Dehydration Of N-butanol Research Articles

Active site requirements for bio-alcohol dehydration: Effect of chemical structure and site proximity

Synthesis-structure-activity relations are reported, describing how interzeolite conversion (IZC) allows synthesis of ZSM-5 (MFI framework) with fixed physicochemical properties, except the variable local acid site (Al) arrangement, by variation of the synthesis time. Local confinement and acidity effects are probed by applying both H-ZSM-5 and Na-ZSM-5 samples in alcohol dehydration. Pyridine and divalent cobalt ion probing are used to quantify the amount of accessible acid sites and of Al in close proximity. Al in close proximity shows a strong influence on n-butanol dehydration turnover rates. The turnover rates are also strongly dependent on local confinement: in Na-form, ZSM-5 synthesized with more Al present as isolated species is a factor of 3–7 times more active than Na-ZSM-5 with fewer isolated Al. However if the zeolites are in proton form, ZSM-5 with more proximate sites show a higher activity compared to ZSM-5 with more isolated sites. Linear butene selectivity increases in Na-ZSM-5 compared to H-ZSM-5, caused by a suppressed dibutyl ether formation. The selectivity towards 1-butene is enhanced to a greater extent on proximate sites, likely due to a local/steric constraint at the active site. Decomposition of DBE over Na-ZSM-5 is more active compared to n-butanol dehydration, independent of acid site proximity. Also for 2-propanol dehydration, Na-ZSM-5 is less active than H-ZSM-5, yet the activity difference is attenuated compared to n-butanol dehydration. Essentially, due to the intrinsic higher reactivity of 2-propanol, the acid site requirement is less stringent. These findings highlight the importance of local confinement and Al proximity in acid-catalyzed conversion of oxygenated compounds.

Enhancing the catalytic performance of H-ZSM-5 in bio n-butanol dehydration by zeolite crystal engineering

NH4F etching is used as an unbiased chemical etching technique to hierarchize commercially available nano-sized ZSM-5 crystals. A structure-function relationship is reported, describing how the introduction of mesoporosity in a microporous ZSM-5 zeolite significantly increases its catalytic performance in (aqueous) n-butanol dehydration. Three parent samples are etched under two severity modes: mild (5 minutes of etching) and harsh (40 minutes of etching). Intrinsic features of the parent ZSM-5’s, such as their silanol populations, influence the outcome of the etching procedure. For all materials, crystallinity is unaffected, total pore volume increases while micropore volume is almost constant, and active site accessibility increases. For all materials, etching increases the catalytic activity for n-butanol dehydration. Cofeeding water to n-butanol further increases the stability of all catalysts. Microkinetic modeling reveals that the increased activity is related to a decreased stability of dibutyl ether (DBE), the most abundant surface intermediate. A decreased DBE adsorption energy, due to the increased accessibility of the acid sites, facilitates its desorption. NH4F etching, a flexible and easy technique to engineer zeolites' textural properties, does not affect the intrinsic nature and quantity of their active sites, leading to superior catalytic performances. Our results highlight the possibility to further increase the efficiency of zeolite catalysis in biomass conversion processes.

Engineering fast water-selective pathways in graphene oxide membranes by porous vermiculite for efficient alcohol dehydration

Graphene oxide (GO) lamellar membranes with well-aligned architecture hold promising potential for molecular separations. However, the tortuous transport pathways and weak interlamellar interactions between stacked GO nanosheets cause low flux and poor stability, which are major drawbacks for their practical applications. Herein, we report a strategy to engineer fast and robust water-selective pathways within GO-based lamellar membranes by porous vermiculite (PVMT), a naturally layered magnesium aluminosilicate. PVMT nanosheets conferred abundant in-plane pores, which decreased the tortuosity and shortened the mass transport distance inside lamellar membranes. Meanwhile, PVMT nanosheets enhanced the hydrophilicity and fixed the interlayer distance, contributing to robust water-selective transport. The physicochemical properties of membranes, such as thickness and hydrophilicity, were manipulated by the loading amount of PVMT nanosheets. The resulting lamellar membranes exhibited excellent n-butanol dehydration performance with a permeation flux of 9554 g m−2 h−1 and a separation factor of 2678, which increased by up to 91% and 328% compared to pristine GO/PTFE membranes. Moreover, membranes remain stable for 192 h operation. Our study may stimulate further research on precise construction of mass-transfer pathways within lamellar membranes.

PVA/UiO-66 mixed matrix membranes for n-butanol dehydration via pervaporation and effect of ethanol

In this work, pervaporative mixed matrix membranes (MMMs) composed of porous UiO-66 filler newly-synthesized and poly (vinyl alcohol) (PVA) have been investigated for dewatering n-butanol (BuOH) from BuOH/H2O and BuOH/ethanol/H2O solutions. The influences of the filler loading, feed concentration and feed temperature on the membrane dehydration performance are investigated in detail in terms of pervaporation flux/separation factor, pervaporation separation index and component permeance/selectivity. It is found that with the increase in feed water concentration or temperature, total permeation flux across the MMM substantially rises while the dehydration separation factor decreases considerably. With the increase in feed temperature, pronounced increase in the driving force is resulted, yielding the decline in the partial permeance and water/n-butanol selectivity but increase in the component flux. As the water content increases, the water permeance and water/n-butanol selectivity are reduced while both BuOH flux and permeance increase. Over the filler loading range considered here, the MMM with 15 wt% UiO-66 has reached the largest pervaporation separation index of 2560 kg/m2·h at 70 °C and 10 wt% water in the feed. In the case of using 10 wt% ethanol for BuOH in the feed, the dewatering separation performance has varied substantially as compared to the binary feed, leading to reduced separation factor and elevated permeation flux for the 15 wt% UiO-66 filled MMM. In the meantime, the MMM has maintained excellent separation performance over a testing duration of 240 h. Our results show that pervaporative UiO-66/PVA MMMs have demonstrated great potential in practical BuOH dehydration applications.

UV light enhanced catalytic performance of heteropolyacid-TiO2 systems

A series of catalysts based on TiO2 polymorphs were designed with tungstophosphoric acid H3PW12O40 (HPW), either alone or with addition of Fe2O3. These HPW@Fe2O3@TiO2 nanocomposites showed satisfactory performance in the dehydration of n-butanol at 120 – 200 °C in gas-phase under both the thermocatalytic and the photothermocatalytic conditions. The highest catalytic activity in this reaction was achieved over HPW supported on the home-designed TiO2 (HPW/hp), on hp with the addition of Fe2O3 (HPW/Fe/hp) and on the hydrophobic titanium oxide T805 (HPW/T805). The main product turned out to be cis-butene, apart from trans-butene, di-n-butyl ether (DNBE) and butyraldehyde that have also been detected. The influence of the light on the course of the catalytic alcohol conversion was discussed. Basing on proposed energy diagram with electron and hole transfer paths for the HPW@Fe2O3@TiO2 catalysts the probable mechanism of charge transfer upon UV irradiation was proposed.

Exploring the potential of highly selective deep eutectic solvents (DES) based membranes for dehydration of butanol via pervaporation

N-butanol has unique physicochemical and combustion properties, similar to gasoline, which makes it an environmentally friendly alternative to conventional fuels. To improve the efficiency, the dehydration of butanol is necessary. This paper aims to investigate the performance of Deep Eutectic Solvents (DESs) based membranes for the dehydration of n-butanol by the pervaporation process. Three DES with different combinations of hydrogen bond donors and acceptors, i.e., DL-menthol: Lauric acid (DES), DL-menthol-Palmitic acid (DES), and [TETA] Cl: Thymol (DES), were used. We hypothesized that (i) incorporation of hydrophobic DES would increase the hydrophobicity of the membranes; (ii) specific functional groups (phenolic group, amine group) in DESs would enhance the butanol-philic character of membranes, and (iii) hydrophobic DESs would increase the butanol separation efficiency and permeability of membranes. FTIR analysis and physicochemical parameters of the resultant liquid mixture validated the DESs' production. The DESs were then filled into the permeable support, resulting in supported liquid membranes (SLMs). An additional layer of polydimethylsiloxane (PDMS) was coated directly on the DES-PSf layer to prevent leaching out of DES. A feed containing a 6 wt % aqueous solution of butanol under varying temperatures was studied. The results showed that among all membranes, [TETA] Cl: Thymol DES-based membrane showed the highest sorption of 36% at room temperature. The introduction of DES in membranes resulted in a remarkable increase in the separation factor while sustaining a reasonable flux. Among all the membranes, the DL-menthol: Lauric acid (DES) based membrane exhibited the highest separation factor of 57 with a total flux of 0.11 kg/m2. h. Significantly high butanol-water separation was attributed to the low viscosity and high butanol solubility of the chosen DES, which makes it a suitable substitute to conventional ILs.

Conversion of butanol to propene in flow: A triple dehydration, isomerisation and metathesis cascade

A combined three-step flow cascade conversion of n-butanol to propene is demonstrated. Zeolite H-ZSM-5 gives high conversion in the initial n-butanol dehydration step (98%). Subsequent isomerisation of terminal butenes to internal butenes over zeolite H-Fer takes place with good conversion (87%). Finally, cross-metathesis with ethene over a tungsten on acid-washed SiO2/Al2O3 catalyst affords propene with good selectivity (65%). Coupling these three steps into a single flow sheet gives an overall yield of 64% propene from n-BuOH. Ethene cross-metathesis catalyst performance was probed using 2-pentene as a model co-substrate giving good conversion (~90%) and moderate selectivity to butenes (67%).

Vapor-liquid interfacial polymerization of covalent organic framework membranes for efficient alcohol dehydration

Covalent organic frameworks (COFs) with well-ordered pore structures and versatile functionalities hold tremendous promise as membrane building blocks. The facile and controllable fabrication of COF membranes remains a critical challenge. Herein, we presented a one-step vapor-liquid interfacial polymerization (VLIP) method to in-situ fabricate COF membranes on substrates under mild conditions. This VLIP method features controllable COF growth at the vapor-liquid interface, acquiring COF membranes with tunable physicochemical structure. The time-dependent amorphous-to-crystalline COF growth improved the crystallinity of COF membranes, thus improving the molecular sieving property. The increased monomer concentration endowed COF membranes with higher hydrophilicity, intensifying the water sorption ability. The resultant COF membranes conferred numerous hydrophilic pathways for water-selective transport, exhibited a high and stable n-butanol dehydration performance with permeation flux of 8160 g m−2 h−1 and separation factor of 1023 over 14 days. This VLIP method may evolve into a generic platform technique to fabricate COF membranes for efficient molecular separation.

Graphene oxide membranes tuned by metal-phytic acid coordination complex for butanol dehydration

For two-dimensional (2D) lamellar graphene oxide (GO) membranes, tuning the interlayer distance and enhancing surface hydrophilicity are two efficient strategies to achieve high selectivity and permeation flux for solvent dehydration. Herein, Fe3+-phytic acid (PA) coordination complex was designed as both the intercalator and surface modifier to fabricate hydrophilic GO membranes. Fe3+-PA complexes interacted with the oxygen-containing functional groups of GO nanosheets through non-covalent interactions to fix the interlayer distances to 0.61 nm in 90 wt% n-butanol/water mixture.Moreover, Fe3+-PA complexes enhanced the surface hydrophilicity of GO membranes, which promoted the water sorption ability of the membrane and facilitated the fast water-transport. The pervaporation n-butanol dehydration performance was investigated as a function of Fe3+-PA complex content and feed temperature. GO-PA-Fe3+/PTFE membranes with an optimized PA addition amount of 50 wt% exhibited a separation factor of 1059 and a permeation flux of 10.57 kg/(m2 h) under 80 °C for 90 wt% n-butanol/water mixture. This study provides a novel avenue to fabricating 2D lamellar separation membranes by incorporating multifunctional metal-coordinated complexes.

The role of TiO2 polymorphs as support for the Keggin-type tungstophosphoric heteropolyacid as catalysts for n-butanol dehydration

An effect of using different TiO2 polymorphs as support for H3PW12O40 heteropolyacid on the (photo)catalytic performance of the H3PW12O40/TiO2 catalyst was investigated. Two kinds of synthesis methods of the catalysts have been applied. In the first, the H3PW12O40/TiO2 catalyst was prepared by impregnation of either the pure anatase (A), or rutile (R), or a mixture of the two (P25) in a solution of H3PW12O40. In the second method, an additional pre-treatment is being applied to all three types of support, A, R and P25, consisting of hydrothermal sonication with KOH solution. The catalysts and supports were characterized by XRD, SEM, BET analysis and FTIR spectroscopy. Catalytic tests show that H3PW12O40/P25 catalyst exhibits a higher (photo)activity to n-butanol dehydration in gas phase compared to the catalysts supported on either of pure polymorphs and that the sonication pre-treatment did not improve the activity of the catalysts so prepared. The application of the not treated P25 - the mixture of anatase and rutile as the support of heteropolyacid allowed to find the efficient heterogeneous catalyst.

Conferring efficient alcohol dehydration to covalent organic framework membranes via post-synthetic linker exchange

Covalent organic frameworks (COFs) have gained tremendous interest as membrane building blocks owing to rigid, long-range ordered and easily functionalized skeletons. The facile, controllable and task-specific construction of COF membranes lies in the frontier of membrane technology. Herein, we explored a post-synthetic linker exchange (PLE) method to engineer COF membranes for efficient alcohol dehydration. The proposed PLE method, utilizing the reversible breaking-reformation basis between pristine COF membranes and post-introduced linkers, narrowed the effective pore size to intensify molecular sieving property. Moreover, the PLE method also endowed COF membranes with more hydrophilic groups, thus improving the water sorption ability of COF membranes. The resultant COF membranes exhibited superior n-butanol dehydration performances with 3620 of selectivity, 11.35 kg m−2 h−1 of total flux and remained stable in 15-day operation. This PLE method may flourish the library of engineering COF membranes for efficient molecular separations.

Dehydration of n-butanol on phosphate-modified carbon nanotubes: active site and intrinsic catalytic activity

Dehydration of n-butanol (nB) to corresponding olefins (butene) is an important reaction route to realize efficient utilization of bulk bio-alcohols.

Construction of graphene oxide membrane through non-covalent cross-linking by sulfonated cyclodextrin for ultra-permeable butanol dehydration

Two-dimensional (2D) lamellar graphene oxide (GO) membranes represent promising porous materials in alcohol dehydration. The separation performance can be manipulated by the physicochemical properties of interlayer channels. The relatively low flux and poor stability of GO-based membranes in aqueous environment are the major drawbacks. Herein, we intercalated a supramolecular compound, sulfobutyl-β-cyclodextrin (SCD), into the interlayer pores/channels of GO membranes. The sulfonic acid groups on SCD molecules are able to cross-link adjacent GO nanosheets throughnon-covalent interactions. The GO-SCD membranes possess excellent water affinity due to the presence of high hydrophilic sulfonic acid groups. For the n-butanol dehydration, the GO-SCD/PTFE membranes with well-defined interlayer pores exhibited ultrahigh permeation flux of 12955 g m-2 h-1 and separation factor of 1299 under 80 oC. The membranes remained stable in 144 h separation performance evaluation test and exhibited obviously enhanced thermal stability.

Oxygen assisted butanol conversion on bifunctional carbon nanotube catalysts: Activity of oxygen functionalities

Catalytic conversion of n-butanol to high-value-added product is considered as a highly important route towards biomass derived fine chemicals. The present work reports the applications of non-metallic multi-walled carbon nanotube (CNT) as bifunctional catalysts for oxygen assisted n-butanol conversion reactions. Oxidative dehydrogenation (ODH) and dehydration of n-butanol on CNT yielded aldehyde and alkene compounds via redox and acid catalytic routes, respectively. CNT exhibited high activity (over 50% n-butanol conversion) and stability (over 120 h) under gentle reaction conditions (<330 °C), which are competitive to conventional metal-based catalysts. Carboxylic acid groups were identified as catalytic active sites for dehydration reactions via linking the reactivity (kinetic parameters) with the surface composition and structural information of CNT catalysts. The redox activity could be related to ketonic carbonyl groups, and interestingly the intrinsic ODH catalytic activity is also influenced by degree of graphitization for CNT materials.

Renewable Butene Production through Dehydration Reactions over Nano-HZSM-5/γ-Al2O3 Hybrid Catalysts

The development of new, improved zeolitic materials is of prime importance to progress heterogeneous catalysis and adsorption technologies. The zeolite HZSM-5 and metal oxide γ-Al2O3 are key materials for processing bio-alcohols, but both have some limitations, i.e., HZSM-5 has a high activity but low catalytic stability, and vice versa for γ-Al2O3. To combine their advantages and suppress their disadvantages, this study reports the synthesis, characterization, and catalytic results of a hybrid nano-HZSM-5/γ-Al2O3 catalyst for the dehydration of n-butanol to butenes. The hybrid catalyst is prepared by the in-situ hydrothermal synthesis of nano-HZSM-5 onto γ-Al2O3. This catalyst combines mesoporosity, related to the γ-Al2O3 support, and microporosity due to the nano-HZSM-5 crystals dispersed on the γ-Al2O3. HZSM-5 and γ-Al2O3 being in one hybrid catalyst leads to a different acid strength distribution and outperforms both single materials as it shows increased activity (compared to γ-Al2O3) and a high selectivity to olefins, even at low conversion and a higher stability (compared to HZSM-5). The hybrid catalyst also outperforms a physical mixture of nano-HZSM-5 and γ-Al2O3, indicating a truly synergistic effect in the hybrid catalyst.

Hybrid macromolecular stars with fullerene(C60) core included in polyphenyleneisophthalamide membranes for n-butanol dehydration

The problem of n-butanol ‒ water separation arises from the widespread interest to the search for alternative energy sources. To solve the problem by membrane technique, pervaporation membranes were developed on the basis of polyphenyleneisophthalamide modified with hybrid star macromolecules containing six arms of polystyrene and six arms of poly-tert-butyl methacrylate on the fullerene (C60) core. The structure was studied by scanning electron microscopy that reveal a tendency to form domains in the membranes modified by star macromolecules. Modification of the membrane by star fullerene (C60)-containing macromolecules led to a sharp increase in the selectivity and permeability of the membrane. Transport properties of novel membranes were studied in pervaporation of n-butanol‒water mixtures to separate n-butanol from water admixture for further use of this alcohol as industrial solvent and biofuel. It was found that introduction up to 5 wt% star modifier increases the separation efficiency of membranes in dehydration of n-butanol (water content in the permeate reaches 99.9 wt% while pervaporation separation index comes up to 400 kg/m2h), which allows obtaining high-purity n-butanol.

Butanol-1 Dehydration via Pervaporation Using Membranes Based on Thermally Rearranged Polymer

The process of dehydration of n-butanol as one of the most used solvents and a biofuel base has been studied by a membrane separation method with the use of vacuum pervaporation. Nonporous diffusion membranes based on a thermally rearranged polymer and its hydrolytically stable prepolymer have been selected as the objects of the research. The main physicochemical parameters of the membranes, such as contact angles, surface tension, membrane density, and the results of sorption tests, are reported. Transport properties of the membranes have been studied for separation the water–n-butanol mixture with the water content in the mixture varied from 10 to 75 wt %. It has been shown that thermal rearrangement of the polymers leads to structure compacting and to more selective penetration of water molecules through the polymer matrix, thereby facilitating effective removal of water impurities from n-butanol.

SHS Membrane for the Dehydrogenation of n-Butanol to Butadienes

We have synthesized catalytically active membranes based on α- and γ-Al2O3 powders for the dehydration and dehydrogenation of butyl alcohol to butadiene and hydrogen. The open porosity of the samples obtained in this study is 41% in the case of α-Al2O3 and 38% in the case of γ-Al2O3. The open pore size is 4.6–5.1 μm in the α-Al2O3 material and 0.5–0.8 μm in the γ-Al2O3 material. We have implemented a hybrid, membrane–catalytic process for the dehydrogenation of butanol by combining reaction and hydrogen separation steps in a single device. It has been demonstrated that the dehydration of n-butanol on a γ-Al2O3 converter leads to the formation of a butylene fraction with a selectivity of 99.88–100% at a temperature of 300°C, which is 50°C lower than in the case of commercially available gamma-alumina granules. The dehydrogenation of butylene to butadiene on an α-Al2O3 membrane with selective hydrogen removal from the reaction zone has made it possible to raise the 1,3-butadiene output from 16.5 to 22.6 L/(h gact. comp.), with the degree of ultrapure hydrogen extraction reaching ~16%. After the experiment was run for 20 h, no decrease in the catalytic activity of the system was detected, as distinct from commercial solutions, in which a regeneration step is necessary every 8–15 min.

Study of n-butanol conversion to butenes: Effect of Si/Al ratio on activity, selectivity and kinetics

As bio-butanol is gaining more and more interest as a commercially available bioresource, the dehydration of this alcohol towards butenes and higher carbons gains more of interest. In general HZSM-5 has shown to be the most promising catalyst for this conversion. The role of the zeolite’s Si/Al ratio in the butanol dehydration reaction is still not fully understood. Experimental data obtained for a series of HZSM-5 with decreasing Si/Al ratio revealed an increase in activity of the catalyst per active site without affecting the selectivity profile. To understand the underlying effects, a microkinetic model was constructed for H-ZSM-5 with a Si/Al ratio of 25, based on literature DFT calculations, and the model was further modified by fitting the key parameters to the measured data at the four different temperatures studied in this work. This resulted in an adequate model for the dehydration of butanol across the evaluated temperature range of 503 K to 533 K. Investigation of the occurring mechanisms indicated a inhibiting effect due to the strong adsorption of di-n-butylether. This ‘poisoning’ of the catalyst surface resulted in a peculiar S-like curve for the conversion site time relation, which was also experimentally observed. This newly fitted base model was used to obtain more insight in the effect of the Si/Al ratio by implementing an additional ΔΔH parameter, which is related to the adsorption strength of n-butanol in the base model. ΔΔH varies between −4.8 to +11.3 kJ/mol and provides a good fit for Si/Al ratios ranging from 15 to 140. The higher dehydration rates observed with decreasing Si/Al can be traced back to an increase in adsorption strength resulting in an overall increase in surface coverage. The constant selectivity-conversion profile can be explained by a similar dependency of all elementary steps on the adsorption strength. The model developed in this study enables to simulate and understand the experimentally observed effects of temperature and Si/Al ratio on the n-butanol dehydration.

Covalent organic framework membranes through a mixed-dimensional assembly for molecular separations

Covalent organic frameworks (COFs) hold great promise in molecular separations owing to their robust, ordered and tunable porous network structures. Currently, the pore size of COFs is usually much larger than most small molecules. Meanwhile, the weak interlamellar interaction between COF nanosheets impedes the preparation of defect-free membranes. Herein, we report a series of COF membranes through a mixed-dimensional assembly of 2D COF nanosheets and 1D cellulose nanofibers (CNFs). The pore size of 0.45–1.0 nm is acquired from the sheltering effect of CNFs, rendering membranes precise molecular sieving ability, besides the multiple interactions between COFs and CNFs elevate membrane stability. Accordingly, the membranes exhibit a flux of 8.53 kg m−2 h−1 with a separation factor of 3876 for n-butanol dehydration, and high permeance of 42.8 L m−2 h−1 bar−1 with a rejection of 96.8% for Na2SO4 removal. Our mixed-dimensional design may inspire the fabrication and application of COF membranes.