Summary Part I
The objective of this part is to synthesize zeolites from low cost locally available silicon sources. These materials will have great potential as catalyst, ion-exchange and adsorbent. This is the first extensive study that has been conducted in the synthesis of zeolite in Kurdistan region of Iraq. Suitable silica sources for direct preparation of zeolites had not been easily available locally. Therefore, silica is first extracted from Chert rock, Barley husk and Shale clay owing to its different high silica content according to their sources then different types of zeolites are prepared, Mordenite from chert rock, Faujasite NaY from barley husk, Faujasite NaX from shale clay and then after zeolite NaX modified by acid and base. Since Sunflower husk, Sesame husk and Popcorn waste did not contain a significant amount of silica, they are not used as a silica source. These zeolites were hydrothermally synthesized from locally available low-cost materials without addition of a templating agent, seed powder, structure-directing agent, and additives.
The synthesized zeolites were characterized by Fourier Transform Infrared (FTIR) spectroscopy, X-ray diffraction (XRD), and Field Emission Scanning Electron Microscopy (FESEM). The X-ray Fluorescence (XRF) was utilized to determine the Si:Al ratio. The average pore size, pore volume, Surface area were determined by Brunauer-Emmett and Teller (BET) method. Finally, Transmission Electron Microscopy (TEM) was used to find the average crystal size and shape of zeolite. The results verified that synthesized zeolites obtained from the hydrothermal condition, present a good zeolitic property and then can be suitable for using in adsorption, ion exchange and catalysis experiments. The properties of zeolites formed are strongly depending upon the composition and the type of raw materials used.
Summary Part II
This part aims to develop consistent and reliable methods for the synthesis of useful zeolites utilizing microwave and ultrasonic techniques for hydrothermal crystallization. These materials were then being compared with their counterparts synthesized from conventional hydrothermal crystallization. Most principals of green chemistry have participated their employees as much as possible throughout this project. More specifically the materials used and the materials synthesized will have great potential for catalysis adsorption and ion exchange. Zeolites are among the least-known products for environmental pollution control, separation science and technology. Different zeolite crystallites were prepared in a microwave oven for 5-20 min and characterized. The results were compared with those prepared by conventional hydrothermal crystallization for more than 12 hours. Analysis showed that, zeolites synthesized by microwave technique were NaX type.
On the other hand, a series of experiments were carried out in the presence of ultrasound 30KHz at 60°C and for different crystallization times (5,10 and 15 hours) and the results were compared with those obtained by performing conventional alkaline hydrothermal static syntheses under similar conditions and Crystallization time of (90 hours). The products, were analyzed using; IR, FT-IR, XRD and XRF, N2 sorption, FESEM and SEM. The experimental data ascertained the formation of Zeolite successfully. Crystallization by ultrasound has been demonstrated to offer the possibilities of increasing the nucleation and crystallization rates of zeolites, improving the yield and directing the synthesis towards different crystal phases.
Summary Part III (Direct Synthesis of Mesoporous Zeolite)
Mesoporous zeolites offer advantages of thermal stability, high surface areas, and shape selective catalysis but in addition larger pores widen the number of large molecules and chemical reactions which can be catalyzed by these materials. A mesoporous ZSM-5 zeolite was hydrothermally synthesized using sucrose as a template; the synthesized solids were characterized using FTIR XRD, BET method is used for nitrogen adsorption analysis and FESEM. XRD results showed that sample synthesized using sucrose produced the crystalline ZSM-5 structure. Tetraethylorthosilicate (TEOS) is the best silica source that can be used in synthesizing mesoporous ZSM-5 by this method since fume silica and rice husk ash were not dissolved during the preparation of gel. Nitrogen adsorption analysis revealed that synthesized solids have mesoporous structures type IV isotherm with average pore sizes of 6.6338 nm and surface areas of 682.6557m²g-1.
Summary Part III (Indirect Synthesis of Mesoporous Zeolite)
This part of the study focuses on changing the microporous ZSM-5 to mesoporous ZSM-5 using (NaOH) and various templates. Post synthesis treatment of ZSM-5 by alkaline solution, Cetayltrimethylammoniumbromide (CTAB), Tetrapropylammoniumhydroxide (TPAOH), and mixture of (CTAB, TPAOH) dramatically changes morphology of the ZSM-5, leading to the formation of mesopores whose size is almost uniform without destruction of microporous structure. The meso-zeolite formed by (NaOH) has smaller mesopores (ca.3.66 nm), while for CTAB, TPAOH and mixture of (CTAB, TPAOH) larger mesopores were formed (ca. 14.85, 11.12 and 15.21 nm) respectively. The obtained samples were characterized using FTIR, XRD, BET, and FESEM. (CTABr,TPAOH) mixed with ZSM-5 have higher mesoporosity as proven by higher BET surface area as compared to (untreated) microporous ZSM-5 with different pore structure as proven by pore distribution.
Summary Part IV
The present work deals with the synthesis of mesoporous ZSM-5 by different method:
i-modified untreated ZSM-5 by NaOH, TPAOH, and CTABr and mixed from [CTABr+TPAOH].
ii- adding sucrose to obtain mesoporous ZSM-5, used as a solid acid catalyst for acylation of anisole by propionic anhydride. The reaction parameters such as reaction time, temperature, anisole: propionic anhydride molar ratio and catalyst quantity were all investigated. It was observed that after modification and adding sucrose the pore size of zeolite becomes larger and facilitates the reactant to get entered into it and promoted the conversion. Under the optimum reaction conditions 100°C, anisole: propionic anhydride ratio of 30:30, mesoporous ZSM-5 proved to be an active catalyst in the Friedel-Crafts acylation of anisole and propionic anhydride. The conversion percent of anisole to p- methoxypropiophenone by mixed template and sucrose were found to be 90.4% and 91.5% while the percent of selectivity were 95.98% and 97.30% respectively. The activity depends on the acid strength and the total number of acid sites, surface area and average pore size distribution. It was found that both mesoporous ZSM-5 zeolites had a potential to be a selective para catalyst for producing only product with para orientation.
All the zeolite catalysts used, produced only p-methoxypropiophenone as a main. The proposed mechanism for this reaction involved electrophilic aromatic substitution which included the formation of acylium ions from the Brønsted acid sites in the catalysts. In addition, the effect of reaction time and temperature on the Friedel-Crafts acylation, and their conversion percent and selectivity as Friedel-Crafts acylation were compared.
Summary Part IV (Pb Adsorption)
Adsorption experiments were investigated in terms of the potential for the decontamination of model solutions, artificially polluted with Pb in order to compare the efficiency of different types of zeolites as adsorbents. The BET surface area, total pore volume and average pore size distribution of these synthesized zeolites were determined by adsorption isotherms for N2, the surface area and total pore volume of their sources were found by adsorption isotherm of N2 gas. The adsorption equilibrium was measured after 24h at room temperature (R.T) and concentration 10 µg mL-1 of Pb (II) was used. The decontamination potential of synthesized zeolites (LTA from Montmorillonite clay, FAU(Y)-B.H (G2) from Barley husk, Mordenite (G1) from Chert rock, FAU(X)-S.C (G3) from shale clay and modified Shale clay by oxalic acid (N1) and sodium hydroxide (N2), were compared with that of the sources using batch experimental method. The adsorption equilibrium capacity (Qm) for Pb (II) ion on different synthesized zeolites were in the following order: N1>N2>LTA>G3>G2>G1 and for the sources order was: Shale clay >Montmorilonite> Barley husk>Chert rock. The AAS was used for monitoring Pb(II) concentration with time, the obtained results showed that the synthesized zeolites were efficient ion exchangers for removing Pb, in particular, the zeolite synthesized from shale clay modified by oxalic acid.
14 – 06 – 2017