Catalytic cracking of light naphtha over hierarchical ZSM-5 using rice husk ash as silica source in presence of ultrasound energy: Effect of carbon nanotube content

Hierarchical structured ZSM-5 was prepared by sonochemical assisted carbon nanotube templated method and their catalytic activity was examined in catalytic cracking of light naphtha. Different amounts of carbon nanotubes (5, 15, 30?wt%) was introduced into the synthesis gel, as a hard template, for mesopore creation. The rice husk ash was used as a silica source. In order to analyse physicochemical properties of synthesized catalysts, multi-techniques such as XRF, XRD, BET, FE-SEM, NH₃-TPD and TGA were used. The obtained results revealed that by adjusting the amount of carbon nanotube, catalyst properties can be favorably tuned. The XRD analysis confirmed successful synthesis of high crystalline ZSM-5 zeolite. According to the FE-SEM analysis, small rough spheres of ZSM-5 were synthesized in all samples. The use of carbon nanotube led to creating new mesopores in the ZSM-5 structure. However, increase in carbon nanotube content led to destruction of micropores of ZSM-5. The acidity of ZSM-5 slightly changed. Results from catalytic activity test showed that high catalyst stability can be achieved in presence of mesopores along with the micropores. The highest olefin yield (54?wt%) and the best catalytic stability were obtained over the synthesized ZSM-5 with 15?wt% carbon nanotube.     

Synthesis of mixed-phase uniformly infiltrated SBA-3-like in SBA-15 bimodal mesoporous silica from rice husk ash

The mixed-phase bimodal mesoporous silicas (BMS) were simply synthesized via sol-gel technique using rice husk ash-derived sodium silicate as a silica source, and Pluronic P123 and cetyltrimethyl ammonium bromide (CTAB) as the pore structure-directing agents. The gel solution composition in the synthesis process was based on SiO₂:Pluronic P123:CTAB:HCl:H₂O molar ratio of 1:0.088:0.088:4:200. The effect of mixing sequences of starting materials on BMS structures was investigated. The phase separation among SBA-15, SBA-3-like porous silica and xerogel was found when the gel solutions of SBA-15 and SBA-3-like were prepared separately in the primary stage, whereas the mixed-phase uniformly infiltrated SBA-3-like in SBA-15 bimodal porous silica was successfully synthesized when CTAB was added into the SBA-15 gel solution and the secondary micelle structure was formed inside the primary SBA-15 framework.     

Properties of geopolymer with seeded fly ash and rice husk bark ash

In the present work, compressive strength of inorganic polymers (geopolymers) produced of seeded fly ash and rice husk bark ash has been investigated. Different specimens made from a mixture of fly ash and rice husk bark ash in fine and coarse form were subjected to compressive strength tests at 7 and 28 days of curing. The curing regime was different: one set of the specimens were cured at room temperature until reaching to 7 and 28 days and the other sets were oven cured for 36 h at the range of 40-90 °C and then cured at room temperature until 7 and 28 days. The results indicate that in both 7 and 28 days regimes, the highest strengths are related to the specimens by SiO₂/Al₂O₃ ratio equals 2.99 cured at 80 °C. For these specimens, those contained finer fly ash particles show more compressive strength. Thermogravimetric analysis and Fourier transform infrared spectroscopy both also are in agreement with the obtained results from compressive strength tests. In addition, SEM micrographs of the specimens show that the finer the particle size of the utilized ashes, the denser the microstructure which confirms the results obtained by the strength tests.     

High-temperature and short-time hydrothermal fabrication of nanostructured ZSM-5 catalyst with suitable pore geometry and strong intrinsic acidity used in methanol to light olefins conversion

High temperature hydrothermal synthesis method was developed to preparation of nanostructured ZSM-5 molecular sieves at short crystallization time. A series of catalysts were synthesized at various temperatures and crystallization times for achievement of pure ZSM-5 phase with MFI structure. The synthesized catalysts were investigated with XRD, FESEM, EDX, BET-BJH, FTIR and TPD-NH₃ techniques. The results revealed that hydrothermal synthesis conditions generally affected the nucleation rate, particle size, textural properties and acidic nature of ZSM-5 catalysts. It was found that pure ZSM-5 materials with high crystallinity could be obtained at specific crystallization conditions of about 300?°C for 1.5?h and also 350?°C for 0.5?h. Increasing the hydrothermal temperature to 350?°C and decreasing the crystallization time to 0.5?h led to the formation of small particles with high specific surface area of 392?m²/g. Furthermore, ammonia TPD spectra showed that ZSM-5(300-1.5) catalyst contained higher amount of acid sites and less acid strength compared to ZSM-5(350-0.5) catalyst. The catalytic performance of samples was studied for conversion of methanol to light olefins under different reaction conditions. Interestingly, the proper pore geometry along with the strong intrinsic acidity resulted in a tendency for excessive production of light olefins for ZSM-5(350-0.5) catalyst. The selectivity of light olefins over this catalyst was increased about 94% in the long time on stream (2100?min). Also, the possible reaction pathway for ZSM-5 synthesis at high temperatures was discussed in details.     

Synthesis and surface characteristics of nanosilica produced from alkali-extracted rice husk ash

Rice husk is a form of agricultural biomass that provides an abundant silicon source. This study used rice husk as a raw material to prepare nanosilica without adding an extra surfactant. This work investigated a dissolution-precipitation technique as a function of acid treatment, sodium silicate concentration, gelation pH, aging temperature, and aging time to establish optimum conditions for preparing silica nanoparticles. Experimental results showed that silica produced by hydrochloric acid possesses higher surface area than that of sulfuric, oxalic, and citric acids. Surface characteristics of the sample depend mainly upon gelation pH. The highest surface area and pore volume of silica samples were 634 m²/g and 0.811 cm³/g. Pore diameters were controllable from 3 to 9 nm by adjusting the solution pH value. Particles had a uniform size of 5-30 nm. The objective of this study was to develop a method of nanosilica preparation that enhances the economic benefits of re-using rice husk waste.     

Use of ultrafine rice husk ash with high-carbon content as pozzolan in high performance concrete

Rice husk ash (RHA) has been generated in large quantities in rice producing countries. This by-product can contain non-crystalline silica and thus has a high potential to be used as cement replacement in mortar and concrete. However, as the RHA produced by uncontrolled burning conditions usually contains high-carbon content in its composition, the pozzolanic activity of the ash and the rheology of mortar or concrete can be adversely affected. In this paper the influence of different grinding times in a vibratory mill, operating in dry open-circuit, on the particle size distribution, BET specific surface area and pozzolanic activity of the RHA is studied, in order to improve RHA’s performance. In addition, four high-performance concretes were produced with 0%, 10%, 15%, and 20% of the cement (by mass) replaced by ultrafine RHA. For these mixtures, rheological, mechanical and durability tests were performed. For all levels of cement replacement, especially for the 20%, the ultra-fine RHA concretes achieved superior performance in the mechanical and durability tests compared with the reference mixture. The workability of the concrete, however, was reduced with the increase of cement replacement by RHA.     

A new approach for synthesis of well-crystallized Y zeolite from bentonite and rice husk ash used in Ni-Mo/Al2O3-Y hybrid nanocatalyst for hydrocracking of heavy oil

A series of Ni-Mo/Al₂O₃-Y hybrid nanocatalysts were synthesized for hydrocracking of heavy oil. The well crystallized Y zeolite was synthesized from mineral bentonite and rice husk ash by a two-step synthesis method. The solution combustion method was applied to develop a fast and simple technique for preparing of alumina-supported NiMo catalyst with high hydrodesulfurization activity. Such activity may be due to the morphological and textural modification as a consequence of the release of a high amount of exhaust gases during the combustion process. The XRD analysis revealed that the P zeolite was a competitive phase presented in the obtained product that could be eliminated using a two-step synthesis method. Compared to a one-step method, the pore volume and external surface area of the synthesized zeolite by the two-step method increased by 74 and 62%, respectively. The hydrocracking results illustrated that the synthesized zeolite was able to convert 66% of heavy oil to lighter products and reduce the viscosity up to 60%. Furthermore, the amount of sulfur removal was found to be 58%. The spent catalyst characterization suggested that the type of deposited coke was hard coke with the unsaturated aromatic ring which could be responsible for the pores blockage after the cracking reaction.     

Synthesis of b-axis oriented ZSM-5 zeolite by mechanochemical-assisted quasi-solvent-free method and its MTO catalytic performance

In this paper, b-axis oriented ZSM-5 zeolite was synthesized by solvent-free method with ammonia as growth regulator. Zeolites were characterized by modern detection techniques such as XRD, SEM, BET and NH₃-TPD. The results showed that ammonia could not only promote the crystallization of ZSM-5 zeolite, but also direct the synthesis of ZSM-5 zeolite with b-axis oriented morphology, which was beneficial to enhance the selectivity of light olefins. B-axis oriented ZSM-5 zeolite did not need to be mixed and aged in aqueous solution, which could reduce the discharge of sewage, and avoided the generation of autogenic pressure in the crystallization process. Furthermore, it is consistent with the concept of environmental friendliness, which could guide the green preparation of industrial ZSM-5 zeolites.     

Mechanical properties of roller compacted concrete containing rice husk ash with original and recycled asphalt pavement material

This study focused on the effects of rice husk ash (RHA) on the mechanical properties of roller compacted concrete (RCC) designed with original and reclaimed asphalt pavement (RAP) materials. The RCC mixes were produced by partial substitution of cement with RHA at varying amounts of 3% and 5%. Four aggregate combinations including the mix with original aggregate, coarse RAP + fine original aggregate, coarse original aggregate + fine RAP and total RAP were considered. The main experimental design consisted of the compressive strength and three points bending tests. Bending test was used to measure the modulus of rupture, material’s energy absorbency and analyse the fatigue response of RCC mixes. All tests were performed after 7, 28 and 120 days curing except the fatigue test that performed on 120 days specimens. Adding RHA resulted in higher optimum moisture content (OMC) and lower maximum dry density. Furthermore, adding RAP with different dimensions reduced the OMC and maximum dry density. The material’s flexibility improved upon replacing 3% cement by RHA. However, the energy absorbency reduced by increasing the RHA content to 5%. The fatigue life of RCC mixes containing RAP material was lower than the conventional one. Furthermore, replacing the coarse aggregate by RAP led to higher fatigue life than the fine aggregate. There was a strong relationship (R² > 0.90) between the energy absorbency and fatigue response of RCC mixes. At higher stress ratios of 0.72, the mix with higher energy absorbency behaved better under repeated loadings. Besides, a reverse relationship was found between the fatigue life and material porosity. Adding 3% RHA reduced the porosity especially after 120 days curing and improved the fatigue resistance. However, the addition of RHA to 5% resulted in higher porosities and lower fatigue lives.     

Performance and properties of mortar mixed with nano-CuO and rice husk ash

This paper presents an experimental study on a new mixture scheme of mortar. Unlike most of existing work, the present study investigates nano-CuO (NC), and its combined effects with cement replacement i.e., rice husk ash (RHA) on durability performance, as well as strength and permeability properties of mortars. Comprehensive observations of both the performance and properties improvements on RHA-containing mortar specimens were determined with the addition of NC. To this end, a series of tests for examining the strength both directly (compressive strength) and indirectly (Ultrasonic Pulse Velocity), electrical resistivity, chloride permeability, water absorption and microstructure characteristics (i.e., SEM micrographs, Mercury intrusion porosimetry (MIP) & capillary analyses) of mortar specimens were performed. A relationship between the Rapid chloride permeability test (RCPT) and electrical resistivity was also studied in order to recommend an alternative method for quality control in the presence of RHA and NC. Finally, a mixture scheme which provides relatively satisfactory properties improvement with positive environment credential is suggested.