This research aimed at improving p-xylene selectivity in toluene disproportionation over ZSM-5 zeolite by exploring the effect of crystal size and various post synthetic modification methods. A comprehensive study of the effect of different modifications on the physicochemical properties of ZSM-5 was investigated using X-ray diffraction (XRD), pyridine adsorption, Fourier transform infra-red (FTIR), 29Si magic-angle spinning nuclear magnetic resonance (MAS NMR), BET surface area by N2 adsorption, inductively coupled plasma (ICP) and scanning electron microscopy (SEM). The catalytic performance of each catalyst was studied in a fixed bed reactor at a temperature 475 °C, WHSV 3-83 h-1 and two different pressures (1 and 10 bar). ZSM-5 zeolites with different crystal sizes (5, 50 and 100 ÂÂμm) were synthesized in house and compared with the commercially obtained ZSM-5 having a crystal size of 0.5 ÂÂμm. The increase in crystal size improved p-xylene selectivity which was attributed to the diffusion constraints imposed by the longer diffusion path lengths of large crystals. The highest p-xylene selectivity (58 %) was achieved over ZSM-5 with the largest crystal size 100 ÂÂμm at the highest WHSV 83 h-1. However, it was accompanied by a low conversion (2 wt. %). ZSM-5 with crystal size of 5 ÂÂμm delivered the best results in terms of the combination of para-selectivity (40 %) and toluene conversion (15 wt. %). The p-xylene produced in the channels of ZSM-5 can quickly isomerise to o-xylene and m-xylene on the external unselective acid sites. Different post modification methods were applied in this study in attempt to suppress the fast isomerization reaction by deactivating the external acid sites. This was achieved to some extent by depositing an inert silica layer using different silica agents, amounts and number of modification cycles and as a result p-xylene selectivity was significantly improved (84 %), especially over large crystals 5 ÂÂμm. The decrease in Brà̧nsted acidity (FTIR) suggested the success of the silylation method. Furthermore, impregnation of lanthanum and phosphorus on ZSM-5 improved p-xylene selectivity (40 %). FTIR measurements showed a drastic drop in the number of Brà̧nsted and Lewis acid sites after loading phosphorus which led to a large reduction in toluene conversion. Lanthanum impregnation had less effect on conversion and increased selectivity with decreased Brà̧nsted sites and pore volume reduction showed by N2 adsorption suggesting some pore narrowing. There are several approaches that can be considered in future to further improve p-xylene selectivity. Improving the synthesis of large crystals to balance acidity and crystal size can lead to the enhancement of p-xylene selectivity. Also, performing toluene disproportionation on optimised pre-coked ZSM-5 large crystals at high pressure can help to maintain the conversion while increasing p-xylene selectivity. Another approach would be to apply silylation modification to extruded large crystals ZSM-5.

Bioprocesses for air pollution control can generally be categorized as bioscrubber, biofilter, and biotrickling filter systems. These processes have been proven to be economical and effective for control of volatile organic compounds (VOCs) with concentrations of <1,000 mg C m-3 in gas streams. First, an activated sludge aeration tank (W x L x H = 40 x 40 x 300 cm) with a set of 2 mm orifice air spargers was utilized to treat gas-borne VOCs (toluene, p-xylene, and dichloromethane) in air streams. The effects of liquid depth (Z), aeration intensity (G/A), the overall mass transfer rate of oxygen in clean water (KLaO2), the Henry¡¦s law constant of the tested VOC (H), and the influent gaseous VOC concentration (C0) on the efficiency of removal of VOCs were examined and compared with a literature-cited model. Results show that the measured VOC removal efficiencies and those predicted by the model were comparable at a G/A of 3.75 ¡V 11.25 m3 m-2 hr-1 and C0 of around 1,000 ¡V 6,000 mg m-3. Experimental data also indicate that the designed gas treatment reactor with KLaO2 = 5 ¡V 15 hr-1, could achieve > 85% removal of VOCs with H = 0.24 ¡V 0.25 at an aerated liquid depth of 1 m, and > 95% removal of dichloromethane with H = 0.13 at a 1 m liquid depth. The model predicts that, for gas treatment in common activated sludge tanks, with KLaO2 = 5 ¡V 10 hr-1, depth = 3 ¡V 4.5 m, G/A = 9 ¡V 18 m3 m-2 hr-1, > 92% VOC removal can be achieved with operating parameters of Z of 3.0 m and KLaVOC/(G/A) of about 0.28 m-1, for VOCs with H < 0.3, such as most oxygen-containing hydrocarbons with low molecular weights, and benzene, toluene, ethylbenzene, and dichloromethane. Second, an activated sludge aeration tank and a sieve-plate column with six sieve plates were utilized to treat gas-borne VOCs in air streams. The tank was used for the biodegradation of the absorbed VOCs from the column which utilized the activated mixed liquor drawn from the tank as a scrubbing liquor. This research proposed a model for VOC absorption to a down-flow activated sludge liquor in a sieve-plate column. The experimental setup consisted of a pilot-scale activated-sludge tank and a sieve-plate tower, as demonstrated. The sieve-plate tower was constructed from a 25 x 25 x 162 cm (W x L x H) acrylic column with six custom-made sieve plates. Each plate has 382 holes which are 3 mm in diameter arranged on a square pitch. The holes give an open area of 3.82% of the whole plate area for gas flow. Two 25 mm-i.d. down-comer pipes were also equipped to allow for the downflow of the activated sludge liquor. Ports were provided at the column inlet, outlet, and each plate for gas and liquid sampling. Experiments were conducted and the model verified based on the results of tests on the removal efficiencies of isopropyl alcohol (IPA), toluene and p-xylene in the system operated at a range of influent VOC concentrations, air application rates, and liquid/gas flow ratios (L/G). The model developed by a material balance for the gaseous- and liquid-VOC over each plate of the column was developed and experimentally verified in this study. Superficial gas velocity over the column plate (U), number of plates (N), volumetric liquid-phase VOC-transfer coefficient (KLaVOC), aerated liquid depth over the plate (Z), volumetric liquid/gas flow-rate ratio (L/G), dimensionless Henry¡¦s law coefficient of the VOC to be absorbed (H), VOC content of the influent scrubbing liquor (xN+1), and the biodegradation rate constant of the VOC in the activated sludge mixed liquor (k) are among the affecting parameters to the effectiveness of the VOC removal. Model application by the model for effects of affecting parameters on the VOC removal effectiveness indicates that L/G, plate number N, biodegradation rate constant k, Henry¡¦s law constant of VOC H are among the important ones. A L/GH of greater than 2 and N of around 6 are enough for the effective (>90%) removal of the influent VOCs with H < 0.01 if no biodegradation occurred in the column. However, a N of over 16 is required for the influent VOCs with H of around 0.2. Biodegradation with a rate constant of around 100 hr-1 in the column greatly improves the column performance.

Sick building syndrome (SBS) is a particular concern in places with inadequate ventilation and frequently attributed to chemical contaminants such as volatile organic compounds (VOCs)released from indoor sources that are frequently encountered in everyday life such as adhesives, carpeting, upholstery, manufactured wood products, copy machines, pesticides, cleaning agents inside buildings, plumbing vents, and painting. Furthermore, it is a major issue for modern human beings who spend most of their time indoors or must stay indoors for self-isolation due to special circumstances such as the coronavirus disease-19 (COVID-19) pandemic that occurred in 2019 and 2020. Main indoor VOCs are trichloroethylene (TCE), benzene, toluene, and para-xylene (p-xylene). In general, these compounds are not present in indoor spaces at acute concentrations, but prolonged exposure to these compounds can have chronic health effects such as allergic sensitization, increased cancer risks, and respiratory diseases. In this study, the adsorption process with various advantages has been applied to remove VOC’s using commercially available hydrophobic adsorbents. The hydrophobic adsorbents can contribute to reducing the possibility of chemical adsorption (chemisorption) of moisture from the air, which can decrease the capacity of adsorbent by clogging the pores. The adsorption of these major VOCs was investigated in this work for three major types of industrial hydrophobic adsorbents: activated carbons, zeolites, and polymer. This study will show the investigation into finding the most promising hydrophobic adsorbent for removal of TCE, benzene, toluene, and p-xylene, which are the main VOCs found indoors. The promising hydrophobic adsorbent has been determined by comparing Henry’s law constants and heat of adsorption values for the different adsorbents, which were estimated by using a concentration pulse chromatographic technique by utilizing a gas chromatograph equipped with a flame ionization detector. For all adsorbents, Henry’s law constants at room temperature of p-xylene were always the highest followed by toluene, benzene, and TCE. For all adsorbates, Henry’s law constants at room temperature of AC BPL and HiSiv 3000 were higher than the other hydrophobic adsorbents. For a developing modern society dealing with a pandemic, this study can contribute to producing the optimized gas masks and indoor filters for the removal of indoor air pollutants, which can help people who suffer from SBS. It can also help society for taking preventative actions towards dealing with SBS.

Experimental data were obtained for the computation of mole fraction solubilities of three dichloronitrobenzenes in organic solvents at 25oC, and solubility ratios were obtained from this data. Abraham model equations were developed for solutes in tributyl phosphate that describe experimental values to within 0.15 log units, and correlations were made to describe solute partitioning in systems that contain either "wet" or "dry" tributyl phosphate. Abraham model correlations have also been developed for solute transfer into anhydrous diisopropyl ether, and these correlations fit in well with those for other ethers. Abraham correlations for the solvation of enthalpy have been derived from experimental and literature data for mesitylene, p-xylene, chlorobenzene, and 1,2-dichlorobenzene at 298.15 K. In addition, the enthalpy contribution of hydrogen bonding between these solutes and acidic solvents were predicted by these correlations and were in agreement with an established method. Residual plots corresponding to Abraham models developed in all of these studies were analyzed for trends in error between experimental and calculated values.