Conventional Oil Bath Heating Research Articles

Demulsification of heavy crude oil-in-water emulsions: A comparative study between microwave and thermal heating

Oil-in-water (O/W) emulsions are an innovate manner by which otherwise highly viscous heavy and extra-heavy crude oils can be transported from producing sites to transforming sites through pipelines. In spite of the important reduction in viscosity and pressure drops, water must be removed from the crude oil before further process or refining. Hence, the present study discusses the demulsification of an O/W emulsion prepared with Mexican heavy crude oil. A comparative study was carried out between microwave and oil bath heating with regard to water separation time. The effect of a chemical demulsifier and salt content of the O/W emulsion’s aqueous phase was also investigated. Microwave dielectric heating of O/W emulsions showed a greater degree of water separation in less time than conventional oil bath heating. Water separation of O/W emulsions increased with microwave power and salt content of the aqueous phase, and in the presence of a chemical demulsifier. Finally, the fluorescence emission spectra of the initial and treated O/W emulsions were in agreement with the water separation results and provide a quick and effective way to study the demulsification processes.

Microwave-assisted rapid conversion of carbohydrates into 5-hydroxymethylfurfural by ScCl3 in ionic liquids

In this study, synthesis of HMF from carbohydrates was carried out in ionic liquids 1-butyl-3-methylimidazolium chloride ([Bmim]Cl) catalyzed by ScCl3 under microwave irradiation. Under the optimal reaction conditions, HMF was obtained in a high yield of 73.4% in 2mins with the microwave power at 400W. Compared with the conventional oil-bath heating manner, the use of microwave irradiation not only reduced reaction times from hours to minutes, but also improved HMF yield. This catalytic system could be reused several times without losing its catalytic activity. This efficient catalytic system will generate a promising application strategy for biomass transformation.

Enhanced decomposition of dimethyl phthalate via molecular oxygen activated by Fe@Fe2O3/AC under microwave irradiation

In this study, we demonstrate that the decomposition of dimethyl phthalate under microwave irradiation could be greatly enhanced over Fe@Fe2O3 nanowires supported on activated carbon (Fe@Fe2O3/AC). The great enhanced decomposition of dimethyl phthalate could be attributed to a unique microwave induced molecular oxygen activation process. Upon microwave irradiation, electrons could be transferred from activated carbon to zero-valent iron, and then react with molecular oxygen to form O2− and OH radicals for the decomposition of dimethyl phthalate. The deactivation and the regeneration of Fe@Fe2O3/AC catalyst were systematically studied. We also found that microwave heating could accelerate the electron transferring from AC to Fe@Fe2O3 to generate more reactive oxygen species for the decomposition of DMP than conventional oil bath heating. This novel molecular oxygen activation approach may find applications for wastewater treatment and drinking water purification.

Exploration of structure and mechanism of insoluble gels formed in microwave-assisted Suzuki coupling for poly(9,9-dihexylfluorene)s

A series of poly(9,9-dihexylfluorene)s (PDHFs) have been synthesized via microwave-assisted Suzuki and Yamamoto coupling reactions. Compared with the conventional oil-bath heating (48 h, Mw 20100 g/mol by Suzuki reaction and Mw 24000 g/mol by Yamamoto reaction), microwave-assisted polymerization can yield PDHFs with higher molecular weights (Mw 37200 g/mol by Suzuki reaction and Mw 43400 g/mol by Yamamoto reaction) in shorter time (14 and 60 min). However, sometimes formation of insoluble gels was observed together with PDHF in Suzuki coupling reaction. PDHF and insoluble gels were analyzed by XPS, elemental analysis, FTIR, TGA and DSC. Experimental results demonstrated that H2O might take part in the Suzuki coupling reaction under microwave condition, which could make the cross-linking reaction occur and form gels.

Efficient Conversion of Glucose into 5-Hydroxymethylfurfural by Chromium(III) Chloride in Inexpensive Ionic Liquid

An efficient process was developed for the conversion of glucose into 5-hydroxymethylfurfural (HMF) in the relatively low-toxicity and inexpensive catalytic system of chromium(III) chloride (CrCl3·6H2O) catalyst and tetraethylammonium chloride (TEAC) ionic liquid. An HMF yield of 71.3% was achieved at 130 °C for only 10 min under conventional oil-bath heating. The TEAC/CrCl3·6H2O system was found to be tolerant to high water content and high glucose concentration and could be recycled, exhibiting stable activity after five successive runs. Moreover, satisfactory results were achieved when fructose, sucrose, and cellobiose were used as feedstocks. This work might also provide useful information for the production of HMF from biomass.

Microwave-assisted liquefaction of wood with polyhydric alcohols and its application in preparation of polyurethane (PU) foams

Microwave radiation was used as the heating source in southern pine wood liquefaction with PEG/ glycerin binary solvent. It was found that microwave heat- ing was more efficient than conventional oil bath heating for wood liquefaction. The wood residue content of the H2SO4 catalyzed liquefied wood dropped to zero within 5 min with microwave heating. The resulting liquefied wood polyols have suitable hydroxyl values for the preparation of rigid PU foams. Both the compressive strength and apparent modulus of the liquefied-wood-based PU foams increased as the iso- cyanate index increased from 80 to 120. The foams from H3PO4 catalyzed polyols had lower densities than those from H2SO4 and the petroleum-based controls. They also showed lower strength and modulus than those from H2SO4. Liquefied-wood-based PU foams generally have lower com- pressive strength and apparent modulus than the petroleum- based controls. However, they showed better restorability from deformation than the petroleum-based controls.

Direct conversion of cellulose to 1-(furan-2-yl)-2-hydroxyethanone in zinc chloride solution under microwave irradiation

Conversion of cellulose to 1-(furan-2-yl)-2-hydroxyethanone has been demonstrated in concentrated zinc chloride solution under microwave irradiation. Compared with the conventional oil-bath heating mode, microwave irradiation significantly reduced the reaction time and increased the yield of 1-(furan-2-yl)-2-hydroxyethanone. A typical degradation reaction with cellulose produced 1-(furan-2-yl)-2-hydroxyethanone in 12.0% molar yield in ZnCl 2 solution (ZnCl 2–H 2O ratio = 2.25:1, w/w) with microwave irradiation at 600 W for 5 minutes at 135 °C.

Microwave assisted synthesis of pH-responsive swellable adducts of chitosan–polyuronic acids

A facile method for synthesizing super-swellable, pH-responsive and insoluble adducts (e.g. CH–PMA and CH–PGA) of acid-soluble chitosan (CH) with alkali-soluble poly-mannuronic (PMA) and poly-guluronic (PGA) acids using microwave (MW) heating is described. The reactions were also carried out using conventional oil bath heating method. Microwave heating to 100 °C for 5 min produced greatest yields (95–97%) and swelling ratios (2700–3000%) with these two acids. The conventional heating method, however, required 60 min to produce greatest yields (74–80%) and swelling ratios (1450–1900%), which plateaued even on heating up to 120 min. Adducts were characterized by FT-IR and CP-MAS 13C NMR techniques.

Microwave-assisted regioselective alkylation of naphthalene compounds using alcohols and zeolite catalysts

Regioselective alkylation of naphthalene compounds with alcohols smoothly proceeded in the presence of zeolite catalysts under microwave irradiation. A H-mordenite (H-M) zeolite catalyst (SiO 2/Al 2O 3 ratio = 240) showed the highest efficiency. In the microwave reactions, high reaction rates and high selectivities for 2,6-dialkylnaphthalenes were achieved. In the best case for the reaction of 2-isopropylnaphthalene with isopropyl alcohol, the conversion and the selectivity were 43.5% and 66.4%, respectively. In di- tert-butylation of naphthalene with tert-butyl alcohol, the conversion and the selectivity reached 86.5% and 70.4%, respectively. The conversions and the selectivities were generally higher than those obtained by conventional oil bath heating.

Microwave-assisted Conversion of Carbohydrates into 5-Hydroxymethylfurfural Catalyzed by ZnCl2

A convenient system for producing 5-hydroxymethylfurfural (HMF) through dehydration of carbohydrates by microwave heating in the presence of ZnCl2 was studied. The use of ZnCl2 gave higher selectivity than other metal salts in the conversion of glucose. With ZnCl2 as catalyst, sucrose could be utilized effectively. Under the conditions of microwave irradiation (300 W, 8 min), HMF yields were 54.6, 55.1, and 80.6% from glucose, fructose and sucrose, whereas upon conventional oil bath heating (0.11 gmL−1 sugar solution, weight ratio of ZnCl2 to substrate = 1 : 4, 189 °C, 60 min) HMF yields from glucose, fructose and sucrose were only up to 37.7, 42.7, and 57.7%, respectively.

Solid acid and microwave-assisted hydrolysis of cellulose in ionic liquid

Solid acid-catalyzed hydrolysis of cellulose in ionic liquid was greatly promoted by microwave heating. H-form zeolites with a lower Si/Al molar ratio and a larger surface area showed a relatively higher catalytic activity. These solid catalysts exhibited better performance than the sulfated ion-exchanging resin NKC-9. Compared with conventional oil bath heating mode, microwave irradiation at an appropriate power significantly reduced the reaction time and increased the yields of reducing sugars. A typical hydrolysis reaction with Avicel cellulose produced glucose in around 37% yield within 8 min.

Fast synthesis of optically active polyamides containing l-methionine linkages in ionic liquid via a microwave-assisted process

Several optically active aromatic polyamides have been synthesized via direct polycondensation of chiral diacid monomer 1 containing l-methionine moiety with diverse aromatic diamines 2a–2h in a green medium, namely 1,3-dipropylimidazolium bromide as a room temperature ionic liquid. In order to evaluate the advantages of microwave promotion of these polymerization reactions, we compared microwave irradiation (method I) with conventional oil bath heating (method II) by means of reaction rates, conversions, and inherent viscosities. The inherent viscosities of resulting polymers were ranging between 0.47–0.65 and 0.35–0.57 dL/g in methods I and II, respectively. These polymers were characterized by means of 1H-NMR, FT-IR, elemental, organosolubility, differential scanning calorimetry, and thermal gravimetric analysis techniques. The obtained polymers show thermal stability up to 273 °C under nitrogen atmosphere and good solubility in polar organic solvents. Polymerization reactions proceeded in higher yields and moderate inherent viscosities under microwave irradiation conditions besides the dramatically shorter reaction times and achieving the more pure products.

Three-Component Synthesis of 1,5-Benzo-diazepines

Reported is the one-pot synthesis of substituted benzodiazepines from acyl chlorides, alkynes and ortho-aminoanilines. Sonogashira-type cross-coupling leads to the formation of the intermediate alkynone, which then undergoes reaction with the aminoaniline to give the di­azepine. Conventional oil-bath heating appeared to give better yields than microwave conditions, but the former required longer reaction times. The availability of substituted phenylenediamines is, of course, crucial to the achievable substitution patterns of the product benzodiazepines.

Rapid Microwave‐Promoted Synthesis of Polyurethanes from a Fluorene Unit‐Containing Diol and Diisocyanates

AbstractA fluorene diol derivative, 9,9‐bis[4‐(2‐hydroxyethoxy)phenyl]fluorene (1), reacted with diisocyanates such as 1,3‐bis(isocyanatomethyl)cyclohexane (2a), 1,6‐diisocyanatohexane (2b), and 1,3‐bis(isocyanatomethyl)benzene (2c) under temperature‐controlled microwave irradiation to form the corresponding polyurethanes with $\overline M _{\rm w}$ being 30 000 to 60 000, measured by GPC with reference to polystyrene standards within 5 to 10 min at 160 to 200 °C. In the reactions of 2a and b, the molecular weights were 15 to 20 times higher than those obtained by conventional oil bath heating. For a solvent of the microwave‐promoted reaction, a hydrocarbon compound, decalin, is preferably used to undergo the polymerization cleanly without unfavorable coloration and/or gelation.magnified image

Deeper Insight into Structures of Modified AEROSIL Particles Synthesized via Conventional Heating and Microwave Heating

AbstractThe contribution deals with the comparison of microwave heating and conventional oil bath heating. Silicon dioxide nanoparticles were grafted with MPTMS under acid conditions. Those particles contain a polysiloxane shell with physically adsorbed and chemically bound fractions which can be separated by Soxhlet extraction. The resulting fractions were analyzed with TGA and MALDI‐TOF MS; one to determine the amount of physically adsorbed and chemically bound fractions and the other to get deeper insight into the polysiloxane structures. Furthermore, it was our aim to clarify which fraction can be visualized using MALDI‐TOF MS. Our results show that the ratio of chemically bound MPTMS is higher when using microwave heating, but the same structures in the physically adsorbed fraction were built in both cases.magnified image

Microwave Accelerated Polymerization of 2‐Phenyl‐5,6‐dihydro‐4H‐1,3‐oxazine: Kinetics and Influence of End‐Groups on Glass Transition Temperature

AbstractSummary: The ring‐opening polymerizations of 2‐phenyl‐5,6‐dihydro‐4H‐1,3‐oxazine (PhOZI) with methyl tosylate (MeOTs) and butyl iodide (BuI) as initiators were performed in refluxing butyronitrile. Reaction kinetics under microwave irradiation was compared with conventional oil bath heating. The polymerization rates, under microwave irradiation, showed an acceleration by a factor of 1.8 (independently from the used initiator). The investigation of the thermal properties of the obtained poly(N‐benzoyl‐trimethyleneimine) showed the influence of molecular weight and end‐groups on the glass transition temperature.The ring‐opening polymerizations of 2‐phenyl‐5,6‐dihydro‐4H‐1,3‐oxazine performed in refluxing butyronitrile.magnified imageThe ring‐opening polymerizations of 2‐phenyl‐5,6‐dihydro‐4H‐1,3‐oxazine performed in refluxing butyronitrile.

Selective introduction of a fluorine atom into carbohydrates and a nucleoside by ring-opening fluorination reaction of epoxides

Ring-opening fluorination reactions of epoxides using tetrabutylammonium bifluoride (TBABF)-KHF 2, or Et 3N-3HF under microwave irradiation were applied for the introduction of a fluorine atom into the carbohydrate molecules. When TBABF-KHF 2 was used as the fluorination reagent, a fluorine atom was introduced regioselectively and various functional groups can tolerate the conditions. When Et 3N-3HF was used under microwave irradiation, the reaction time could be remarkably shortened compared with the conventional oil-bath heating.

Microwave‐Assisted Synthesis of Metallic Nanostructures in Solution

AbstractFor Abstract see ChemInform Abstract in Full Text.

Copper-free palladium-catalyzed sonogashira-type coupling of aryl halides and 1-aryl-2-(trimethylsilyl)acetylenes

A one-pot procedure for the direct coupling of 1-aryl-2-trimethylsilylacetylenes with aryl halides to give diaryl acetylenes is reported. The procedure does not involve the use of copper(I) iodide. Improvement in reaction yields has been obtained by replacing conventional oil bath heating with the use of microwave dielectric heating.

Microwave‐Assisted Synthesis of Metallic Nanostructures in Solution

Microwave (MW) rapid heating has received considerable attention as a new promising method for the one-pot synthesis of metallic nanostructures in solutions. In this concept, advantageous application of this method has been demonstrated by using some typical examples for the preparation of Ag, Au, Pt, and AuPd nanostructures. Not only spherical nanoparticles, but also single crystalline polygonal plates, sheets, rods, wires, tubes, and dendrites were prepared within a few minutes under MW heating. Morphologies and sizes of nanostructures could be controlled by changing various experimental parameters, such as the concentration of metallic salt and surfactant polymer, the chain length of the surfactant polymer, the solvent, and the reaction temperature. In general, nanostructures with smaller sizes, narrower size distributions, and a higher degree of crystallization were obtained under MW heating than those in conventional oil-bath heating. The origin of these characteristic features under MW irradiation is discussed in terms of thermal and non-thermal effects under MW irradiation.