Function Of Water pH Research Articles

PH effect on wettability of –NH+-brine-muscovite system: Implications for low salinity effect in sandstone reservoirs

Wettability alteration remains the main mechanism of low salinity water flooding (LSWF) which is controlled by several factors including crude oil composition. Although presence of acidic components in crude oil confirmed to be necessary to enhance wettability during LSWF, yet the effect of basic components remain unclear. In this work we used the concept of surface energy to explicate the dependency of wettability on a high base number (BN) oil as a function of water pH, ion type and salinity. We measured Oil/Brine contact angle and interfacial tension, which then were used to compute Oil/Solid (mica) interfacial tension using Neumann's equation of state. In addition, we measured the zeta potential and simulated the concentration of base components (–NH+ groups) in the oil using a surface complexation model to understand the underlying mechanisms of wettability and interfacial tension alterasion. We found that wettebility is also dependant on the basic components of crude oil where pH plays a major role and salinity and ion type play a secondary role. Increasing pH (from pH=3 to pH=11) decreased the contact angle moving the system to a more hydrophilic or water-wet state (contact angle decreased from 162° to 68° for CaCl2 solution and from 163° to 66° for NaCl solution). We also found that Oil/Solid interfacial tension increased with pH, where changes were more pronounced in the presence of divalent cations compared to monovalent. We hypothesise that changes in the contact angle and Oil/Solid interfacial tension are due to the chemo-physical adsorption of –NH+ groups at the oil surface to the muscovite negative sites. The hypothesis is consistent with the changes in the zeta potential and –NH+ surface concentration computed from the surface complexation model. The results of this study underscore the importance of the basic component on system wettability as a function of pH, providing insights into the low salinity EOR in sandstone reservoirs.

Effect of ammonia stress on immune variables of Pacific white shrimp Penaeus vannamei under varying levels of pH and susceptibility to white spot syndrome virus

Of late, Pacific white shrimp Penaeus vannamei culture has intensified globally and is a major contributor to the cultured shrimp produced worldwide. Intensification of its culture has led to elevated ammonia concentration during grow-out. Ammonia toxicity is a function of water pH, temperature, salinity and beyond the optimum range, creates stress to cultured aquatic species which can reduce growth, increase susceptibility to diseases and eventually mortality. The present study was aimed at quantifying the toxic effect of total ammonia nitrogen (TAN) (1, 3, 6 & 9 mg/l) and pH levels (6, 8 & 10) individually and in combination on median survival (50% lethal time) of shrimp (8 g) after exposure for 14 days followed by post-stress challenge with white spot syndrome virus (WSSV) for 9 days. Mortality risk factor and the toxicity effect on the immune variables were evaluated. Individual stressors showed a risk factor of 1–13 times, whereas combined treatments considerably increased the risk of dying compared to control. Low survival (15%) was observed in pH6TAN9 and pH10TAN3 treatments and was substantiated by prominent histological obliteration in gills of shrimp. The cumulative mortality in post-stress WSSV challenged trials was 1–5 times and 1–35 times in individual and combination treatments, respectively compared to control. The study revealed that variations in ammonia and pH beyond the optimal range significantly influence the non-specific immune mechanisms in P.vannamei and increases the susceptibility to WSSV especially in combination treatments.

Adsorption of Mefenamic Acid From Water by Bentonite Poly urea formaldehyde Composite Adsorbent

Poly urea formaldehyde –Bentonite (PUF-Bentonite) composite was tested as new adsorbentfor removal of mefenamic acid (MA) from simulated wastewater in batch adsorption procedure. Developed a method for preparing poly urea formaldehyde gel in basic media byusing condensation polymerization. Adsorption experiments were carried out as a function ofwater pH, temperature, contact time, adsorbent dose and initial MA concentration .Effect ofsharing surface with other analgesic pharmaceuticals at different pH also studied. Theadsorption of MA was found to be strongly dependent to pH. The Freundlich isotherm modelshowed a good fit to the equilibrium adsorption data. From Dubinin–Radushkevich model themean free energy (E) was calculated and the value of 5 KJ/mole indicated that the mainmechanism governing the adsorption of MA on PUF-Bentonite composite was physical innature. The kinetics of adsorption tested for first order, pseudo second order models andElovich’s equation, results showed the adsorption followed the pseudo-second-order model.

Lanthanide luminescent gold nanoparticles: pH-driven self-assembly formation between Eu(III)-cyclen conjugated AuNPs and sensitising β-diketonate antenna in water

The formation of a self-assembly between water soluble gold nanoparticles AuNP-1.Eu, functionalised with a heptadentate macrocyclic Eu(III) cyclen conjugate via an alkyl thiol spacer, and a naphthalene β-diketone antenna was investigated as a function of pH in water. In the study, the changes in the absorption spectra of the antenna and the gold surface plasmon resonance band, the fluorescence and the delayed Eu(III) emission of the self-assembly were all monitored. We demonstrate that the Eu(III) emission arising from the self-assembly formation on AuNP is significantly modulated as a function of pH, where within the physiological pH range, the emission is ‘switched on’ and that a direct connection can be made between theses changes and the quenching in the antenna as a function of pH.

Transition-state effects in acid-catalyzed aryl epoxide hydrolyses.

The hydronium ion-catalyzed hydrolyses of 5-methoxyindene 1,2-oxide and of 6-methoxy-1,2,3,4-tetrohydronaphthalene-1,2-epoxide were each found to yield 75-80% of cis diol and only 20-25% of trans diol as hydrolysis products. The relative stabilities of the cis and trans diols in each system were determined by treating either cis or trans diols with perchloric acid in water solutions and following the approach to an equilibrium cis/trans mixture as a function of time. These studies establish that the trans diol in each system is more stable than the corresponding cis diol. Thus, acid-catalyzed hydrolysis of each epoxide, which proceeds via a carbocation intermediate, yields the less stable cis diol as the major product. Transition-state effects, presumably of a hydrogen-bonding nature, selectively stabilize the transition state for attack of water on the intermediate 2-hydroxy-1-indanyl carbocation leading to the less stable cis diol in this system. Transition-state effects must also be responsible for formation of the less stable cis diol as the major product in the acid-catalyzed hydrolysis of 5-methoxy-1,2,3,4-tetrahydronaphthalene 1,2-epoxide. However, in this system steric effects at the transition state may be more important than hydrogen bonding in determining the cis/trans diol product ratio. The synthesis of 5-methoxyindene 1,2-oxide and a study of its rate of reaction as a function of pH in water and dioxane-water solutions are reported. Both an acid-catalyzed reaction leading to only diol products and a pH-independent reaction yielding 71% of 5-methoxy-2-indanone and 29% of diols are observed; the half-life of its pH-independent reaction in water is only 2.4 s.

An improved calibration curve between soil pH measured in waterand CaCl2

A new pH water to pH CaCl2 calibration curve was derived from data pooled from 2 National Land and Water Resources Audit projects. A total of 70465 observations with both pH in water and pH in CaCl2 were available for statistical analysis. An additive model for pH in CaCl2 was fitted from a smooth function of pH in water created by a smoothing spline with 6 degrees of freedom. This model appeared stable outside the range of the data and performed well (R2 = 96.2, s = 0.24). The additive model for conversion of pHw to pHCa is sigmoidal over the range of pH 2.5 to 10.5 and is similar in shape to earlier models. Using this new model, a look-up table for converting pHw to pHCa was created.

Acidichromic effects in 1,2-di- and 1,2,4-tri- hydroxyanthraquinones. A spectrophotometric and fluorimetric study

Absorption and fluorescence spectra of alizarin (1,2-dihydroxyanthraquinone) and purpurin (1,2,4-trihydroxyanthraquinone) were investigated as a function of pH in water–dioxane (2:1, v/v) in the pH range 2–14. Absorbance changes with pH are accompanied by color changes; by increasing the pH, the spectra shift to the red. These molecules exhibit fluorescence emissions over the whole pH range explored; fluorescence quantum yields increase with increasing pH and are greater for purpurin (ΦF = 10−3–10−2) than for alizarin (ΦF = 10−4–10−3). The fluorescence lifetimes were measured by the phase-shift technique for the three species derived from purpurin (neutral, τ = 150 ps; mono-anion, τ = 2600 ps and di-anion, τ = 380 ps), and only for the di-anion of alizarin (τ = 80 ps). Both spectrophotometric and fluorimetric titrations gave pKs of the first and second dissociation steps in the ground state. Excited-state pK*s were calculated by the Förster cycle. In the ground state, purpurin (pK1 = 4.7; pK2 = 9.5) is a stronger acid than alizarin (pK1 = 6.6; pK2 = 12.4) in both the first and second dissociation steps; in the excited state, purpurin is a weaker acid in both dissociation steps. Copyright © 2000 John Wiley & Sons, Ltd.

Kinetic study of the chemical reactivity of ?-acetolactate as a function of pH in water, and in fresh and fermented culture media used for Lactococcus lactis spp. lactis bv. diacetylactis cultivation

Spontaneous oxidative decarboxylation of α-acetolactic acid (ALA) to diacetyl has been assessed under anaerobiosis as a function of pH in water, and in fresh and filtered Lactococcus lactis spp. lactis bv. diacetylactis SD 933 fermented culture media. Whatever the reaction medium, ALA was shown to be potentially reactive, depending on the pH of medium. Diacetyl production mechanism by this strain is discussed on the basis of these kinetic data.