Simon Ivar Andersen

Zeolite-catalyzed biomass conversion to fuels and chemicals

Heterogeneous catalysts have been a central element in the efficient conversion of fossil resources to fuels and chemicals, but their role in biomass utilization is more ambiguous. Zeolites constitute a promising class of heterogeneous catalysts and developments in recent years have demonstrated their potential to find broad use in the conversion of biomass. In this perspective we review and discuss the developments that have taken place in the field of biomass conversion using zeolites. Emphasis is put on the conversion of lignocellulosic material to fuels using conventional zeolites as well as conversion of sugars using Lewis acidic zeolites to produce useful chemicals.

Aggregation of asphaltenes as determined by calorimetry

The critical micelle concentrations (CMCs) of petroleum asphaltenes were determined at 25°C in mixtures of n-alkanes and toluene using a calorimetric titration method. CMC was correlated to the Hildebrand solubility parameter. CMC determinations in polar solvents showed that the correlation is valid only for the alkane-toluene system. The role of resins in formation of the micelle was investigated, showing that resins may lead to formation of a different kind of micelle that may be more stable toward precipitation. The resins did not act as cosolvents in the asphaltic solution.

Thermodynamic models for asphaltene solubility and precipitation

A number of different models that have been applied to modeling of asphaltene precipitation and estimating asphaltene solubility in various systems are critically reviewed. Particular attention is paid to the basic assumptions and the performance of the models as compared to the present knowledge of composition and phase equilibrium of asphaltenes. In all models a number of parameters are tuned to obtain best fits to the experimental data. The main parameter was, as proposed in the reviewed works, the molecular weight of the asphaltene and only a few models take the aggregating nature of the asphaltenes into account. Even though the models are based on thermodynamic concepts, they remain empirical because of the number of parameters used in the calculations. When the solubility parameter is employed as the basis for a model, the calculation of asphaltene solubility cannot be calculated or estimated without extensive modification to the model. In summary, the models employed for predictability of asphaltenes precipitation are lacking in several respects and are not quantitatively accurate.

PETROLEUM RESINS: SEPARATION, CHARACTER, AND ROLE IN PETROLEUM

In petroleum science, the term resin generally implies material that has been eluted from various solid adsorbents, whereas the term maltenes (or petrolenes) indicates a mixture of the resins and oils obtained as filtrates from the asphaltene precipitation. Thus, after the asphaltenes are precipitated, adsorbents are added to the n-pentane solutions of the resins and oils, by which process the resins are adsorbed and subsequently recovered by the use of a more polar solvent, and the oils remain in solution. The resin fraction plays an important role in the stability of petroleum and prevents separation of the asphaltene constituents as a separate phase. Indeed, the absence of the resin fraction (produced by a variety of methods) from the maltenes influences the ability of the de-resined maltenes to accommodate the asphaltenes either in solution or as a stable part of a colloidal system. In spite of the fact that the resin fraction is extremely important to the stability of petroleum, there is surprisingly little work reported on the characteristics of the resins. This article summarizes the work that has been carried out in determining the character and properties of the resin constituents. Suggestions are also made regarding current thoughts of the role of these constituents on the structure and stability of petroleum.

Evaluation of activity coefficient models in prediction of alkane solid-liquid equilibria

Abstract In the petroleum industry, the absence of a proper model to describe the liquid phase non-ideality for mixtures of alkanes with large size differences is still one of the main problems in solid-liquid equilibrium calculations. A search is made for a reliable model for the prediction of activity coefficients in these systems. The models investigated were originally developed for the polymer mixtures. The performances of original Flory-Huggins, modified UNIFAC, GCFLORY model, Flory free-volume, Entropic free-volume and some empirical modifications of these last two models are analysed extensively and compared using the deviations between experimental and predicted values of solid appearance temperature as criteria. A comprehensive experimental SLE data base with around 60 binary systems and more than 1000 data points for mixtures of linear, branched and cyclic alkanes is used. An analysis of the errors introduced by the simplifying assumptions more commonly used is also performed. Activity coefficient models that have been used in wax formation predictions, but which are not included in this comparison, are briefly discussed. It is shown that the original Flory-Huggins activity coefficient model, the regular solution theory and the ideal solution behavior, used in several wax formation models, as well as the modified UNIFAC and original Entropic free-volume models, are not appropriate for the description of the liquid phase in alkane systems. The importance of a free-volume contribution to the phase behavior description of liquid mixtures whose components have significant size differences is evident. The Flory free-volume and a modified version of Entropic free-volume seem to be the simplest and most reliable models.

Molecular size of asphaltene fractions obtained from residuum hydrotreatment

Previously, fluorescence depolarization techniques (FD) have been shown to measure asphaltene molecular size, thereby establishing the substantial difference between asphaltenes derived from crude oil vs from coal. Here, FD is used to track the changes of the asphaltenes from a petroleum atmospheric resid feedstock that has been subjected to increasing thermal severity of catalytic hydrothermal cracking. Changes in asphaltene properties with increasing cracking are readily observed and understood. In addition, asphaltene molecular size is measured for various asphaltene solubility fractions in binary solvent mixtures of toluene with either n-heptane or acetone; a strong dependence is found of asphaltene properties on the particular solvent mixtures in accord with recent publications.

Observations on the critical micelle concentration of asphaltenes

Abstract Micelle formation in petroleum fractions is discussed, including reinterpretation of recent surface tension data in terms of the Gibbs excess adsorption equation.

DIBSOLUTION OF SOLID BOBCAN ASPHALTENES IN MIXED SOLVENTS.

ABSTRACT Solid petroleum asphaltenes have been fractionated according to solubility in toluene/n-heptane mixtures of increasing toluene content. A large hysteresis was observed between this dissolution and the precipitation from the crude oil. In order to shed light on the solution mechanism, the fractions obtained have been analyzed using size exclusion chromatography (SEC-HPLC-UV-vis), VPO, elemental analysis, UV-vis adsorption spectroscopy and phenol interaction values and methylene content by FTir. Less polar non-associating low molecular weight species are dissolved and a specific extraction of porphyrins is observed. An increased association in the insolubles is indicated. More basic interaction sites are available on the asphaltenes in both fractions relative to the native asphaltene. From the SEC chromatograms it was seen that the soluble fractions did not associate as the insoluble fractions even when making up more than 60 % of the total asphaltenes.

A local composition model for paraffinic solid solutions

The description of the solid-phase non-ideality remains the main obstacle in modelling the solid-liquid equilibrium of hydrocarbons. A theoretical model, based on the local composition concept, is developed for the orthorhombic phase of n-alkanes and tested against experimental data for binary systems. It is shown that it can adequately predict the experimental phase behaviour of paraffinic mixtures. This work extends the applicability of local composition models to the solid phase.

Prediction of solid–fluid phase diagrams of light gases–heavy paraffin systems up to 200 MPa using an equation of state–GE model

Abstract This paper presents a procedure for the simultaneous prediction of fluid–fluid and solid–fluid equilibria of light gases–heavy hydrocarbons systems under pressure. The fluid phases behaviour is described by the modified LCVM, an equation of state–G E model and the solid phase non-ideality is represented by the Wilson equation using the predictive local composition concept. This procedure was tested for several binary and ternary systems as well as multi-component systems leading to a good representation of both fluid–fluid and solid–fluid equilibria with a typical average absolute deviation of 1.5 K for the solid–fluid phase boundary of binary and ternary mixtures and of 0.5 K for multi-component systems. The AAD% in the fluid–fluid phase boundary of multi-component systems is of 3.2%.