Rahoma S. Mohamed

Interfacial and colloidal behavior of asphaltenes obtained from Brazilian crude oils

In this work, we present new data on the interfacial and colloidal behavior of asphaltenes in model aromatic solvents and crude oils and discuss the implications of these data on the aggregation, adsorption on solid surfaces, inhibition of deposition and emulsion stabilization capacities for two types of asphaltenes obtained from Brazilian crude oils. Surface tension measurements in solutions formed by any of these two types of asphaltenes, pentane insolubles (C5I) or heptane insolubles (C7I), in aromatic solvents suggested the occurrence of an aggregation phenomenon of asphaltenes in each of the solvents studied. Viscosity measurements in these same solutions revealed yet another type of aggregation at higher asphaltene concentrations. Both aggregation processes were found to be a function of temperature and type of asphaltenes. For the asphaltenes investigated, C7I was always more prone to aggregation, a characteristic ascribed to its higher asphaltene and lower resin content as revealed by SARA chromatographic analysis, and to its larger average molecular weight as determined by VPO. The effect of temperature on theses two processes confirmed the exothermic nature of both. A number of block copolymers, ionic and non-ionic surfactants, were tested for their effectiveness as asphaltenes stabilizers in crude oil. The results revealed different and distinct mechanisms for solubilization/dispersion of asphaltenes in aromatic (aliphatic) solvents and for the inhibition of asphaltene precipitation in crude oils. The two types of asphaltenes (C5I and C7I) were found to be effective in the stabilization of water/oil emulsions as well as water/toluene emulsions, with larger effects for C7I in water/toluene emulsions, consistent with its greater surface activity and its larger tendency to self-associate. Finally, the interaction of asphaltenes with solid surfaces was evaluated by determining the adsorption isotherms of asphaltenes on silica and activated carbon. The organic adsorbent was found to be much more efficient in removing asphaltenes due, perhaps, to the similar chemical nature of the adsorbing species and adsorbent. In all cases, evidence points to multilayer formation, in agreement with the previously detected tendency of asphaltenes to aggregate.

Induction of pilocarpine formation in jaborandi leaves by salicylic acid and methyljasmonate

Jaborandi seedlings were subjected to different treatments in order to study the induction of pilocarpine in the leaves. In addition four extraction methods were assessed to extract the alkaloid from dried leaves. The highest yielding extraction and recovery was observed when dried leaves were first treated with base and then extracted with chloroform. Salt stress (NaCl), wounding, hypoxia, and N and K omission of the nutrient soln caused reductions in pilocarpine contents. Whereas complete nutrient soln and P omission maintained normal levels of the alkaloid. Salicylic acid and methyljasmonate induced a 4-fold increase of pilocarpine, but this increase was dependent on the concentration and time after exposure.

Extraction of cocoa butter from Brazilian cocoa beans using supercritical CO2 and ethane

This work explores the use of supercritical CO 2 and ethane, both acceptable and non-contaminating solvents for food products, in the recovery of cocoa butter from Theobroma cacao cocoa beans. Continuos extractions were performed using a high pressure apparatus. Extractions were first performed using processed cocoa butter to assess and compare the extraction efficiencies of CO 2 and ethane. These extractions were carried out at 323.2 K, pressures of 15.2 and 24.8 MPa, and CO 2 and ethane flow rates of 1.3 and 0.9 g min -1 , respectively. Extraction yields of cocoa butter using ethane were an order of magnitude higher than obtained with CO 2 . Extractions to explore the capacity of supercritical fluids in the extraction of cocoa butter from cocoa beans were subsequently performed with ethane at 323.2 and 343.2 K, pressures of 15.2, 24.8 and 28.3 MPa and ethane flow rate of 0.9 g min -1 . The results revealed a pronounced effect of pressure on the extraction yield at all temperatures investigated. Extraction curves showed a retrograde behavior for the two temperatures in the whole pressure range. This behavior suggests a range of possibilities for the extraction of cocoa butter from cocoa beans. Cocoa butter fractions with varying fatty acids concentrations were also obtained.

REVERSIBILITY AND INHIBITION OF ASPHALTENE PRECIPITATION IN BRAZILIAN CRUDE OILS

ABSTRACT A fundamental understanding of the aggregation and precipitation of asphaltenes in petroleum crudes is important for the development of preventive and curative measures for the potential problem of asphaltene deposition occurring during production, transport and refining operations. The question of reversibility of asphaltene precipitation, yet a controversial issue, is crucial for a clear and unequivocal understanding of the precipitation phenomenon, development of mathematical models that describe the behavior of asphaltenes in petroleum fluids, and the design of inhibitors. In this work, the behavior of precipitated asphaltenes in Brazilian crude tank oil samples following flocculant removal and gradual addition of fresh oil was investigated. The results obtained revealed a re-dissolution of precipitated asphaltene particles following flocculant removal and oil addition. On the inhibition of asphaltene precipitation, the capacity of a number of surfactants and block copolymers to inhibit aspha...

AGGREGATION OF ASPHALTENES OBTAINED FROM A BRAZILIAN CRUDE OIL IN AROMATIC SOLVENTS

Abstract Surface and interfacial tensions in model systems formed by a Brazilian crude oil n-pentane insolubles (C5I) and n-heptane insolubles (C7I) in three different aromatic solvents: toluene, pyridine and nitrobenzene, were measured at room temperature, employing an automatic tensiometer and using the ring method. The results obtained indicated possible asphaltene aggregation and allowed the determination of critical micelle concentrations (c.m.c) for both C5I and C7I fractions in each of the three solvents considered. In toluene and pyridine solutions, the C5I fraction consistently presented higher c.m.c. values indicating a lower tendency of association for the organic fraction contained in the C5I, and absent in the C7I. In nitrobenzene solutions, this extra organic fraction appears to facilitate asphaltene association, possibly due to the formation of mixed aggregates. Average molecular areas for asphaltenes adsorbed at different interfaces were estimated using measured tensions and found to be in...

An equation of state for property prediction of alcohol–hydrocarbon and water–hydrocarbon systems

Abstract Equations of state have been widely used in the petroleum and chemical industries for thermodynamic property calculation. In the presence of polar substances that self-associate through hydrogen bonding (such as water or alcohol), equations of state are of very limited use. One way to account for the association is to consider the equation of state to be formed of two contributions: physical and chemical. In this work, we develop an equation of state consisting of two terms as proposed by Andreko [Fluid Phase Equilib. 65 (1991) 89], a chemical and a physical term, for correlation of thermodynamic properties of mixtures containing an associating species. This equation of state is used to correlate vapor pressure data for a number of associating molecules, such as alcohol and water, as well as bubble point pressure data for binary water–hydrocarbon and alcohol–hydrocarbon systems. The results obtained are in good agreement with the experimental data and requiring the use of only one adjustable parameter for each binary system.

Supercritical CO2 recovery of caffeine from green coffee oil: new experimental solubility data and modeling

The caffeine solubility in supercritical CO2 was studied by assessing the effects of pressure and temperature on the extraction of green coffee oil (GCO). The Peng-Robinson1 equation of state was used to correlate the solubility of caffeine with a thermodynamic model and two mixing rules were evaluated: the classical mixing rule of van der Waals with two adjustable parameters (PR-VDW) and a density dependent one, proposed by Mohamed and Holder2 with two (PR-MH, two parameters adjusted to the attractive term) and three (PR-MH3 two parameters adjusted to the attractive and one to the repulsive term) adjustable parameters. The best results were obtained with the mixing rule of Mohamed and Holder2 with three parameters.

EXTRAÇÃO E FRACIONAMENTO DE PRODUTOS DE OCORRÊNCIA NATURAL COM FLUIDOS SUPERCRITICOS

The use of supercritical fluids in the extraction of natural products reveals to be a potential future technology with a number of advantages when compared to common liquid solvents. Many extraction processes involving natural products include applications that range from those already developed on a commercial scale such as coffee decaffienation to those being studied on a laboratory scale such as the extraction of alkaloids and the encapsulation of chemotherapeutic agents with the recrystallization from near critical mixtures and /or by the utilization of supercritical fluids as anti-solvents. With the objective of obtaining fundamental information from experiment and theory that can contribute to the scientific development of this promising new and potential technology which explores the distinct properties of supercritical fluids in Brazil, the Laboratory of Process Engineering of the Department of Thermo Fluid Dynamics at the Faculty of Chemical Engineering at the State University of Campinas (UNICAMP), have dedicated a good part of its research activities to the study of the extraction of active principles from plant material using supercritical fluids. In this work, we present a brief exposition of the activities being carried out and some of the results obtained to date.

EXTRAÇÃO DOS ALCALÓIDES: CAFEÍNA E TRIGONELINA DOS GRÃOS DE CAFÉ COM C SUPERCRÍTICO

Caffeine, aby-product of coffee decaffeination by-product, acts as a stimulant and diuretic in the human organism. Most of the caffeine is used in the cola soft drink and pharmaceutical industries. Supercritical CO2 has long been used to decaffeinate coffee beans. However, little is known about the extraction of other alkaloids such as trigonelline. This alkaloid and the products generated by its thermal degradation (nicotinic acid - the vitamin niacin) have received a lot of attention because of their nutritional importance. Trigonelline acts mainly on the nervous central system, the secretion bile and the intestine. The main objective of this work was to obtain experimental data on the extraction of the alkaloids caffeine and trigonelline from canephora (Robusta) coffee beans using supercritical CO2. The decaffeination of this coffee can be economically attractive to obtain caffeine and to upgrade the value of this variety of coffee. New data on the continuouos fractionation of Brazilian Robusta coffee beans using supercritical CO2 at 313, 323 and 343 K and pressures ranging from 9,5 to 23,5 MPa for the extraction and separation of caffeine and trigonelline are presented. Caffeine and trigonelline in the extracted mixture were analyzed using HPLC. A thermodynamic model that uses a quartic equation of state was successfully employed to correlate the solubility behavior of pure caffeine in supercritical CO2.

An introduction to petroleum production research in Brazil

Brazil is made up of diverse population and a vast land. The Natives who were the original inhabitants of Brazil included the Carib and Arawak groups in the north, the Gas in eastern and southern Brazil, the Tupı́Guaranı́s in the East Coast of Brazil and in the Amazon River valley, and the Panos in the west. For the most part these groups of natives were essentially seminomadic, who subsisted by hunting and gathering and simple agriculture. Those groups in the more remote areas of the interior of Brazil maintained their traditional ways of life until the late 20th century, when their existence was threatened by the advancing frontier. The Spanish navigator Vicente Yáñez Pinzón is the first known European who visited the region now constituting Brazil. He landed near the site of present-day Recife on January 26, 1500. He subsequently drifted northward as far as the mouth of the Orinoco River. In April 1500, Pedro Alvarez Cabral, a Portuguese navigator, arrived in what today is known as the state of Bahia. He officially dedicated the land to god and the king of Portugal. Brazilians consider him the discoverer of Brazil. In 1530 the Portuguese King John III initiated a program of systematic colonization of Brazil. In 1555, the French founded a colony on the shores of what they