chemical industry, playing a crucial role in the synthesis of a variety of compounds. Developing a low-cost and efficient synthesis route for these chemicals is highly desirable but also presents significant challenges due to the complexity of the reactions involved. Herein, we designed three pathways for the production of 1,3-cyclohexanediamine (1,3-CHDA), including the one-pot reductive amination of resorcinol (RES) with ammonia and molecular hydrogen, the reductive amination of 1,3-cyclohexandione (1,3-CHD) with ammonia, and the oximation–hydrogenation of 1,3-CHD. Through systematical investigation, we finally developed a low-cost, simple operation and an efficient methodology for the synthesis of 1,3-CHDA as follows: RES was firstly hydrogenated in H₂O over Raney Ni to obtain 1,3-CHD, and then the obtained liquid reaction mixture was used directly for the subsequent oximation with hydroxylamine hydrochloride without further purification to form the oxime intermediate, followed by the hydrogenation of the oxime in methanol over Raney Ni to achieve the target product 1,3-CHDA with a high yield. Full article

In this investigation, the parent clay mineral montmorillonite (Mnt) was acid activated using sulfuric acid (H₂SO₄) at a specific mass of acid to clay mineral of 0.2 (A-Mnt) prior to the preparation of the porous clay heterostructure precursor. The derived porous acid-activated clay heterostructure (PACH) exhibited properties different from those of the conventional one (PCH). The synthesized materials were characterized using different physiochemical techniques, such as X-ray fluorescence (XRF), powder X-ray diffraction (XRD), thermogravimetric analysis (TA), ²⁹Si MAS-NMR, nitrogen adsorption–desorption, and acidity using cyclohexylamine (CHA) as a probe molecule. The PACH had a surface area of 890 m²/g and an acidity of 0.56 mmol of protons/g. An evaluation of PCH materials was conducted to assess their effectiveness in removing basic blue 41 (BB-41) from aqueous solutions. The removal process was analyzed based on the initial concentration and pH of the BB-41 solution, and the amount of solid used, employing a batch approach. The removal efficiency was found to be greater at higher pH values, specifically between six and nine. Using the Langmuir model, the maximal removal capabilities of the studied materials were determined to be between 274 and 300 mg/g. According to the results of the regeneration tests, PACH materials could still be employed after seven cycles with a 25% efficiency loss and a 50% efficiency loss for PCH materials. Utilizing the Langmuir model equations and mass balance, a single-stage batch design was suggested to estimate the required masses to remove BB-41 at different percentages from a starting concentration of 200 mg/L. Full article

The present work details the development of carbon fiber-reinforced epoxy membranes with excellent rejection of small-molecule dyes. It is a proof-of-concept for a more sustainable membrane design incorporating carbon fibers, and their recycling and reuse. 4,4′-methylenebis(cyclohexylamine) (MBCHA) polymerized with either bisphenol-A-diglycidyl ether (BADGE) or tetraphenolethane tetraglycidylether (EPON Resin 1031) in polyethylene glycol (PEG) were used to make monolithic membranes reinforced by nonwoven carbon fibers. Membrane pore sizes were tuned by adjusting the molecular weight of the PEG used in the initial polymerization. Membranes made of BADGE-MBCHA showed rejection of Rose Bengal approaching 100%, while tuning the pore sizes substantially increased the rejection of Methylene Blue from ~65% to nearly 100%. The membrane with the best permselectivity was made of EPON-MBCHA polymerized in PEG 300. It has an average DI flux of 4.48 LMH/bar and an average rejection of 99.6% and 99.8% for Rose Bengal and Methylene Blue dyes, respectively. Degradation in 1.1 M sodium hypochlorite enabled the retrieval of the carbon fiber from the epoxy matrix, suggesting that the monolithic membranes could be recycled to retrieve high-value products rather than downcycled for incineration or used as a lower selectivity membrane. The mechanism for epoxy degradation is hypothesized to be part chemical and part physical due to intense swelling stress leading to erosion that leaves behind undamaged carbon fibers. The retrieved fibers were successfully used to make another membrane exhibiting similar performance to those made with pristine fibers. Full article

Commercial NH₄-Beta and Na-ZSM-5 zeolites were fluorinated with different amounts of NH₄F and using different procedures (room temperature, conventional refluxing, microwave refluxing). Samples were characterized by XRD, N₂ physisorption, FTIR, ¹H NMR, SEM-EDS, and TGA of adsorbed cyclohexylamine. An increase in the concentration of NH₄F led to fluorinated zeolites with higher surface areas and slightly lower amounts of Brønsted acid sites due to some dealumination. Fluorination by conventional or microwave refluxing at shorter times did not dealuminate ZSM-5, resulting in the formation of higher particle sizes. Ni/fluorinated beta catalysts were more active than Ni/fluorinated ZSM-5 catalysts for the hydrodeoxygenation of guaiacol at 180 °C and 15 bar of H₂ for 1 h due to their higher amount of acid sites. The appropriate proportion of metallic and Brønsted acid centers allowed for the selective obtention of cyclohexane (58%) for the Ni supported on beta fluorinated with NH₄F 0.1 M catalyst. The combination of this fluorinated beta to a Ni/ordered mesoporous carbon catalyst significantly boosted its selectivity to cyclohexane from 0 to 65%. Fluorinated ZSM-5 samples, although having stronger Brønsted acid sites, as observed by ¹H NMR, they had lower amounts, leading to higher selectivity to cyclohexanol when used as catalytic supports. Full article

Materials with monolithic structures, such as epoxy monoliths, are used for a variety of applications, such as for column fillers in gas chromatography and HPLC, for separators in lithium-ion batteries, and for precursor polymers for monolith adhesion. In this study, we investigated the fabrication of epoxy monoliths using 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane (TETRAD-C) as the tetrafunctional epoxy and 4,4′-methylenebis(cyclohexylamine) (BACM) as the amine curing agent to control pore diameters using polyethylene glycols (PEGs) of differing molecular weights as the porogenic agents. We fabricated an epoxy monolith with micron-order pores and high strength levels, and which is suitable for the precursors of composite materials in cases where smaller PEGs are used. We discussed the effects of the porous structures of monoliths on their physical properties, such as tensile strength, elongation, elastic modulus, and glass transition temperatures. For example, epoxy monoliths prepared in the presence of PEGs exhibited an elastic modulus less than 1 GPa at room temperature and Tg values of 175–187 °C, while the epoxy bulk thermoset produced without any porogenic solvent showed a high elastic modulus as 1.8 GPa, which was maintained at high temperatures, and a high Tg of 223 °C. In addition, the unique adhesion characteristics of epoxy monolith sheets are revealed as a result of the combinations made with commercial epoxy and acrylic adhesives. Epoxy monoliths that are combined with conventional adhesives can function as sheet-type adhesives purposed with avoiding problems when only liquid-type adhesives are used. Full article

Leishmaniasis is considered one of the most untreated tropical diseases in the world. In this study, we investigated the in vitro leishmanicidal activity and cytotoxicity of various isolated lichen substances, including atranorin (1), usnic acid (2), gyrophoric acid (3), salazinic acid (4), galbinic acid (5), and parietin (6), and some semi-synthetic imine derivatives of usnic acid (7, 8, 9) and atranorin (10, 11, 12, 13). Imine condensation reactions with hydrazine and several amines were assisted by microwave heating, an efficient and eco-friendly energy source. The most interesting result was obtained for compound 2, which has high leishmanicidal activity but also high cytotoxicity. This cytotoxicity was mitigated in its derivative, 9, with better selectivity and high antileishmanic activity. This result may indicate that the usnic acid derivative (9) obtained using condensation with two cyclohexylamine groups is a promising lead compound for the discovery of new semisynthetic antiparasitic drugs. Full article

Heat-resistant polymers with an intense, visible photoluminescence (PL) functionality are presented. A polybenzoxazole (PBO) containing hexafluoroisopropylidene (HFIP) side groups exhibited an intense purple PL with a quantum yield, Φ_PL, of 0.22 (22%), owing to the effectively disturbed concentration quenching (CQ) in the fluorophore units by the bulky HFIP side groups. The chain ends of a wholly cycloaliphatic polyimide (PI), derived from 1,2,3,4-cyclobutanetetracarboxylic dianhydride (CBDA) and 4,4′-methylenebis(cyclohexylamine) (MBCHA), were modified with conjugated monoamines. The PI derived from 2,3,6,7-naphthalenetetracarboxylic dianhydride (2,3,6,7-NTDA) and MBCHA exhibited a very high glass transition temperature (T_g = 376 °C) and purple fluorescence from the S₁(π,π*) state. However, its Φ_PL value was lower than expected. A pronounced effect of fluorophore dilution using CBDA on the PL enhancement was observed. This is closely related to the planar structure of the 2,3,6,7-NTDA-based diimide units. By contrast, the counterpart using an 2,3,6,7-NTDA isomer, 1,4,5,8-NTDA, was virtually non-fluorescent, despite its sufficient dilution using CBDA. The PI film obtained using 3,3″,4,4″-p-terphenyltetracarboxylic dianhydride (TPDA) with a non-coplanar structure and MBCHA exhibited an intense blue fluorescence spectrum (Φ_PL = 0.26) peaking at 434 nm. The dilution approach using CBDA enhanced its fluorescence up to a high Φ_PL value of 0.41. Even when TPDA was combined with an aromatic diamine, 2,2′-bis(trifluoromethyl)benzidine (TFMB), the intense blue fluorescence was observed without charge-transfer fluorescence. A semi-cycloaliphatic PI derived from TFMB and a novel cycloaliphatic tetracarboxylic dianhydride, which was obtained from a hydrogenated trimellitic anhydride derivative and 4,4′-biphenol, was used as another host polymer for 9,10-bis(4-aminophenyl)anthracene (BAPA). The BAPA-incorporating PI film resulted in a significant PL enhancement with a considerably high Φ_PL of 0.48. This PI film also had a relatively high T_g (265 °C). A reactive dye, N,N′-bis[4-(4-amino-3-methylbenzyl)-2-methylphenyl]-3,4,9,10-perylenetetracarboxydiimide, was harnessed as a fluorescence probe to explore transamidation between polyimide precursors in solution. Full article

The production of renewable chemicals using lignocellulosic biomass has gained significant attention in green chemistry. Among biomass-derived chemicals, secondary amines have emerged as promising intermediates for synthetic applications. Here, we report a systematic study on the reductive amination of phenolics with cyclohexylamine using Pd/C and Rh/C as catalysts. The catalytic tests were performed in batch reactors under different reaction conditions (various: amine concentration (0.1–0.4 mol/L), hydrogen pressure (0–2.5 bar), temperature (80–160 °C), and substituted phenols (phenol, o-cresol, p-cresol, and methoxyphenol)) and using tert-amyl alcohol as a solvent. The experimental observations were consistent with a multi-step mechanism, where hydrogenation of phenol to cyclohexanone is followed by condensation of the ketone with cyclohexylamine to form an imine, which is finally hydrogenated to produce secondary amines. In addition, there was evidence of parallel self-condensation of the cyclohexylamine. The study also supported a limited dehydrogenation capacity of Rh/C, unlike Pd/C, which increases this capacity at higher temperatures generating a higher yield of cyclohexylaniline (up to 15%). The study of the alkylated phenols demonstrated that the nature and propensity of hydrogenation of the phenolic controls their amination. Kinetic analysis revealed reaction orders between 0.4 and 0.7 for H₂, indicating its dissociative adsorption. Meanwhile, phenol’s order (between 1–1.8) suggests a single participation of this compound in the hydrogenation step. The order of 0.4 for cyclohexylamine suggests its participation as a surface-abundant species. The apparent activation energies derived from a power law approximation were of 37 kJ/mol and 10 kJ/mol on Pd/C and Rh/C, respectively. Full article

Treatment of the double nuclear complex 1a, di-μ-cloro-bis[N-(4-formylbenzylidene)cyclohexylaminato-C6, N]dipalladium, with Ph₂PCH₂CH₂)₂PPh (triphos) and NH₄PF₆ gave the single nuclear species 2a, 1-N-(cyclohexylamine)-4-N-(formyl)palladium(triphos)(hexafluorophasphate). Reaction of 2a with Ph₂PCH₂CH₂NH₂ in refluxing chloroform via a condensation reaction of the amine and formyl groups to produce the C=N double bond, gave 3a, 1-N-(cyclohexylamine)-4- N-(diphenylphosphinoethylamine)palladium(triphos)(hexafluorophasphate); a potentially bidentate [N,P] metaloligand. However, attempts to coordinate a second metal by treatment of 3a with [PdCl₂(PhCN)₂] were to no avail. Notwithstanding, complexes 2a and 3a left to stand in solution spontaneously self-transformed to give in either case the double nuclear complex 10, 1,4-N,N-terephthalylidene(cyclohexilamine)-3,6-[bispalladium(triphos)]di(hexafluorophosphate), after undergoing further metalation of the phenyl ring, then bearing two mutually trans [Pd(Ph₂PCH₂CH₂)₂PPh)-P,P,P] moieties: an unprecedented and serendipitous result indeed. On the other hand, reaction of the double nuclear complex 1b, di-μ-cloro-bis[N-(3-formylbenzylidene)cyclohexylaminato-C6, N]dipalladium, with Ph₂PCH₂CH₂)₂PPh (triphos) and NH₄PF₆ gave the single nuclear species 2b, 1-N-(cyclohexylamine)-4-N-(formyl)palladium(triphos)(hexafluorophasphate), Treatment of 2b with H₂O/glacial MeCOOH gave cleavage of the C=N double bond and of the Pd···N interaction, yielding 5b, isophthalaldehyde-6-palladium(triphos)hexafluorophosphate, which then reacted with Ph₂P(CH₂)₃NH₂ to yield complex 6b, N,N-(isophthalylidene(diphenylphosphinopropylamine)-6-(palladiumtriphos)di(hexafluorophosphate), with two pairs of non-coordinated nitrogen and phosphorus donor atoms. Treatment of 6b with [PdCl₂(PhCN)₂], [PtCl₂(PhCN)₂], or [PtMe₂(COD)] gave the new double nuclear complexes 7b, 8b and 9b, palladiumdichloro-, platinumdichloro- and platinumdimethyl[N,N-(isophthalylidene(diphenylphosphinopropylamine)-6-(palladiumtriphos)(hexafluorophosphate)-P,P], respectively, showing the behavior of 6b as a palladated bidentate [P,P] metaloligand. The complexes were fully characterized by microanalysis, IR, ¹H, and ³¹P NMR spectroscopies, as appropriate. The X-ray single-crystal analyses for compounds 10 and 5b have been previously described as the perchlorate salts by JM Vila et al. Full article

Catalytic hydrogenation of nitrocyclohexane proved to be an attractive alternative source of various chemical compounds: cyclohexanone oxime, cyclohexanone, cyclohexanol, cyclohexylamine and dicyclohexylamine. A growing interest in this reaction has been observed in the last few years. Herein, we present the catalytic performance of Cu/SiO₂, Co/SiO₂ and CuCo/SiO₂ in gas and liquid flow nitrocyclohexane hydrogenation. The analysis of synthesized catalysts morphology (BET, TPR, XRD, TEM) in terms of their catalytic behavior allows us to draw general conclusions and determine the optimal conditions for the production of desired products. Application of the monometallic copper leads to the formation of cyclohexanone as the main product, but with low activity. On the other hand, Co/SiO₂ shows high activity but gives cyclohexylamine. Bimetallic system CuCo(3:1)/SiO₂ allows for the efficient production of 100% cyclohexanone at 5 bar and 75 °C. Full article

A versatile, functional nanomaterial for the removal of ionic and non-ionic pollutants is presented in this work. For that purpose, the high charge mica Na-4-Mica was exchanged with the cationic surfactant (C₁₆H₃₃NH(CH₃)₂)⁺. The intercalation of the tertiary amine in the swellable nano-clay provides the optimal hydrophilic/hydrophobic nature in the bidimensional galleries of the nanomaterial responsible for the dual functionality. The organo-mica, made by functionalization with C₁₆H₃₃NH₃⁺, was also synthesized for comparison purposes. Both samples were characterized by X-ray diffraction techniques and transmission electron microscopy. Then, the samples were exposed to a saturated atmosphere of cyclohexylamine for two days, and the adsorption capacity was evaluated by thermogravimetric measurements. Eu³⁺ cations served as a proof of concept for the adsorption of ionic pollutants in an aqueous solution. Optical measurements were used to identify the adsorption mechanism of Eu³⁺ cations, since Eu³⁺ emissions, including the relative intensity of different f–f transitions and the luminescence lifetime, can be used as an ideal spectroscopic probe to characterize the local environment. Finally, the stability of the amphiphilic hybrid nanomaterial after the adsorption was also tested. Full article