Comparison of potassium catalysts on zeolite sodium A and X in transesterification of palm oil and active species specification.

Heterogeneous catalysts consisting of potassium supported on zeolites are active for transesterification, but the effect of zeolite properties is not clearly understood. This work compares catalysts containing 12 wt.% potassium on zeolite sodium A and X (12K/NaA and 12K/NaX) in terms of performance and physicochemical properties. Both catalysts were prepared by ultrasound-assisted impregnation with potassium acetate buffer. 12K/NaA is a better catalyst in transesterification of palm oil, giving a higher biodiesel yield than 12K/NaX in the first run (99.1 ± 0.3 % and 77.9 ± 2.2 %, respectively). From characterization by CO2-TPD, XRD, FTIR, XPS, and SEM-EDS, both catalysts have similar basicity but different dispersion of carbonates and interaction on the zeolites. The 12K/NaA has those species on external surfaces and more monodentate carbonate than 12K/NaX. Ion exchange occurs between potassium ions from the precursor and sodium ions from the zeolite. Moreover, 12K/NaA is more stable, providing higher biodiesel yields in the second and third catalytic cycles.

Extraction of silica from sugarcane bagasse ash and its utilization in zeolite 4A synthesis for CO2 adsorption.

Sugarcane bagasse ash (SCBA) is a solid waste containing a high amount of silica (SiO2) and is suitable to utilize as a silica source for synthesizing zeolite NaA. SCBA is typically calcined at high temperatures before silica extraction. The method is not environmentally friendly because it consumes energy and produces CO2. This work demonstrates an alternative extraction method of SiO2 from SCBA by treating it with hydrochloric (HCl) and sodium hydroxide (NaOH) solution. The obtained mixture was separated by paper filter No. 1 (P) and a combination of paper filter and syringe filter (PS). The solution was neutralized by HCl solution, producing silica (SiO2-P and SiO2-PS) with a purity of 98 wt%. Both SiO2 samples and SCBA were utilized to synthesize zeolite NaA for CO2 adsorption. The CO2 adsorption capacities of NaA-P and NaA-PS were 4.30 and 4.10 mmol gadsorbent -1, in the same range as commercial NaA. The capacity is influenced by the total basicity of zeolite. The CO2 adsorption behavior of all samples correlates well with the Toth model. The CO2 adsorption kinetics agrees well with the pseudo-second-order kinetic model. Overall, this work shows the successful extraction of silica via using a direct NaOH solution, yielding high-purity silica sufficient for synthesizing zeolite NaA, a promising adsorbent of CO2.

The Synthesis of Well-Dispersed and Uniform-Sized Zeolite NaY by Adding Non-Refluxed and Acid-Refluxed Cogon Grass.

Zeolite NaY synthesized from a typical procedure could suffer from agglomeration. Adding non-refluxed cogon grass (NG) to the synthesis gel could produce NaY with good dispersion and uniform crystal size. Small molecules produced from cogon grass in alkaline conditions could prevent agglomeration. The obtained zeolite (Y-NG) has a crystallinity and surface area comparable to the synthesis without grass (Y-WG). Y-NG demonstrated similar paraquat adsorption capacity to Y-WG at high initial concentrations. On the other hand, the zeolite from the addition of acid-refluxed grass (Y-RG) has the lowest crystallinity, smallest surface area, and poorest paraquat adsorption capacity. The effect of grass amount on the zeolite structure was studied. One gram of cogon grass was the optimum amount to add to the synthesis gel.

Synthesis and Characterization of Zeolite NaY Dispersed on Bamboo Wood.

Zeolites in powder form have the potential to agglomerate, lowering access to active sites. Furthermore, a suspension of fine zeolite powder in liquid media is difficult to separate. Such drawbacks could be improved by dispersing zeolite crystals on support materials. This work demonstrates the dispersion of zeolite NaY crystals on bamboo wood by mixing the wood with zeolite gel before hydrothermal treatment. The syntheses were performed with acid-refluxed and non-refluxed wood. The phase of zeolites, particle distribution and morphology, zeolite content in the wood, and zeolite-wood interaction were investigated using X-ray diffraction, X-ray tomography, scanning electron microscopy, thermogravimetric analysis, nitrogen sorption analysis, and X-ray photoelectron spectroscopy. Higher zeolite content and better particle dispersion were obtained in the synthesis with the acid-refluxed wood. The composite of NaY on the acid-refluxed wood was demonstrated to be an effective adsorbent for Ni(II) ions in aqueous solutions, providing a higher adsorbed amount of Ni(II) per weight of NaY.

Structural elucidation of hexavalent Cr adsorbed on surfaces and bulks of Fe3O4 and α-FeOOH.

Magnetite (Fe3O4) and goethite (α-FeOOH) were synthesized via a hydrothermal approach and utilized as adsorbents for Cr6+ removal in an aqueous medium. The typical crystal structures of the synthesized Fe3O4 and α-FeOOH were confirmed by XRD and TEM. Fe3O4 in a spherical shape with a surface area of 32 m2 g-1 was established. While α-FeOOH had a rod-like form with a larger surface area of 84 m2 g-1. Cr6+ removal in an aqueous solution was studied in various conditions to evaluate thermodynamic and kinetic parameters. The adsorption isotherms on both adsorbents fit the Langmuir model indicating monolayer adsorption. Fe3O4 showed a better adsorption ability than α-FeOOH even though it had a lower surface area. XAS and XPS analysis strongly evidenced the production of stable Cr3+ species of Fe(1-x)Cr x OOH and Fe(3-x)Cr x O4 by Cr6+ reduction and migration processes into the bulk structure. Thus, the existence of stable Cr-species in Fe3O4 structure strongly affected Cr-adsorption ability rather than the surface area of the adsorbent. However, the precipitated Cr2O3 and HCrO4 - molecules electrostatically adsorbed on the outer surface of α-FeOOH without bulk transformation. The presence of physisorbed FeO-HCrO4 species on α-FeOOH led to low reducibility and adsorption capability of Cr6+.

Comparative Properties of K/NaX and K/NaY from Ultrasound-Assisted Impregnation and Performance in Transesterification of Palm Oil.

This work aims to compare physicochemical properties and catalytic performance of potassium supported on zeolite NaX and NaY (K/NaX and K/NaY, respectively) prepared by ultrasound-assisted impregnation from potassium acetate buffer precursor. Calcination converts the potassium precursor to carbonate, which occupies the zeolite cavities and disperses on the external surface. Both calcined samples show a decrease in zeolite phases, BET surface areas, and pore volumes. With the smaller changes, K/NaX is more stable than K/NaY. Moreover, K/NaX has higher basicity than K/NaY and is more active in the decomposition of 2-methylbut-3-yn-2-ol (MBOH), producing dominant products from basic sites. Both K/NaX and K/NaY are active in the transesterification of palm oil, producing more than 94% of the biodiesel yields in the first run. However, the yields drop in the second run because of the leaching of potassium species into glycerol and biodiesel products. The spent K/NaX has a similar phase to the fresh one, whereas the spent K/NaY shows more structure collapse. With better structural stability, less potassium leaching, and less decline in biodiesel yields in the second run, K/NaX is a better catalyst than K/NaY.

Paraquat adsorption on NaX and Al-MCM-41.

The aim of this work is to determine paraquat adsorption capacity of zeolite NaX and Al-MCM-41. All adsorbents were synthesized by hydrothermal method using rice husk silica. For Al-MCM-41, aluminum (Al) was added to the synthesis gel of MCM-41 with Al content of 10, 15, 20 and 25 wt%. The faujasite framework type of NaX and mesoporous characteristic of Al-MCM-41 were confirmed by X-ray diffraction. Surface area of all adsorbents determined by N2 adsorption-desorption analysis was higher than 650 m2/g. Al content and geometry were determined by X-ray fluorescence and 27Al nuclear magnetic resonance, respectively. Morphology of Al-MCM-41 were studied by transmission electron microscopy; macropores and defects were observed. The paraquat adsorption experiments were conducted using a concentration range of 80-720 mg/L for NaX and 80-560 mg/L for Al-MCM-41. The paraquat adsorption isotherms from all adsorbents fit well with the Langmuir model. The adsorption capacity of NaX was 120 mg/g-adsorbent. Regarding Al-MCM-41, the 10% Al-MCM-41 exhibited the lowest capacity of 52 mg/g-adsorbent while the other samples had adsorption capacity of 66 mg/g-adsorbent.

Paraquat adsorption on porous materials synthesized from rice husk silica.

The goal of this work was to utilize rice husk silica (RHS) and porous materials synthesized with RHS, including mesoporous material (MCM-41) and microporous materials (zeolite NaY and NaBEA), for adsorption of herbicide paraquat. The adsorption occurred although cation exchange and the capacity decreased in the following order: NaY > NaBEA > MCM-41 > RHS, consistent with the amount of Al. The adsorption on all adsorbents fitted well with the Langmuir model and the maximum adsorption capacity of 185.2 mg/g-adsorbent was obtained on NaY. In addition, blue dye in commercial grade paraquat did not interfere with paraquat adsorption. Although MCM-41 was the most efficient adsorbent for the blue dye, RHS was favorable in terms of production cost. A mixture of NaY and RHS is recommended for simultaneous adsorption of paraquat and blue dye.