Zhengbao Wang

Microstructural optimization of MFI-type zeolite membranes for ethanol–water separation

High quality pure-silica MFI-type zeolite membranes are successfully prepared by simply controlling the amount of structure directing agent (SDA), i.e., tetrapropylammonium (TPA+) in the synthesis solution for seeded growth. The effects of several synthesis parameters such as alkalinity (OH−/Si), TPA+ concentration (TPA+/Si), and crystallization time on the membrane pervaporation performance are investigated in detail. The synthesized MFI-type zeolite membranes are thoroughly characterized by scanning electron microscopy (SEM), energy dispersive X-ray (EDX) spectroscopy, the water contact angle test, X-ray diffraction (XRD), the pervaporation test and gas permeation. The membrane microstructure is very sensitive to the TPA+/Si ratio of the synthesis solution. At a high TPA+/Si ratio (typically 0.17), parasitic twin crystals are intergrown in the zeolite layer, thus resulting in the formation of membrane defects during SDA removal treatment (calcination at 500 °C). When the membrane is prepared with a low TPA+/Si ratio (≤0.05), the appearance of twin crystals can be significantly suppressed and the synthesized dense MFI-type zeolite membranes exhibit pervaporation separation factors higher than 85 for 5 wt% ethanol–water mixtures at 60 °C. We demonstrate for the first time that controlling the SDA concentration in the precursor solution is beneficial to the elimination of membrane microstructural defects, showing a pathway to high quality MFI-type zeolite membranes.

Synthesis of highly b-oriented zeolite MFI films by suppressing twin crystal growth during the secondary growth

Highly b-oriented MFI films are synthesized by simply controlling TPA+ concentration of the secondary synthesis solution to suppress the formation of a-oriented crystals. A formation mechanism is discussed for the films and also in the context of general MFI nucleation and crystallization.

Synthesis of Zeolite ZSM-5 Small Particle Aggregates by a Two-Step Method in the Absence of an Organic Template

The preparation of zeolite ZSM-5 without using a template was extensively investigated. Zeolite ZSM-5 small particle aggregates were synthesized in the absence of a template using sodium silicate as the silica source and by controlling the nucleation time at high temperature with a simple two-step method in a rotating autoclave on a spit within an oven. The first stage at higher temperature consisted of accelerating the nucleation and the second stage at lower temperature consisted of obtaining small crystals in the absence of a template. The resulting zeolites were characterized by X-ray powder diffraction, scanning electron microscopy, ammonia temperature-programmed desorption, and N2 adsorption. Compared with the micron-sized zeolite crystals that are synthesized in the one-step method, zeolite ZSM-5 small particles prepared by the two-step method have a higher specific surface area and an equivalent acid site content. The sample synthesized by the two-step method mainly contains Bronsted acid sites and a few Lewis acid sites indicating that Al is incorporated into the framework of the zeolite.

Fabrication of b‐Oriented MFI Zeolite Films under Neutral Conditions without the Use of Hydrogen Fluoride

The fabrication of MFI zeolite films with particular b-axis orientation is especially fascinating. Unlike the conventional alkaline or hydrofluoric acid (HF) assisted neutral synthesis route, here we develop a novel neutral synthesis solution system of TPABr/fumed silica/H2 O without the use of HF and successfully synthesize highly b-oriented MFI zeolite films on glass-plate substrates by secondary growth. The localized weak alkaline environment created by the dissolved Na2 O species from the substrate is identified as the key factor for the depolymerization of fumed silica and subsequently the in-plane growth of zeolite seed layers. Continuous b-oriented MFI films can also be synthesized on other substrates in the presence of a glass plate or a trace amount of NaOH, which making our neutral synthesis route promising for the direct synthesis of MFI zeolite films and membranes on various substrates.

Controlling Crystal Transformation between Zeolite ZSM-5 and Mordenite without Organic Structure-Directing Agent

Abstract Zeolite crystals were synthesized at a lower temperature (150°C) by adding a nucleation solution prepared at higher temperature (190°C) to the mother solution. The effects of the Na 2 O/SiO 2 ratio, nucleation time of the nucleation solution, and the ratio of Na 2 O/SiO 2 ratio in the mother solution on crystal transformation between ZSM-5 and mordenite were investigated. The transformation between zeolite ZSM-5 and mordenite could be controlled effectively by changing the overall Na 2 O/SiO 2 ratio in the overall solution. A Na 2 O/SiO 2 ratio of 0.18 formed a boundary between ZSM-5 and mordenite phases when the overall solution had a composition of x Na 2 O:100SiO 2 :2.5Al 2 O 3 :12SO 4 2− :4000H 2 O. When the Na 2 O/SiO 2 ratio was increased higher than 0.18 by altering the composition of the mother solution, the ZSM-5 product formed by nucleation at higher temperature (190°C) could be transformed into mordenite crystals during crystallization at lower temperature (150°C). When the Na 2 O/SiO 2 ratio was ≤ 0.18, a product containing both ZSM-5 and mordenite crystals was obtained during nucleation at higher temperature that could be transformed into ZSM-5 crystals during crystallization at lower temperature. A precondition for crystal transformation between ZSM-5 and mordenite was that the crystallinity of the product formed during nucleation at higher temperature must be ≤ 30%.

Ru-Zn catalysts for selective hydrogenation of benzene using coprecipitation in low alkalinity

Abstract Several unsupported Ru-Zn catalysts were successfully prepared using the coprecipitation method under low alkaline conditions, and their catalytic performance was evaluated for the selective liquid-phase hydrogenation of benzene. The effect of the amount of ZnCl2 added to the coprecipitation solution on the physical and catalytic properties of the Ru-Zn catalysts was studied whilst keeping the amount of the NaOH precipitant constant. The properties of the resulting catalysts were characterized by N2 adsorption, X-ray diffraction, and temperature-programmed reduction. The effects of the stirring rate and the amount of ZnSO4 additive on the catalytic properties of the Ru-Zn catalysts were investigated using the optimal Zn content. The recyclability of the optimal Ru-Zn catalyst was also explored. The results revealed that the optimal Zn content for the Ru-Zn catalysts was 16.7 wt%, and the selectivity for cyclohexene could reach up to 80% (yield > 45%) when the benzene conversion was 57% in an aqueous solution of ZnSO4 (0.45 mol/L) under the optimal reaction conditions (i.e., hastelloy reactor, 1200 r/min, 150 °C and 5 MPa of H2 pressure). The presence of ZnO crystals in the Ru catalysts was found to be critical to obtaining high selectivity for cyclohexene (>80%). The Ru-Zn catalysts prepared under the low alkaline conditions also showed good stability, which indicates that they could potentially be used for industrial application.

Dynamic Hydrothermal Synthesis of a b-Oriented MFI Zeolite Film

Abstract Continuous b -oriented MFI zeolite films were prepared on stainless steel substrates by dynamic hydrothermal synthesis using a rotating convection oven. The influences of rotation speed, crystallization temperature and crystallization time were studied. X-ray diffraction was used to identify the orientation of the zeolite films. Compared with the static method, a shorter synthesis time, a more uniform particle size distribution and better film orientation were observed for the dynamic method, and this is attributed to the low concentration and thermal gradients that exist in the bulk solution and to the washing action of the bulk solution toward the substrate surface.

Angiokeratoma corporis diffusum in a patient with Hodgkin lymphoma: a new paraneoplastic skin manifestation?

MADAM, Angiokeratoma corporis diffusum (ACD) is a member of the group of angiokeratomas, which are vascular lesions characterized by superficial vascular ectasia with secondary epidermal reaction changes, including acanthosis and hyperkeratosis. Clinically, it appears as multiple, often clustered, dark-red papules or plaques, mostly in the bathing-trunk area. ACD is often considered to be the cutaneous hallmark of Fabry disease, a rare disorder due to a deficiency in the activity of the lysosomal enzyme a-galactosidase A, although it can also occur in other hereditary lysosomal storage diseases, such as fucosidosis, sialidosis and mannosidosis. However, ACD has been reported in patients with no recognizable enzyme abnormalities. Since 1984 there have been at least 10 cases reported. Four cases had other systemic findings, such as Turner syndrome, mental impairment and gout, but not tumour. Herein, we describe a patient with Hodgkin lymphoma (HL) presenting with ACD. A 27-year-old man with a 15-year history of asymptomatic lumps in the right neck and axilla presented in October 2005 with a new, generalized, papular and nodular skin rash, which had been present for 6 months. In September 1990, two soybean-sized asymptomatic lumps were noticed by the patient in his right neck and axilla. In September 1998, the lumps suddenly enlarged to the size of a walnut, but were otherwise asymptomatic. In June 2003, after a surgical excision in a local hospital (not for histological examination), the lumps relapsed rapidly and enlarged to about 4 cm in diameter. At the time, the patient was suspected as having scrofula, and was treated with oral antituberculosis drugs in another local hospital. He was compliant with his drugs and was treated for 1Æ5 months. However, this failed to improve his clinical condition. In April 2005 a papular and nodular skin rash appeared initially on the right buttock of the patient, and within 6 months it gradually spread over the left buttock, the extensor surfaces of the extremities, and the face. The patient denied a history of fever, night sweats, weight loss, hypohidrosis, myalgia, arthralgia, paraesthesias and a family history of similar skin lesions. Physical examination revealed a 3Æ0 · 3Æ0-cm firm, nonmobile and not painful or tender cervical lymph node and a 5Æ0 · 5Æ0-cm axillary lymph node. Numerous dark-red, firm, fixed and dome-shaped papules and nodules, ranging from 2 to 6 mm in diameter, were observed on the face, buttocks and the extensor surfaces of the extremities (Fig. 1a–c). The lesions of the extremities were clustered, and the lesions of the buttocks were larger, with some ulcerated and bleeding (Fig. 1b,c). Laboratory testing showed a normal white blood cell count (6Æ3 · 10 cells L), moderate anaemia (red blood cell count 3Æ03 · 10 cells L, haemoglobin 69 g L), increased C-reactive protein (69 mg L), elevated erythrocyte sedimentation rate (129 mm h), low albumin (29Æ1 g L), high globulin (46 g L), inversion of the albumin–globulin ratio (0Æ63), low prealbumin (90 mg L) and high immunoglobulin (28Æ06 g L). Ultrasonography displayed hepatosplenomegaly, bilateral enlarged kidneys and enlarged lymph nodes in the right neck and axilla. Smears of the right axillary lymph nodes revealed Reed–Sternberg cells scattered in the background of mature lymphocytes. Biopsies from the right buttock nodule revealed markedly dilated erythrocyte-filled papillary capillaries and orthokeratosis (Fig. 2). A diagnosis of lymphocyte-rich classical HL (stage IIIA) with ACD was made. The patient was treated with seven cycles of ABVD (doxorubicin, bleomycin, vinblastine and dacarbazine) chemotherapy from October 2005 to April 2006, resulting in complete regression of the enlarged lymph nodes and significant regression of the papules and nodules, although some left hyperpigmentation and scars (Fig. 1d). After follow-up for 5 years the patient was well and had no cutaneous eruption or tumour recurrence. To our knowledge, only one case has been reported describing a patient with HL with localized angiokeratoma (of the vulva). Widespread ACD has not yet been reported with HL, and this is the first case. We did not investigate the activity of related enzymes of lysosomal storage diseases, although these disorders, including Fabry disease, could be excluded from our patient by the clinical manifestations. Notably, the ACD occurred after the recurrence of HL and cleared up progressively with HL regression. This confirms a causal relationship, and ACD should be considered a paraneoplastic dermatosis of HL. The pathogenesis of these ACDs is unclear. Some authors believe they may represent partial enzyme deficiency or enzyme mosaicism. However, in our case, it is obvious that ACD has an association with HL. We believe that the immune abnormalities of HL may involve the vascular ectasia of ACD, especially in circulating immune complexes in HL containing tumour neoantigens and antitumour cell antibodies

Thermal processing of zeolite seed layers for the fabrication of compact oriented MFI zeolite films

A method of thermal processing was demonstrated to treat zeolite seeded substrates prior to secondary growth. Due to the formation of a strong covalent linkage between the seed layer and the substrate during heat treatment, a compact and uniform b-oriented MFI zeolite film was obtained after secondary growth. The applicability of this method is validated by employing various film substrates.

An efficient synthesis of NaA zeolite membranes from direct crystallization of gel-dipped macroporous alumina tubes with seeds

Compact NaA zeolite membranes are successfully synthesized by direct crystallization of gel-dipped macroporous Al2O3 tubes. Before gel-dipping, NaA seeds are pasted on Al2O3 tubes, followed by macropore-plugging with liquid. After the gel-dipping, a thin gel-layer formed on the Al2O3 tube is directly crystallized into NaA zeolite membranes at 100 °C for 4 h in the absence of any excess liquid. The as-synthesized NaA membranes exhibit high pervaporation performance with a remarkable separation factor larger than 10 000 and high flux of 2.73 kg m−2 h−1 for dehydration of 90 wt% ethanol at 75 °C. This new efficient synthesis is potentially significant for preparation of high-performance, low-cost, and reproducible zeolite membranes.