In Situ Visualization of the Phase Behavior of Oil Samples Under Refinery Process Conditions

Summary

This article describes a setup and method for the in situ visualization of oil samples under a variety of temperature and pressure conditions that aim to emulate refining and upgrading processes. It is primarily used for studying isotropic and anisotropic media involved in the fouling behavior of petroleum feeds.

Abstract

To help address production issues in refineries caused by the fouling of process units and lines, we have developed a setup as well as a method to visualize the behavior of petroleum samples under process conditions. The experimental setup relies on a custom-built micro-reactor fitted with a sapphire window at the bottom, which is placed over the objective of an inverted microscope equipped with a cross-polarizer module. Using reflection microscopy enables the visualization of opaque samples, such as petroleum vacuum residues, or asphaltenes. The combination of the sapphire window from the micro-reactor with the cross-polarizer module of the microscope on the light path allows high-contrast imaging of isotropic and anisotropic media. While observations are carried out, the micro-reactor can be heated to the temperature range of cracking reactions (up to 450 °C), can be subjected to H₂ pressure relevant to hydroconversion reactions (up to 16 MPa), and can stir the sample by magnetic coupling.

Observations are typically carried out by taking snapshots of the sample under cross-polarized light at regular time intervals. Image analyses may not only provide information on the temperature, pressure, and reactive conditions yielding phase separation, but may also give an estimate of the evolution of the chemical (absorption/reflection spectra) and physical (refractive index) properties of the sample before the onset of phase separation.

Introduction

The study of the phase behavior of oil samples in a wide range of temperatures, pressures, and reactive conditions can yield very useful information for the operator of a refinery that processes a variety of feeds. In particular, the fouling of process units and lines by an uncontrolled formation of coke or sediments can severely affect production (loss of throughput) and energy efficiency (increase in heat transfer resistance)^1,2,3. Possible plugging caused by the accumulation of fouling material may require a shutdown for clean-up purposes, which would have a highly negativ....

Protocol

Caution: Use all appropriate safety practices when performing an experiment under high temperature and pressure conditions, including the use of engineering controls (H₂ flow limiter, pressure regulators, and rupture disc assembly) and personal protective equipment (safety glasses, temperature-resistant gloves, lab coat, full-length pants, and closed-toe shoes). Consult all relevant material safety data sheets (MSDS) before use. Carry out micro-reactor loading and clean-up in a fume hood, as these steps involve the use of harmful volatile organic solvents (toluene and dichloromethane).

NOTE: Setup description (see supplemental fi....

Results

The visual evolution of Athabasca Vacuum Residue is representative of the behavior of asphaltenic heavy crude oil samples and asphaltenic vacuum residue samples under thermal cracking conditions. However, using different samples and/or different temperature, pressure, or reaction conditions can give rise to a wide variety of phase behaviors. Micrographs corresponding to the thermal cracking experiment on an Athabasca Vacuum Residue sample at final set-point conditions of 435 °C and P_.......

Discussion

Critical Steps within the Protocol

The first critical step in the protocol is ensuring the integrity of the metal-to-sapphire seal, especially if the experiment is to be carried out under pressure. Thus, the parallelism, the smoothness, and the cleanliness of the sealing surfaces should be carefully inspected, and the leak tests should be thorough. Since the modulus of rupture of sapphire is a decreasing function of temperature¹⁴, thicker sapphire windows should be used fo.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Sapphire window, C-plane, 3 mm thick - 20 mm diam., Scratch/Dig: 80/50	Guild Optical Associates
C-seal	American Seal & Engineering	31005
Type-K thermocouple	Omega	KMQXL-062U-9
Ferrule (1/16")	Swagelok	SS-103-1	Inserted for creating a clearance gap between the magnet and the window surface
Coil Heater	OEM Heaters	K002441
Temperature controller	Omron	E5CK
Inverted microscope	Zeiss	Axio Observer.D1m	Require cross-polarizer module
Toluene, 99.9% HPLC Grade	Fisher	Catalog # T290-4	Harmful, to be handled in fume hood
Methylene chloride, 99.9% HPLC Grade	Fisher	Catalog # D143-4	Harmful, to be handled in fume hood
Acetone, 99.7 Certified ACS Grade	Fisher	Catalog # A18P-4