In situ analysis of volatiles obtained from the catalytic cracking of polyethylene

The effects of the solid‐acid‐catalyst pore size and acidity on polyethylene catalytic cracking were examined with a comparison of the temperature‐dependent volatile‐product‐slate changes when the polymer was cracked with HZSM‐5 and HY zeolites and the protonated form of MCM‐41. Volatile‐product distributions depended on the catalyst acidity and pore size. With HZSM‐5, paraffins were detected initially, and olefins were produced at somewhat higher temperatures. Aromatics were formed at temperatures 30–40°C higher than those required for olefin production. Small olefins (C₃–C₅) were the most abundant products when HZSM‐5 and MCM‐41 catalysts were employed for cracking polyethylene. In contrast, cracking with HY produced primarily paraffin volatile products (C₄–C₈). HY pores were large enough and the acid sites were strong enough to promote disproportionation reactions, which led to the formation of volatile paraffins. Compared with the other catalysts, HZSM‐5 with its smaller pores inhibited residue formation and facilitated the production of small alkyl aromatics. Volatile‐product variations could be rationalized by a consideration of the combined effects of catalyst acidity and pore size on carbenium ion reaction pathways. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 3118–3125, 2001     

Solution‐processable exfoliated zeolite nanosheets purified by density gradient centrifugation

Highly crystalline exfoliated MFI‐nanosheets can pave the way for large‐scale deployment of sub‐500‐nm zeolite membranes due to their processing and packing advantages. Exfoliated MFI‐nanosheets prepared by melt compounding contain a large amount of polymer and unexfoliated particles which are detrimental to the fabrication of ultrathin zeolite membranes. Complete removal of polystyrene from the nanosheet suspension in toluene is demonstrated by centrifugation of the suspension across chlorobenzene as confirmed by thermogravimetric analysis (TGA) data and transmission electron microscopy (TEM) images. Rate‐zonal centrifugation in a nonlinear density gradient fractionated exfoliated MFI‐nanosheets from unexfoliated particles. The purified nanosheets were highly crystalline as indicated by high‐resolution TEM (HRTEM) and electron diffraction (ED). Coating of purified MFI‐nanosheets on a smooth α‐alumina support, fabricated by filtration of α‐alumina suspension, led to a compact, b‐oriented, 80‐nm‐thick film. A mild hydrothermal treatment of the film led to a 200‐nm‐thick membrane, which demonstrated molecular sieving properties. © 2013 American Institute of Chemical Engineers AIChE J, 59: 3458–3467, 2013     

Effect of water saturation on gas slippage in circular and angular pores

A unified model for gas slip flow through circular and angular pores in both single phase flow and two‐phase flow conditions is developed, and the effect of water saturation on gas slippage factors in different pore shapes are revealed. For circular pores, the water saturation retains as thin film binding on pore surfaces without changing the shape of the cross section, and the hydraulic diameters continuously reduce as water saturation increases, directly leading to an increase in the slippage factor. However, for angular pores, the water saturation retains as both films at boundaries and condensations at corners, and the film‐water and corner‐water gradually change their cross‐section shape (from sharp corners to round corners), which further affects the gas slip behavior. Due to the presence of round corners, the ratio of the cross‐sectional area and perimeter, which can also be regarded as the reciprocal of a specific surface area, can even increase at a low water saturation condition. Thus the collisions between gas molecules and pore boundaries weaken, resulting in a slight reduction in the gas slippage factor. This interesting finding in the angular pore case directly explains the contradiction of the published experimental results with the general knowledge (i.e., the gas slip factor always increases as water saturation increases). Thus, the validity of the common assumption regarding actual porous media as capillaries with a circular cross‐section must be considered more carefully. © 2018 American Institute of Chemical Engineers AIChE J, 64: 3529–3541, 2018     

A new catalytic process for high‐efficiency synthesis of p‐xylene by methylation of toluene with CH3Br

A new catalytic process for p‐xylene synthesis from the methylation of toluene with CH₃Br was proposed. CH₃Br was prepared from the catalytic bromination of natural gas (CH₄), by using H₂O + HBr + O₂ as mediator over supported Rh catalyst. The methylation conditions were investigated using HZSM‐5 or modified HZSM‐5 catalyst. Under optimal reaction conditions, p‐xylene selectivity is up to 93%, and p‐xylene yield is more than 21% at 673 k over the Si—P modified HZSM‐5 catalyst. Compared to the processes using MeOH or dimethyl carbonate (DMC) as methylation agent, this new process is very attractive in an economic standpoint since CH₄ is much cheaper than MeOH and DMC. In addition, the process has other advantages, such as mild reaction conditions, simple operation, high‐product yield, and so on. It is predicted that the process has good industrial potential for para‐xylene production. © 2012 American Institute of Chemical Engineers AIChE J, 59: 532–540, 2013     

Converting Alkali Lignin to Biofuels over NiO/HZSM‐5 Catalysts Using a Two‐Stage Reactor

A series of NiO/HZSM‐5 catalysts were used to convert alkali lignin to hydrocarbon biofuels in a two‐stage catalytic pyrolysis system. The results indicated that all NiO/HZSM‐5 catalysts reduced the content of undesirable phenols, furans, and alcohols of the biofuel compared to non‐catalytic treatment. The NiO/HZSM‐5 catalyst with the lowest amount of NiO generated the highest biofuel yield in all catalytic treatments, and it also produced biofuel with the highest content of hydrocarbons. The emission of carbon oxides (CO and CO₂) increased in the treatments with higher‐NiO loading HZSM‐5 due to the redox reaction between NiO and the oxygenated compounds in the bio‐oil. Ni₂SiO₄ was generated in the used NiO/HZSM‐5 catalysts during the high‐temperature pyrolysis process.     

Controllable fabrication and catalytic activity of highly b‐oriented HZSM‐5 coatings

Multilayer b‐orientated HZSM‐5 catalytic coating is controllably synthesized by repeated growth of zeolite layer on Ti?OH‐modified surface of sublayer. The as‐prepared zeolite coating shows performance enhancement up to 110% in catalytic cracking of n‐dodecane ascribed to enhanced mass transfer in its straight and short pathway along the b‐axis. © 2014 American Institute of Chemical Engineers AIChE J, 60: 1964–1968, 2014     

The effect of pretreatment procedures on the activities of Fe- and Mn-promoted sulfated zirconia catalysts

The vapour phase acylation of furan and pyrrole was carried out over HZSM‐5(19.7), HZSM‐5(30), HZSM‐5(280), CeHZSM‐5(30), LaHZSM‐5(30), HY and CeHY zeolites in a fixed bed reactor at atmospheric pressure using acetic anhydride as an acylating agent. The catalytic activity of the zeolite catalysts was dependent on the reaction temperature and the type of cation promoter used in the modification of the zeolite surface. The activity of the catalysts varied with the acidity of the zeloite systems tested. The yields of 2‐acetylfuran and 2‐acetylpyrrole with respect to the conversion of furan and pyrrole were 67.5% and 75.5% respectively. The acylation was found to be more active on Brønsted acidic sites available over zeolite systems.     

Propane Aromatization over HZSM‐5 and Ga/HZSM‐5 Catalysts

The selective transformation of light alkanes to aromatics that are more valuable and versatile feedstocks for the chemical industry is one of the major challenges of catalytic chemistry. The complexity of the aromatization chemistry makes it difficult to unravel reaction mechanisms and, mechanistic information is largely developed from observed product distributions. This article reviews the current mechanistic understanding for the conversion of propane to aromatic compounds over HZSM‐5 and Ga/HZSM‐5 catalysts based on experimental as well as theoretical studies.

Following a general discussion of acidity and confinement effects in these systems, this review focuses on understanding specific reactions occurring on Brønsted acid sites in HZSM‐5. Mechanistic details available from Density Functional Theory (DFT) calculations, as well as kinetic modeling efforts for various complex hydrocarbon systems are critically reviewed. A detailed, tabulated review of the literature compares the catalytic performance of gallium modified ZSM‐5 catalysts and subsequently the promotional effect of gallium as an additive is critically discussed in terms of the nature of the active sites, as well as the new reaction pathways introduced by gallium addition.     

Enhanced water flux through graphitic carbon nitride nanosheets membrane by incorporating polyacrylic acid

Membranes assembled from two‐dimensional (2‐D) layered materials have shown potential use in water purification. Recently, a 2‐D graphitic carbon nitride (g‐C₃N₄) nanosheets membrane exhibits considerable separation performance in water purification. In this study, to further improve this water separation performance, polyacrylic acid (PAA) was introduced to tune the nanochannels formed between the g‐C₃N₄ nanosheets. The fabricated g‐C₃N₄‐PAA hybrid membranes possessed higher water flux without sacrificing much rejection rate compared with that of the g‐C₃N₄ membrane; however, noticeable fouling was observed upon addition of the PAA into the membrane composite structure. In addition, the effect of PAA on the morphology, surface hydrophilicity, separation performance, and antifouling properties of the g‐C₃N₄ membrane were examined in detail. Overall, incorporating PAA into the g‐C₃N₄ nanosheets membrane was an effective and convenient method to improve the water separation performance, which could promote the application of the 2‐D g‐C₃N₄ nanosheets membrane in practical ultrafiltration processes. © 2018 American Institute of Chemical Engineers AIChE J, 64: 2181–2188, 2018     

Expandable graphite encapsulated by magnesium hydroxide nanosheets as an intumescent flame retardant for rigid polyurethane foams

Encapsulation of expandable graphite (EG) particles by organic or inorganic shells has been proved to efficiently enhance the expandability of EG, and thus to improve the flame‐retardant efficiency of EG. In this study, magnesium hydroxide (MH) nanosheets were utilized to fabricate core–shell EG@MH flame‐retardant particles through a heterocoagulation method. It was observed that after the encapsulation by MH nanosheets, the edges of the char residue of the EG layer were sealed after combustion, which contributed to the enhancement of expandability. The expansion volume of EG@MH increased dramatically to 456 mL/g, in contrast to 338 mL/g for pure EG. By incorporating 11.5 wt % of flame‐retardant particles, polyurethane foam containing EG@MH (here PU‐EG@MH) displayed excellent flame retardancy. Compared with the physically mixed sample, PU‐EG+MH, the limiting oxygen index value for the PU‐EG@MH sample increased from 29.8% to 32.6%. Furthermore, the shell of MH nanosheets was beneficial for improving the interfacial adherence between EG and the rigid polyurethane foam (RPUF) matrix, due to the reaction between isocyanate functional groups and MH. The cell structure and storage modulus of PU‐EG@MH were improved. In other words, the shell of MH nanosheets successfully improved the flame‐retardant efficiency and enhanced the interface adhesion between EG and the matrix. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46749.     

Vapor‐Phase Transport Crystallization of Micro‐HZSM‐5 Zeolite Coatings

A novel structured catalyst of binderless micro‐HZSM‐5 zeolite coating was prepared on stainless‐steeled tubes (i.d. 2 mm) through wash coating and vapor‐phase transport (VPT) crystallization method. The subsequent crystallization of amorphous SiO₂ binders improved the coatings adhesion tremendously by more than 10 times with the least amount of binders (<20% by weight), attributed to the remarkably enhanced interlock by the formed Mordenite Framework Inverted structure between zeolite particles. Catalytic cracking of supercritical n‐dodecane (500°C, 4 MPa) was used to examine the catalytic performance of the coatings as prepared, indicating that MZC‐V0.2 exhibited a catalytic activity improvement by 8% and a decreased deactivation rate by 48%. The improved catalytic performance may result from its high acid sites amount by incorporating extra‐framework Al into HZSM‐5 framework, and the possible depressing of pore‐mouth deactivation through partial modification of surface acid sites during VPT treatment. This work provides a potential technique to prepare mechanically stable zeolite coatings with high catalytic activity but less binder usage.     

Acid Sites in HZSM‐5 Upon Copper Exchange by FTIR and DSC Using Ammonia

The acidity of the parent HZSM‐5 zeolite and Cu‐HZSM‐5 catalyst has been examined by FTIR and DSC using ammonia desorption. Sites of different strength were found in HZSM‐5, desorbing ammonia at a relative temperature difference of about 100 °C. Upon copper exchange a fraction of Brønsted sites were transformed to Lewis sites, but the acid strength of the remaining Brønsted sites was increased. Aside from Lewis sites originating from copper exchange, there might be some additional sites formed from precipitated copper. This could explain the quantity of adsorbed NH₃ on Cu‐ZSM‐5 which is higher than theoretically expected. While changing their nature, acid sites of higher strength keep their location, which is manifested by some diffusion effect towards ammonia.     

Preparation and Performances of Hierarchical Structured HZSM‐5 Washcoating on Stainless‐Steel Substrates

The washcoats of the hierarchical HZSM‐5 zeolite (through desilication) were prepared on the inner surface of SS304 stainless‐steel tubes. The properties of slurries and coatings were characterized by analysis of particle size, measurements of rheological property, loading, adhesion, and finally the catalytic cracking test. It was found that introducing mesoporosity on the zeolite crystals was beneficial for reducing the particle size during ball milling for slurries preparation, which was helpful for improving loading due to a significant change in the rheological property. As the interaction between the particles with different sizes was enhanced after ball milling, the adhesion of the prepared coatings was improved. The catalytic activity and stability of the hierarchical HZSM‐5 coatings for the catalytic cracking of n‐dodecane were 56% and 75% higher than that of the conventional one, respectively. This probably resulted from the enhanced diffusion rate of reactant and products in the crystals and the coatings.     

Preparation of polyimide/siloxane‐functionalized graphene oxide composite films with high mechanical properties and thermal stability via in situ polymerization

An effective approach to prepare polyimide/siloxane‐functionalized graphene oxide composite films is reported. The siloxane‐functionalized graphene oxide was obtained by treating graphene oxide (GO) with 1,3‐bis(3‐aminopropyl)‐1,1,3,3‐tetra‐methyldisiloxane (DSX) to obtain DSX‐GO nanosheets, which provided a starting platform for in situ fabrication of the composites by grafting polyimide (PI) chains at the reactive sites of functional DSX‐GO nanosheets. DSX‐GO bonded with the PI matrix through amide linkage to form PI‐DSX‐GO films, in which DSX‐GO exhibited excellent dispersibility and compatibility. It is demonstrated that the obvious reinforcing effect of GO to PI in mechanical properties and thermal stability for PI‐DSX‐GO is obtained. The tensile strength of a composite film containing 1.0 wt% DSX‐GO was 2.8 times greater than that of neat PI films, and Young's modulus was 6.3 times than that of neat PI films. Furthermore, the decomposition temperature of the composite for 5% weight loss was approximately 30 °C higher than that of neat PI films. © 2015 Society of Chemical Industry     

Pools and Constraints in Methanol Conversion to Olefins and Fuels on Zeolite HZSM5

Large reserves of natural gas are causing high actual interest for olefins and automotive fuels via methanol conversion on zeolite HZSM5. The chemistry of this process involves spatial constraints in the zeolite pores and a set of reacting compounds hosted dynamically in the pores. The kinetic scheme of reactions in this pool regime is a matter of current debate––a problem being the complexity of product composition and its temporal changes. However, the multi-compound product composition, if measured accurately and even time-resolved––including the compounds retained in/on the catalyst––is a profound source of information. Methanol conversion has been studied with zeolite HZSM5 and zeolite HY accordingly. The pool mechanism has been developed further, specifically as depending on frustration for distinct reactions. Particular pools as for olefins or for gasoline are specified. Mechanism changes with reaction time and with reaction temperature are described, including the surprising phenomenon of reanimation and the mechanisms of catalyst deactivation.     

Flexible patch‐type hydrochromic polydiacetylene sensor for human sweat pore mapping

Owing to their stimulus‐responsive colorimetric property, polydiacetylenes (PDAs) have been extensively investigated in the context of sensor applications. Incorporation of PDAs in matrix polymers can be utilized to add additional advantageous features into these sensors, like processability, mechanical flexibility, and mass production capability. In the current investigation, a new type of hydrochromic PDA sensor, which consists of a polydiacetylene‐polyethylene oxide (PDA‐PEO) composite film, was developed. The results of the study demonstrate that the hydrochromic film, which displays a blue‐to‐red color transition upon hydration, can be used to map human sweat secreting pores. The hygroscopic PEO component of the system enables local sweat to penetrate into the sensor film. The highly π‐conjugated, imidazolium group containing PDA in the system functions as the hydrochromic material, which undergoes a blue‐to‐red transition and a corresponding fluorescence turn‐on in response to contact with a nanoliter of sweat. In response to deposition of a fingerprint, water arising from individual sweat secreting pores promotes a change that leads to formation of a discrete fluorescence microdot pattern. The most important feature of the new sensor film is mechanical flexibility that gives it with the ability to be utilized to map sweat pores located on highly curved skin surfaces, such as those found on palms, soles, backs, and faces. Accordingly, this attribute offers critical advantages in cosmetics and biomedical applications because it enables recognition of active and inactive sweat pores on curved skin surfaces where rigid or paper‐type sweat pore sensors are ineffective. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44419.     

On reduced modeling of mass transport in wavy falling films

In many industrial units such as packing columns, falling film reactors, etc., the liquid phase is designed as a falling film. It is well known that the mass and heat transfer in laminar wavy film flows is significantly enhanced compared to flat films. The kinetic phenomena underlying the increase in mass and heat transfer are, however, still not fully understood. For an efficient design of falling film units, computational models that account for these enhanced transport mechanisms are of key importance. In this article, we present a reduced modeling approach based on a long‐wave approximation to the fluid dynamics of the film. Furthermore, we introduce a new two‐dimensional (2D) high‐resolution laser‐induced luminescence measurement technique. Both in the numerical simulation results and in the high‐resolution 2D‐concentration measurements obtained in the experiments we observe similar patterns of high concentrations locally, especially in the areas close to the wave hump. © 2018 American Institute of Chemical Engineers AIChE J, 64: 2265–2276, 2018     

Fabrication of honeycomb‐structured porous films from poly(3‐hydroxybutyrate) and poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) via the breath figures method

Formation of porous films from poly(3‐hydroxybutyrate) (PHB) and poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) (PHBV) using the breath figures (BF) method was investigated by evaporating solutions in chloroform in humid air and examining film structure using optical and scanning electron microscopy (SEM). BF films were successfully fabricated from PHB (M_w = 486,000 g/mol) and displayed hexagonal arrays of pores, which varied in diameter (D = 7–2 μm) with solution concentrations (0.5–2.00%). SEM of fractured films also showed subsurface closed nano‐pores (D = 500–700 nm). BF films cast from PHBV (5% HV) formed arrays with smaller pores and apparent surface defects. Differential scanning calorimetry showed that porous PHB and PHBV films produced using the BF method were more crystalline than nonporous solvent cast films of PHB and PHBV. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers     

Thermal and catalytic upgrading of a biomass‐derived oil in a dual reaction system

The thermal and catalytic upgrsding of bio‐oil to liquid fuels was studied at atmospheric pressure in a dual reactor system over HZSM‐5, silica‐alumina and a mixed catalyst containing HZSM‐5 and silica‐alumina. This bio‐oil was produced by the rapid thermal processing of the maple wood. In this work, the intent was to improve the catalyst life. Therefore, the first reactor containing no catalyst facilitated thermal cracking of blo‐oil whereas the second reactor containing the desired catalyst upgraded the thermally cracked products. The effects of process variables such as reaction temperature (350°C to 410°C), space velocity (1.8 to 7.2 h^?1) and catalyst type on the amounts and quality of organic liquid product (OLP) were investigated, In the case of HZSM‐5 catalyst, the yield of OLP was maximum at 27.2 wt% whereas the selectivity for aromatic hydrocarbons was maximum at 83 wt%. The selectivities towards aromatics and aliphatic hydrocarbons were highest for mixed and silica‐alumina catalysts, respectively. In all catalyst cases, maximum OLP was produced at an optimum reaction temperature of 370°C in both reactors, and at higher space velocity. The gaseous product consisted of CO and CO₂, and C₁‐C₆ hydrocarbons, which amounted to about 20 to 30 wt% of bio‐oil. The catalysts were deactivated due to coking and were regenerated to achieve their original activity.     

Coupling hybrid of graphene oxide and layered zirconium phosphonate to enhance phenolic resin–based friction materials

A two‐dimensional (2D) heterogeneous coupling nanoparticle composed of graphene oxide and zirconium phosphonate (GO‐ZrP) was synthesized layer by layer in a self‐assembly manner. A rigid layer of zirconium phosphonate can inhibit the curling of graphene oxide and then improve its dispersion. The GO‐ZrP was then applied to phenolic resin–based friction materials by blending and hot pressing to improve their friction properties. The results show that the phenolic resin–based friction materials modified by GO‐ZrP possess excellent tribological, mechanical, and thermal properties. Also, the specific wear rate of the material decreased nearly fivefold with the optimal loading, while the friction coefficient was basically stable. Synergistic effects between GO and ZrP nanosheets provide good prospects for the application of 2D nanofillers in friction materials. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46543.