Dr. Ing.

CHARACTERIZATION OF CRUDE OILS AND HEAVIES

Kaushik Gandhi Department of Chemical and Fuels Engineering, University of Utah

Outline
• Introduction • Characterization tools • Applications of Characterization of Crude Oil and its components • Results from characterization methods

Introduction
• Characterization of crude oil and heavies is necessary to be able to understand and predicttheir behavior. • During production, transportation and processing various problems such as solids deposition, clogging and coking occur due to presence of heavy components in oil. • Characterization can be based on single carbon number or on compound class.

Introduction, contd.
• A compound class characterization common in industry is SARA (Saturate, Aromatic, Resin and Asphaltene)characterization. • Asphaltene- highly polar high molecular weight solids, the fraction of oil insoluble in lowmolecular weight aliphatic hydrocarbons. Highly condensed aromatic ring system with high N, S, O and metal content. • Soluble part of oil is termed as maltenes. Consists of Saturate, Aromatic and Resin fractions separated by column chromatography.

Introduction, contd.
• Saturates- Consists ofsaturated hydrocarbons with straight or branched chains without ring structure (paraffins) or with one or more rings attached (cycloparaffins). Contain little or no N, S, O and metals. • Aromatics- Hydrocarbons containing one or more aromatic ring. • Resins- Also known as polars. Second heaviest fraction in crude oils.

Introduction, contd.
• Characterization of the individual SARA fractionscan help in providing a map of the crude oil and its behavior. • Crude oils from different sources will have different SARA distributions and different properties. • High asphaltene content in crude oils has been linked to deposition problems during production and coke formation during processing. Highly paraffin oils are prone to wax formation and deposition.

Introduction, contd.
• Detailedcharacterization of the heavier components like asphaltenes and resins from crude oils and resids can help in providing better models for prediction of properties.

Characterization Tools
• SARA characterization methods employ adsorption chromatography for fractionation step. • In column chromatography the adsorbent is contained in a tube, the sample is introduced at one end of the adsorbentbed and induced to flow throw the bed by means of a suitable solvent. • As the sample moves through the bed the various components are held (adsorbed) to a greater or lesser extent depending on the chemical nature of the component. • Choice of a suitable adsorbent and solvents is thus important .

Characterization Tools, contd.
• SARA methods differ in the type of adsorbent and solvent elutionscheme used. • In most methods asphaltenes are first isolated as a separate fraction. This is because their highly polar nature would cause them to be irreversibly adsorbed on the adsorbent. • Preparative (prep.) scale SARA separation methods have been developed so that the fractions obtained can be further characterized using different techniques.

Characterization Tools, contd.
• Twodifferent methodologies have been developed for this separation – Prep. Scale Low Pressure Liquid Column chromatography (Wet chemistry method) – Prep. Scale High Pressure Liquid Column Chromatography (HPLC) • The asphaltenes were first isolated from the samples and chromatographic separation of the deasphalted oil (Maltenes) followed. Sample may need to be distilled or topped to remove volatile fraction.Characterization Tools, contd.
• n-heptane is used as the solvent for precipitation of the asphaltenes from the crude oil or resid sample. A 40:1 ratio of n-heptane to sample is used. It is important to remember that asphaltenes are a solubility class. Initial sample weight of up to 35 grams. • Precipitated asphaltenes are separated by vacuum filtration, dried in an oven and weighed. •...