Sevgi Polat

Thermal decomposition behavior of tobacco stem Part I: TGA-FTIR-MS analysis

ABSTRACT In the present study, the thermal degradation behavior of tobacco stem was examined by means of a thermogravimetric analyzer (TGA) under nitrogen atmosphere at temperature range of 25–1,000°C. The TG curve indicated that the pyrolysis process of tobacco included three zones, and main pyrolysis occurred in the second zone by means of the decomposition of hemicellulose, cellulose, and lignin in a temperature range of 180–540°C. Furthermore, the gases evolved during the degradation were analyzed simultaneously via TGA coupled with a Fourier transform infrared spectrometer (FTIR) and mass spectrometer (MS). Carbon dioxide, methane, water, formaldehyde, and propanal were the main volatiles detected via MS and confirmed by FTIR.

Thermal decomposition behavior of tobacco stem Part II: Kinetic analysis

ABSTRACT As a continuation of the previous study on the thermal degradation behavior of tobacco stem, this work is focused on the kinetics of pyrolytic decomposition. Thermogravimetric analysis of tobacco stem samples was conducted under nitrogen atmosphere at different heating rates of 5, 10, 15, and 20°C/min at a temperature range of 25–1,000°C. The kinetic parameters, such as activation energy, pre-exponential factor, and reaction order, were determined by applying the Coats–Redfern method for the main pyrolysis occurred in the second zone by means of the decomposition of hemicellulose, cellulose, and lignin at a temperature range 180–540°C. In addition, the activation energy was calculated using various degradation models, including Kissinger, Friedman (FR), Flynn–Wall–Ozawa (FWO), and Kissinger–Akahira–Sunose (KAS). The average activation energy of tobacco stem was calculated to be 150.40, 230.76, 216.97, and 218.56 kJ/mol by the Kissinger, FR, FWO, and KAS models, respectively.

Impact of glutamic acid on the transformation of calcium sulfate hemihydrate to dihydrate: Characterization, equilibrium, kinetics, and thermodynamics

ABSTRACT In this study, the characteristics and mechanisms of glutamic acid adsorption on the transformation process of calcium sulfate hemihydrate to calcium sulfate dihydrate were investigated in a batch-type crystallizer. The phase transformation was followed by conductivity measurements in both the absence and the presence of glutamic acid used as additive. The structure of the samples obtained during this process was characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, Brunauer–Emmett–Teller, thermogravimetric analyzer-mass spectrometer, and ATR-FTIR analyses. From the results, it was shown that the uptake of glutamic acid caused a retarding effect in the transformation rate. It was also found that the thin- and weak-layered structure was replaced by a thick and compact plate-like structure. The adsorption isotherms, kinetics, and thermodynamics were also explored to describe the process. According to the results, the Langmuir isotherm model fit quite well, as demonstrated by the high R2 value, calculated using a linear and nonlinear procedure, and the maximum adsorption amount of 169.49 mg/g. The pseudo-first-order and pseudo-second-order kinetic models were applied to analyze the kinetic experimental data, and it was determined that the adsorption of glutamic acid followed the pseudo-second-order model, which indicates that the adsorption rate depended on chemisorption. The thermodynamic results illustrated that the adsorption of glutamic acid in the transformation process was spontaneous and endothermic.

Effect of ultrasonic irradiation on morphology and polymorphic transformation of glycine

The polymorphic phase transformation of β-glycine to α-glycine was analyzed in the absence and presence of three different intensities of ultrasonic irradiation in a batch system at 25 °C. The experiments were performed to explore the effects of ultrasonic irradiation and its intensity on phase transformation time, morphology, storage stability, and filtration characteristics. The crystals obtained with and without ultrasound were characterized by X-ray diffraction (XRD). The XRD results showed that the ultrasound tended to reduce the transformation time. According to the scanning electron microscopy (SEM) images, the ultrasound had a significant effect on the crystal morphology. The highest ultrasound power applied yielded more rounded crystals compared to the crystals prepared in the absence of ultrasound. In addition to SEM analysis, detailed crystal shape analysis was performed and shape factors, namely the circularity, elongation, and convexity values, were determined quantitatively to get more information about the morphological changes related to the variations in the size and shape of the end products. From the morphological point of view, the circularity values of the crystals obtained under ultrasound were higher but the elongation values were smaller compared to the crystals obtained in the absence of ultrasound. It was also found that higher ultrasound decreased the length and width of the crystals, and the application of ultrasound increased the aspect ratio value from 0.483 to 0.657.

Assessment of propionic acid adsorption performance on the phase transformation of calcium sulfate hemihydrate to dihydrate

ABSTRACT The adsorption of propionic acid during the transformation process of calcium sulfate hemihydrate to calcium sulfate dihydrate was studied in a batch-type crystallizer with respect to contact time, additive concentration and temperature in pure media, and in the presence of propionic acid used as an additive. The adsorbent was characterized by X-ray diffraction, scanning electron microscopy and thermogravimetric analysis combined with a Fourier-transform infrared spectrometer and a mass spectrometer. The adsorption characteristics were also investigated by means of evaluating the isotherm, kinetic and thermodynamic properties. The results of this investigation showed that propionic acid can serve as a good accelerator for the transformation process from calcium sulfate hemihydrate to dihydrate.

TÜTÜN TARLA ATIĞININ TGA-FTIR-MS İLE TERMAL DAVRANIŞININ BELİRLENMESİ

Bu calismada, tutun tarla atigi icin termal bozundurma islemi termogravimetrik analiz (TGA) cihazi ile 20 °C baslangic sicakligindan 1000°C’ye kadar 5, 10, 15 ve 20 °C /dk isitma hizlarinda ve azot atmosferi altinda gerceklestirilmistir. TGA’dan elde edilen egriler ve veriler yardimiyla, tutun tarla atigi icin Coats-Redfern yontemi kullanilarak, aktivasyon enerjisi, reaksiyon mertebesi ve frekans faktoru belirlenmistir. Yapilan calismada, termogravimetrik analiz cihaziyla birlestirilmis Fourier Transform Infrared Spektroskopisi ve Kutle Spektroskopisi (TGA-FTIR-MS) kullanilarak, hammaddenin bozunmasi sirasinda aciga cikan gazlar tespit edilmistir. Tutun tarla atiginin pirolizi sirasinda aciga cikan baslica urunlerin, metan, amonyak, su, hidrojen siyanur, formaldehit, karbon dioksit ve propanal oldugu belirlenmistir.