Marta Szymula

Adsorption of asphaltenes from toluene on mineral surface

Abstract Undesirable adsorption of asphaltenes on rock minerals was studied. Asphaltenes are an important component of crude oil, being also natural surfactant stabilising water/crude oil emulsions. Owing to their chemical nature, asphaltenes are able to associate, form micelles and create a surface charge at the interface. Asphaltenes may be adsorbed on rock reservoir from the organic solvents in crude oil and as an organic colloid, they can adsorb electrolyte ions from aqueous solution. In order to simulate natural conditions we used asphaltenes from local drills, toluene as solvent and several typical oxides and carbonate rock components or minerals as adsorbents. Our study included natural Brazilian quartz, dolomite, calcite and kaolin, as well as pure oxides: Fe 2 O 3 and TiO 2 . The typical shape of asphaltene adsorption isotherms was obtained for all systems studied with the characteristic ‘steps’ which indicate changes in the state of asphaltene molecules in the solution and at the mineral surface. Those changes are related to the asphaltene association and further formation of hemimicelles and micelles.

Adsorption of asphaltenes from toluene on typical soils of Lublin region

Adsorption of asphaltenes on soils is one of the important problems, though largely underestimated, in environment protection of Lublin region. Asphaltene adsorption properties affect the way the contamination spreads in soil. Analysis of this phenomenon may help in localisation and elimination of oil spills. The asphaltenes studied were obtained from local drills (Swidnik near Lublin, Poland). In our previous paper, we investigated adsorption of asphaltenes from toluene on rock components (quartz, dolomite, calcite, kaolin as well as pure iron and titanium oxides). In order to simulate the natural oil spill conditions, we used toluene as solvent and typical soils from Lublin region as adsorbents (black earth, peat soil, lessive soil, brown soil, sandy podsolised soil, pararendzina soil). Main physicochemical properties of these soils were reported. Moreover, basic adsorption properties (nitrogen adsorption, adsorption of surfactants from water solutions, acidity, etc.) of several soil fraction were studied. We decided to use only certain mineral fractions with highest adsorption capacity, as other fractions have limited impact on total adsorption. Adsorption on soil fraction gives also some insight into relative importance of various soil components on summary soil properties. The results of adsorption measurements are described in terms of physical adsorption on heterogeneous solids. # 2002 Published by Elsevier Science B.V.

A Comparison of Atmospheric and Electrochemical Oxidation of Vitamin C in SDS Systems

ABSTRACT Ascorbic acid (AA, H2A) can be solubilized up to 60% by weight into a microemulsion formed by water, pentanol, and sodium dodecylsulfate (SDS). Addition of AA to the aqueous solution caused systematic reduction of the microemulsion region in the phase diagrams of the system. Ascorbic anion interacts with dodecylsulfate association structures changing W/O microemulsions towards O/W systems. The polar part of AA is exposed to the aqueous solution and subject to oxidation. The results of kinetic determination of AA decomposition are in accordance with a suggested model. They show enhanced oxidation of AA with increasing pentanol concentration in the system. The system aqueous AA solution/SDS, of concentration in excess of critical micellization concentration (cmc), was found to be more resistant to oxidation in air than aqueous AA solution. This was confirmed by electrochemistry studies of the anodic oxidation of AA on glassy carbon electrode. Sodium dodecylsulfate shifted the AA oxidation potential E pa to more positive values and decreased the peak current I pa . Antioxidation activity of AA was diminished in the presence of SDS micelles.

Atmospheric Oxidation of β‐Carotene in Aqueous, Pentanol, SDS Microemulsion Systems in the Presence and Absence of Vitamin C

Abstract The atmospheric oxidation of β‐carotene in an anionic surfactant system [aqueous sodium dodecyl sulphate (SDS)] as well as the role that the ascorbic acid plays towards β‐carotene action was studied. β‐Carotene can be solubilized into microemulsions formed by water, pentanol, and SDS. As a symmetrical, nonpolar hydrocarbon it is located in hydrophobic regions of micelles. It is more stable in W/O microemulsions than in the O/W type or in bicontinuous systems. The hydrophobic barrier of SDS association structures in W/O microemulsion can hinder electron transfer from β‐carotene molecules and thereby makes theirs oxidation difficult. Vitamin C addition into the system does not considerably change the antioxidant properties of β‐carotene, which is still a better antioxidant in O/W microemulsion. The presence of β‐carotene influences vitamin C antioxidant action. Vitamin C is more easily oxidized when the concentration of pentanol decreases in the system (in O/W microemulsion). In our earlier studies, when only vitamin C was present in microemulsion, we had observed a totally different behavior of the system, i.e., an oxidation enhancement with increasing pentanol concentration occurred. It can be concluded that in anionic surfactant systems an antioxidant synergism of β‐carotene and vitamin C exists.

Use of a Dynamic Light Scattering Technique for SDS/Water/Pentanol Studies

The interpretation of micelle/aggregate size obtained by use of the DLS technique for SDS/water/pentanol systems was discussed by comparison of the results of measurement with theoretical data. For most of the studied systems, the apparent radii (R h,app ) did not satisfactorily characterize the size of the aggregates (R h,app < 1 nm). The use of a correction factor (f = 0.26) confirmed that the discrepancies were associated with the electrostatic intermicellar interactions. However, the fuzzy optical interface between dispersed and dispersing phases can also be the reason of such results. An increase of pentanol content caused a decrease of the droplet radius in w/o systems but in o/w systems the changes were negligible.

ELECTROCHEMICAL PROPERTIES OF ASPHALTENE PARTICLES IN AQUEOUS SOLUTIONS

Abstract The electrical properties of colloidal asphaltene/water solution interface were determined by carrying out the potentiometric titration and electrokinetic measurements. Asphaltenes in aqueous solutions exhibit typical organic colloid properties i.e. surface charge and electrophoretic mobility. It was considered that the surface charge at the asphaltene particles is a result of protonation and dissociation reactions of surface functional groups. On the base of the surface charge density data vs. pH the surface reaction constants were calculated by numerical method. The agreement of these values with calculated ones, on the base of ζ potential data, is noticeable. The characteristic feature of the investigated systems is the maximum, appearing on the curve ζ potential vs. electrolyte concentration. This behaviour is explained by ”hair layer ” structure of the asphaltene surface

ATMOSPHERIC OXIDATION OF VITAMIN C AND E IN THE SURFACTANT SYSTEM

Abstract The association of ascorbic acid (H2A, AA) with α-tocopherol (α-T) enhances the antioxidant capability of the two vitamins in a microemulsion formed by water, pentanol and sodium dodecyl sulphate. The comparison of vitamin C oxidation kinetics in the presence and absence of α-T in the system shows that there are no tangible differences in the time of the ascorbic acid decomposition. The main effect is the enhancement of the H2A oxidation with increased pentanol concentration in the system. Ascorbic anion interacts with surfactant association structures, changing W/O microemulsion towards O/W system. The polar part of H2A is exposed to aqueous solution and subjected to oxidation. For the vitamin C to vitamin E weight ratio equal 0.13, ascorbic acid stimulates α-T decomposition as long, as it does in the non-oxidised form. When not all amounts of both vitamins are decomposed their activity is similar to each other in the anionic surfactant system. It means they are both good antioxidants in W/O microemulsions. After some time, when vitamin C is completely decomposed, all these micellar systems become more stable with regard to vitamin E. Vitamin E occurs to be a better antioxidant in O/W microemulsion.

Effect of xanthate chain length on decrease of xanthate concentration in solutions in contact with copper sulphides

The mechanism of long-chain xanthate sorption on djurleite and chalcopyrite surface was investigated. The crystal structure of metal sulphides, the geometry of the xanthate groups and the xanthatemetal sulphides interaction were taken into account. A spectacular increase in sorption rate of higher xanthates on the mineral surface was observed.

Flotation of synthetic zinc carbonate using potassium ethylxanthate — Reply

Abstract An attempt at flotation of fine grains of zinc carbonate using potassium ethylxanthate as the collector and sulphydryl and copper ions as the activators has been undertaken. Results of the flotation tests have been interpreted in terms of the adsorption of activating agents as well as the grain size effect.

Co‐Adsorption of CTAB and Propyl Gallate on the Hydrophilic Silica Surface

Propyl gallate (PG) adsolubilization in the cationic surfactant micelles formed in the bulk solution and at the silica/solution interface has been investigated. It was found that in the absence of surfactant, propyl gallate does not adsorb on the silica surface from aqueous solution. However, in the presence of hexyltrimethylammonium bromide (CTAB), its uptake by silica strongly increases. The amount of PG in the surface layer depends on its concentration in the bulk solution and the amount of CTAB in the adsorbed layer.