Acid Dealumination Research Articles

Valorisation of waste biomass and plastics toward light aromatics: Co-catalytic fast pyrolysis of torrefied bamboo and polyethylene over alkali and acid treated hierarchical HZSM-5

Light aromatics are extremely important building blocks which can be prepared from the co-catalytic fast pyrolysis (Co-CFP) of biomass and polyethylene. In this study, the bamboo was torrefied to remove part of oxygen element prior to pyrolysis, then being co-fed with polyethylene (HDPE, PE and LDPE) during CFP over alkali (NaOH and Na2CO3) and acid (H3PO4 and HCl) treated HZSM-5. 40.3% oxygen element in bamboo could be eliminated at torrefaction temperature of 300 °C. After the acid dealumination or alkali desilication treatments, the mesopore was creased in HZSM-5, transforming into hierarchical structure with larger pore size and lower acidity. The effect of torrefaction temperature, the species of alkali or acid solutions and their concentrations, the mass ratio of HDPE-to-torrefied bamboo, the CFP temperature on the yields of light aromatics was systematically discussed. The maximum yield of BTX was 4.39 × 108 a.u./mg which was obtained by Co-CFP of torrefied bamboo (250 °C) and HDPE at mass ratio of 1:2 with 800 °C over 0.2 M NaOH treated hierarchical HZSM-5. The aromatization reaction of olefins, the deoxygenation reaction of oxygenates, and the Diels-Alder reaction between furans and olefins were key reactions for the formation of BTX during Co-CFP of torrefied bamboo and polyethylene.

Highly stable VSi-beta zeolite synthesized by a post-synthesis strategy for efficiently catalyzing styrene epoxidation

To enhance the doping of vanadium in zeolites and achieve high stability, the selection of vanadium precursors containing specific vanadium species can effectively overcome this crucial problem. Two series of VxSi-Beta(A) and VxSi-Beta(N) zeolites have been prepared by a two-step post-synthesis method at pH = 1 and pH = 7. The properties and environments of vanadium in samples are investigated by UV–vis, XPS, EPR, H2-TPR and 51V MAS NMR. The bonding between vanadium and framework in VSi-Beta(A) is stronger than that of VSi-Beta(N). After the two are calcined or hydrated, the vanadium species in the former are relatively stable, while the pseudo-tetrahedral V(V) species and pseudo-octahedral V(V) species in the latter are interconverted. The changes of vanadium species in the supernatant during the preparation have been investigated by 51V static NMR. At low concentration and pH = 1, there is a unique mononuclear cation (VO2+) in the aqueous NH4VO3 solution, which is favorable for the interaction with the negatively charged hydroxyl nests generated after the nitric acid dealumination, and enables the V atoms to be tightly inserted into the framework. In styrene epoxidation, the type of V(V) species in the catalyst could significantly affect its catalytic performance, and the catalytic activity and stability of VxSi-Beta(A) are superior than that of VxSi-Beta(N).

Chromic acid dealumination of zeolites

Commercial zeolites with CHA, MFI, and LTL framework topology are subjected to acid treatment with chromic acid (H 2 CrO 4 ) solutions with concentrations ranging between 0.1 and 10 w /%. As chromic acid forms polymeric species as a function of concentration, specific effects are obtained with these three zeolites, differing by their framework topology, pore size, Si/Al ratios and crystal size. The etched zeolites are characterized by X-ray diffraction, SEM, TEM, N 2 physisorption, ICP-AES, 27 Al and 29 Si MAS NMR, 29 Si{ 1 H} cross-polarization spectra, EDX. Their acidic properties are probed with pyridine and d 3 -acetonitrile by in situ FTIR. Results indicate that the 8 MR (CHA) and 10 MR (MFI) zeolites are more resistant to acid treatment with chromic acid than the 12 MR (LTL) zeolite. This paves the way for rational control of zeolite dealumination since adjusting chromic acid concentration will generate anions appropriate for treating a particular zeolite. • CHA, MFI, and LTL zeolites are subjected to treatment with chromic acid (H 2 CrO 4 ). • Chromic acid forms polymeric species as a function of concentration. • CHA and MFI zeolites resist more to the chromic acid treatment than the LTL zeolite. • Tuning the acid concentration yields anions apt for treating a particular zeolite.

Catalytic oligomerization of isobutyl alcohol to jet fuels over dealuminated zeolite Beta

Various dealuminum methods of zeolite Beta to generate the jet fuels by converting isobutyl alcohol has been investigated in detail. And related factors of the zeolite catalyst such as acid site, pore structure, and pore size which can influence reactive activity, were also studied utilizing XRD, SEM, XRF, Nitrogen adsorption-desorption, NH3-TPD, Py-FTIR, and 27Al solid-state NMR. Removal of extra-framework aluminum or part of framework aluminum by hydrochloric acid dealumination, is able to improve the diffusion property of the products in the channel of zeolite Beta via increasing the ratio of Lewis/Brønsted. Consequently, isobutyl alcohol can be quantitatively oligomerized over dealuminated zeolite Beta with the selectivity of C8−16 exceeding 50 % at a conversion of 98 %. Moreover, the deactivated catalyst can be easily regenerated by calcining it in flowing air. High conversion, high jet fuels selectivity, and facile regeneration make it an attractive potential catalyst for isobutyl alcohol oligomerization reaction.

Effect of Dealumination of Citric Acid-Modified Hβ Molecular Sieve on Hydroisomerization Performance of n-Hexadecane

Hβ molecular sieves with SiO2/Al2O3 ratio of 40 were modified by citric acid dealumination (Hβ-Cn) and Hβ-Cn loading Pd (0.5 wt%) bifunctional catalysts(Pd/Hβ-Cn) were prepared by hydrothermal synthesis and incipient wetness impregnation. The structure, morphology, pore and acid properties of Hβ-Cn and Pd dispersion of Pd/Hβ-Cn were characterized using XRD, SEM, N2 physical adsorption, NH3-TPD and H2 chemical absorption. The skeleton structure of all Hβ-Cn was not damaged and their relative crystallinity increased somewhat after the treatment of citric acid. With the increase of citric acid concentration, the change of morphology,structure and pore properties of Hβ-Cn was very little, but the amount of weak acid, strong acid and total acid of Hβ-Cn, and Pd dispersion for Pd/Hβ-Cn decreased significantly. It was known from hydroisomerization perforamce of n-C16H34 that the hydroisomerization reaction temperature over Pd/Hp-Cn slightly rises under the condition of the same conversion of n-C16H34, but the amount of multi-branched iso-C16H34 over Pd/Hβ-Cn, especially Pd/Hβ-C2 (60.51%) and Pd/Hβ-C3 (57.84%) was much higher than that over Pd/Hβ (36.99%). This could be due to the remove of partial skeleton aluminum species with strong acid sites to effectively inhibit the further cracking of the muti-branched isomerized products.

Perengkahan n-Butana Menggunakan Katalis Nanopartikel Zeolit Alam Klaten

Increasing demand on olefins, high energy consumption of thermal cracking and oil depletion are the driving force to find new process to produce olefins. Catalytic cracking of n-butane is promising route to produce olefins. In this paper, we synthesized nanoparticle from natural zeolites by ball milling-recrystallization method and studied the effect of acid dealumination over the nanozeolites on the catalytic properties. Particle size was evaluated visually by using scanning electron microscope. X-Ray Diffraction analysis was performed to study zeolites phase and its crystallinity. Acid dealumination effect over nanosized mordenite on the acidity were evaluated by ammonia TPD and pyridine FTIR. Textural properties of zeolites were characterized by nitrogen physisorption at -196 oC. The catalysts were tested in a fixed bed reactor for n-butane cracking to olefins product. Various temperature conditions were applied ranging from 350 oC to 650 oC for n-butane cracking in a fixed bed reactor. Conversions of n-butane were 15% and 90% at 350 oC and 650 oC, respectively. Selectivity to olefins was increase from 1% at 350 oC to 47% at 650 oC.

Selective Isomerization of n-Butane over Mordenite Nanoparticles Fabricated by a Sequential Ball Milling–Recrystallization–Dealumination Route

For the first time, a sequential fabrication step involving mechanochemistry, recrystallization, and dealumination was developed to convert low-cost natural zeolites to mordenite (MOR) nanoparticles. Natural zeolites are mostly found having poor textural properties and a high aluminum content, which are not suitable for most industrial catalytic reactions. The parent natural zeolites within the size of 1–10 μm were treated by ball milling to obtain nanosized particles with size in the range of 20–160 nm. The nitrogen physisorption study revealed that the external surface area and intercrystalline mesopore volume of the milled nanoparticles increased by 4- and 7-fold, respectively. Recrystallization by hydrothermal treatment in basic silicate solution was applied to recover the MOR crystallinity at 170 °C for 6 h. The recrystallized MOR samples were further subjected to acid dealumination treatment over different periods. The H-MOR samples were evaluated in a fixed-bed reactor for n-butane isomerization. T...

The comparison of chemical liquid deposition and acid dealumination modified ZSM-5 for catalytic pyrolysis of pinewood using pyrolysis-gas chromatography/mass spectrometry

Catalyst deactivation is the main reason for low petrochemical yield in catalytic fast pyrolysis (CFP) of biomass. ZSM-5 catalysts modified by chemical liquid deposition (CLD) and acid dealumination (AD) were prepared to improve petrochemical yields for CFP of pinewood. The results showed that CLD by SiO2 led to the coverage of strong acid sites, while AD favored the removal of superficial acid sites. CFP of pinewood showed that the relative area ratio of BTX was boosted by 37.2% and 30.4% over modified ZSM-5 catalysts by CLD and AD, respectively. The yield of indenes and naphthalenes which were important precursors of heavy coke decreased sharply. Considering environmental cost and catalytic performance, CLD seems to be a preferable modification method over ZSM-5 in the catalytic pyrolysis of biomass for petrochemicals.

Full Mechanism of Zeolite Dealumination in Aqueous Strong Acid Medium: Ab Initio Periodic Study on H-Clinoptilolite

Periodic quantum-chemistry methods as implemented in the Crystal14 code were considered to study the mechanism of the dealumination of H-clinoptilolite in aqueous acid medium. A series of models consisting of the primitive cell of a monoaluminated structure of HEU (heulandite) framework type together with water molecules and HCl as catalyzer were considered. Stable and transition state structures together with their relative Gibbs free energy values were computed at the hybrid density functional theory (DFT) level of theory with dispersion correction (PBE0-D2) employing atomic basis sets. Four different steps for the mechanism have been considered. Each of them corresponds to the hydrolysis of the bonds that connect the Al atom with the framework providing as final product Al(OH)3 adsorbed on a silanol nest. Results show that the free reaction energy for the whole acid dealumination is about −49 kJ mol–1. The crucial way the HCl intervents in the reaction is studied in detail, and the polar nature of most...

Dimethyl ether to olefins over dealuminated mordenite (MOR) zeolites derived from natural minerals

Recent development in shale gas production ensures the availability of cheap feedstock for petrochemicals. Dimethyl ether (DME) is one of the most promising derivatives from natural gas. In this work, we developed catalysts from low-cost natural minerals for the conversion of DME to olefins as one of the most important feedstocks for the petrochemical industry. The catalytic performance of a series of hierarchical mordenite zeolites derived from natural mineral by nitric acid dealumination was studied in the conversion of dimethyl ether (DME) to light olefin compounds. The degree of dealumination was strongly dependent on the treatment period. The DME conversion and olefins selectivity over these materials were investigated at 350 °C and 1 atm. The nitric acid dealumination has a positive effect on both DME conversion and ethylene to butylene selectivity. The fabrication of hierarchical zeolites from natural minerals will stimulate related studies to produce cost-effective catalysts derived from natural resources.

Synthesis of Sn‐Beta with Exclusive and High Framework Sn Content

AbstractSn‐Beta zeolite was prepared by acid dealumination of Beta zeolite, followed by dehydration and impregnation with anhydrous SnCl4. The formation of extraframework Sn (EFSn) species was prevented by the removal of unreacted SnCl4 in a methanol washing step prior to calcination. The resulting Sn‐Beta zeolites were characterized by X‐ray diffraction, Ar physisorption, NMR, UV/Vis, and FTIR spectroscopy. These well‐defined Lewis acid zeolites exhibit good catalytic activity and selectivity in the conversion of 1,3‐dihydroxyacetone to methyl lactate. Their performance is similar to a reference Sn‐Beta zeolite prepared by hydrothermal synthesis. Sn‐BEA zeolites that contain EFSn species exhibit lower catalytic activity; the EFSn species also catalyze formation of byproducts. DFT calculations show that partially hydrolyzed framework Sn‐OH species (open sites), rather than the tetrahedral framework Sn sites (closed sites), are the most likely candidate active sites for methyl lactate formation.

The catalytic stability of some selected bifunctional nanoporous-based catalysts in the hydroisomerisation of n-C7 and the effect of post-synthesis modification techniques

In this work, some commercial and in-house nanoporous-based catalysts, such as USY, beta and mordenite zeolites, and mesoporous aluminosilicate molecular sieves such as MCM-48 and SBA-15, loaded with metals and acting as mono- and bimetallic bifunctional catalysts, were used for hydroisomerisation experiments in a fixed-bed reactor at pressures between 1 and 15 bar and at feed space time ranging from 2.57 to 10.26 h−1 (35.14–140.6 kg s mol−1) to hydroisomerise n-heptane over a temperature range of 210–270 °C. The effect of post-synthesis treatments of micro- and mesoporous catalysts was examined, regarding their activity, selectivity and stability, such as acid and steam dealumination techniques, acid leaching via a chelating agent, bimetal loading techniques, different platinum loading methods, and composite or hybrid catalyst generation. Results show that pore architecture is the most important factor affecting coke formation and deactivation in zeolite catalysts. It was found that those catalysts with high Si/Al ratios and those which had been acid-leached or steamed showed better activity, higher selectivity towards isomeric products and better time stability. Moreover, the balance between the number of metal sites and the number of acid sites played an important role in determining the activity, selectivity and stability of the bifunctional catalysts. Higher metal loading improves catalytic stability, due to a better balance and closeness of the catalytic functions. Moreover, the bimetallic catalyst improves the formation of smaller metal particles and better dispersion, which may affect selectivity and stability.

Improved THETA-1 for Light Olefins Oligomerization to Diesel: Influence of Textural and Acidic Properties

The increase in diesel demand, especially in Europe, and the need for high fuel quality requirements are forcing refiners to move into additional processes for production of high cetane diesel in order to meet the present market trends. Oligomerization of light olefins into middle distillate range products is a viable option. The fuel produced through this technology is environmentally friendly, free of sulfur and aromatics, and the adequate choice of the heterogeneous catalyst will direct the selectivity towards low branched oligomers, which will result in a high quality product. In this work we show the benefits of combining basic desilication treatments for generation of additional mesoporosity in mono-directional Theta-1 zeolite, with selective acid dealumination steps that restore not only the microporosity to values close to those of the parent samples, but also the total and strong Brønsted acidity. These modified Theta-1 zeolites present an outstanding catalytic behavior for oligomerization of propene, with a largely increased initial activity, a much higher resistance to deactivation with time on stream, and an improved selectivity to products in the diesel fraction, as compared to the original microporous Theta-1.

Alum Production from some Nigerian Kaolinite Deposits

The Development of Sustainable Processing Technologies for the Vast Mineral Resources Available in Nigeria and their Varied Applications Is a Major Pursuit by the Federal Ministry of Science and Technology. in this Work, Alum Was Produced from Three Different Kaolin Deposits in Nigeria Namely Kankara Brown, Bauchi and Kankara White by Acid Dealumination of the Metakaolin Obtained by Calcination of the Beneficiated Kaolinites and the Yields Were Measured to Ascertain the Process Repeatability. the Reproducibility Studies Carried Out on Samples from each Deposit Showed a Mean Yield of 80 %, 92 % and 87 % and Standard Deviation of 2.50 %, 1.063 % and 1.296 %, for Kankara Brown, Bauchi and Kankara White Respectively. the Values from the Three Deposits Fall within 3 Standard Deviations of the Mean in Accordance with the 68-95-99.7/three-Sigma Rule. the Alum Quality Also Compares Well with Available Commercial Alums in the Market. BET Analysis, of the Alumina Obtained by Calcination of the Alum (Kankara White), Gave a Surface Area of 192.2441m2/g Comparable to Commercial Alumina. these Results Suggest/establishes the Huge Possibility of Commercial Alum Production, Including Alumina, Using Kaolinite Clay from these Deposits as Starting Materials.

Influence of Chemical Surface Characteristics of Natural Zeolite on Catalytic Ozone Abatement

In this article, the effect of zeolite chemical surface properties on gaseous ozone removal was investigated. Zeolite samples with different surface chemical composition were prepared from a Chilean natural zeolite. Such treatments included acid de-alumination, and thermal treatment at 400 °C and 550 °C prior to contact with ozone. Chemical modification of natural zeolite showed that the generation of new Lewis acid sites on zeolite surface increases ozone removal. It is concluded that Lewis acid sites present on zeolite surface play a key role enhancing the gaseous ozone elimination.

Study of the effect of the acid dealumination on the physico-chemical properties of Y zeolite

The aim of the present work was to combine different physicochemical techniques, namely X ray diffraction, IR spectroscopy, and multinuclear (29Si and 27Al) solid-state NMR spectroscopy, to study the aluminum distribution and to determine the silicon–aluminum ordering in the Y-zeolite framework when the latter was submitted to acid leaching (HCl, HNO3, H2SiF6). It was shown that all acids were effective in removing Al from the framework. Moreover, the extra-framework Al extraction from the lattice was dependent on the nature and the concentration of the acid. After the dealumination treatment, different species (silanol nest, six-coordinated non-framework Al) were detected. The investigation showed that the breakdown of the parent Y-zeolite mainly depends on the degree of dealumination.

Steam and acid dealumination of mordenite: Characterization and influence on the catalytic performance in linear alkylbenzene synthesis

A systematic study of both acid and steam dealumination of mordenite has been carried out aiming to obtain a mordenite featuring high acid strength active sites along with a secondary mesoporous system, in order to maximize both catalytic performance and time-on-stream stability of the material in solid-acid catalyzed alkylation of benzene with 1-dodecene. Detailed assessment of the textural (XRD, N 2 adsorption–desorption) and acid (FTIR of pyridine adsorption) properties of the obtained materials was performed. It has been found that catalysts obtained by combined steam dealumination and acid washing show a dramatic increase in the intrinsic activity and a significantly lower tendency to suffer deactivation when compared to the parent zeolite and samples obtained by acid treatments. This improved behaviour of the steam-treated sample is attributed to its increased mesoporous surface area, lower acid sites concentration and less hydrophilic surface.

Effect of dealumination severity on the pore size distribution of mordenite

Acid leaching with nitric acid was conducted for the framework dealumination of H-mordenite. The parent as well as the samples obtained after acid treatment were characterized by XRD, surface area, pore volume and pore size distribution for identifying structural changes after dealumination. For the parent (HM) and two acid leached (ATHM-1 and ATHM-3) samples studied, the surface area and micro pore volumes were increased in the order of HM < ATHM-1 < ATHM-3. Nitrogen adsorption studies at 77 K indicated that the increase in micro pore volume is not uniform for the pores of diameter 0–20 Å, where the entire range of micropores were classified into three groups, namely smaller micropores belong to side pockets, micropores belong to main channels, and the secondary micropores that are larger than main channels. The pore volume in small and larger micropores was increased, where as that of the main channels was decreased in the order of HM < ATHM-1 < ATHM-3, and the detailed analysis could provide a direct evidence for the opening of side pockets of mordenite by acid dealumination. The dealuminated samples ATHM-1 and ATHM-3 exhibited enhanced n-hexane isomerization activity.

Factors affecting isomer yield for n-heptane hydroisomerization over as-synthesized and dealuminated zeolite catalysts loaded with platinum

Pt loaded Y, USY, beta, mordenite, ZSM-12, and ZSM-5 zeolites with different Si/Al ratios and a USY and ZSM-12 sample having enhanced activity were studied for the hydroisomerization of n-heptane. All the possible heptane isomers were obtained over Pt/H-ZSM-12 and the product distribution was closer to that over Y and beta catalysts, but very different from that over Pt/H-ZSM-5. Shape-selective effects in ZSM-12 resulted in a significantly higher isomer yield than the beta and Y-zeolite catalysts. For Y, beta, and ZSM-12 samples having very little extraframework aluminum, changing the Si/Al ratio did not affect the isomer yield. However, USY and ZSM-12 samples that showed enhanced activity were very sensitive to the Pt precursor and Pt loading, which caused huge differences in their activity and isomer selectivity. The Pt dispersion in the enhanced activity catalysts was also much lower. A careful optimization of the precursor, amount of Pt loaded, and pretreatment conditions is essential to achieve good balance between the metal and the acid functions in these catalysts. The optimized enhanced activity catalyst is able to provide isomer yields approaching that obtained over the regular catalysts, which suggests that zeolite acidity is not directly affecting the isomer selectivity. These results indicate that the maximum isomer yield for a Pt/H-zeolite catalyst is obtained when the metal and acidic functions of the catalysts are well balanced. Therefore, it may not be possible to increase the isomer yield beyond this maximum by modifying the acidity characteristics of the catalyst. Mordenite and ZSM-5 catalysts showed low isomer yields, but acid dealumination of the parent mordenite improved the isomer yield, possibly due to creation of mesopores.

Factors affecting isomer yield for n-heptane hydroisomerization over as-synthesized and dealuminated zeolite catalysts loaded with platinum

Pt loaded Y, USY, beta, mordenite, ZSM-12, and ZSM-5 zeolites with different Si/Al ratios and a USY and ZSM-12 sample having enhanced activity were studied for the hydroisomerization of n -heptane. All the possible heptane isomers were obtained over Pt/H-ZSM-12 and the product distribution was closer to that over Y and beta catalysts, but very different from that over Pt/H-ZSM-5. Shape-selective effects in ZSM-12 resulted in a significantly higher isomer yield than the beta and Y-zeolite catalysts. For Y, beta, and ZSM-12 samples having very little extraframework aluminum, changing the Si/Al ratio did not affect the isomer yield. However, USY and ZSM-12 samples that showed enhanced activity were very sensitive to the Pt precursor and Pt loading, which caused huge differences in their activity and isomer selectivity. The Pt dispersion in the enhanced activity catalysts was also much lower. A careful optimization of the precursor, amount of Pt loaded, and pretreatment conditions is essential to achieve good balance between the metal and the acid functions in these catalysts. The optimized enhanced activity catalyst is able to provide isomer yields approaching that obtained over the regular catalysts, which suggests that zeolite acidity is not directly affecting the isomer selectivity. These results indicate that the maximum isomer yield for a Pt/H-zeolite catalyst is obtained when the metal and acidic functions of the catalysts are well balanced. Therefore, it may not be possible to increase the isomer yield beyond this maximum by modifying the acidity characteristics of the catalyst. Mordenite and ZSM-5 catalysts showed low isomer yields, but acid dealumination of the parent mordenite improved the isomer yield, possibly due to creation of mesopores .