Photosynthetic membranes, 21. Immobilization of catalase by photochemically grafted ultrafiltration membranes

Catalase has been immobilized in membranes prepared by photoinduced grafting onto microporous polymeric supports and its catalytic activity on hydrogen peroxide decomposition has been studied under ultrafiltration conditions by means of a recirculation apparatus. The membranes showed a very good catalytic performance and the enzyme reaction took place exclusively within the membrane structure. Initial reaction rates measured in the temperature range 5 – 35°C as a function of both substrate concentration and enzyme amount immobilized per unit membrane surface indicate that the mechanism of action of catalase is not altered after immobilization.     

Characterization of the activity of β-galactosidase immobilized on Teflon membranes preactivated with different monomers by γ-irradiation

The activity of β-galactosidase, immobilized by grafting technique on Teflon membranes preactivated with four different monomers, has been characterized from the biochemical and biophysical points of view. The monomers used were acrylic acid or acrylamide, or methacrylic acid and 2-hydroxyethyl methacrylate. When 2-hydroxyethyl methacrylate was used in the second grafting, the first three monomers have been used in the first modification step. The behavior of the free and immobilized enzyme has been analyzed as a function of temperature and pH. For each catalytic membrane, we have found general equations relating the absolute enzyme activity to pH and temperature. From these expressions, the experimental conditions giving the best yield of each catalytic membrane have been calculated. The kinetic parameters for the four membranes have also been determined. The advantages of using these membranes in nonisothermal bioreactors are also indicated. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68: 613–623, 1998     

超声波对固定化辣根过氧化物酶活性影响研究

为了研究超声波对固定化酶活性的影响,以固定化辣根过氧化物酶为对象,研究了不同超声波处理条件(超声功率,超声时间)以及超声条件下催化体系的pH、温度对固定化酶活性的作用。同时对超声波处理后固定化酶活的重复利用性进行测定。结果表明,超声波处理对提高固定化酶在高温、强酸碱条件下催化活性有一定帮助,最佳处理条件为:超声波功率50 W,超声时间30 min,pH 8,温度35℃,在此条件下,与未经超声波处理相比,固定化酶活性提高了17.6%,固定化酶重复利用性增强,经7次使用后,固定化酶催化活性是未经处理的1.8倍。     

Acrylic acid γ-ray irradiation-grafted nylon 4 membranes

This study was to improve the performances of nylon 4 membranes for washing waste-water treatment of nuclear power plants, e.g., removal of detergent and salt by membranes. The effects of the degree of grafting and ionization on the reverse osmosis performances of acrylic acid (AA)-grafted nylon 4 membranes by γ-ray irradiation modification were investigated. The relationships of operating conditions, such as feed concentrations of salt and detergent, operating temperature, and pressure, and the performances of water flux and solute rejection of the prepared membranes were obtained. Water flux of the prepared membranes was highly sensitive with the operating temperature. It was found that an increase in the operating pressure could increase the water flux and the impaction effect directly. Water flux and salt rejection were significantly improved by both ionized and nonionized AA-grafted nylon 4 membranes compared to ungrafted nylon 4 membranes. Water flux increased rapidly and solute rejection dropped off slightly as the grafted membranes were ionized. The 100% detergent rejection could be obtained by the nonionized AA-grafted nylon 4 membranes with 38.6 and 69.6% degrees of grafting under various operating conditions. Results obtained showed that these modified nylon 4 membranes were usable for washing waste-water treatment of nuclear power plants. © 1993 John Wiley & Sons, Inc.     

The comparative kinetic study of non-isothermal and isothermal dehydration of swollen poly(acrylic acid) hydrogel using the Weibull probability function

The isothermal and non-isothermal dehydration of swollen poly(acrylic acid) hydrogel has been investigated. The possibility of calculating the isothermal conversion curves from the non-isothermal conversion curves was examined. It was found that the experimental conversion curves under non-isothermal and isothermal conditions can be described by the Weibull probability distribution function. Changes in the values of distibution parameters with heating rate (non-isothermal dehydration) and operating temperature (isothermal dehydration) were identified. The mathematical procudere for determining the non-isothermal kinetic conversion curves, based on the functional relationship between distribution parameters and the heating rate was developed. In addition, the new mathematical procedure for calculating the isothermal kinetic curves from the non-isothermal ones at a certain temperature was established. It was found that the large deviation exists between the experimental and calculated isothermal conversion curves. In order to explain the difference in the mechanism of hydrogel dehydration under non-isothermal and isothermal conditions, the dependence of the apparent activation energy on the degree of conversion (E_a = E_a(α)) was performed using the isoconversional (model-free) methods. It was found that in the case of non-isothermal dehydration, the apparent activation energy exhibits a concave decrease with the degree of conversion (α), while for the isothermal dehydration, the apparent activation energy exhibits a convex increase with α. Certain changes in a variety of E_a with α are explained on the basis of different relaxation processes, that take place during non-isothermal and isothermal hydrogel dehydration. The characteristic features of density distribution functions of the apparent activation energies are derived in the case of non-isothermal and isothermal dehydration. It was found that the differences in characteristic properties of derived distribution functions are a consequence of different relaxation processes, which taking place under various experimental conditions.     

Simultaneous covalent immobilization of glucose oxidase and catalase onto chemically modified acrylonitrile copolymer membranes

Ultrafiltration membranes from acrylonitrile copolymer were chemically modified with different concentrations of hydrogen peroxide (from 5 to 30% H₂O₂). The amount of the amide groups in the modified membranes was determined. The water flow and permeability coefficients of the initial and modified membranes were also researched. The modified membranes were used as carriers for covalent immobilization of the dual enzyme system of glucose oxidase and catalase (GOD+CAT). It was found that the best matrices for immobilization of the dual system were membranes modified with 20% H₂O₂ and the optimal activity ratio was GOD : CAT = 1 : 5. The glucose conversion efficiency with the dual enzyme system was twice as high as that of bound GOD alone. Some of the basic characteristics (optimum pH, optimum temperature, pH, temperature stability, and storage stability) of the dual enzyme system were determined and compared with characteristics of free and bound enzymes. The catalytic parameters of the enzyme reaction (K_m and V_max) were determined with GOD immobilized alone and with the dual system GOD+CAT. The higher rate observed with the dual enzyme system clearly showed the advantage and the efficiency of the immobilized system. Glucose oxidase without catalase was deactivated by H₂O₂ more rapidly than the immobilized dual GOD+CAT system. These experimental evidences can be explained by the protecting effect of catalase on glucose oxidase from inhibition by H₂O₂. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91: 4057–4063, 2004     

金属氧化物对生物质半焦气化特性和反应动力学影响

为测试生物质半焦中金属氧化物的催化作用,本研究利用热重分析仪比较脱灰半焦(ALC)及负载金属氧化物半焦(ALC-K2O, ALC-Na2O, ALC-CaO, ALC-Fe2O3, ALC-MgO)的气化特性,并进行动力学计算。为提高结果准确性,采用等温和非等温实验方法,并利用分布活化能模型(DAEM)和Flynn-Wall-Ozawa (FWO)等转化率法求算动力学。结果表明,金属氧化物对半焦催化效果有明显差异。等温条件下,其气化活性依次为ALC-K2O>ALC-Na2O>ALC-CaO>ALC-Fe2O3>ALC-MgO>ALC。非等温条件下,相同升温速率下,各半焦的特征汽化温度(初始温度、最大速率下温度、结束温度)由小到大依次为ALC-K2O, ALC-Na2O, ALC-CaO, ALC-Fe2O3, ALC-MgO, ALC,低特征反应温度表明其高反应活性。动力学分析发现,无论是等温还是非等温气化,活化能数据依次为ALC-K2O相似文献   

聚碳酸酯在亚临界乙醇中的催化解聚

以氢氧化钠为催化剂、在投料比1∶6.3（20.0 g PC/126.2 g乙醇）、温度140～220℃、压力1.1～5.9 MPa、反应时间15～60 min条件下,利用间歇式高压反应釜研究了聚碳酸酯（PC）在亚临界乙醇中的催化解聚,产物分别采用傅里叶红外光谱（FT-IR）、气质联谱（GC-MS）和气相色谱（GC）进行分析。结果表明,PC的解聚率随温度的升高、反应时间的延长而增加;主产物双酚A（BPA）的收率随反应温度升高、反应时间延长而下降。在投料比1∶6.3、温度170℃、反应时间15 min、压力1.7 MPa、催化剂投加量1.0 g·（160.0 ml 乙醇）^-1条件下,PC解聚率为84.2%,BPA收率可达到95.7%。根据PC在亚临界乙醇中催化解聚产物的分析,并结合PC链结特点,提出了PC的催化解聚机理。通过实验数据关联,得出亚临界乙醇中PC催化解聚反应级数为一级,反应活化能为40.15 kJ·mol^-1。     

水性聚氨酯的结晶动力学参数及其在鞋用胶黏剂的应用

以聚己二酸1,4-丁二醇酯（PBA）、六亚甲基二异氰酸酯（HDI）和异佛尔酮二异氰酸酯（IPDI）为主要原料,制备了不同软段分子量和不同硬段含量的水性聚氨酯（WPU）乳液。采用DSC技术表征了WPU胶膜在非等温和等温条件下的结晶行为,并以莫志深方程和Avrami方程为模型,对WPU胶膜的结晶行为进行了研究。WPU胶膜的非等温结晶动力学分析结果表明,随着WPU相对结晶度的增加,非等温结晶动力学参数F（T）增大,说明适当提高活化温度可提高WPU胶黏剂的结晶速率和初黏强度;WPU胶膜的等温动力学分析结果表明,不同软段分子量和不同硬段含量的WPU胶膜的等温结晶动力学参数t_1/2与相应WPU胶黏剂的开放时间存在对应关系,即t_1/2较大者,相应WPU胶黏剂的开放时间较长。     

Covalent immobilization of penicillin G acylase onto amine-functionalized PVC membranes for 6-APA production from penicillin hydrolysis process. II. Enzyme immobilization and characterization

This article describes the covalent immobilization of penicillin G acylase (PGA) onto glutaraldehyde-activated NH₂-PVC membranes. The immobilized enzyme was used for 6-aminopenicillanic acid production from penicillin hydrolysis. Parameters affecting the immobilization process, which affecting the catalytic activity of the immobilized enzyme, such as enzyme concentration, immobilization's time and temperature were investigated. Enzyme concentration and immobilization's time were found of determine effect. Higher activity was obtained through performing enzyme immobilization at room temperature. Both optimum temperature (35°C) and pH (8.0) of immobilized enzyme have not been altered upon immobilization. However, immobilized enzyme acquires stability against changes in the substrate's pH and temperature values especially in the higher temperature region and lower pH region. The residual relative activities after incubation at 60°C were more than 75% compared to 45% for free enzyme and above 50% compared to 20% for free enzyme after incubation at pH 4.5. The apparent kinetic parameters K_M and V_M were determined. K_M of the immobilized PGA (125.8 mM) was higher than that of the free enzyme (5.4 mM), indicating a lower substrate affinity of the immobilized PGA. Operational stability for immobilized PGA was monitored over 21 repeated cycles. The catalytic membranes were retained up to 40% of its initial activity after 10.5 working h. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Physicochemical processes involved in migration of bisphenol A from polycarbonate

Results of experiments, conducted by different polycarbonate (PC) producing companies, on migration of bisphenol A (BPA) from PC into different liquids, were supplied to the author for compilation, review, and discussion. The observed BPA migration levels were found to be nearly independent of the concentration of residual BPA in the PC resins. Hydrolysis of PC is the dominant mechanism responsible for the release of BPA from the polymer surface into the contacting aqueous liquid. Experiments with PC spiked with deuterated BPA revealed that diffusion‐controlled migration play a minor role in the overall release of BPA from PC. The influence of a number of experimental parameters on the migration of BPA into aqueous liquids was studied. Factors found to be of importance included the temperature, pH, and ozone concentration of the liquids, as well as the surface ageing of the PC. All of the BPA migration levels obtained from experiments performed under standard conditions as given in the EU legislation and its associated guidance documents were found to be well below the EU specific migration limit of 600 μg/kg food which applies to plastics in contact with foodstuffs (EU Directive 2002/72/EC as amended). Migration is lower in oil than in the aqueous food‐simulants water, 3% acetic acid, and 10 or 50% ethanol. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Hybrid low-pressure submerged membrane photoreactor for the removal of bisphenol A

The efficiency of a hybrid system combining photocatalysis and membrane filtration in a single module was investigated. Low-pressure submerged hollow fibre membranes were used to retain the TiO₂ particles in the system. Bisphenol A (BPA) was used as a model pollutant. Ninety-seven per cent photodegradation and more than 90% photomineralization of 10 ppm of BPA were achieved after 90 and 120 min of UV illumination, respectively. Aeration was applied in the submerged membrane photoreactor (SMPR) to provide mixing, dissolved oxygen, mechanical agitation to prevent agglomeration of TiO₂ particles as well as providing shear forces to remove TiO₂ particles from the membrane surface. The optimum aeration rate used in our 0.8-L reactor was 0.5 L/min. It was found that intermittent permeation enhanced the sustainability of the submerged membranes but showed no effect on the photoactivity of the system. An intermittence frequency (IF) of 0.1 was sufficient to reduce the fouling rate of the membrane under the experimental conditions. The SMPR appears to be very effective and can achieve removal of low-concentration organics (such as BPA) in a compact, low-energy system.     

Removal of phenol and Bisphenol A by immobilized Laccase on poly (Acrylonitrile-co-Styrene/Pyrrole) nanofibers

ABSTRACT

Enzymatic oxidative polymerization of phenol and Bisphenol A (BPA) catalyzed by Laccase enzyme immobilized into poly (Acrylonitrile-co-Styrene/Pyrrole) nanofibers (AN-co-ST/Py) in an aqueous solution was investigated in a batch adsorption mode. The prepared poly (AN-co-ST/Py) copolymeric material was electrospun to nanofibers via electrospinning technique. Gas chromatography/mass spectrometry (GC-MS) was used to detect the residual phenol and BPA in the aqueous medium after the removal process. Optimization of solution’s pH, temperature, initial concentration of phenolic pollutants, and amount of adsorbent and agitation speed was investigated. The results showed that the removal of phenol and BPA by Laccase in the immobilized form was higher than that in the free form.The optimum removal by the immobilized form was achieved at these conditions (Temp: 50°C, pH: 5, Agitation rate: 120 rpm, Contact time: 120 min).     

Urease immobilized on chitosan membrane: Preparation and properties

Urease was covalently immobilized on glutaraldehyde-pretreated chitosan membranes. The optimum immobilization conditions were determined with respect to glutaraldehyde pretreatment of membranes and to reaction of glutaraldehyde-pretreated membranes with urease. The immobilized enzyme retained 94% of its original activity. The properties of free and immobilized urease were compared. The Michaelis constant was about five times higher for immobilized urease than for the free enzyme, while the maximum reaction rate was lower for the immobilized enzyme. The stability of urease at low pH values was improved by immobilization; temperature stability was also improved. The optimum temperature was determined to be 65°C for the free urease and 75°C for the immobilized form. The immobilized enzyme had good storage and operational stability and good reusability, properties that offer potential for practical application.     

Effect of a double‐structured microporous polymer support on the catalytic activity,stability and aggregation behavior of immobilized enzymes

A double‐structured microporous polymer composite support consisting of a microporous skeleton for protection of immobilized enzymes and a gel‐like polymer bearing different functionalities has been synthesized for immobilization of various enzymes. Among three approaches based on two types of interactions (physical and chemical), we found that under our experimental conditions the covalent bonding between amine moieties of enzymes and epoxide groups of the support was the best, with enzyme leaching being reduced to as low as zero for nine enzymes and catalytic activities increased by factors of 1–4 for two lipases. The improvement in catalytic activity could be attributed to the amphiphilic soft gel which might create a kind of lipid–water interface or microenvironment in aqueous solution, favoring the interfacial activation of certain lipases. Furthermore, the thermal and operational stability, and reusability of all the enzymes could be enhanced to varying degrees. We also found that enzyme aggregates of different sizes could be formed on the spherical support surface at quite low enzyme concentrations, which might also influence the final catalytic activities of the immobilized enzymes. © 2015 Society of Chemical Industry     

Adsorption of bismuth(III) by bayberry tannin immobilized on collagen fiber

The adsorption behavior of collagen fiber‐immobilized bayberry tannin towards Bi(III) at acidic pH values was investigated. The adsorption capacity of the adsorbent towards Bi(III) was 0.348 mmol g^?1 at 303 K, and increased with the rise in temperature. The adsorption isotherms of Bi(III) were in the shape of so‐called type II isotherms and could be described by an empirical equation, ln q_e = k + (1/n)C_e, which implies that chemical adsorption is predominant at lower concentrations of Bi(III) and that physical adsorption is involved at higher concentrations. The adsorption kinetics of Bi(III) on the immobilized bayberry tannin could be well described by the pseudo‐second‐order rate model, and the adsorption capacities calculated by the model were almost the same as those determined by actual measurements. The adsorbent could be regenerated by using 0.02 mol dm^?3 ethylenediaminetetraacetic acid (EDTA) solution after adsorption of Bi(III). The adsorption selectivity of the immobilized bayberry tannin towards Bi(III) in a Cu(II)–Bi(III) binary solution in acidic medium was remarkable. Therefore, it is strongly suggested that the immobilized bayberry tannin could be applied to the removal of Bi(III) from crude Cu(II) samples under proper conditions. Copyright © 2006 Society of Chemical Industry     

Characteristics of LDPE pyrolysis

Pyrolysis of low-density polyethylene (LDPE) was studied in order to relieve environmental pollution and recover the monomer or fuel. LDPE was thermally decomposed with and without catalyst. First, efficiency of oil production was analyzed according to the variation of reaction conditions such as reaction temperature, types of additives and catalyst, and contacting method. In non-catalytic LDPE pyrolysis, isothermal reaction was almost similar to non-isothermal reaction. Light oil was produced with low reaction temperature (430 °C) in the isothermal reaction, but low heating rate caused light oil production in the non-isothermal reaction. When pyrolyzed polyethylene (PE oil) was applied as an additive, no significant effect showed in the isothermal reaction. In catalytic LDPE pyrolysis (10%NiO/S-A) with additives, efficiency greatly increased especially with polystyrene (PS) addition. It was also found that the molecular weight distribution of product oil could be controlled by applying different additives. When a catalytic reactor was used, the amount of the low molecular weight compound increased as flow rate of thermally decomposed gas was lowered. This paper is dedicated to Professor Wha Young Lee on the occasion of his retirement from Seoul National University.     

Rheo-kinetics of bovine serum albumin in catanionic surfactant systems

The effects of catanionic surfactant systems consisting of mixtures of cationic cetyltrimethylamonium bromide (CTAB) and anionic sodium dodecyl sulfate (SDS) on the rheological properties and kinetics of bovine serum albumin (BSA) were investigated. The ionic strength of the solution was varied by using different mixing ratio of SDS and CTAB. Gelation curves observed in dynamic viscoelastic measurements were fitted with gelation kinetics models to describe the gelation under isothermal and non-isothermal conditions. Overall, the gelation of BSA in cationic-rich solutions was found to be more energetically favorable when compared with BSA solvated in anionic-rich solutions. Consequently, highest gel temperature (T_gel) and time (t_gel) were observed for anionic-rich solutions with SDS/CTAB molar ratio of 4.0 (i.e., SDS/CTAB=4.0), while lowest gel temperature and time were found for cationic-rich solutions with SDS/CTAB molar ratio of 0.25 (SDS/CTAB=0.25). BSA in equal molar ratio of the mixed surfactants (SDS/CTAB=1.0) showed a gel temperature and time in the halfway between the anionic and cationic-rich regions. Interestingly, under isothermal and non-isothermal conditions, BSA in equimolarly mixed and anionic-rich solutions showed a heat-dependent protective effect against thermal denaturation and gelation. The protective effect on BSA gelation in equimolar and anionic-rich solutions was diminished by increasing the catanionic concentration under non-isothermal conditions, while under isothermal conditions, protective effect on BSA gelation increased with catanionic concentration. On the other hand, cationic-rich solutions did not protect BSA from thermal denaturation and gelation, and therefore the gelation rate increased with catanionic concentration in all heating conditions examined.     

废旧光盘在离子液体中的甲醇醇解反应

以离子液体［Bmim］［Cl］为反应介质和催化剂,对废旧光盘的甲醇醇解反应进行了研究。考察了反应温度、反应时间、催化剂用量、甲醇用量对醇解反应结果的影响,得到的较佳醇解反应条件为反应温度110℃,反应时间1.5 h,n(甲醇)∶n(光盘)=8∶1,m(［Bmim］［Cl］)∶m(光盘)=1∶1,在上述条件下,光盘醇解率≥98%,双酚A收率≥93%。对离子液体的回用性能进行了考察,结果表明,离子液体回用8次后光盘的醇解率和BPA的收率无明显变化。采用FT-IR技术对醇解产物进行了表征。