共查询到20条相似文献,搜索用时 15 毫秒
1.
研究了硝酸溶液中聚丙烯基聚偕氨肟(PPAO)—硫脲(TU)络合物引发丙烯腈(AN)聚合动力学。在[TU]/[PPAO]<0.5摩尔比的条件下,表观聚合速度(R_p)是R_p=9.1×10~4e~(-45.2k J/RT)[AN]~(2.0)[HNO_3]~(1.5)[TU]~(1.0)聚合物分子量随聚合温度升高而下降,并与硝酸浓度的1.5次方和硫脲浓度的1.0次方成反比,与丙烯腈浓度和 PPAO 浓度无关。可表示为_m=K·1/T·(1/[HNO_3]~(1.5)[TU]~(1.0))=K_M·1/T·(R_p/R_t)根据实验结果,提出了“络合—质子转移”引发机理。 相似文献
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The polymerization of acrylonitrile (AN) initiated by polypropylene based-polyamidoxime (PPAO)-thiourea (TU) system was investigated at [TU]/[PPAO]>0.5 molar ratio. It shows that the variation of the concentrations of PPAO, thiourea and nitric acid does not exert an observable influence on the reaction rate. The overall rate of polymerization (R_p) isR_p = 2.07e~(-7,800/RT)[ AN]~(2.0)The zero order dependence on PPAO and thiourea concentrations and the lowest value of the collision frequence factor were considered to be a feature of the primary radical termination. 相似文献
4.
Manoj Kumar J. Udhayakumar Ashutosh Dash 《Journal of Radioanalytical and Nuclear Chemistry》2011,288(1):53-58
Aiming the selective recovery of palladium from high level radioactive liquid waste (HLW), a chelating thiamide type sorbent,
CWP–TU, was prepared by the modification of Japanese cedar wood powder (CWP). Convection oven and microwave heating were separately
used for modification purpose and found that microwave heating is more effective over oven heating. CWP–TU was extensively
studied for the adsorption of Pd(II) from nitric acid medium. The batch test showed that nitric acid concentration of 3 M
or higher is favorable for Pd(II) loading. Consistent adsorption of Pd(II) under gamma irradiation condition demonstrated
the feasibility of using CWP–TU in real HLW. Also, Pd(II) only adsorption from simulated HLW solution verified the palladium
only selectivity of the sorbent as well as the lack of influence of coexisting metal ions on its affinity toward Pd(II). CWP–TU
holds maximum Pd(II) loading capacities of 0.98 mol/kg at 30 °C and 1.04 mol/kg under gamma irradiation. A comparative study
using some ion exchange resins revealed that the resins are either ineffective in nitrate medium or lack stability under irradiation. 相似文献
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研究了笼形聚羧酸钒(PV)-硫脲(TU)体系在硝酸溶液中引发丙烯腈(AN)聚合动力学。表观聚合速度(R_p)是 R_p=9.7×10~5e~(-10500)/RT[AN]~1.0[PV]~0.50[TU]~0.76[HNO_3]~1.5聚合诱导期(τ)随反应条件而变化,聚合温度越高,引发种浓度越大,聚合诱导期越短,但与单体浓度的变化无关。 1/τ=4.6×10~(12)e~(-13500)/RT[AN]~0[PV][TU]~(-3/2)[HNO_3]~3=K_τ·R_i聚合物分子量随单体浓度增大而提高,但随聚合温度及引发种浓度增大而下降,即 笼形聚羧酸钒—硫脲体系引发丙烯腈聚合的动力学参数和引发机理与杨梅型聚羧酸钒—硫脲体系在相同的条件下引发聚合的行为有明显的区别,认为是和两种树脂大分子链的空间结构所引起的传质阻力有关。 相似文献
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The kinetics of polymerization of acrylonitrile (AN) initiated by quinquevalent vanadium (V~(5+))-thiourea (TU) redox system has been investigated in aqueous nitric acid in the temperature range from 30 to 50℃. The polymerization rate (R_p) can be expressed as follows: In the copolymerization of acryionitrile with methyl acrylate (MA), the reactivity ratios were found to be 1.0 and 1.1, respectively. The experimental observations suggest that the initiating species is probably a complex consisting of a central ion of Lewis acid-VO_2~+ and the ligands of Lewis bases-acrylonitrile, thiourea, and nitrate anions, while the initiating system in lower concentration, the polymerization of acrylonitrile does not occur if the thiourea is acidified prior to its reaction with quinquevalent vanadium. This indicates that the primary radicals (or the monomeric radicals in the present article) are produced by associated thiourea rather than isothlourea. 相似文献
8.
KIO3-I2氧化法同时测定TU,TD和TT 总被引:3,自引:0,他引:3
以I2和KIO3为氧化剂,建立了同时测定硫脲(TU),二氧化硫脲(TD)和三氧化硫脲(TT)的方法.强酸性条件下,用I2氧化TU;适当酸度条件下,用KIO3氧化TU和TD;强碱性条件下用I2氧化TU,TD和TT.方法已用于合成样品和TD结晶母液的分析. 相似文献
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研究了杨梅形聚肟偕亚氨二乙酸树脂负载VO~(2+)(PV)与疏脲(TU)组合在硝酸溶液中引发丙烯腈(AN)的聚合反应。在实验条件下,表观聚全速度可表示为 R_p=1.91×10~5e~(-45.0/RT)c~(1.9)(AN)c~(1.0)(HNO_3)c~(0.60)(PV)c~(1.50)(TU) 聚合诱导期(τ)与反应物浓度和聚合温度关系是 1/τ=8.27×10~7e~(-38.3/RT)c~(1.9)(HNO_3)c~(0.60)(PV)C~(1.50)(TU)=K_τ;·R_i/R_p 在酸性介质中,氨羧基的协同作用促使键合的VO~(2+)氧化为VO_2~+,随后硫脲配位并通过氢桥缔合,后者分解生成初级自由基,引发丙烯腈的聚合反应。 相似文献
10.
P. Giridhar K. A. Venkatesan T. G. Srinivasan P. R. Vasudeva Rao 《Journal of Radioanalytical and Nuclear Chemistry》2005,265(1):31-38
Summary A systematic study on the extraction of U(VI) from nitric acid medium by tri-n-butylphosphate (TBP) dissolved in a non-traditional diluent namely 1-butyl-3-methylimidazolium hexafluorophosphate (bmimPF6) ionic liquid (IL) is reported. The results are compared with those obtained using TBP/n-dodecane (DD). The distribution ratio for the extraction of U(VI) from nitric acid by 1.1M TBP/bmimPF6 increases with increasing nitric acid concentration. The U(VI) distribution ratios are comparable in the nitric acid concentration range of 0.01M to 4M, to the ratios measured using 1.1M TBP/DD. In contrast to the extraction behavior of TBP/DD, the D values continued to increase with the increase in the concentration of nitric acid above 4.0M. The stoichiometry of uranyl solvate extracted by 1.1M TBP/IL is similar to that of TBP/DD system, wherein two molecules of TBP are associated with one molecule of uranyl nitrate in the organic phase. Ionic liquid alone also extracts uranium from nitric acid, albeit to a small extent. The exothermic enthalpy accompanying the extraction of U(VI) in TBP/bmimPF6 decreases with increasing nitric acid and with TBP concentrations. 相似文献
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S. K. Milonjić Dj. M. Čokeša R. V. Stevanović 《Journal of Radioanalytical and Nuclear Chemistry》1992,158(1):79-90
Adsorption of uranium(VI) and zirconium(IV) from aqueous nitric acid solution on silica gel has been investigated under dynamic conditions. The influence of temperature, nitric acid concentration (pH), and solution flow rates was studied. If the nitric acid concentration in the solution is higher than 0.05 mol/l, then it is possible to achieve separation of uranium(VI) and zirconium(IV) by passing the solution through a column filled with silicagel. 相似文献
12.
Sun Guo-Xin Cui Yu Han Jing-Tian Shao Hua Bao Bo-Rong 《Journal of Radioanalytical and Nuclear Chemistry》2000,246(2):431-432
The extraction of U(VI) from nitric acid solutions with di-(1-methylheptyl) phosphoric acid has been investigated. The dependence on nitric acid concentration, DMHPA concentration and temperature has been considered and the infra-red spectra of extracted species and extractant were recorded. The mechanism of extraction is discussed in the light of the results obtained. 相似文献
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Y.-Z. Wei B. Fang T. Arai M. Kumagai 《Journal of Radioanalytical and Nuclear Chemistry》2004,262(2):409-415
Electrochemical reduction of U(VI) in nitric acid-hydrazine solution is greatly influenced by the concentration of nitric
acid. In low acidity nitric acid solution such as 0.1M (M=mol/dm3) HNO3, U(VI) was firstly reduced to U(V) and then partially reduced to U(IV). In high acidity nitric acid solution, e.g., 3-6M
HNO3, an electrode process of two-electron transfer was involved in the reduction of U(VI). A higher U(IV) yield could be achieved
in nitric acid solution with higher concentration. Hydrazine was very effective in suppressing the reduction of concentrated
nitric acid, and the optimal concentration of hydrazine added was 0.075 to 0.15M in 6M HNO3
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
14.
The polymerization of acrylonitrile (AN) in aqueous nitric acid initiated by " cage " vanadyl polycarboxylate (P=VO)-thiourea (TU) complex was investigated. The overall rate ofpolymerization isThe relationship between the induction period (τ) and the temperature of polymerization as well as the concentrations of reactants can be expressed as follows :The molecular weight of polyacrylonitrile increases with increasing monomer concentration and decreases with increasing temperature of polymerization and concentrations of vanadyl polycarboxylate and thioureaThe polymerization mechanism was proposed and discussed. 相似文献
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The polymerization of acrylonitrile (AN) in aqueous nitric acid initiated by metavanadate-containing anion exchange resin (PV)-thiourea (TU) redox system at 20—40℃. has been investigated. The overall rate of polymerization (R_p) is given byR_p=1.92×10~4e~(-6.860/RT) [AN]~(1.2) [PV]~(0.44) [TU]~(1.0)[HNO_3]~(1.0)The kinetic parameters differed from those of V~(5+)-TU system indicated that the generation of the primary radicals is mainly a difffusion-controlled reaction. The effect of macromolecular field arisen from the polymer matrix exerts a great influence on the polymerization process. 相似文献
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Y. Kondo 《Journal of Radioanalytical and Nuclear Chemistry》1999,242(2):515-526
The influence of urea on initiation and termination of the reaction between nitric and formic acids was experimentally examined.
The urea injection can terminate the denitration reaction in 2 to 10M salt-free nitric acid solutions and the simulated high
level liquid wastes (HLLWs) with a nitric acid concentration of 2 to 6M. An excess of urea can interrupt the initiation of
denitration in both simulated HLLW and salt-free nitric acid solutions. The initiation and termination of denitration are
in relation with nitrous acid formation and decomposition. Urea reacts with nitrous acid easily in the denitrating solution
and decomposes nitrous acid. As the urea concentration increases in the solution, the continuance of denitration become impossible
because the decomposition rate of nitrous acid exceeds the generation rate. In addition, the nitrous acid concentration can
not be high enough to initiate the denitration in the solution with an excess of urea because nitrous acid is decomposed by
urea. 相似文献
18.
The extraction of copper(II) from strongly acidic solution (0.01-8M hydrochloric and 0.01-5M nitric acid) with ammonium 1-pyrrolidinecarbodithioate in di-isobutyl ketone has been studied. Compared with the hydrochloric acid system, a considerably larger amount of the reagent is needed for complete extraction of copper chelate from nitric acid solution as the extract is more unstable in the nitric acid system. The decomposition of copper chelates extracted from nitric acid is based on the oxidation of the reagent and the chelate; the spectral change of the extract from nitric acid suggests that the copper(II) chelate is initially oxidized to copper(II) and then decomposes. The upper limit of the acidity of both acids from which the copper chelate can be quantitatively extracted strongly depends on the reagent concentration; the limit with 8 x 10(-2)M APCD (500-fold reagent: metal molar ratio) was taken as 8 and 4M for hydrochloric and nitric acid, respectively. 相似文献
19.
T. Sato 《Journal of Radioanalytical and Nuclear Chemistry》1992,158(2):391-399
Extraction of yttrium and some of the lanthanoids by diisodecylphosphoric acid (DIDPA) has been studied as a function of nitric acid concentration in the aqueous phase and concentration of the DIDPA in n-dodecane. The distribution ratio of yttrium was found to increase with the second power of concentration of the extractant and decrease with the third power of concentration of nitric acid. As the concentration of yttrium in the organic phase increased, an amorphous solid was found to precipitate and the composition of the solid was determined to be Y(DIDP)3. To dissolve Y(DIDP)3 into n-dodecane, a 14-fold molar excess of DIDPA was required over Y(DIDP)3. The distribution ratio of yttrium was found to be too high to back-extract this element by nitric acid of medium concentration. 相似文献