Microwave assisted ecofriendly recycling of poly (ethylene terephthalate) bottle waste

Glycolysis of poly (ethylene terephthalate) bottle waste was carried out using microwave energy. A domestic microwave oven of 800 W was used with suitable modification for carrying out the reaction under reflux. The catalysts used for the depolymerization in ethylene glycol (EG) were zinc acetate and some simple laboratory chemicals such as sodium carbonate, sodium bicarbonate and barium hydroxide. Comparison of results was made from the point of view of the yield of bis (2-hydroxyethylene) terephthalate (BHET) and the time taken for depolymerization. It was observed that under identical conditions of catalyst concentration and PET:EG ratio, the yield of BHET was nearly same as that obtained earlier by conventional electric heating. However, the time taken for completion of reaction was reduced drastically from 8 h to 35 min. This has led to substantial saving in energy.     

Organocatalytic depolymerization of poly(ethylene terephthalate)

We describe the organocatalytic depolymerization of poly(ethylene terephthalate) (PET), using a commercially available guanidine catalyst, 1,5,7‐triazabicyclo[4.4.0]dec‐5‐ene (TBD). Postconsumer PET beverage bottles were used and processed with 1.0 mol % (0.7 wt %) of TBD and excess amount of ethylene glycol (EG) at 190 °C for 3.5 hours under atmospheric pressure to give bis(2‐hydroxyethyl) terephthalate (BHET) in 78% isolated yield. The catalyst efficiency was comparable to other metal acetate/alkoxide catalysts that are commonly used for depolymerization of PET. The BHET content in the glycolysis product was subject to the reagent loading. This catalyst influenced the rate of the depolymerization as well as the effective process temperature. We also demonstrated the recycling of the catalyst and the excess EG for more than 5 cycles. Computational and experimental studies showed that both TBD and EG activate PET through hydrogen bond formation/activation to facilitate this reaction. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

吡咯烷酮酸性离子液体中硼酸酯的催化合成

研究了硼酸与频哪醇和环己醇在离子液体1-甲基-2-吡咯烷酮硫酸氢盐（[Hnmp]HSO4）、1-丁基-3-甲基咪唑四氟硼酸盐（[Bmim]BF4）及1-丁基-3-甲基咪唑六氟磷酸盐([Bmim]PF6)中生成2-环己氧基-4,4,5,5-四甲基-1,3,2-二氧硼烷的酯化反应。 考察了不同离子液体、反应温度、反应时间和离子液体与反应物物质的量比等对反应的影响。 结果表明,当n(硼酸)∶n(频哪醇)∶n(环己醇)∶n([Hnmp]HSO4)=1∶1∶1∶1,反应温度为70 ℃和反应时间为4 h时,硼酸酯的产率为72.5%,离子液体重复使用4次,催化活性无明显降低。     

Sub- and supercritical glycolysis of polyethylene terephthalate (PET) into the monomer bis(2-hydroxyethyl) terephthalate (BHET)

Sub- and supercritical glycolysis of polyethylene terephthalate (PET) with ethylene glycol (EG) to bis(2-hydroxyethyl) terephthalate (BHET) was investigated for the purpose of developing a PET recycling process. Supercritical glycolysis was carried out at 450 °C and 15.3 MPa while subcritical glycolysis was carried out at 350 °C and 2.49 MPa or at 300 °C and 1.1 MPa. High yields (gt; 90%) of the monomer BHET were obtained in both super- and subcritical cases. For the same PET/EG weight ratio of about 0.06, the optimum reaction time was 30 min for supercritical glycolysis and 75 and 120 min for two cases of subcritical glycolysis. GPC, RP-HPLC, ¹H NMR and ¹³C NMR, and DSC were used to characterize the polymer and reaction products. Supercritical glycolysis will be suitable to a process requiring a high throughput due to its short reaction time.     

碱性离子液体催化甘油合成1,2-甘油碳酸酯(英)

以离子液体为催化剂,在无溶剂体系中,考察了生物质平台化合物甘油转化1,2-甘油碳酸酯的反应.与酸性离子液体和常用无机碱性催化剂相比,碱性离子液体咪唑基1-丁基-3-甲基咪唑([Bmim]Im)、氢氧化1-丁基-3-甲基咪唑([Bmim]OH)、咪唑基1-烯丙基-3-甲基咪唑([Amim]Im)、氢氧化1-烯丙基-3-甲基咪唑([Amim]OH)在甘油与碳酸二甲酯的酯交换反应中表现出优异的活性.其中,以[Bmim]Im离子液体为催化剂时甘油转化率为98.4%和甘油碳酸酯选择性接近100%.另外,该离子液体可以回收重复利用3次后甘油转化率仍可达92%,甘油碳酸酯选择性可近100%.此碱性离子液体催化方法具有反应结果较好、产物分离简单、条件温和以及环境友好等特点.     

Depolymerisation of poly(ethylene terephthalate) fibre wastes using ethylene glycol

Poly(ethylene terephthalate) [PET] fibre wastes from an industrial manufacturer was depolymerised using excess ethylene glycol [EG] in the presence of metal acetate as a transesterification catalyst. The glycolysis reactions were carried out at the boiling point of ethylene glycol under nitrogen atmosphere up to 10 h. Influences of the reaction time, volume of EG, catalysts and their concentrations on the yield of the glycolysis products were investigated. The glycolysis products were analysed for hydroxyl and acid values and identified by different techniques, such as HPLC, ¹H NMR and ¹³C NMR, mass spectra, and DSC. It was found that the glycolysis products consist mainly of bis(hydroxyethyl)terephthalate [BHET] monomer (>75%) which was effectively separated from dimer in quite pure crystalline form.     

Ultrafast 99% Polyethylene terephthalate depolymerization into value added monomers using sequential glycolysis-hydrolysis under microwave irradiation

Effective and efficient hybrid depolymerisation technologies are emerging as high potential sustainable routes with considerable benefits over conventional recycling methods for the achievement of circular economies for plastics. Herein, combined green and fast glycolysis-hydrolysis depolymerization of polyethylene terephthalate (PET) was carried out under microwave irradiation (MW) with excellent efficiencies. In MW assisted glycolysis of PET, the catalytic activity of two deep eutectic solvents (DES) based on (choline chloride-urea (DES 1)) and (choline chloride-thiourea (DES 2)) was evaluated and compared. Optimised glycolysis conditions were determined using Box Behnken Design (BBD) to attain maximum weight loss of PET, low crystallinity and increased carbonyl index of residual PET. DES volume of 4 mL, 5.5–6 mL of ethylene glycol, and 0.5 min MW irradiation time resulted in a prominent rise in PET weight loss and carbonyl index of residual PET. DES 2 showed an improved catalytic activity than that of DES 1 which is associated to its stronger interaction with EG and PET polymer chains during the course of the reaction. Residual PET obtained post glycolysis reaction was further depolymerized using MW assisted hydrolysis in the presence of weakly basic Na₂CO₃ and EG. Within 3-minute, the proposed sequential depolymerization technologies facilitated ≈99% conversion of PET to terephthalic acid (TPA), monohydroxyethyl terephthalate (MHET), and bis (2-hydroxyethyl) terephthalate (BHET) monomers produced at a yield of 62.79–80.66%, 17.22–34.79% and 0.54–0.59% respectively. Application on post-consumer PET sample also revealed very satisfactory results with 96.77–98.25% PET conversion and 60.98–78.10% yield of TPA.     

Glycolysis of poly(ethylene terephthalate) catalyzed by ionic liquids

Poly(ethylene terephthalate) (PET) from an industrial manufacturer was depolymerized by ethylene glycol in the presence of a novel catalyst: ionic liquids. It was found that the purification process of the products in the glycolysis catalyzed by ionic liquids was simpler than that catalyzed by traditional compounds, such as metal acetate. Qualitative analysis showed that the main product in the glycolysis process was the bis(hydroxyethyl) terephthalate (BHET) monomer. Thermal analysis of the glycolysis products was carried out by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The influences of experimental parameters, such as the amount of catalyst, glycolysis time, reaction temperature, and water content in the catalyst on the conversion of PET, selectivity of BHET, and distribution of the products were investigated. Results show that reaction temperature is a critical factor in this process. In addition, a detailed reaction mechanism of the glycolysis of PET was proposed.     

离子液体/H_2O_2体系脱硫实验研究

选取四种不同种类离子液体(ILs),1-丁基-3-甲基咪唑溴化物([Bmim]Br)、1-丁基-3-甲基咪唑四氟硼酸盐([Bmim]BF_4)、1-丁基-3-甲基咪唑硫酸氢盐([Bmim]HSO_4)、1-丁基-3-甲基咪唑磷酸二氢盐([Bmim]H_2PO_4)与30%H_2O_2溶液在温和条件下对两种高硫脱灰煤样(LS、QX)进行脱硫实验研究。用化学法测定脱硫前后煤样形态硫含量,并利用傅里叶变换红外光谱(FT-IR)、X射线光电子能谱(XPS)、扫描电子显微镜(SEM)及热重(TG)对脱硫前后的煤样进行表征。结果表明,离子液体的加入使H_2O_2氧化脱硫能力增强,煤中硫铁矿硫和有机硫化物硫被显著脱除;经ILs/H_2O_2体系作用后的煤样中小粒径的颗粒减少,颗粒间的缝隙增大,煤表面的凹坑明显,热重实验结果表明,ILs/H_2O_2体系作用后的煤样相对于原煤热失重增大,部分挥发性物质释放峰温提前。     

咪唑根碱性离子液体在水介质Knoevenagel反应中的催化作用

报道了咪唑根1-丁基-3-甲基咪唑([Bmim]Im)碱性离子液体的合成与表征,该离子液体具有强碱性和较好的热稳定性.碱性离子液体[Bmim]Im用于催化水介质中Knoevenagel反应,发挥了碱催化剂与相转移催化剂双重作用.此外,离子液体[Bmim]Im及其水溶液还具有良好的循环使用性能.水介质、低催化剂用量、室温...     

不同离子液体中硝基苯的电化学还原

研究了硝基苯在N-甲基咪唑对甲基苯磺酸([Mim][PhSO3])和1-丁基-3-甲基咪唑六氟磷酸([Bmim][PF6])两种离子液体中的电化学还原反应.循环伏安法测试显示,硝基苯在[Mim][PhSO3]中只出现一个还原峰,是一个受扩散控制的不可逆电化学反应,而在[Bmim][PF6]中出现两对氧化还原峰,表明其还原产物随离子液体性质的不同而异.     

Improvement of the Friedel–Crafts benzoylation by using bismuth trifluoromethanesulfonate in 1-butyl-3-methylimidazolium trifluoromethanesulfonate ionic liquid under microwave irradiation

Bismuth trifluoromethanesulfonate (bismuth triflate) catalyzed the Friedel–Crafts benzoylation of activated aromatic compounds when dissolved in 1-butyl-3-methylimidazolium trifluoromethanesulfonate ([BMIM]OTf) ionic liquid. Immobilization of bismuth triflate (5 mol %) in [BMIM]OTf allowed the synthesis of aryl ketones in good to excellent yields with short reaction times under microwave irradiation. This catalytic system was easily recovered and reused several times without any significant loss of the activity.     

Thermodynamic Properties of Binary Mixtures of the Amino Acid Ionic Liquids [Bmim][Glu] or [Bmim][Gly] with Methanol at T=298.15 to 313.15 K

Densities, viscosities and refractive indices were determined for two ionic liquid mixtures formed by the 1-butyl-3-methylimidazolium glutamic acid salt ([Bmim][Glu]) or the 1-butyl-3-methylimidazolium glycine acid salt ([Bmim][Gly]), respectively, with methanol over the mole fraction from 0.1 to 0.9 and at temperatures ranging from 298.15 K to 313.15 K at intervals of 5 K and at atmospheric pressure. Excess molar volumes, viscosity deviations and refractive index deviations have been calculated from the experimental data and fitted to a Redlich–Kister polynomial function. The results have been interpreted in terms of ion-dipole interactions, and structural factors of the ionic liquid and alcohol molecular liquids.     

An unexpected reaction between 5-hydroxymethylfurfural and imidazolium-based ionic liquids at high temperatures

A new compound was detected during the production of 5-hydroxymethylfurfural (HMF) from glucose and cellulose in the ionic liquid 1-butyl-3-methylimidazolium chloride ([Bmim]Cl) at high temperatures. Further experiments found that it was derived from the reaction of HMF with [Bmim]Cl. The structure of new compound was established as 1-butyl-2-(5'-methyl-2'-furoyl)imidazole (BMI) based on nuclear magnetic resonance and mass spectrometry analysis, and a possible mechanism for its formation was proposed. Reactions of HMF with other imidazolium-based ionic liquids were performed to check the formation of BMI. Our results provided new insights in terms of side reactions between HMF and imidazolium-based ionic liquids, which should be valuable for designing better processes for the production of furans using biomass and related materials.     

Experiments and model for the surface tension of (MDEA + [Bmim][BF4]) and (MDEA + [Bmim][Br]) aqueous solutions

The surface tension (γ) of 1-butyl-3-methylimidazolium tetrafluoroborate ([Bmim][BF₄]), 1-butyl-3-methylimidazolium bromide ([Bmim][Br]), (N-methyldiethanolamine(MDEA) + [Bmim][BF₄]) and (MDEA + [Bmim][Br]) aqueous solutions were measured by using the BZY-1 surface tension meter. The temperature ranged from (293.2 to 323.2) K. The mass fraction of MDEA ranged from 0.35 to 0.45. A thermodynamic equation was proposed to model the surface tension of (MDEA + ionic liquids) (ILS) aqueous solutions and the calculated results agreed well with the experiments. The effects of temperature, mass fractions of MDEA and ILS on the surface tension were demonstrated on the basis of experiments and calculations.     

Low-temperature heat capacities of 1-alkyl-3-methylimidazolium bis(oxalato)borate ionic liquids and the influence of anion structural characteristics on thermodynamic properties

Two chelated orthoborate ionic liquids (ILs), 1-butyl-3-methylimidazolium bis(oxalato)borate ([Bmim][BOB]) and 1-hexyl-3-methylimidazolium bis(oxalato)borate ([Hmim][BOB]), were prepared and characterized. Their thermodynamic properties were studied using adiabatic calorimetry and differential scanning calorimetry (DSC). The thermodynamic properties of the two ILs were evaluated and compared with each other, and then with those of other [Bmim] type ILs. The results clearly indicate that for a given cation (or anion) and at a certain temperature, the more atoms in the anion (or cation), the higher the heat capacity; the higher glass-transition temperatures of [BOB] type ILs than others are mainly caused by the higher symmetry of the orthoborate anion structure. It is suggested that a high content of strong electronegative atoms and C(n) or C(nv) (n = 1,2,3,…,∞) point group symmetry in the anion are favorable for the design and synthesis of room temperature ILs with a wide liquid range.     

Ionic liquid 1-butyl-3-methylimidazolium bromide: A green reaction media for the efficient synthesis of 3-methyl-1,4-diphenyl-1,4,5,7-tetrahydro-pyrazolo[3,4-d]pyrimidine-6-ones/thiones using phthalimide-N-sulfonic acid as catalyst

A simple, green and environmentally benign procedure was developed for the one pot synthesis of 3-methyl-1,4-diphenyl-1,4,5,7-tetrahydro-pyrazolo[3,4-d]pyrimidine-6-one/thiones using catalytic amount of phthalimide-N-sulfonic acid (PISA) in 1-butyl-3-methylimidazolium bromide ([Bmim][Br]) ionic liquid via the three-component reaction of 1-phenyl-3-methyl-1H-pyrazole-5(4H)-one, aromatic aldehyde and urea/thiourea. [Bmim][Br] as reaction media offers several advantages including non-toxic, non-corrosive, shorter reaction times, high yield of the products, mild reaction conditions as well as simple experimental and isolation procedures.     

Lyotropic liquid crystalline phases formed by phyosterol ethoxylates in room-temperature ionic liquids

The phase behaviors of four phytosterol ethoxylates surfactants (BPS-n, n = 5, 10, 20, and 30) with different oxyethylene units in room temperature ionic liquid, 1-butyl-3-methylimidazolium tetrafluoroborate ([Bmim]BF₄), have been studied. The polarized optical microscopy and small-angle X-ray scattering techniques are used to characterize the phase structures of these binary systems at 25 °C. The structure and ordering of the liquid crystalline (LC) phases in such BPS-n/[Bmim]BF₄ systems are found to be influenced by BPS-n concentration and the temperature. Due to the bulky and rigid cholesterol group, the phytosterol ethoxylates surfactants exhibit different properties and interaction mechanism from the conventional C_nEO_m type nonionic surfactant systems. The rheological measurements indicate a highly viscoelastic nature of these lyotropic LC phases and disclose a lamellar phase characteristic with a rather strong rigidity at high surfactant concentrations. The control experiment with Brij 97(polyoxyethylene (10) oleyl ether)/[Bmim]BF₄ system and the FTIR measurements help to recognize that the solvophobic interaction combining with the hydrogen bonding are the main driving forces for the LC phases formation.     

Extraction and mechanism investigation of trace roxithromycin in real water samples by use of ionic liquid-salt aqueous two-phase system

The ionic liquid, as a green solvent, has several advantages over the organic solvents in traditional liquid-liquid extraction. Aqueous two-phase system (ATPS) consisting of a hydrophilic ionic liquid (1-butyl-3-methylimidazolium tetrafluoraborate, [Bmim]BF₄) and Na₂CO₃, which is a novel, simple, non-toxic and effective sample pretreatment technique coupled with molecular fluorescence spectrophotometry, was developed for the simultaneous separation, enrichment and rapid analysis of roxithromycin. The extraction yield of roxithromycin in [Bmim]BF₄-Na₂CO₃ aqueous two-phase system is influenced by the types of salts, concentrations of Na₂CO₃ and [Bmim]BF₄, as well as the extracting temperature. Under the optimum conditions, the average extraction efficiency is up to 90.7%. The mechanism of ionic liquid-salt ATPS formation was discussed by hydration theory, and the extraction mechanism of the [Bmim]BF₄-salt ATPS was investigated by FT-IR spectroscopy and UV-vis spectroscopy. The results demonstrate that no chemical (bonding) interactions are observed between ionic liquid and roxithromycin, while the nature properties of the roxithromycin are not altered. This method was practical when applied to the analysis of roxithromycin in real water samples with the detection limit of 0.03 μg mL⁻¹, relative standard deviation (RSD) of 1.9% (n = 13), and linear ranges of 1.00-20.00 μg mL⁻¹. The proposed extraction technique will be promising in the separation of other small biomolecules.     

Dechlorination of poly(vinyl chloride) by 1-butyl-3-methylimidazoliumhydroxide

Highly efficient dechlorination of PVC has been realized at 180 °C and at atmospheric pressure, using 1-butyl-3-methylimidazoliumhydroxide ([Bmim]OH) as an environment-friendly reaction medium: in the absence of an external base or solvent the dechlorination efficiency is as high as 91.2%, while it is only 38.1% for PVC without ionic liquids. The dechlorination process follows first-order kinetics with apparent activation energy of 44 kJ mol⁻¹. Mechanistic analysis provides evidence for the equilibrium presence of carbene species, together with the hydroxide ions in [Bmim]OH, thus enhancing the dechlorination of PVC via a combined elimination and substitution mechanism.