Effect of the carboxylate group distribution on potentiometric titration of acrylamide-acrylic acid copolymers

Improved Soil Amendment by Integrating Metal Complexes and Biodegradable Complexing Agents in Superabsorbents

The superabsorbents' application as materials for the preparation of modern mineral fertilizers of controlled activity is presented. Under the static conditions, the commercial acrylic-based Agro® Hydrogel was used as a sorbent for Cu(II), Fe(III), Mn(II), and Zn(II) ions in the presence of three biodegradable complexing agents of the new generation: (N-1,2-dicarboxyethyl)-D,L-aspartate acid (IDHA), N,N-ethylenediaminedisuccinic acid (EDDS) and N,N-bis(carboxymethyl) glutamic acid (GLDA). The ions and complexes concentrations were determined by the inductively coupled plasma optical emission spectrometer (ICP-OES). The characterization of hydrogel before and after the adsorption process was made using the Fourier transform infrared spectroscopy (FT-IR), surface area determination (ASAP), scanning electron microscopy (SEM-EDS) as well as the thermogravimetric (TGA) methods. The influence of the phase contact time, initial concentration, and pH on the adsorption capacities was investigated. The kinetic and adsorption parameters were determined. The Langmuir, Freundlich, Dubinin-Radushkevich, and Temkin adsorption models were applied to describe the experimental data. The Langmuir isotherm model accurately characterized the equilibrium process. The adsorption process was fast, and it reached equilibrium after 60 min of the phase contact time. The research on the adsorption of Cu(II), Fe(III), Mn(II), and Zn(II) onto Agro® Hydrogel with IDHA, EDDS, and GLDA indicates that these complexing agents improve process efficiency.

Enzymatically and chemically de-esterified lime pectins: characterisation, polyelectrolyte behaviour and calcium binding properties

A series of pectins with different levels and patterns of methyl esterification was produced by treatment of a very highly methylated pectin with acid, alkali, plant pectin methyl esterase and fungus pectin methyl esterase. The intrinsic pK values, as well as the free fractions of monovalent and calcium counterions, were determined on pectin salt-free solutions. The variations of pK(a) versus the ionisation degree were found to depend on the de-esterification process but a unique value of 2.90+/-0.15 was estimated for the intrinsic pK value. Calcium binding properties of chemically and enzymatically de-esterified pectins were investigated and experimental results were compared to Manning's theoretical values. A progressive dimerisation process for pectins with a blockwise distribution of carboxyl groups in the presence of calcium ions is hypothesised.

Polymer Adsorption/Retention in Porous Media: Effects of Core Wettability and Residual Oil

Abstract

Low polymer retention in the reservoir is essential to the success of a polymer EOR operation. It is usually estimated from laboratory core flood experiments conducted under conditions as. close as possible to those prevailing in the field. This work addresses the effects of core meltability and oil saturation on polymer adsorption/retention.

Adsorption of water-soluble polymers onto oil or, more generally, hydrophobic substrates, is characterized from a series of core flood experiments on siliceous and (otherwise similar) alkane-coated substrates. It is found that, for the most common EOR polymers, adsorption increases with surface hydrophobicity, the effect being stronger for neutral synthetic polymers (polyacrylamide) and polysaccharides (scleroglucan and xanthan) than for anionic synthetic polymers (hydrolyzed polyacrylamide).

In a second series of core flood experiments, polyacrylamide adsorption/retention in cores under residual oil saturation is measured and compared to the adsorption/retention in similar oil-free, 100% brine saturated, cores. In oil-wet cores, retention decreases considerably in presence of oil, while it slightly increases in water-wet systems.

These effects may be explained in terms of water/rock and water/oil interfacial area distribution within the pore space, which is governed by wettability. In water-wet cores, droplets of residual oil offer an additional adsorbing surface to the polymer, whereas in oil-wet cores the oil wetting film offers to the polymer a small adsorbing surface compared to the no longer accessible rock surface.

Introduction

Water-soluble polymers provide an efficient way of increasing the viscosity of injection water and therefore its sweep efficiency. However, polymer waterflooding is in many cases uneconomical due to excessive retention in the reservoir. Evaluating polymer retention is needed prior to any field implementation. It is usually inferred from core flood experiments which mimic the EOR process at the laboratory scale. These core flood experiments should indeed be performed under conditions reflecting those prevailing in the reservoir. Among them, core wettability and presence of oil are known to influence polymer retention in a significant, but poorly understood, manner.

Literature survey

Lund and coworkers have very recently measured the retention of a xanthan biopolymer in Brent shaly sandstones. The cores were cleaned with different solvents and had therefore different wettabilities.