Hydrothermal liquefaction of wheat straw in hot compressed water and subcritical water–alcohol mixtures

Hydrothermal liquefaction of lignocellulosic biomass (wheat straw) into bio-oil has been investigated under subcritical conditions (temperature up to 350 °C, pressure up to 200 bar) in water and water–alcohol mixtures using ethanol and isopropanol in a continuously operated tubular reactor. The effect of different reaction parameters such as temperature, pressure and water–alcohol ratio on the biomass conversion, cracking products yield and the higher heating value (HHV) of the received bio-oil was studied. The water–ethanol mixture was found to be a very reactive medium showing a complete biomass conversion and >30 wt% yield of high caloric oil (HCO). A maximum HHV of 28 MJ/kg for HCO was achieved. In addition, Ru (5 wt%) on H-Beta support was used as catalyst in a run with hydrogen in the feed showing deeper deoxygenation of reaction intermediates and highest HHV of the product oil (30 MJ/kg). This work demonstrated the usability of water–ethanol mixtures for an effective depolymerization of lignocellulosic biomass to bio-oils under subcritical reaction conditions with more than doubled HHV compared to the feedstock, in particular using a catalyst and the presence of hydrogen for further deoxygenation.     

Development of novel grafted hybrid PVA membranes using glycidyltrimethylammonium chloride for pervaporation separation of water–isopropanol mixtures

Tetraethylorthosilicate incorporated hybrid poly(vinyl alcohol) membranes were grafted with glycidyltrimethylammonium chloride (GTMAC) in different mass%. The resulting membranes were subjected to physico-chemical investigations using Fourier transform infrared (FTIR) spectroscopy, wide-angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC), thermogravimetry analysis (TGA) and scanning electron microscopy (SEM). The effects of grafting and feed composition on pervaporation performance of the membranes were systematically investigated. The membrane containing 30 mass% of GTMAC exhibited the highest separation selectivity of 1570 with a flux of 1.92 × 10^?2 kg/m² h at 30 °C for 10 mass% of water in the feed. The total flux and flux of water are almost overlapping each other, manifesting that these membranes could be used effectively to break the azeotropic point of water–isopropanol mixtures. From the temperature dependent diffusion and permeation values, the Arrhenius activation parameters were estimated. The activation energy values obtained for water permeation (E_pw) are two to three times lower than those of isopropanol permeation (E_pIPA), suggesting that the developed membranes have higher separation ability for water–isopropanol system. The E_p and E_D values ranged between 63.73 and 33.07, and 62.78 and 32.75 kJ/mol, respectively. The positive heat of sorption (ΔH_s) values was obtained for all the membranes, suggesting that Henry's mode of sorption is predominant in the process.     

Application of microwave heating to pervaporation: A case study for separation of ethanol–water mixtures

Membrane pervaporation experiments for dewatering of water–ethanol mixtures were conducted, using a polymeric hydrophilic membrane, under microwave and conventional heating in a multimode microwave oven and a convection oven, respectively. Three feed temperatures (33.5, 45.5 and 51.5 °C) and two feed compositions (5.5 wt% and 20 wt% water in the feed) were considered. At 20 wt% water content, higher water fluxes through the membrane were obtained in the convection oven. At lower water content in the feed (5.5 wt%), the opposite effect was observed; the water fluxes were higher under microwave heating over the considered temperature range. These differences may arise from the different dielectric properties and consequently thermal behaviour of the feed mixtures under microwave heating. Microwave coupling with ethanol is stronger than with water. Moreover, unlike water, the dielectric loss factor of ethanol increases with temperature, which makes microwave dissipation preponderant in hot areas. Hence, high ethanol concentrations in the feed can easily induce thermal gradients.     

Removal of heavy metal ions from water by an combined sorption–crystallization process using activated clays

The degree of comminution of materials in an ultrasonic field has been theoretically estimated by calculating the maximum and minimum energy inputs necessary for this process (upper and lower estimates have been obtained). The degree of comminution of kaolin in an ultrasonic bath determined by light and electron microscopy is in satisfactory agreement with the theoretical estimates. The efficiencies of heavy metal ion (Cu²⁺, Ni²⁺) removal from aqueous solutions in the following processes have been compared: adsorption on natural materials (kaolin and bentonite), chemical precipitation in homogeneous crystallization, and integrated sorption–crystallization process using activated clays. The highest purification efficiency has been attained in the integrated process preceded by ultrasonication of the clay slurry and alkaline reagent. Use of these sonochemically activated additives has shortened the duration of the integrated process and has increased the degree of removal of toxic metals to 10²–10³. Clays have been demonstrated to act as a sorbent, a heterogeneous crystallization stimulator, and a coagulant accelerating the sedimentation of the solid phase.     

Mixed matrix membranes of Matrimid 5218 loaded with zeolite 4A for pervaporation separation of water–isopropanol mixtures

Mixed matrix membranes were prepared by incorporating zeolite 4A into polyimide of Matrimid 5218 using solution-casting technique. The fabricated membranes were characterized by scanning electron microscopy (SEM), differential scanning calorimeter (DSC) and thermo gravimetric analysis (TGA). It was found that the higher annealing temperature of 250 °C is more favorable to improve adhesion between zeolite and polymer phases. Effects of different parameters such as temperature (30–60 °C), water content in feed (10–40 wt.%), zeolite loading (0–15 wt.%) and polymer content (10 and 15 wt.%) on pervaporation dehydration of isopropanol were studied. Sorption studies were carried out to evaluate degree of swelling of the membranes in feed mixtures of water and isopropanol. The experimental results showed that both pervaporation flux and selectivity increase simultaneously with increasing the zeolite content in the membranes. The membrane containing Matrimid 5218 (10 wt.%)–zeolite 4A (15 wt.%) exhibits the highest separation factor (α) of 29,991 with a substantial permeation flux (J) of 0.021 kg/m² h at 30 °C for 10 wt.% of water in the feed. The PV performance was also studied in term of pervaporation separation index (PSI). Permeation flux was found to follow the Arrhenius trend over the investigated temperature range.     

Ignition of droplets of coal–water–oil mixtures based on coke and semicoke

To permit expansion of the resource base and utilize industrial waste, coal–water–oil fuels may be prepared on the basis of coke and semicoke, as well as common petroleum derivatives (fuel oil and spent compressor, turbine, and transformer oils). The minimal oxidant temperature corresponding to stable ignition of coal–water–oil slurries is established. Typical variation in fuel temperature in the course of reaction is determined, as well as the delay time of ignition and the total combustion time for individual droplets of such fuel suspensions. For droplets of initial size 0.5–1.5 mm, the influence of the various factors (droplet size, oxidant temperature, and concentration of the components) on the threshold (minimum) temperature and inertia of ignition is studied. It is shown that stable ignition of coke and semicoke in such fuel is possible at moderate oxidant temperatures: 700–1000 K.     

Description of butanol aqueous solution transport through commercial PDMS pervaporation membrane using extended Maxwell–Stefan model

The mass transport of components during the pervaporation of binary butanol aqueous solutions using commercial PDMS membranes has been investigated. A simplified approach of the Maxwell–Stefan model was extended to include the effect of membrane swelling and temperature on the diffusion coefficients and sorption properties. Partial permeate fluxes obtained at different temperatures and concentrations have been fitted to determine the extended model parameters. The sorption properties and diffusion coefficients of components have been estimated using fitted parameters. Predicted values of the solubility and diffusivity were used to calculate and compare the permeability of the components under different operating conditions.

Abbreviations: HPLC - High performance liquid chromatography; MS - Maxwell–Stefan; PDMS - Polydimethylsiloxane; SEM - Scanning electron microscope     

Influence of maleation of polypropylene on the interfacial properties between polypropylene and ethylene–vinyl alcohol copolymer

In order to improve the miscibility between the components of a blend, it is possible to modify the chemical structure by functionalizing one or more of the components. This results in better adhesion at the interface between the components and, consequently, in better mechanical properties. In this work, the influence of maleation of polypropylene on the interface between polypropylene and ethylene–vinyl alcohol copolymer was studied using the measurement of interfacial tension, surface analysis with electron spectroscopy for chemical analysis (ESCA), and morphological observation, using scanning electron microscopy (SEM). The interfacial tension between a 0.1-wt % maleated polypropylene and ethylene–vinyl alcohol copolymer was shown to be 25% lower than the interfacial tension between nonmaleated polypropylene and ethylene–vinyl alcohol copolymer. This resulted in better adhesion between maleated polypropylene and ethylene–vinyl alcohol copolymer. The surface analysis indicates that this decrease of interfacial tension is due to migration of the maleic groups of the maleated polypropylene to the interface between the 2 polymers and that, probably, a chemical interaction occurs at the interface between maleated polypropylene and ethylene–vinyl alcohol copolymer. It is also shown in this work that additives, such as SiO₂, found in commercial polymers, can influence the interfacial tension between 2 polymers. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 70: 75–87, 1998     

Dehydration of C2–C4 alcohol/water mixtures via electrostatically enhanced graphene oxide laminar membranes

The dehydration of alcohol/water mixtures using pervaporation membranes requires less energy than is required by conventional separation technologies. In this paper, we report electrostatically enhanced graphene oxide (GO) membranes for the highly efficient pervaporation dehydration of C₂–C₄ alcohol/water mixtures. Positively charged molecules were introduced as the interlayer of negatively charged GO layers via layer-by-layer assembly, thereby creating an electrostatic attraction that drives the assembly of GO nanosheets into ordered interlayer channels. The effects of the feed temperature, water concentration, and continuous operation on the membrane transport behavior were systematically investigated. In the dehydration of 90 wt% alcohol/water mixtures at 70°C, the membrane exhibited ethanol/water, isopropanol/water, and n-butanol/water fluxes of 2.35, 2.98, and 4.69 kg/(m² hr), respectively, as well as separation factors for the same mixtures of 3,390, 5,790, and 4,680, respectively. This excellent alcohol/water dehydration performance outperforms those of state-of-the-art polymeric membranes and GO-based membranes.     

Effect of Pre‐Filtration on Selective Isolation of Tat Protein by Affinity Membrane Separation: Analysis of Flux,Separation Efficiency,and Processing Time

Abstract

The isolation and purification of Tat protein from bacterial lysate using avidin‐biotin interaction in microfiltration membranes have been reported in the literature. To increase the efficacy of the technique, improvements in flux, Tat separation efficiency, and processing time are essential. In the current research work a pre‐filtration step was introduced to remove unwanted high molecular weight proteins and other impurities from feed prior to affinity membrane separation. Significant enhancement in flux and separation efficiency of Tat was observed. Processing time was also reduced significantly. For example, with UF pretreatment step the total Tat recovery was around four times higher (with processing time 25% lower) than that observed with the untreated feed. The quality of purified Tat was analyzed by SDS‐PAGE, Western Blot, and biotin analysis. Flux behavior in affinity separation was described by model equations.     

Solubility of ammonium oxalate in water–acetone mixtures and metastable zone width of their solutions

Experimental results on the solubility c of ammonium oxalate in mixed water–acetone solvents containing acetone content x < 0.55 by weight at different saturation temperature T are presented and discussed using the theory of regular solutions. It was found that: (1) the dependence of the solubility c of ammonium oxalate in solutions of different mixed water–acetone solvents on temperature T follows an Arrhenius-type relation, (2) the dependence of c on acetone content x at different temperature T follows the relation: ln(c + δ) = a − bx, where the parameters a and b are measures of deviation of a solution from ideality and the correction factor δ is related to the activity coefficient f_a of the solution, which decreases with an increase in c, and (3) the dependence of the solubility c of ammonium oxalate in solutions of different compositions x of water–acetone mixtures is related to the dielectric constant ?* of the solvent mixture, following the relation ln c = C + C₁?*, where C and C₁ are related to the parameters a and b, respectively. Study of the metastable zone width, defined as maximum undercooling ΔT_max a solution saturated at a particular temperature T can withstand, of some selected solutions of mixed water–acetone solvents at different T revealed that ΔT_max decreases with an increase in antisolvent content x. The results are discussed using the self-consistent Nývlt-like approach.     

Screening of ionic liquids as entrainers for the separation of 1-propanol + water and 2-propanol + water mixtures using COSMO-RS model

The COSMO-RS model was used to screen potential ionic liquids for the separation of aqueous azeotropic mixtures 1-propanol?+?water and 2-propanol?+?water. A combination of 22 cations (involving imidazolium, pyridinium, pyrrolidinium, quinolinium, and ammonium) and 36 anions were investigated. The anions chloride [Cl] and dihydrogen phosphate [H₂O₄P] were found to strongly influence the vapor liquid equilibrium behavior, whereas the ammonium-based cations diethanol ammonium [(Et)₂AMM]⁺ and tetra methyl ammonium [M₄AMM]⁺ were the most promising cations. In addition, the study of mixing enthalpy and excess Gibbs free energy confirmed that the molecular interaction of ionic liquids with water was found to be much larger than that with alcohols 1-propanol and 2-propanol, indicating the presence of a strong hydrogen bonding between the ionic liquids and water. Further, the addition of ionic liquids to the alcohol–water mixture reduces the activity coefficient of water and increases the relative volatility of the mixture, facilitating easier separation. Ionic liquids [(Et)₂AMM][Cl], [(Et)₂AMM][H₂O₄P], [M₄AMM][Cl], and [M₄AMM][H₂O₄P] are expected to be effective entrainers for the separation of the industrially important 1-propanol?+?water and 2-propanol?+?water systems.     

Improving microisotacticity of Ziegler–Natta catalyzed polypropylene by using triethylaluminum/triisobutylaluminum mixtures as cocatalyst

Propylene was polymerized with TiCl₄/Di/MgCl₂ catalyst and cocatalysts containing triethylaluminum (TEA) and triisobutylaluminum (TiBA) in the presence of Ph₂Si(OMe)₂ (external donor) and hydrogen. Chain structure of the formed polypropylene (PP) was characterized by temperature-rise elution fractionation (TREF) combined with DSC and ¹³C NMR analysis of the main fractions. Increasing the amount of TiBA in cocatalyst leads to decrease of isotactic index of PP, meanwhile the microisotacticity of the main TREF fractions of PP was enhanced. PP produced with the catalyst activated by a 50/50 TEA/TiBA mixture has the same content of highly isotactic chains as PP produced with the TEA activated catalyst, but main TREF fractions of the former has higher microisotacticity than the later. Fast alkyl exchanges in TEA/TiBA mixtures are found by ¹H NMR analysis of the mixtures. By analyzing alkanes released from hydrolyzed catalysts that have been treated with the cocatalyst, alkylation power of TEA/TiBA mixture was found to decrease with increasing its TiBA content. The effects of TEA/TiBA mixture in propylene polymerization is explained by the weaker alkylation power and lower Lewis acidity of the mixed alkylaluminums than pure TEA. Decrease in the alkylation power leads to reduction of active centers with the highest stereospecificity, meanwhile decrease in Lewis acidity intensified the role of De in enhancing stereospecificity of different active centers. When the amount of TiBA in TEA/TiBA mixture falls in a suitable range, the later effect becomes dominant, and evident improvement in microisotacticity of PP can be achieved.     

Liquid-phase hydrogenation of benzene to cyclohexene catalyzed by Ru/SiO2 in the presence of water–organic mixtures

The liquid-phase hydrogenation of benzene to cyclohexene was studied using a Ru/SiO₂ catalyst prepared by reduction of ruthenium(III) chloride impregnated in a hydrophilic non-porous silica. In a biphasic water/benzene system at 423 K and 5 MPa of hydrogen pressure, a 14% cyclohexene yield was obtained at 60% benzene conversion. Increased cyclohexene yields and selectivities were observed in the presence of ethylene glycol/water and glycerol/water mixtures, which consist mainly of hydrated organic molecules that can enhance the hydrophilicity around the ruthenium particles favoring the cyclohexene desorption.     

Synthesis and characterization of composites based on polyaniline and styrene–divinylbenzene copolymer using benzoyl peroxide as oxidant agent

This work presents a method to prepare composites based on polyaniline (Pani) and styrene–divinylbenzene copolymers (SD) by in situ polymerization of aniline using benzoyl peroxide as oxidant agent. The composites were obtained from copolymers with two degrees of porosities which have higher and lower surface areas. Emeraldine Pani was prepared using hydrochloric acid as dopant. One cycle or four cycles of aniline polymerization were performed. The copolymers and their respective composites characterizations were performed by infrared spectroscopy, thermogravimetric analysis, physical nitrogen adsorption–desorption measurements, morphology analysis, elemental analysis and determination of Brönsted acid sites. The Pani was distributed overall porous SD copolymer producing composites with high surface area. Then, they were evaluated as catalysts for esterification reaction of a fat acid. It was found that that composites prepared with four cycles of in situ polymerization presented best catalytic activity than one cycle composites.     

Surface modification of silica aerogels by hexamethyldisilazane–carbon dioxide mixtures and their phase behavior

The surfaces of monolithic silica aerogels were rendered hydrophobic using hexamethyldisilazane (HMDS) as surface modification agent and scCO₂ as solvent. The treatment led to hydrophobic silica aerogels which are as transparent as untreated aerogels. The effects of HMDS concentration in the fluid phase and the reaction time were investigated and the contact angles were found to be 130° at different conditions. FTIR spectra indicated a reduction in hydrophilic surface silanol groups and the emergence of hydrophobic CH₃ groups. The bubble point pressures of the HMDS–CO₂ system were obtained at temperatures 298.2 K, 313.2 K, 327.7 K and 342 K at various concentrations. At a fixed temperature, the bubble point pressure decreased as the concentration of HMDS increased. At a fixed composition, bubble point pressure increased as the temperature increased. The bubble point pressures were modeled using the Peng–Robinson Stryjek–Vera Equation of State (PRSVEOS) and compared well with the experimental data.     

Photocatalytic degradation kinetics of cationic and anionic dyes using Au–ZnO nanorods: Role of pH for selective and simultaneous degradation of binary dye mixtures

Photocatalysis with ecofriendly and low cost materials is attractive for degradation of organic pollutants without aid of strong reagents. In this regard, Au nanoparticle decorated ZnO nanorods (Au–ZnO) with good crystalline quality was synthesized by cost-effective and scalable hydrothermal method followed by photo-reduction of Au salt. This study addresses variation of photocatalytic degradation kinetics of different nature of dyes with various scavengers and pH conditions. Further, the process versatility is demonstrated by selective or simultaneous degradation of binary dye mixtures with optimized parameters. From Langmuir-Hinshelwood kinetic model, dye concentration range for first order limiting case was determined, and further validated from measured surface area of photocatalyst and change in dye absorbance before irradiation. Better adsorption with faster degradation exhibited by Methylene Blue (MB) dye showed efficient mineralization, revealed from chemical oxygen demand measurements. In Au–ZnO photocatalysis, generation of hydroxyl radical and its significant role in dye degradation was demonstrated using different scavengers. Variation of dye adsorption with pH dependent surface charge characteristics of photocatalyst resulted about one order higher degradation rate constant of MB at high pH. Strong pH dependent MB degradation is shown to be useful for its selective or simultaneous degradation with other dyes. Results of this study are useful for designing photo-reactors and these nanoparticles are efficient for degradation of different dyes, their combinations and industrial effluents under low power UV lamp for treatment different organic pollutants.