Volume 18, Issue 4 -

Transesterification of propylene carbonate (PC) and ethanol is a potent non-phosgene route for the synthesis of diethyl carbonate (DEC). In the present study, hydroxyapatite was synthesized and modified using Zn and Mg (Zn/HAP and Mg/HAP). Modified hydroxyapatite was used as catalyst for the synthesis of DEC. The thermal analysis of the catalytic precursor was studied using thermogravimetric-differential thermal analysis. The structural analysis, surface morphology, and nature of active sites over the catalyst surface were studied using techniques such as Fourier transform infrared spectroscopy, X-ray diffraction, N 2 adsorption-desorption, scanning electron microscopy, and CO 2 temperature-programmed desorption. Effects of reaction conditions like reaction temperature, reaction time and ethanol/PC molar ratio on DEC yield were also studied. The effects of Mg and Zn on HAP were found to be promotional for the synthesis of DEC using PC and ethanol. Mg/HAP was found to be the best among the three catalysts studied owing to its high basicity. Maximum DEC yield of 52.1 % was obtained in 5 h at 433 K using Mg/HAP catalyst.

A modified rotating packed disc contactor (RPDC) with the maximum working volume of 65 liter is designed for biological waste water treatment. A hollow disc with radial vanes mounted on the disc was a modified design of this contactor. Stimulus-response experiments were conducted in the contactor to understand liquid mixing behavior under different operating conditions. The recycle stream was also used in the operation of the contactor. Experiments were conducted for different number of discs, rotational speeds and recycle ratios. The disc design and recycle ratio had marked influence on the mixing behavior. An increase in disc rotation and recycle ratio produced a well-mixed flow behavior. Moreover, the surface area available in the RPDC was about 4 times more than the surface area available in a standard rotating biological contactor (RBC) operating at similar conditions. A mathematical model was developed for the flow behavior under recycle and a good agreement was found between the model and experimental results.

Activated carbon (AC) was modified by using non-thermal plasma in O 2 , N 2 and O 2 /N 2 atmospheres to increase its Cu(II) adsorption capacity and quantify the influences of the modifying atmospheres. SEM, BET, FT-IR and XPS were used to characterize the surface physical and chemical properties of AC. The results show that the AC modified by using plasma had significantly better Cu(II) adsorption performance than the raw AC. Among the O 2 , N 2 and O 2 /N 2 atmospheres, the AC with plasma modification in N 2 showed best Cu(II) adsorption performance and the Cu(II) adsorption capacity was 369.5% higher than the raw AC. The AC modified in O 2 atmosphere can form C—COOH groups, while the AC modified in N 2 atmosphere can form C—NH 2 groups. These two groups are both beneficial for Cu(II) adsorption, where the —NH 2 groups are more effective for Cu(II) adsorption compared to —COOH groups. The chemisorption dominated the Cu(II) adsorption on the plasma modified AC and the adsorption performance was dependent on the surface functional groups properties of AC.

The performance of a newly designed static mixer is explored in this paper by numerical simulations. It concerns a converging/diverging circular tube equipped with opposing and staggered baffles. This new design of static mixer presents a cost-effective, easy-to-design, easy-to-maintain choice, with a minimum pressure drop and a good mixing index at low Reynolds numbers (from 60 to 700), to the currently used static mixers. The investigation was carried out numerically for different baffle clearances ( cl/D  = 0.3, 0.5, 0.7 and 1.0, respectively) and inclination angles ( α  = 0°, 30° and 45°, respectively), different ratios of inlet diameter-to-outlet diameter ( D d  =  d/D  = 0.6, 0.8, 1.0, 1.2 and 1.4, respectively) and different Reynolds number values. The obtained results revealed that the diverging tube favors the mixing index while reducing the pressure drop. For a dimensionless baffle clearance ( cl/D ) of 0.5 and Re  = 700, the mixing index has been increased from 0.78 for a simple tube ( d/D  = 1) having vertical baffles ( α  = 0°) until 0.95 for a diverging tube at the ratio ( d/D ) of 1.4 with the same vertical baffles ( α  = 0°). The increase in the ratio d/D has also yielded a decrease in pressure losses. Compared to the simple static mixer without baffles and having the same inlet as outlet sections, the maximum enhancement in mixing index was about 315.84% when d/D  = 1.4 and Cl/D  = 0.3 and α  = 0°. However, a reduction in pressure drop by about 92% may be obtained when α  = 30° with only a reduction in mixing index by 14% (compared to α  = 0°).

Bioreactors are used in many biochemical industries to produce commercial life products such as medicines, enzymes, perfumes, paints and antibiotics. In the presented study, a specially shaped bioreactor has been designed, built and operated to increase the mass transfer coefficient. The constructed bioreactor, according to type of microorganisms, can provide high amounts of oxygen or carbon dioxide. Moreover, the manuscript was aimed at investigating the hydrodynamic properties of the bioreactor. The bioreactor was constructed from three parts including shower in upper part, middle section for mass transfer and bottom section as a reservoir. Liquid flow rate, shower holes diameter, aeration velocity and the middle part height of the bioreactor have been studied as factors influencing the hydrodynamics. The results showed that the highest mass transfer coefficient was 30.1 1/h which was achieved when the liquid flow rate, the shower holes diameter, aeration velocity and middle part height of the bioreactor were 280 mL/min, 2 mm, 0.03 vvm and 60 cm, respectively.

Present study deals with the treatment of coking waste water (CWW) for the reduction of pollutants COD, phenol and cyanide using catalytic thermolysis (CT). For screening of catalyst and optimization of pH the CT was performed at 100 °C, pH = 3–11 using catalyst mass loading C w  = 3 g/L. In this study Cu (NO 3 ) 2 gave best performance. Further, CT was carried out using Cu (NO 3 ) 2 catalyst in high pressure reactor (HPR). The investigated parameters range were initial pH (pH i ) = 3–11, C w  = 1–5 g/L, temperature (T) = 100–160 °C and treatment time (t R ) = 6 h. The maximum percentage reduction for COD, phenol and cyanide were 83.33, 80.57 and 97.61%, respectively at pH = 9, Cw = 4 g/L, T = 140 °C and t R  = 6 h. The CT did not give complete reduction of pollutant; therefore it was further treated using adsorption process as second stage treatment. The initial value of COD = 610 mg/L, phenol = 70.58 mg/L and cyanide = 0.45 mg/L were further reduced to 98.85, 100.00 and 55.55%, respectively, when adsorption process was performed at pH = 9, adsorbents dose A w  = 4 g/L, t R  = 2 h. The response surface methodology (RSM) was performed through central composite design (CCD) for the designing of experiments and optimization of both the process. The kinetics studies of CT at HPR showed first order with respect to COD and phenol, and 0.24–0.608 order with respect to C W . Highlights – Thermolysis and adsorption process were applied for the treatment of coking wastewater (CWW). – The parameters like, pH, catalyst amount, time and temperature were studied for removal of pollutants by thermolysis process. – In adsorption process, the effect of pH, adsorbent dosage and treatment time were studied for removal of pollutants. – The two stage treated effluent have COD = 8 mg/L, phenol = 0.00 mg/L and cyanide = 0.2 mg/L. – The treated effluent can be used in same industry for various purposes thus gives zero discharge.

In this article the experimental results related to various wall heating conditions for a batch reactive distillation (BRD) are presented. A solid catalyzed esterification reaction between acetic acid and methanol to produce methyl acetate and water is chosen as the system for study. An experimental apparatus with reboiler and a rectification column along with top total condenser is used. As a novelty the rectification column is provided a jacket through which hot water can be circulated. The dynamics of temperature in the reboiler, the time for onset of distillate and the purity of product in the distillate were recorded. The wall temperature of rectification column is varied to study its effect. Another two sets of conditions with air filled jacket and insulated conditions were also studied. The reboiler is supplied a constant heat input rate at three different values. An objective function pertaining to high throughput of the desired product in distillate is defined to select the most suitable option among all the above mentioned operating conditions.

Activated carbon derived from raw corncob (CCAC), which prepared with steam as the activating agent, was used to adsorb bisphenol S (BPS) from aqueous solution. Characterizations of CCAC were measured by using the Brunauer-Emmett-Teller, scanning electron microscopy, and Fourier transform infrared spectroscopy. Adsorption conditions including initial BPS concentration, contact time, adsorbent dosage and pH were optimized by response surface methodology (RSM). The results show that adsorption equilibrium was well described by the Langmuir and Koble–Corrigan models. The maximum monolayer adsorption capacity of BPS was found to be 617.29 mg g −1 at 298 K. Based on the thermodynamic parameters analysis, the BPS adsorption process was turned out to be spontaneous and exothermic. The adsorption process of BPS was well described by the pseudo-second-order kinetic model. It also found that H-bonding, π–π interaction, and electrostatic interaction were the main mechanisms in the process of BPS adsorption onto the CCAC.

Metronidazole (MNZ) is one of the pharmaceutical products which is considered as one of the most important pollutants in the environment due to its wide use and resistance to biodegradation. Hence, the purpose of this study is the optimization of the electrochemical degradation of the metronidazole (MNZ) antibiotic using electrochemical oxidation on a stainless steel316 coated with beta lead oxide (SS316/β-PbO 2 ) anode. In the studied electrochemical process, the response surface methodology (RSM) involving a five-level ((pH (A) and electrolysis time (B), current density (C), and MNZ concentration (D)). The central composite design (CCD) was employed for optimizing and modeling of the electrochemical process in the degradation of MNZ. The preparation of SS316/β-PbO 2 anode was accomplished using the electro-deposition method. Scanning electron microscope (SEM), energy-dispersive X-ray (EDX), and X-ray diffraction (XRD) analyses were conducted for accurate evaluation and characterization of the coated electrode. The effect of influencing factors on electrochemical degradation of MNZ was studied, and the highest MNZ degradation efficiency was observed to be 98.88% after 120 min under the optimal conditions including the supporting electrolyte concentration of 1.0 g/100 cc, the initial MNZ concentration of 30.1 mg/L, pH of 4 and the current density of 9.99 mA/cm 2 . The linear regression coefficient ( R 2 ) between experiments and different response values in the model was 0.99. Moreover, the statistical analysis of the results indicated that in the range studied, the most effective parameters in MNZ degradation are MNZ concentration and pH. In general, it can be concluded that the electrochemical process using SS316/β-PbO 2 anode can effectively eliminate metronidazole, and it can be considered as an efficient method in the degradation of various pollutants.

In the present investigation transalkylation of cumene with toluene was carried over a series of zeolite containing rare earth metals such as lanthanum (La), cerium (Ce), and praseodymium (Pr). The modified zeolites were further characterized by EDS, XRD, BET and TPD. The surface area and acidities of the modified zeolite catalysts were reported. The transalkylation reactions were carried out varying different parameters such as metal loading (2–10 wt%), temperature (448–573 K), reactant ratio (1–15), and space-time (3.2–9.29 kg h/kmol). Praseodymium-modified X zeolite (PrX) showed the highest cumene conversion (60 wt%) and cymene selectivity (65.7 wt%) compared to the other zeolites. The maximum cumene conversion and cymene selectivity were obtained at 523 K, the toluene-to-cumene ratio of 9:1, and space-time of 9.29 kg h/kmol. Mass transfer resistances were studied in the said reaction conditions.