Attempts to Improve the Performance and Biodegradation of Kinetic Hydrate Inhibitors–More Lessons Learned

Kinetic hydrate inhibitors (KHIs) have been used for over 25 years to prevent gas hydrate formation in oil and gas production flow lines but are some of the most expensive oilfield production chemicals. The main component in industrial KHI formulations is one or more water-soluble polymers with many amphiphilic groups. In our quest to develop improved and more environmentally acceptable KHIs for practical use in the oil and gas industry, we have carried out several projects that in our hands, only led to partial success. However, as with most laboratory research projects, useful data have been obtained, and some important lessons have been learned. These lessons can be helpful in several ways. First, to understand the scope and limitations of chemicals that could be used as KHIs, from a performance, environmental, or practical application viewpoint. Second, to highlight mechanistic aspects of KHI theory. Finally, the work may help inspire others to develop related, but more successful, research projects. In this paper, the results of five partially successful KHI research projects are presented and explanations given as to why each of these projects was undertaken, the results obtained, and the lessons learned. Four of the projects concern new classes of polymer, and the remaining project describes what was hoped to be a new class of nonpolymeric synergists for KHI polymers. All new KHI products were investigated for their performance in high pressure multiple steel rocking cells using a synthetic natural gas blend (76 bar) and the slow (1 °C/h) constant cooling test method

Surfactant-Triggered Fluorescence Turn “on/off” Behavior of a Polythiophene-<i>graft</i>-Polyampholyte

Polythiophene-<i>graft</i>-polyampholyte (PTP) is synthesized using <i>N</i>,<i>N</i>-dimethylaminoethyl methacrylate and <i>tert</i>-butyl methacrylate monomers by grafting from polythiophene backbone, followed by hydrolysis. The resulting polymer exhibits aqueous solubility via formation of small-sized miceller aggregates with hydrophobic polythiophene at the center and radiating polyionic side chains (cationic or anionic depending on the pH of the medium) at the outer periphery. The critical micelle concentration of PTP in acidic solution (0.025 mg/mL, pH = 2.7) is determined from fluorescence spectroscopy. PTP exhibits reversible fluorescence on and off response in both acidic and basic medium with the sequential addition of differently charged ionic surfactants, repeatedly. The fluorescence intensity of PTP at pH 2.7 increases with the addition of an anionic surfactant, sodium dodecyl benzenesulfonate (SDBS), due to the self-aggregation forming compound micelles. The fluorescence intensity of these solutions again decreases on addition of a cationic surfactant, cetyltrimethylammonium bromide (CTAB), because of assembling of SDBS with CTAB, thus deassembling the PTP–SDBS aggregates. At pH 9.2, these turn on and turn off responses are also shown by PTP with the sequential addition of cationic surfactant (CTAB) and anionic surfactant (SDBS), respectively. This result shows that PTP has potential for surfactant-induced reversible fluorescence turn on and off using ionic surfactant (SDBS and CTAB) through self-assembling and deassembling of the ionic aggregates. The reversible aggregation and disaggregation process of PTP with the surfactants at both acidic and basic pH is supported from dynamic light scattering and Fourier transform infrared spectroscopy. The morphology of the above systems studied by transmission and scanning electron microscopy also supports the above aggregation and disaggregation process

Influence of Hofmeister I^– on Tuning Optoelectronic Properties of Ampholytic Polythiophene by Varying pH and Conjugating with RNA

A significant tuning of optoelectronic properties of polythiophene (PT) chains due to Hofmeister iodide (I^–) ion is demonstrated in ampholytic polythiophene [polythiophene-<i>g</i>-poly­{(<i>N</i>,<i>N</i>,<i>N</i>-trimethylamino iodide)­ethyl methacrylate-<i>co</i>-methacrylic acid}, APT] at different pHs. In acidic medium, the absorption and emission signals of PT chromophore exhibit appreciable blue shift in the presence of I^– as counteranion only. The cooperative effect of undissociated -COOH and quaternary ammonium groups immobilize I^– near the apolar PT chain causing threading of grafted chains and hence twisting of the backbone attributing to the blue shift. As medium pH is increased, dethreading of the PT backbone occurs due to ionization of -COOH group, releasing quencher iodide ions from the vicinity of the PT chains resulting in a red shift in absorption and a sharp hike in fluorescence intensity (390 times) for an increase of excitons lifetime. With an increase of pH, morphology changes from a multivesicular aggregate with vacuoles to smaller size vesicles and finally to nanofibrillar network structure. Dethreading is also found when APT interacts with RNA showing a significant hike of fluorescence (22 times) for displacing iodide ions forming a nanofibrillar network morphology. Threading and dethreading also affect the resistance, capacitance, and Warburg impedance values of APT. Molecular dynamics simulation of a model APT chain in a water box supports the threading at lower pH where the iodide ions pose nearer to the PT chain than that at higher pH causing dethreading. So the influence of Hofmeister I^– ion is established for tuning the optoelectronic properties of a novel PT based polyampholyte by changing pH or by conjugating with RNA

Folic Acid-Polyaniline Hybrid Hydrogel for Adsorption/Reduction of Chromium(VI) and Selective Adsorption of Anionic Dye from Water

A porous 3D folic acid (F)-polyaniline (PANI) hybrid hydrogel (F-PANI), produced by in situ polymerization of aniline, exhibit highest compressive stress (15.1 kPa), 3D hierarchical network morphology with BET surface area 236 m²/g. Here, PANI is present in emeraldine salt (ES) state, which facilitates excellent adsorption of anionic pollutants. It exhibits an extremely high adsorption capacity for Cr­(VI) and during adsorption Cr­(VI) is reduced to Cr­(III).The electrical impedance spectra of the Cr­(VI) adsorbed xerogel, support the conversion of PANI chains from ES to pernigraniline base­(PB) making the xerogel more resistive. It also selectively adsorbs anionic dyes, the adsorption capacity increases with decrease of pH. Both the adsorption data are found to be well explained through pseudo-second-order kinetic model, and they obey Langmuir adsorption isotherm. F-PANI2 showed high adsorption capacities selectively toward anionic pollutants, for example, Cr­(VI), eosine yellow, rose bengal, methyl orange, and low adsorption capacities for Hg­(II), Pb­(II), rhodamineB, bismark brownY methylene blue, and neutral red. The removal of Cr­(VI) and anionic dyes are very much effective at neutral and acidic pH. After dye/Cr­(VI) adsorption the Nyquist plot indicate significant decrease in the capacitance of xerogels. Cyclic experiments show that, F-PANI xerogels can be effectively reused to remove Cr­(VI) from different contaminated water

Conductive MoS₂ Quantum Dot/Polyaniline Aerogel for Enhanced Electrocatalytic Hydrogen Evolution and Photoresponse Properties

The low conductivity and poor active sites of MoS₂ sheet present a huge barrier for it is exploitation of catalytic applications in the hydrogen evolution reaction (HER). To alleviate this difficulty, we have synthesized MoS₂ quantum dots (QDs) having greater quantity of catalytic edge sites by breaking up the bulk MoS₂ sheet using the solvent exfoliation technique. The synthesized MoS₂ QDs are embedded into polyaniline (PANI)–<i>N</i>,<i>N</i>′-dibenzoyl-l-cystine (DBC) hydrogel matrix by in situ polymerization of aniline where DBC acts as a gelator, dopant, and cross-linker. The hybrid conducting aerogels (DBC-MoS₂-PANI) thus produced act as an efficient electrocatalyst showing lower HER overpotential in comparison to MoS₂ QDs. It exhibits an optimum overpotential value of 196 mV at 10 mA cm^–2, a favorable Tafel slope of 58 mV/dec, and an excellent cyclic stability. Also, DBC-MoS₂-PANI aerogel is used in photoresponding devices. The DBC-MoS₂-PANI hybrid aerogel exhibits a better photoresponse compared to the DBC-PANI aerogel and MoS₂ QDs upon white light illumination of 1 sun. The hybrid aerogel exhibits a maximum enhancement of photocurrent to the value of 3.95 mA at 2 V bias, and the time-dependent photoillumination shows much faster rise and decay of photocurrent compared to those of DBC-PANI aerogel and MoS₂ QDs