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1.
BACKGROUND: The influence of different hydrating agents on the pH of the hydrating solutions, rate of hydration of MgO to Mg(OH)2 and product surface area was studied as a function of temperature of hydration. Hydrating agents used were aqueous solutions of ammonium chloride, magnesium acetate, magnesium nitrate, nitric acid, acetic acid, magnesium chloride, sodium acetate and hydrochloric acid and distilled water as control. These were chosen to determine either the effect of addition of a common ion, the effect of changing the solution pH or due to the presence of an acetate ion, found earlier to have a beneficial effect on the hydration of MgO. RESULTS: There was no significant difference in the hydration behaviour of the hydrating agents up to 50 °C, where less than 10% of magnesium hydroxide was formed. The amount of hydroxide increased at temperatures above 60 °C. When compared with the hydration in water, all the hydrating agents, with the exception of sodium acetate, showed a significant increase in the degree of hydration. Sodium acetate formed the lowest amount of magnesium hydroxide, ranging between 1.2 and 12.2% magnesium hydroxide. The largest percentage (56.7%) of magnesium hydroxide was formed from hydration in magnesium acetate. CONCLUSION: It seems that MgO hydration is a dissolution‐precipitation process controlled by the dissolution of MgO. The increased degree of hydration in magnesium acetate is possibly due to the presence of acetate and Mg2+ ions. Copyright © 2010 Society of Chemical Industry  相似文献   

2.
The kinetics of the hydration of magnesia to produce magnesium hydroxide is described by a kinetic model with no diffusive contribution, including an additional resistance to the reactive flux due to the transient variation of the porosity of the material during reaction. The proposed model has been applied to data from the literature and obtained by hydration of MgO samples with distinct physical characteristics. The model describes well the mechanism of hydration of powder and single crystal MgO in liquid and vapour water with temperatures varying from 35°C to 200°C.  相似文献   

3.
BACKGROUND: Hexyl laurate has been applied widely in cosmetic industries and is synthesized by chemical methods with problems of cost, environmental pollution, and by‐products. In this study, Lipozyme® IM77 (from Rhizomucor miehei) was used to catalyze the direct‐esterification of hexanol and lauric acid in a solvent‐free system by utilizing a continuous packed‐bed reactor, wherein the aforementioned difficulties could be overcome. Response surface methodology (RSM) and three‐level‐three‐factor Box‐Behnken design were employed to evaluate the effects of synthesis parameters, such as reaction temperature (45–65 °C), mixture flow rate (0.25–0.75 mL min?1) and concentration of lauric acid (100–300 mmol L?1) on the production rate (µmol min?1) of hexyl laurate by direct esterification. RESULTS: The production rate was affected significantly by the mixture flow rate and lauric acid concentration. On the basis of ridge‐max analysis, the optimum synthesis conditions for hexyl laurate were as follows: 81.58 ± 1.76 µmol min?1 at 55 °C, 0.5 mL min?1 flow rate and 0.3 mol L?1 lauric acid. CONCLUSION: The lipase‐catalyzed synthesis of hexyl laurate by Lipozyme® IM‐77 in a continuous packed‐bed bioreactor and solvent‐free system was successfully developed; optimization of the reaction parameters was obtained by Box–Behnken design and RSM. Copyright © 2008 Society of Chemical Industry  相似文献   

4.
High‐quality magnesium hydroxide powders can be produced by hydrating slow‐reacting magnesia in dilute magnesium acetate solutions. The kinetics of this process are very crucial for process design and control, and for the production of a powder with desirable particle morphology. In this work, industrial heavily‐burned magnesia powders were hydrated in 0.01–0.1 mol dm−3 magnesium acetate solutions at temperatures ranging between 333 and 363 K. Examination of the magnesium hydroxide produced and the analysis of the kinetic data suggest that the hydration of heavily burned magnesia in magnesium acetate solutions is a dissolution–precipitation process controlled by the dissolution of magnesia particles. The activation energy was estimated to be 60 kJ mol−1, while the reaction order with respect to acetate concentration was found to be about one. © 1999 Society of Chemical Industry  相似文献   

5.
Summary: Soluble hyperbranched acrylate copolymers were prepared by the copolymerization of divinylbenzene (0.10 mol · L?1) and ethyl acrylate (0.50 mol · L?1) using dimethyl 2,2′‐azoisobutyrate of high concentrations (0.30–0.50 mol · L?1) as initiator at 70 and 80 °C in benzene. The copolymer formed at 80 °C for 1 h showed the weight‐average molecular weight of 2.5 × 105, the small radius of gyration of 10 nm, the low second virial coefficient of 5.7 × l0?7 mL · g?2 as shown by the MALLS measurements at 25 °C in tetrahydrofuran, and also the very low intrinsic viscosity of 0.10 dL · g?1 at 30 °C in benzene. The hyperbranched copolymer exhibited an upper critical solution temperature (35 °C on cooling) in an acetone‐water (60:11 v/v). The copolymer showed an ability to encapsulate and transfer Rhodamine 6G as a dye probe and could stabilize Ag nanoparticles. The porous film was prepared by simply casting an acetone solution of the hyperbranched copolymer on a cover glass. The copolymer molecules radially arranged on the surface layer of the spherical pores as observed by the polarized optical microscope. The hyperbranched acrylate copolymer was hydrolyzed by KOH to yield poly(carboxylic acid).

Optical microscope image (crossed polarizers) of a porous film from copolymer solution in acetone.  相似文献   


6.
BACKGROUND: The effect of acetic acid, a lignocellulose hydrolysis by‐product, on lipid accumulation by activated sludge cultures grown on glucose was investigated. This was done to assess the possible application of lignocellulose as low‐cost and renewable fermentation substrates for biofuel feedstock production. RESULTS: Biomass yield was reduced by around 54% at a 2 g L?1 acetic acid dosage but was increased by around 18% at 10 g L?1 acetic acid dosage relative to the control run. The final gravimetric lipid contents at 2 and 10 g L?1 acetic acid levels were 12.5 ± 0.7% and 8.8 ± 3.2% w/w, respectively, which were lower than the control (17.8 ± 2.8% w/w). However, biodiesel yields from activated sludge grown with acetic acid (5.6 ± 0.6% w/w for 2 g L?1 acetic acid and 4.2 ± 3.0% w/w for 10 g L?1 acetic acid) were higher than in raw activated sludge (1–2% w/w). The fatty acid profiles of the accumulated lipids were similar with conventional plant oil biodiesel feedstocks. CONCLUSIONS: Acetic acid enhanced biomass production by activated sludge at high levels but reduced lipid production. Further studies are needed to enhance acetic acid utilization by activated sludge microorganisms for lipid biosynthesis. Copyright © 2011 Society of Chemical Industry  相似文献   

7.
The solution polymerization of acrylamide (AM) on cationic guar gum (CGG) under nitrogen atmosphere using ceric ammonium sulfate (CAS) as the initiator has been realized. The effects of monomer concentration and reaction temperature on grafting conversion, grafting ratio, and grafting efficiency (GE) have been studied. The optimal conditions such as 1.3 mol of AM monomer and 2.2 × 10?4 mol of CAS have been adopted to produce grafted copolymer (CGG1‐g‐PAM) of high GE of more than 95% at 10°C. The rates of polymerization (Rp) and rates of graft copolymerization (Rg) are enhanced with increase in temperature (<35°C).The Rp is enhanced from 0.43 × 10?4 mol L?1 s?1 for GG‐g‐PAM to 2.53 × 10?4 mol L?1 s?1 for CGG1‐g‐PAM (CGG1, degree of substitute (DS) = 0.007), and Rg from 0.42 × 10?4 to 2.00 × 10?4 mol L?1 s?1 at 10°C. The apparent activation energy is decreased from 32.27 kJ mol?1 for GG‐g‐PAM to 8.09 kJ mol?1 for CGG1‐g‐PAM, which indicates CGG has higher reactivity than unmodified GG ranging from 10 to 50°C. Increase of DS of CGG will lead to slow improvement of the polymerization rates and a hypothetical mechanism is put forward. The grafted copolymer has been characterized by infrared spectroscopy, thermal analysis, and scanning electron microscopy. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 3715–3722, 2007  相似文献   

8.
After being subjected to preliminary purification, montmorillonite clay was leached with varying concentrations of sulfuric acid (0.5–2 mol L?1) at 90 °C for varying times (0.5–4 h). Acid leaching causes partial amorphization of the montmorillonite and increases its specific surface area by a factor of 3 (from 49.1 to 157 m2 g?1). The bleaching efficiency for Mongolian mare's milk oil, as judged by light absorbance measurements at 400 nm, was increased from 9.5% for the unleached clay to 93.8% for clay leached with 2 mol L?1 H2SO4 for 4 h. Copyright © 2006 Society of Chemical Industry  相似文献   

9.
Vinyl acetate (VAc) was solution‐polymerized at 40°C and 50°C using 4,4′‐azobis(4‐cyanovaleric acid) (ACVA) as an initiator and methanol as a solvent, and effects of polymerization temperature and initiator concentration were investigated in terms of conversion of VAc into poly (vinyl acetate) (PVAc), degree of branching (DB) for acetyl group of PVAc, and molecular weights of PVAc and resulting poly(vinyl alcohol) (PVA) obtained by saponifying with sodium hydroxide. Slower polymerization rate by adopting ACVA and lower viscosity by methanol proved to be efficient in obtaining linear high‐molecular‐weight (HMW) PVAc with high conversion and HMW PVA. PVA having maximum number–average degree of polymerization (Pn) of 4300 could be prepared by the saponification of PVAc having maximum Pn of 7900 polymerized using ACVA concentration of 2 × 10?5 mol/mol of VAc at 40°C. Moreover, low DB of below 1 could be obtained in ACVA system, nevertheless of general polymerization temperatures of 40°C and 50°C. This suggests an easy way for producing HMW PVA with high yield by conventional solution polymerization without using special methods such as low‐temperature cooling or irradiation. © 2006 Wiley Periodicals, Inc. J Appl PolymSci 102: 4831–4834, 2006  相似文献   

10.
Magnesium hydroxide, when melt extruded with poly(trimethylene terephthalate) (PTT) at low concentrations (1–3 wt.%), can be melt processed during extrusion and injection molding. When the polymer is heated in the melt to 295°C, the viscosity of the composite behaves similarly to control samples and the viscosity decreases as a function of temperature. When the temperature of the composite is raised above 295°C (above the normal processing conditions for PTT), a significant change in the melt rheology of the composite is observed relative to unfilled compositions. This change in melt rheology coincides with the decomposition temperature of magnesium hydroxide and formation of magnesium oxide, a common thickening agent employed in unsaturated polyester resins. Lower processing temperature polyesters, including PTT, enable processing of the polymer in the presence of magnesium hydroxide under normal conditions. The viscosity modifier ‘turns on’ when the composite sees elevated temperature where magnesium oxide is known to form. The magnesium oxide is hypothesized to interact with PTT carboxyl end groups, providing the observed increase in viscosity. The rheological response observed in the composites is dependent on the concentration of magnesium hydroxide. During burning, the viscosity modifier results in a non‐dripping formulation of PTT. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

11.
Composites of linear low‐density polyethylene were obtained in toluene slurry by in situ copolymerization of ethylene and 1‐octene in the presence of untreated magnesium oxide–hydroxide nanoparticles (MgO@Mg(OH)2) of ±50 nm and such treated with dibutylmagnesium (DBM) as support for a bis(n‐butylcyclopentadienyl)zirconium dichloride–methylaluminoxane (MAO) catalyst system. Treatment of the nanoparticles with DBM (0.5–6 mmol g?1 MgO@Mg(OH)2) allows one to decrease the amount of MAO by 1.2 mmol Al g?1 MgO@Mg(OH)2, while reaching the same average catalyst activity and a finer distribution of the particles. Energy‐dispersive X‐ray mapping shows that the MAO is mainly associated with the filler. The crystallinity of the matrix polymer decreases with filler content. © 2018 Society of Chemical Industry  相似文献   

12.
Copolymerizations of butadiene (Bd) with styrene (St) were carried out with catalytic systems composed of a rare‐earth compound, Mg(n‐Bu)2 (di‐n‐butyl magnesium) and halohydrocarbon. Of all the rare earth catalysts examined, Nd(P507)3–Mg(n‐Bu)2–CHCl3 showed a high activity in the copolymerization under certain conditions: [Bd] = [St] = 1.8 mol l?1, [Nd] = 6.0 × 10?3 mol l?1, Mg/Nd = 10, Cl/Nd = 10 (molar ratio), ageing for 2 h, copolymerization at 50 °C for 6–20 h. The copolymer of butadiene and styrene obtained has a relatively high styrene content (10–30 mol%), cis‐1,4 content in butadiene unit (85–90%), and molecular weight ([η] = 0.8–1 dL g?1). Monomer reactivity ratios were estimated to be rBd = 36 and rSt = 0.36 in the copolymerization. © 2002 Society of Chemical Industry  相似文献   

13.
A novel method has been developed to modify the natural polymer chitosan. The process utilizes a monomer prepared by employing a Morita–Baylis–Hillman (MBH) reaction. Specifically, the vinyl monomer 2‐[hydroxy(pyridin‐3‐yl)methyl]acrylonitrile (HPA) was synthesized using a high‐yielding MBH reaction of acrylonitrile with pyridine‐3‐carboxaldehyde in the presence of 1,4‐diazabicyclo[2.2.2]octane. Conversion of HPA to 2‐cyano‐1‐(pyridin‐3‐yl)allyl acrylate (CPA) was then carried out by reaction of acryloyl chloride. The highly functionalized monomer CPA was grafted onto chitosan through a reaction in 2% acetic acid containing a persulfate and a sulfite (K2S2O8/Na2SO3) as redox promoter. An optimal grafting percentage of 123% is obtained when the grafting process is conducted at 60 °C for 4 h employing a 1:0.5 ratio of K2S2O8 and Na2SO3 at a concentration of 2.5 × 10?3 mol L?1. Chitosan‐graft‐poly[2‐cyano‐1‐(pyridin‐3‐yl)allyl acrylate] graft copolymers, having various grafting percentages, were characterized using Fourier transform infrared, 1H NMR and 13C NMR spectroscopies, X‐ray diffraction, thermogravimetric analysis and scanning electron microscopy. Finally, the results of studies probing the antimicrobial activities of the polymers against selected microorganisms show that the graft copolymers display higher growth inhibition activities against bacteria and fungi than does chitosan. © 2014 Society of Chemical Industry  相似文献   

14.
BACKGROUND: Gluconic acid (GA) production by immobilized cells of mutant Aspergillus niger ORS‐4.410 on polyurethane sponge (PUS) and calcium‐alginate (Ca‐alginate) was evaluated in repeated batches of solid state surface fermentation (SSF) and submerged fermentation (SmF) conditions, respectively, utilizing rectified grape must as carbon source. RESULTS: The passive immobilization of cells in fermentation medium solid support of having 0.4 cm3 cube size, 4% spore suspension, 0.6 g inoculum of PUS immobilized cells at 32 °C and 2.0 L min?1 resulted in the maximum GA production (88.16 g L?1) with a 92.8% yield, while the Ca‐alginate matrix with a 0.5 cm diameter bead size, 2–3% spore suspension, 15 g inoculum at 34 °C and 150 rpm agitation speed revealed 67.19 g L?1 GA with a 85.2% yield. Repeated use of PUS showed higher levels of GA (110.94 g L?1) in the third–fourth fermentation cycles with 95–98% yield and 22.50 g L?1 d?1 productivity under SSF that was 2.5‐fold higher than the productivity obtained from a typical fermentation cycle, and 54% greater than the productivity obtained with repetitive use of Ca‐alginate immobilized cells of A. niger under SmF. CONCLUSION: Using immobilized cells of A. niger in PUS, the rectified form of grape must can be utilized for GA production as an alternative source of carbohydrate by replacing the conventional fermentation conditions. Copyright © 2008 Society of Chemical Industry  相似文献   

15.
以轻烧粉和氯化铵反应为出发点,研究了氧化镁蒸氨反应过程的动力学和反应机理。结果表明:当反应30 min时,70~90 ℃条件下溶液中镁离子浓度约为0.14 mol/L,100 ℃时浓度为0.5 mol/L。XRD结果表明,蒸氨过程中未反应生成Mg2+的氧化镁以氢氧化镁存在于滤渣中。随着煅烧温度的升高,氧化镁水化反应活化能逐渐增加。当煅烧温度为600 ℃时,反应活化能为64.789 9 kJ/mol;当煅烧温度为800 ℃时,反应活化能为81.350 6 kJ/mol。氢氧化镁和氧化镁按不同物质的量比混合进行蒸氨反应时,蒸氨速率随体系中氢氧化镁含量的增加而升高。氧化镁蒸氨体系可分为2个阶段:第一阶段,氧化镁在铵盐体系中进行水化反应生成氢氧化镁,同时部分氧化镁和氢氧化镁进行蒸氨反应生成镁离子;第二阶段,整个体系完全变成氢氧化镁蒸氨体系。  相似文献   

16.
Chitin and chitosan with improved characteristics were produced from shrimp shell waste preconditioned by limited decay or by treatment with 0.016 mol L?1 benzoic acid. Preconditioned shrimp shells were transparent, had a clean surface and were susceptible to demineralization and deproteinization using 0.68 mol L?1 HCl and 0.62 mol L?1 NaOH, respectively. The ash and protein residues in the final chitosan were about 0.2% and 0.4%, respectively, the viscosity was up to 7000 cps, and the solubility and transparency nearly 100%. In comparison with treatment at ambient temperature (30 °C) without preconditioning, the chemical consumption, the duration of the treatment, ash and protein residues was reduced to 75–25%, whereas viscosity and absence of insolubles improved by a factor of 2–3. Copyright © 2006 Society of Chemical Industry  相似文献   

17.
A series of thermotropic copolyesters were synthesized by direct thermal melt polycondensation of p‐acetoxybenzoic acid (PHB) with transp‐acetoxycinnamic acid (PHC). The dynamic thermogravimetric kinetics of the copolyesters in nitrogen were analyzed by four single heating‐rate techniques and three multiple heating‐rate techniques. The effects of the heating rate, copolyester composition, degradation stage, and the calculating techniques on the thermostability and degradation kinetic parameters of the copolyesters are systematically discussed. The four single heating‐rate techniques used in this work include Friedman, Freeman–Carroll, Chang, and the second Kissinger techniques, whereas the three multiple heating‐rate techniques are the first Kissinger, Kim–Park, and Flynn–Wall techniques. The decomposition temperature of the copolyesters increases monotonically with increasing PHB content from 40 to 60 mol %, whereas their activation energy exhibits a maximal value at the PHB content of 50 mol %. The decomposition temperature, activation energy, the order, and the frequency factor of the degradation reaction for the thermotropic copolyester with PHB/PHC feed ratio of 50/50 mol % were determined to be 374°C, 408 kJ/mol, 7.2, and 1.25 × 1029 min?1, respectively. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 445–454, 2004  相似文献   

18.
BACKGROUND: Currently, the ‘green chemistry’ philosophy is being increasingly adopted by the chemical industry and, therefore, new production procedures of valuable chemicals from biomass‐derived raw materials are being sought. In this work, the synthesis of lactic acid from sorbitol under alkaline hydrothermal conditions is investigated by analyzing the influence on conversions and yields of temperature, NaOH/sorbitol molar ratio (MR), initial sorbitol concentration (SC) and reaction time. RESULTS: A 100% sorbitol conversion and a maximum 39.5% yield of lactic acid on a carbon basis are obtained at 280 °C, 50 min, 1.0 mol L?1 SC and 2.0 MR. Glyceraldehyde was the only identified intermediate while formic acid, acrylic acid, acetic acid, oxalic acid and sodium carbonate were identified as over‐oxidation products, all of them in very low yields with the exception of formic acid (16% yield at a MR of 4 and 280 °C). Several plausible conversion routes of sorbitol involving dehydrations, keto‐enol tautomerisms, reverse aldol condensations, aldol condensations, Cannizzaro reactions and oxidations are proposed. CONCLUSIONS: Considering the high number of parallel conversion routes as a consequence of high functionality of sorbitol, the 39.5% lactic acid yield obtained is a good result. Total carbon mass in all identified products only justifies, at most, 50% of that in sorbitol due to the coexistence of several conversion routes resulting in a large number of products other than lactic acid. Copyright © 2011 Society of Chemical Industry  相似文献   

19.
以聚乙烯吡咯烷酮为控制剂,氯化镁、氢氧化钠和氨水为原料,经静态反应制备出球形氢氧化镁前驱体,再经煅烧得到球形氧化镁。研究了控制剂种类、控制剂用量、反应物浓度、反应时间等因素对球形氧化镁形貌的影响,并用XRD、SEM等分析手段对产物做了表征。结果表明:在控制剂为聚乙烯吡咯烷酮、添加量为1.0%(质量分数)、氯化镁浓度为1.0 mol/L、氢氧化钠浓度为0.25 mol/L、反应时间为24 h的条件下,获得球形氢氧化镁前驱物;前驱物氢氧化镁在600 ℃下煅烧2 h,制得的球形氧化镁颗粒大小均匀、分散性好、球形度高,平均粒径为4.53 μm。  相似文献   

20.
BACKGROUND: The objective of the present work is to report an efficient pre‐treatment process for sunflower oil biodiesel raw glycerol (SOB‐RG) and its fermentation to 1,3‐propanediol. RESULTS: The growth inhibition percentages of Clostridium butyricum DSM 5431 on grade A (pH 4.0) and grade B (pH 5.0) phosphoric acid‐treated SOB‐RG were similar to those of pure glycerol at 20 g glycerol L?1; i.e., 18.5 ± 0.707% to 20.5 ± 0.7% inhibition. In grade A, growth inhibition was reduced from 85.25 ± 0.35% to 32 ± 1.4% (a 53.25% reduction) at 40 g glycerol L?1 by washing grade A raw glycerol twice with n‐hexanol (grade A‐2). The kinetic parameters for product formation and substrate consumption in anaerobic batch cultures gave almost similar values at 20 g glycerol L?1, while at 50 g glycerol L?1 volumetric productivity (Qp) and specific rate of 1,3‐propanediol formation (qp) were improved from 1.13 to 1.85 g L?1 h?1 and 1.60 to 2.65 g g?1 h?1, respectively, by employing grade A‐2 raw glycerol, while the yields were similar (0.5–0.52 g g?1). CONCLUSION: The results are important as the pre‐treatment of SOB‐RG is necessary to develop bioprocess technologies for conversion of SOB‐RG to 1,3‐propanediol. Copyright © 2008 Society of Chemical Industry  相似文献   

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