Monobutyl Phosphate Research Articles

Treatment of tributyl phosphate by fenton oxidation: Optimization of parameter, degradation kinetics and pathway

In nuclear industry, tributyl phosphate (TBP) is used as organic extracting solvent to separate uranium and plutonium. The spent TBP is finally discarded as the radioactive organic waste, which should be treated due to its potential risk. In this study, TBP degradation by Fenton oxidation was investigated in detail, including the optimization of operational conditions, degradation kinetics and degradation products. The optimal conditions for TBP degradation (per 10 ml) by Fenton oxidation was: 95 °C, pH 2, 150 ml 30% H2O2, and 105 ml 0.2 M Fe(II). H2O2 was continuously added with the flow rate of 0.5 ml/min, Fe(II) was intermittently added with the flow rate of 3 ml/10 min. The oil phase volume decreased with time and completely disappeared at the third hour. In contrast, the COD in water phase increased firstly and then decreased. At the end of the experiments, the COD achieved 23.8 g/L. The detection of phosphorus in water phase further confirmed the decomposition of TBP. Mono-butyl phosphate and di-butyl phosphate were identified as the intermediate products of TBP degradation. In addition, other four degradation products with the same m/z of 154 were identified, which may be derived from the hydroxylation of mono-butyl phosphate and di-butyl phosphate. Based on the degradation products, the degradation pathway of TBP was proposed. This study could provide an insight into the TBP degradation by Fenton oxidation, and an potential strategy for treating the spent radioactive organic solvent.

The effect of radiolysis and thermally stimulated acid hydrolysis on tributyl phosphate and its solutions in ISOPAR-M

The radiolytic and post-radiation thermochemical (at 90–170 °C) transformations of tri-n-butyl phosphate (TBP) and its 30% solution into Isopar-M during pre-radiation and post-radiation acidification with nitric acid have been investigated. The assortment of nitrogen-containing products of TBP oxidation during gamma radiolysis, electron beam radiolysis, and thermally stimulated acid hydrolysis is similar. Specific products of radiolysis are TBP dimer and alkyl adducts of dibutyl phosphate, and specific products of thermolysis are ethylbenzene and xylenes. It was shown that, in contrast to 100% TBP, where radiolysis and hydrolysis have approximately the same additive effect on the degradation of TBP, hydrolysis in a 30% solution leads to the degradation of nitrogen-containing radiolysis products and additional formation of dibutyl phosphate and monobutyl phosphate. Temperatures above 110 °C during post-radiation thermolysis intensify the formation of highly volatile compounds from radiolysis products (up to 17 wt% at 170 °C), which increases the fire and explosion hazard of using extraction mixtures.

Isolation and characterization of a recombinant class C acid phosphatase from Sphingobium sp. RSMS strain

Tributyl phosphate (TBP) is extensively used in nuclear industry and is a major environmental pollutant. The mechanism for TBP degradation is not identified in any TBP-degrading bacteria. Here, we report identification of an acid phosphatase from Sphingobium sp. RSMS (Aps) that exhibits high specific activity towards monobutyl phosphate (MBP) and could be a terminal component of the TBP degradation process. A genomic DNA library of the bacteria was screened using a histochemical method which yielded 35 phosphatase clones. Among these, the clone that showed the highest MBP degradation was studied further. DNA sequence analysis showed that the genomic insert encodes a protein (Aps) which belongs to class C acid phosphatase. The recombinant Aps was found to be a dimer and hydrolysed MBP with a Kcat 68.1 ± 5.46 s−1 and Km 2.5 mM ± 0.50. The protein was found to be nonspecific for phosphatase activity and hydrolyzed disparate organophosphates.

Thermal decomposition behaviour of irradiated tri n-butyl phosphate and mixture of di and mono n-butyl phosphate-nitric acid systems

Tri-n-butyl phosphate (TBP) is employed in nuclear reprocessing plants. During the evaporation process, formation of red oil, an unstable compound can cause runaway reaction. In this context, thermal decomposition of TBP-HNO3 and TBP-n-dodecane has been studied as a function of HNO3 concentration using adiabatic calorimeter. Effect of radiolysis on thermal decomposition of TBP has been investigated for the first time. Neat TBP is stable up to 527±1K and the irradiated TBP is up to 513±1K. Thermal decomposition of degradation products of TBP namely, dibutyl and monobutyl phosphates have also been investigated for the first time. Thermo-kinetic parameters e.g. enthalpy of decomposition, activation energy, pre-exponential factor and order of reaction were computed. Enthalpies of decomposition for TBP–4M HNO3 vary from 64 to 495kJmol−1 whereas that of TBP–8M HNO3, 368–1187kJmol−1. TBP-HNO3 on thermal decomposition produces CO, CO2, NOx, hydrocarbons and highly viscous black liquid.

Influence of irradiation on the structure and thermo-kinetic behavior of tri-n-butyl phosphate

Tri-n-butyl phosphate is the primary extractant in the PUREX extraction process of uranium and plutonium. Despite its efficiency as an extractant, its reaction with nitric acid in the presence of irradiation and metal nitrates poses hazards. This study evaluates the effect of γ radiation on tributyl phosphate’s structure and observes its thermal behavior in an accelerating rate calorimeter. The bound water molecules in tributyl phosphate were gradually removed with the increase in radiation dose. The degradation products analyzed by spectroscopic methods revealed breakup of structure of TBP into dibutyl phosphate, monobutyl phosphate and hydrocarbons. It was observed that the effects of irradiation on TBP were minor and could be less hazardous in the absence of acid.

Involvement of phosphoesterases in tributyl phosphate degradation in Sphingobium sp. strain RSMS.

A tri- and dibutyl phosphate (TBP/DBP) non-degrading spontaneous mutant, Sphingobium SS22, was derived from the Sphingobium sp. strain RSMS (wild type). Unlike the wild type strain, Sphingobium SS22 could not grow in a minimal medium supplemented with TBP or DBP as the sole source of carbon or phosphorous. Sphingobium SS22 also did not form any of the intermediates or end products of TBP or DBP degradation, namely DBP, butanol or inorganic phosphate. Proteomic analysis revealed the absence of three prominent proteins in Sphingobium SS22 as compared to wild type. These proteins were identified by MALDI mass spectrometry, and they showed similarities to phosphohydrolase- and exopolyphosphatase-like proteins from other bacteria, which belong to the class of phosphoesterases. Cellular proteins of Sphingobium SS22 showed none or negligible phosphodiesterase (PDE) and phosphomonoesterase (PME) activities at pH7 and displayed approximately five- and approximately twofold less DBP and monobutyl phosphate (MBP) degradation activity, respectively, in comparison to the wild type strain. In-gel zymographic analysis revealed two PDE and PME activity bands in the wild type strain, one of which was absent in the Sphingobium SS22 mutant. The corresponding proteins from the wild type strain could degrade DBP and MBP. The results demonstrate the involvement of phosphoesterase enzymes in the TBP degradation pathway elucidated earlier.

Solutes at the liquid:liquid phase boundary--Solubility and solvent conformational response alter interfacial microsolvation.

A detailed understanding of solvent structure and dynamics at liquid:liquid interfaces is a necessary precursor for control and manipulation of these phase boundaries. Experimentally, amphiphilic solutes are often used to alter transport properties across water:organic interfaces; however, a fundamental model for the mechanism of this action has not been determined. This work compares the solvation profiles of ampiphilic solutes that traverse the phase boundary in binary water:n-hexane, and the individual microsolvation processes for interfacial water and hexane molecules therein. Microsolvation is defined as the rare event where one solvent molecule temporarily penetrates the co-solvent phases and is fully solvated therein. The solutes tri-butyl phosphate (TBP), hydrogen di-butyl phosphate, and di-hydrogen mono-butyl phosphate have been examined as they exhibit a systematic increase in aqueous solubility and selectively partition to the interfacial region at the infinite dilution limit. The relationship between adopted configurations of the solute, orientation of the solvent, and the ability of the solute to enhance microsolvation, specifically the ability of n-hexane to penetrate the aqueous phase, is demonstrated within a 20 Å radius of TBP.

Quantitative analysis of phosphoric acid esters in aqueous samples by isotope dilution stir-bar sorptive extraction combined with direct analysis in real time (DART)-Orbitrap mass spectrometry

A novel hyphenated technique, namely the combination of stir bar sorptive extraction (SBSE) with isotope dilution direct analysis in real time (DART) Orbitrap™ mass spectrometry (OT-MS) is presented for the extraction of phosphoric acid alkyl esters (tri- (TnBP), di- (HDBP), and mono-butyl phosphate (H2MBP)) from aqueous samples. First, SBSE of phosphate esters was performed using a Twister™ coated with 24μL of polydimethylsiloxane (PDMS) as the extracting phase. SBSE was optimized for extraction pH, phase ratio (PDMS volume/aqueous phase volume), stirring speed, extraction time and temperature. Then, coupling of SBSE to DART/Orbitrap-MS was achieved by placing the Twister™ in the middle of an open-ended glass tube between the DART and the Orbitrap™. The DART mass spectrometric response of phosphate esters was probed using commercially available and synthesized alkyl phosphate ester standards. The positive ion full scan spectra of alkyl phosphate triesters (TnBP) was characterized by the product of self-protonation [M+H]+ and, during collision-induced dissociation (CID), the major fragmentation ions corresponded to consecutive loss of alkyl chains. Negative ionization gave abundant [M−H]− ions for both HDnBP and H2MnBP. Twisters™ coated with PDMS successfully extracted phosphate acid esters (tri-, di- and mono-esters) granted that the analytes are present in the aqueous solution in the neutral form. SBSE/DART/Orbitrap-MS results show a good linearity between the concentrations and relative peak areas for the analytes in the concentration range studied (0.1–750ngmL−1). Reproducibility of this SBSE/DART/Orbitrap-MS method was evaluated in terms of %RSD by extracting a sample of water fortified with the analytes. The %RSDs for TnBP, HDnBP and H2MnBP were 4, 3 and 3% (n=5) using the respective perdeuterated internal standards. Matrix effects were investigated by matrix matched calibration standards using underground water samples (UWS) and river water samples (RWS). Matrix effects were effectively compensated by the addition of the perdeuterated internal standards. The application of this new SBSE/DART/Orbitrap-MS method should be very valuable for on-site sampling/monitoring, limiting the transport of large volumes of water samples from the sampling site to the laboratory.

Study of different approaches for management of contaminated emulsified aqueous secondary waste

The underlying objective governing the management of radioactive waste is protection of human being and the environment, now as well as in the future. As a waste management philosophy, utmost emphasis is given to waste volume minimization at all stages of design, operation and maintenance [1]. The development of innovative treatment processes for low and intermediate level wastes (LLW and ILW) in recent times has focused on volume reduction as one of the main objectives [2]. During reprocessing of spent fuel, an optimized mixture of tri-n-butyl phosphate (TBP) and dodecane is used as an extracting agent for actinides. During their repeated use, solvent undergoes chemical/radiolytic degradation, loosing its efficiency and hence to be discarded as spent organic solvent waste. This waste is presently being treated by alkaline hydrolysis process where spent solvent is refluxed with concentrated sodium hydroxide solution at 110°C [3]. TBP component of the spent solvent waste gets hydrolyzed and is converted into sodium salt of di-butyl phosphate (DBP). The other products obtained during hydrolysis include sodium salt of mono-butyl phosphate (MBP), butanol and phosphoric acid. Dodecane component of the spent solvent waste does not take part in the hydrolysis reaction and appears as a clear phase. The dodecane waste thus separated is subjected for thermal destruction by incineration. The emulsified aqueous layer thus obtained retains most of the activity present in the spent solvent waste. The present paper describes experimental studies performed to look for various approaches for management of this type of waste.

Direct determination of phosphate esters in concentrated nitrate media by capillary zone electrophoresis

The potential of capillary zone electrophoresis (CZE) for the determination of dibutyl phosphate (DBP) and monobutyl phosphate (MBP), two degradation products of the tributyl phosphate extractant used in the nuclear fuel reprocessing industry, was evaluated. Analysis conditions were optimised, taking particularly into account that many determinations had to be performed in concentrated aqueous nitrate or nitric acid solutions. Separations were therefore carried out using the counter-electroosmotic mode with cathodic detection in a pH 8.3 electrolyte containing a suitably selected chromophore, salicylate, to ensure the indirect UV detection of the analytes. Various aspects of the method, including its sensitivity, working range, repeatability, and rapidity, were examined. Quantification of both phosphate esters was achieved in less than 3 min at concentrations ranging from 2×10 −6 to 10 −3 mol l −1 in samples containing no macro-component. The lower end of this range increased to 5×10 −6 mol l −1 for MBP and 1.5×10 −5 mol l −1 for DBP in samples containing 5×10 −2 mol l −1 of sodium nitrate, thus enabling their determination in solutions containing nitrate or nitric acid at concentrations up to, respectively, 10 000 and 3000 times higher than the target analyte concentration. This simple, fast and reliable method is routinely applicable to aqueous samples with no other preliminary treatment than a proper dilution; analysis was also performed in organic matrices after a prior extraction. The method was validated by an excellent correlation with the standard DBP analysis technique, gas chromatography (GC). In order to develop appropriate chemical treatments to destroy these compounds, the method was applied to the monitoring of DBP and MBP degradation by hydrogen peroxide in 1 mol l −1 nitric acid solutions.

Improved determination of tributyl phosphate degradation products (mono- and dibutyl phosphates) by ion chromatography

Tributyl phosphate (TBP) is a very important compound in the nuclear industry, particularly in the area of nuclear fuel reprocessing. This compound is used in the PUREX (plutonium and uranium refining extraction) process which consists of the extraction of uranium and plutonium from an aqueous nitric acid phase, for the purpose of recycling. But TBP may be degraded to dibutyl phosphate (DBP) and monobutyl phosphate (MBP) by dealkylation of one or two butoxy groups, respectively. We have compared and evaluated the capacity of two resins manufactured by Dionex (AS11 and AS5A) in the separation and measurement of these two degradation products. AS11 generates two interferences: nitrite/DBP and carbonate/MBP. The first one is the most serious. So, we have developed a method for oxidising nitrite ions to nitrate ions which have no trouble over the measurement. The second resin tested, AS5A, allows a very efficient separation between DBP and NO 2 − ions and a good separation between MBP and CO 3 2− in comparison with the AS11. The detection limits for the AS5A column are 0.13 μ M for MBP and 0.71 μ M for DBP (injection loop=50 μl).

Direct determination of dibutyl and monobutyl phosphate in a tributyl phosphate/nitric aqueous-phase system by electrospray mass spectrometry

Electrospray ionization mass spectrometry was tested for its potential use in the quantification of monobutyl phosphate (H2MBP) and dibutyl phosphate (HDBP), two degradation products of tributyl phosphate (TBP), the extractant used in the nuclear fuel reprocessing known as the PUREX process. Detection and quantification of these phosphate esters by electrospray in positive and negative ionization mode are reported in this study. This fast and reliable method, which does not require any preliminary sample extraction, appears to be very attractive for process control. Negative ionization mode gave abundant [M - H]- ions for both HDBP and H2MBP products. Thus, the concentration of H2MBP between 0.1 and 10 g/L in concentrated aqueous nitrate solutions can be precisely determined. Moreover, the concentration of HDBP up to 1 g/L in a TBP matrix was evaluated in this mode. For HDBP concentrations below 1 g/L, detection in the positive ionization mode appeared to be attractive. TBP and HDBP cluster detection allowed quantitative HDBP determination. Indeed, small amounts of HDBP in commercial TBP (60 mg/L) could be directly quantified using the specific [2TBP, HDBP + H]+ cluster at m/z 743.

Nonphosphate Degradation Products of Tributyl Phosphate and Their Reactivities in Purex Media under Extreme Conditions

The chemical degradation of tributyl phosphate (TBP) in liquid systems, where TBP was in contact with aqueous solutions containing nitric acid and/or uranyl nitrate, was studied experimentally to clarify the mechanisms of the formation and successive reactions of nonphosphate products under atmospheric pressure. Butyl nitrate, propionic acid, acetic acid, butric acid, and butyl alcohol were formed as the nonphosphate butyl products derived from the butyl-groups of TBP in an open system. The total amount of these products almost equals the amount of the major intermediate phosphate products reduced, i.e., di- and monobutyl phosphates and phosphoric acid. Butyl alcohol was found to be the precursor of the other nonphosphate products.Even when the extremely degraded solvent was further contacted with 10 M nitric acid at 90°C, no significant heat evolution was observed at atmospheric pressure. Only butyl alcohol changed into carboxylic acids by exothermic oxidative reactions.

Determination of monobutyl phosphate and dibutyl phosphate in mixed hazardous wastes by ion-pair chromatography

Ion-pair chromatography was tested for its applicability in determining monobutyl phosphate (MBP) and dibutyl phosphate (DBP), which are degradation products of tributyl phosphate, in Hanford tank wastes. In tests with simulant waste mixtures, tetrahexylammonium bromide, an ion-pairing agent, was used to complex with all three phosphate species. Recovery studies indicated that ion-pairing chromatography is quantitative for determining the analytes in spiked samples. Initial results demonstrated that DBP could be detected easily and was fairly well separated from other peaks, but MBP was frequently lost due to large negative peaks. Then a preconcentration column procedure was used to clean up the waste-sample matrix, and the negative peaks disappeared. Results indicated that 80% of MBP and 90% of DBP could be recovered. Most of the radioactivity was removed from actual waste tank samples so that additional sample preparation could be performed safely in a fume hood rather than a hot cell. Dibutyl phosphate was identified in an actual tank waste, but MBP was not found; this result was confimed by ion chromatography with conductivity detection.

Determination of radiolytic products of two-phase tributylphosphate—Water systems by capillary isotachophoresis

A capillary isotachophoresis was used for determination of ionogenic radiolytic products of two-phase tributylphosphate—water systems. Optimum operating conditions for analytical determination of dibutylphosphate (DPP), monobutylphosphate (MBP), H3PO4, formic, acetic, propionic and butyric acid were found.

Kinetics of Formation and Transport Resistances of Zirconium-Monobutyl Phosphate Films

The formation processes of monobutyl phosphate-zirconium films at a liquid-liquid interface have been investigated by observing changes in toluene absorption in a Lewis cell type contactor. Films were formed by adding monobutyl phosphate to the upper (organic) phase and allowing it to react with zirconium dissolved in the lower (aqueous) phase while monitoring the absorption of the organic solvent into the aqueous phase. Results indicate that the film formation occurs over a short period of time but may be preceded by a considerable lag period which depends on concentration, temperature and to a lesser extent, stirring. Mass transfer coefficients were decreased by as much as 40% at higher temperatures. Interfacial tension changes during film formation were also investigated and indicate that significant activity occurs at the interface.

Separation and streaming-current detection of strong acids in normal-phase liquid chromatography

The separation and streaming-current detection of strong acids were studied on a model extraction solution of tributyl phosphate which contains, in addition to others, dibutyl and monobutyl phosphates and orthophosphoric acid. All the components of the sample, starting from hydrocarbons and ending with orthophosphoric acid, can be separated within 10 min, provided that silica gel with a large surface area, treated with perchloric acid, is used as a column packing. 2-Propanol—heptane (15:85), saturated to 30% with water, is used as mobile phase. The streaming current can be sensed from a chromatographic column. Phosphoric acids are detected selectively, with a sensitivity of 1–2 orders of magnitude higher than in refractometric detection.

Determination of dibutyl and monobutyl phosphates in mixtures of kerosene and tributyl phosphate

Dibutyl and monobutyl phosphates were determined by gas chromatography. A procedure involving separation, extraction and methylation was developed and it was found that the use of a flame-photometric detector gave better results. The detection limits of 5 × 10–8 g were found for both dibutyl and monobutyl phosphates.

Determination of dibutyl and monobutyl phosphates in tributyl phosphate kerosene mixtures by solvent extraction and gas chromatography

Determination of dibutyl and monobutyl phosphates in tributyl phosphate kerosene mixtures by solvent extraction and gas chromatography

Niobium(V) extraction by butyl lauryl phosphoric acid-dodecane from nitric acid

Extraction of niobium by tributyl phosphate (TBP) in the Purex process is inefficient; and in spite of this, niobium is found in solvent streams. Alternate mechanisms for niobium transfer into the solvent were sought. Butyl lauryl phosphoric acid (HBLP), a model compound of secondary degradation products of the solvent used in the process, was found to enhance niobium extraction above a threshold concentration of 5 × 10 −4 M. A study of the niobium distribution coefficient dependences in the system HNO 3-HBLP-dodecane on the HBLP, hydrogen ion and nitrate ion concentration suggests an extraction mechanism involving neutralization of an hydroxyl group bound to the niobium and no incorporation of nitrate into the extracted species. These results are supported by chemical analysis of the extracted species which show an empirical formula corresponding to Nb(OH) 4BLP. Silica and zirconium monobutyl phosphate, under certain conditions, disperse adsorbed niobium in the solvent phase in the form of emulsions or suspensions. Centrifugation of these give no net enhancement of niobium transfer.