Dehydrochlorination Reaction Research Articles

Plasma-enhanced atomic layer deposition of carbon films employing a cyclic process of N2/H2 plasma and α, α’-dichloro-p-xylene as a precursor

A novel concept and process were proposed for the plasma-enhanced atomic layer deposition (PE-ALD) of carbon films. α, α’-dichloro-p-xylene (DCX) was used to form the adsorption layer, which was modified using nitrogen/hydrogen (N2/H2) plasma. Through iterative molecular chemisorption and end-group substitution processes, the selective and precise control of carbon deposition by PE-ALD was achieved. The growth per cycle of this process was estimated to be 0.02–0.05 nm/cycle. To determine the chemical reactions that occurred during the PE-ALD process, the IR spectra observed using in-situ Fourier transform infrared spectroscopy were analyzed. The decrease in the Si-OH bond at 3740 cm−1 and the saturation of the increase in CH bending at 1250 cm−1 revealed that the deposition of a DCX monolayer via a dehydrochlorination reaction with isolated OH bonding on SiO2 has been successfully achieved. The change in N(−H)x stretching during the N2/H2 plasma treatment indicated the substitution of exposed C-Cl bonding with C-NH2 bonding on the chemisorbed DCX monolayer surface. Additionally, the composition of the carbon films after 200-cycle PE-ALD was analyzed. Finally, the realization of the concept for PE-ALD of carbon film was confirmed by surface analysis.

Process intensification of heterogeneous dehydrochlorination of β-chlorohydrins by using n-propanol as co-extractant

The synthesis of terminal epoxides, which are vital components in pharmaceuticals and resins, often involves dehydrochlorination of β-chlorohydrins. Although intrinsic kinetics indicate that the dehydrochlorination reaction in the presence of sodium hydroxide could be very rapid, the practical implementation could always be hindered by long reaction time and low conversion rate. Extended contact between the product and the alkaline solution can lead to hydrolysis of the epoxy group, thus necessitating the process intensification to realize higher production efficiency and selectivity. Here, by characterizing thermodynamic equilibrium data and in-situ recording of the reaction that proceeded in a constant interphase reactor, the heterogeneous dehydrochlorination is demonstrated to occur primarily in the organic phase, and the overall reaction rate depends on the equilibrium concentration of sodium alkoxides. This finding, which is fundamentally different from the traditional view that chlorohydrin is first dissolved in the aqueous phase and then reacts with NaOH, leads us to use inert alcohols to assist in the extraction of NaOH. Based on this method, the reaction time can be reduced over 80 % both in batch and continuous reactors. Besides, the method is demonstrated to be effective in the dehydrochlorination of five different long-chain β-chlorohydrins.

Performance Study of Catalysts for Dehydrochlorination Reaction of 1,1,2-TCE Using In Situ FTIR-MS

Performance Study of Catalysts for Dehydrochlorination Reaction of 1,1,2-TCE Using In Situ FTIR-MS

Synthesis, characterization and performance evaluation of a nontoxic functional plasticizer for poly(vinyl chloride) derived from sustainable lactic acid

The use of plasticizers is crucial in enhancing the flexibility of engineering plastics. Currently, the primary plasticizers employed in poly(vinyl chloride) materials are nonrenewable phthalates. These exhibit a detrimental impact on the environment and human health owing to their toxic benzene ring structure. Consequently, the development of easily synthesizable, green plasticizers with excellent properties using biobased resources has been a long-standing objective in the field of resin plasticizing. Herein, we synthesized a branched lactic acid ester (BLAE) plasticizer using esterification and acid anhydride end-capping methods. Further, we investigated its application performance and oral toxicity. The abundance of polar ester groups in the oligolactic acid structure enables them to form secondary bonds with polymer chains. This results in a glass transition temperature is 59% less than that of pure poly(vinyl chloride), thereby improving the mechanical properties of the material. The addition of the BLAE plasticizer not only improved the thermal stability of the compound film but also effectively reduced the self-catalytic dehydrochlorination reaction of poly(vinyl chloride). This overcomes the limitations of unmodified poly(vinyl chloride), such as performance deterioration and color variation due to light exposure. Furthermore, the hydrophobicity of the compound film was substantially enhanced, resulting in outstanding antifouling and self-cleaning properties. These findings suggest that lactic acid-based plasticizer exhibits comparable or even superior overall performance when compared to commercially available plasticizers such as dioctyl phthalate and acetyl tributyl citrate. This work not only addresses the gap in the toxicity assessment of lactic acid plasticizers but also demonstrates their nontoxic characteristics in acute oral toxicity tests. This research offers novel insights into the green synthesis and functional development of biobased plasticizers, showcasing considerable potential for the substituting of dioctyl phthalate.

Catalyst Deactivation Process in 1,1,2-TCE Catalytic Dehydrochlorination Reaction

Catalyst Deactivation Process in 1,1,2-TCE Catalytic Dehydrochlorination Reaction

Lifetime prediction and aging mechanism of unplasticized polyvinyl chloride filled with calcium carbonate under long-term thermal and oxidative conditions

The successful implementation of the low-carbonization strategy is heavily reliant on the development of low-loss and high-efficiency green antenna technology. However, long-term exposure to high heat and oxygen leads to the degradation of antenna materials and the release of harmful substances. Studies on the aging behavior and mechanism of the antenna materials are of essence to realize the low-carbonization strategy. To address this issue, an unplasticized polyvinyl chloride filled with calcium carbonate (uPVC/CaCO3) has been successfully prepared using the injection molding technique. After that, the aging behavior, mechanism, and working lifetime were comprehensively explored under thermal and oxidative conditions. It is found that the composite maintains a high level of functionality for up to 24 years at 60 ℃ and 4.5 years at 70 ℃ on the impact strength failure criterion. The simultaneous oxidation and dehydrochlorination reaction, cross-linking reaction, and deterioration of the interaction between components are responsible for the aging of the uPVC/CaCO3 composite. These findings provide valuable insights into the development of radome materials for achieving low-loss and high-efficiency green antenna technology.

Routes of conversion of 2,2-di-(4-nitrophenyl)-1,1,1-trichloroethane into 4,4′-dinitrobenzophenone by reaction with nitrite ion: quantum chemical approach

Quantum chemical calculations of the transformation of 2,2-di(nitrophenyl)-1,1,1-trichloroethane into 4,4′-dinitrobenzophenone upon reaction with nitrite ion in aprotic polar solvents were performed. It was established that the dehydrochlorination reaction of 2,2-di(nitrophenyl)-1,1,1-trichloroethane proceeds via a synchronous E2H mechanism. A possible scheme for the subsequent formation of 4,4′-dinitrobenzophenone was proposed. For each stage of a multistage process, spatial structures were modeled and the energy parameters of pre-reaction, activated and post-reaction complexes were calculated.

Effect of Bi2O3 nanostructures on X-ray shielding, thermal, mechanical and biological properties of PVC polymer nanocomposites

The effect of Bi2O3 nanoparticles and nanowires as fillers in flexible PVC composites was investigated on the shielding properties against X-ray radiation at radiodiagnostic energies (50–129 kV). The PVC composites were gamma radiation cross-linked at 75 kGy. Materials were characterized by thermal analyses, and microstructure studied by SEM. The evaluation involved attenuation measurements and toxicity through cell viability assay. The mechanical properties and toughness were highly improved, according to DMA results, and the TGA analysis shows a small influence of the Bi2O3 nanostructures in the dehydrochlorination reaction of PVC during its thermal decomposition. Moreover, SEM images show a uniform distribution of the Bi2O3 nanostructures in the PVC matrix. Attenuation measurements showed low levels of X-ray transmission for PVC composites with 50 %wt of Bi2O3 and a mass attenuation coefficient greater than those reported for lead in the energy ranges studied, which is an improvement with the use of Bi2O3 NWs. In addition, PVC composites show low HVL and TVL values, making them feasible for the attenuation property. Density measurements show that the composites are lighter than lead. No-toxicity was observed for these composites through cell viability assay. Therefore, the investigated PVC composites are suitable for preparing new radiation-attenuating materials using Bi2O3 NWs.

Low-temperature catalytic dechlorination of model plastic pyrolytic oil over zeolite catalysts

Catalytic dechlorination of model plastic pyrolytic oil was investigated over different types of zeolites and ion-exchanged 13X zeolites at the low temperatures of 20–120 °C. Among different types of parent zeolites (13X, β, MCM-41), 13X had the highest catalytic dechlorination performance. After ion exchange of 13X with Ag+, its catalytic dechlorination performance was significantly enhanced, and the chlorine removal over Ag-13X reached 97.2 % after reaction for 5 h at 120 °C. The characterization results indicated that the acidity of the zeolite governed its catalytic dechlorination performance, and higher acid amount and stronger acid strength are preferred. Different types of chlorinated compounds followed different dechlorination mechanisms. The primary chlorinated alkanes (e.g., 1-chlorooctane) underwent nucleophilic substitution by the surface –OH groups or H2O to form alcohols and HCl, or dehydrochlorination reaction to produce olefins and HCl, while higher chlorinated alkanes with adjacent hydrogen (e.g., chlorocyclohexane) mainly underwent dehydrochlorination reaction to produce olefins and HCl. Chlorinated aromatics (e.g., chlorobenzene) was removed mainly by physical adsorption. Ag-13X showed good stability, and the chlorine removal still retained 72.1 % after 102 h on stream. After four dechlorination-regeneration cycles, the chlorine removal had only a slight decrease due to the partial collapse of its structure and slight loss of its acid amount.

Matching relation between intrinsic kinetics and liquid-liquid mass transfer of medium-rate reaction: Take 1,1,2-trichloroethane dehydrochlorination as an example

The apparent rate of heterogeneous medium-rate reaction is jointly controlled by liquid-liquid mass transfer performance and intrinsic kinetics. Realizing the matching of them can significantly enhance the efficiency of the reaction. Here, the dehydrochlorination reaction of 1,1,2-trichloroethane with NaOH solution is used as an example to investigate the matching relation between intrinsic kinetics and mass transfer efficiency of medium-rate reactions. Firstly, an apparent reaction model considering mass transfer performance, intrinsic kinetics and physical properties of the system was established. The accuracy of the model was experimentally verified in a standard stirred tank. Based on the model, the mass transfer coefficient matching the intrinsic reaction kinetics at 51 ℃ should beyond 100 s−1, which requires to be achieved in mass transfer intensification reactors instead of conventional stirred tank. Therefore, a rotor-stator homogenizer and a rotating packed bed were used. The experimental results in these two reactors well demonstrated the model prediction.

Investigating the role of different stabilizers of PVCs by using a torque rheometer

Abstract Poly(vinyl chloride) (PVC) is one of the versatile thermoplastic materials that have tremendous applications almost everywhere but it is thermally unstable at high temperatures. Processing of PVC at elevated temperatures requires the use of thermal stabilizers that are considered crucial additives for the protection of PVC during both processing and useful life usage. Several thermal stabilizers are available commercially that mostly obstruct the dehydrochlorination reaction. Choosing appropriate stabilizer systems for a specific application is cumbersome. A Brabender torque rheometer at a constant temperature of 180°C and variable shear stress was used to evaluate the stabilizing efficiency of 12 different stabilizer systems combined with PVC. Fusion time, induction period, minimum torque, and rheological stability time were determined in order to evaluate the investigated stabilizer systems. It was found that dibutyl tin mercaptide was the best stabilizer, while the mixture of lead stabilizers was the worse one.

Comprehensive study on selective dehydrochlorination of 2-chloro-3,3,3-trifluoropropene over carbon-based catalysts and catalyst deactivation

3,3,3-trifluoropropyne (HFY-2223tz) is a novel refrigerant with great physicochemical properties. Though preparation of HFY-2223tz from halogenated olefins is theoretically effective, it remains great challenges for dehydrohalogenation from halogenated olefins, limiting the detailed knowledge. Here, we established a facile investigation to explore the gas-phase dehydrochlorination reaction of 2‑chloro-3,3,3-trifluoropropene (HCFO-1233xf) over various halides (Na, K, Rb, Cs) supported active carbon (AC) catalysts. The CsF was concluded as the optimal active component with best dehydrochlorination selectivity and conversion of HCFO-1233xf. The CO2-TPD results illustrated that dehydrochlorination of HCFO-1233xf proceeded through E1cB mechanism. Mechanism study revealed the evolution of side-products including (Z/E)-1,3,3,3-tetrafluoropropylene, 2,3,3,3-tetrafluoropropylene, (Z/E)-1‑chloro‑3,3,3-trifluoroproene, and 3,3,3-trifluoroprop-1-ene, etc. However, observable deactivation of CsF catalyst was noticed, which, according to combined XRD and XPS results and density functional theory (DFT) calculations, was attributed to the F/Cl exchange between HCFO-1233xf and catalyst, leading to rapid fluorine consumption. This work thus provides basic knowledge about heterogeneous catalytic synthesis of HFY-2223tz from dehydrohalogenation of halogenated olefins.

Available methods for the conversion of dichloropropane to allene and methylacetylene

. The nature of the formation of allene and methylacetylene during the dehydrochlorination of 1,2-dichloropropane and intermediate products (1-chloropropene-1, 2-chloropropene-1, 2-chloropropane, and 3-chloropropene-1) on γ-Al2O3, CaX and expanded clay made it possible to establish that the main source of allene formation on CaX and expanded clay is 2-chloropropene-1, and methylacetylene - 1-chloropropene-1, and on γ -Al2O3, allene formation appears mainly from 2-chloropropane, methylacetylene - from 2-chloroprene. The highest value of the allene: methylacetylene ratio was obtained during the dehydrochlorination of 1,2-dichloro propane and 2-chloroprene on CaX and expanded clay (6.90 and 7.30; 7.70 and 8.19, respectively), while on alumina this indicator is much lower and does not exceed 0.2, and the total the content of the allene-methylacetylene fraction in the presence of the latter is also the lowest. It is also noteworthy that, regardless of the feedstock under study, the course of the dehydrochlorination reaction in the presence of aluminum oxide is characterized mainly by the formation of methylacetylene and an insignificant formation of allene, which is probably a consequence of all methylacetylene isomerization occurring on the catalyst surface. The totality of these data made it enable to establish that the DCP conversion mechanism is carried out in different ways regarding the acid-base nature of the active sites of the catalytic systems: in the presence of γ-Al2O3 - with the participation of Lewis acid sites, and CaX and expanded clay - with the participation of Brønsted acid sites.

Photoaging mechanisms of microplastics mediated by dissolved organic matter in an iron-rich aquatic environment

As emerging pollutants, microplastics (MPs) have aroused worldwide concern due to their ubiquitous distribution, environmental persistence, and potential ecological risks. However, the ageing mechanisms, environmental behaviours and risks of photoaged MPs mediated by environmental factors remain obscure. Herein, systems containing a light source, humic acid (HA) and Fe were established to investigate the natural photoaging process of MPs including polyvinyl chloride (PVC) and polyethylene terephthalate (PET). The dehydrochlorination reaction of PVC-MP was inhibited by HA and Fe, which resulted from the coeffect of photon competition, excited state quenching, radical deactivation or transformation, and defect structure destruction. In contrast, the enhanced fluorescence effect suggested that the photooxidation reactions of PET-MP were promoted by HA and Fe. Therefore, the presence of HA and Fe in the environment inhibited the photoreduction of MPs while favoring the photooxidative process. Additionally, the adsorption capacity for 17α-ethinylestradiol and the cytotoxicity of MPs were increased after ageing in the hv + HA and hv + HA + Fe systems, which was attributed to the changes in morphology, elements and functional groups. This study provided new insight into the ageing behaviours of MPs in the natural environment with widespread dissolved organic matter and Fe.

Simulation and experimental study on mechanism and kinetics of 1,1,2-trichloroethane dehydrochlorination reaction

Dehydrochlorination of 1,1,2-trichloroethane (112TCE) is a widely used method for preparing vinylidene chloride (VDC), which is an important polymeric monomer and intermediate of refrigerant. However, there are few reports on kinetics of this reaction system. In this work, density functional theory (DFT) calculation analyses and experiments were conducted to investigate the reaction mechanism and kinetics of 112TCE dehydrochlorination with sodium hydroxide (NaOH). DFT simulation results unveiled there were three parallel reactions which produce VDC, cis-1,2-dichloroethylene (C12DE) and trans-1,2-dichloroethylene (T12DE) respectively in the reaction process of 112TCE and NaOH. The activation energy of the reaction to produce VDC was lower than those of the other two reactions. Moreover, the kinetic parameters of the three parallel reactions, such as reaction orders, rate constants, pre-exponential factors and activation energies, were experimentally obtained by decoupling the overall reaction kinetics. All the parallel reactions are bimolecular elimination reactions and the rate expression of the intrinsic kinetics for generating VDC isdCtdt=1.668×1011e-75662RTCACB. The reaction rate is three orders of magnitude higher than those of producing C12DE and T12DE, which is consistent with the DFT simulation results. These kinetics results are useful for the process optimization and reactor design in VDC production process.

Dual effect of CaO on waste PVC plastics pyrolysis: A kinetics study using Fraser-Suzuki deconvolution

Green and sustainable treatment of waste plastics emerged as one of the greatest challenging matters facing the world. In this work, the pyrolysis of chlorine-contained PVC plastics was investigated from a kinetic study perspective. The dual effects of calcium oxide (CaO) additive were examined. The Fraser-Suzuki deconvolution function was adopted to fit the differential thermogravimetric (DTG) curves into three pseudo-reactions. The apparent activation enegry (Ea), pre-exponential factor (A) and reaction mechanism models (f(a)) for each pseudo-reaction were identified. The results show that the use of CaO increased significantly the Ea value of the dehydrochlorination reaction but lowered that of the tar cracking reactions, indicating an apparent HCl release mitigation as well as tar compounds decomposition. The mechanism models of the three pseudo-reactions kept identical with or without CaO addition, which were A4 Avrami-Erofeev: ƒ(α)=4(1-α) [-ln(1-α)]3⁄4 for pseudo-reactions 1 and 3 and B1 Prout-Trompkins: ƒ(α)=α(1-α) for pseudo-reactions 2. The kinetic models of the pyrolysis of waste PVC and the mixtures were thus established. The obtained results could be used as a theoretical basis for the development and application of clean and efficient waste PVC plastics pyrolysis technology.

Dehydrochlorination of 1,1,1,3,3-Pentachlopropane promoted by fluoride

The dehydrochlorination of 1,1,1,3,3-pentachloropropane (HCC-240fa) with alkali metal halide in amide to produce tetrachloropropene isomers was taken into investigation. Studies found that E-1,3,3,3-tetrachloropropene (HCO-1230zd(E)), Z-1,3,3,3-tetrachloropropene (HCO-1230zd(Z)) and 1,1,3,3-tetrachloropropene (HCO-1230za) were formed by the selective dehydrochlorination promoted by halide anions, where fluoride had the best reactivity among the four kinds of halide anions. Besides, it was also found when the molecular polarity index (MPI) of the amide was greater than or equal to 14.3 kcal/mol, it was conducive to the dehydrochlorination reaction, and the conversion was close to 100%. Additionally, DFT calculations demonstrated that the selective dehydrochlorination at the 1-position and 2-position of HCC-240fa was easier than that at the 2-position and 3-position, which is consistent with the experimental results.

Regulation of the liquid–solid interface of Cs catalysts for the synthesis of 1,1-Dichloroethylene from 1,1,2-Trichloroethane

There remain considerable challenges for Cs-based catalysts in gas-phase dehydrochlorination of 1,1,2-trichloroethane (TCE) due to their poor catalytic performance and harsh reaction temperature requirements. In this work, we report a novel supported ionic liquid (IL) phase Cs-based system and evaluate its catalytic performance and mechanism, combining the kinetic and DFT calculations. The optimal Cs-IL/SiO2 catalyst achieved the TCE conversion of 60% and the selectivity to 1,1-Dichloroethylene (VDC) of 86% under the mild temperature of 200 °C. It is demonstrated that IL additives can significantly improve the dispersion of Cs species during the catalyst preparation and evaluation process. Moreover, IL promotes the activation of TCE and enhances the desorption efficiency of HCl, which is the main reason for its high activity. The selectivity is improved by changing the adsorption behaviors of the products, which ensures the preferential formation of the main product VDC. The enhanced activity and selectivity of Cs-IL/SiO2 suggest a promising candidate for dehydrochlorination reaction.

Influence of ammonium octamolybdate on flame retardancy and smoke suppression of PVC matrix flame retardant composites

Abstract In order to improve the flame retardancy and smoke suppression of polyvinyl chloride (PVC), ammonium octamolybdate (AOM)/nano-antimony trioxide (nano-Sb2O3)/dioctyl Phthalate (DOP)/PVC composites were prepared by high energy ball milling and melt blending methods using AOM as the smoke suppressant. The effects of AOM on the flame retardancy and smoke suppression of the PVC composites were studied by means of vertical burning tests (UL-94), limiting oxygen index (LOI), thermogravimetric analysis (TGA), scanning electron microscopy (SEM) and cone calorimetry (CCT). The results showed that the flame retardancy of PVC composites containing AOM was improved, namely the UL-94 grade of the composites reached the V-0 grade and the LOI increased from 22.3% to 30.6%, whilst the heat release rate (HRR), total heat release (THR), smoke production rate (SPR), total smoke production (TSR) and smoke factor (SF) decreased significantly. In addition, AOM could promote the dehydrochlorination reaction of the PVC composites at lower temperature, resulting in more compact and continuous char residues. Therefore, AOM is an effective smoke suppressant and has a good synergistic flame retardant effect with nano-Sb2O3 in flame retardant PVC matrix composites.

Synthesis and oxidative transformations of 2-functionalized 2-trifluoromethyltetrahydrothiophenes

2-Acetoxymethyl- and 2-hydroxymethyl-2-(trifluoromethyl)tetrahydrothiophenes have been prepared from readily obtainable 3-hydroxy-3-(trifluoromethyl)tetrahydropyran by its reactions of sulfur-assisted ring contraction. With the aim to explore the synthetic utility of new fluorinated tetrahydrothiophenes and to estimate the influence of trifluoromethyl group on their reactivity, various types of the oxidative transformations, involving oxidation and oxoimination of sulfur atom, oxidation of hydroxymethyl group and chlorination of free α-position to sulfur atom, were studied. Large sterical demand of CF3 group has been revealed from the stereochemical outcome of the oxidation and oxoimination of the sulfur atom. Electron withdrawing properties of CF3 group are evident from low susceptibility of 2-hydroxymethyl-(trifluoromethyl)tetrahydrothiophene to the oxidation of hydroxymethyl group and from low activity of 2-acetoxymethyl-5-chloro-2-(trifluoromethyl)tetrahydrothiophene in nucleophilic substitution and dehydrochlorination reactions. Convenient protocols for the preparation of trifluoromethylated tetrahydrothiophenes with sulfoxide, sulfone, sulfoximino, aldehyde and carboxy functionalities, acetoxy group in the position 5 of the heterocycle, and 2-(acetoxymethyl)-2-(trifluoromethyl)-2,3-dihydrothiophene have been developed. The results of these studies demonstrate that 2-acetoxymethyl- and 2-hydroxymethyl-2-(trifluoromethyl)tetrahydrothiophenes are useful precursors to a variety of new small fluorinated molecules.