Investigation
of the Chemical Composition of the Organic
Material Associated with Inorganic Solids Found in Heat Exchanger
Deposits: Possible Fouling Precursor in Refinery Operation
posted on 2023-09-19, 13:13authored byMatthew Hurt, Cesar Ovalles, Dave Murray, Parviz Rahimi
In the oil sand literature, the deposits containing organics
associated
with solids and insoluble in toluene are often referred to as toluene-insoluble
organic material (TIOM). In this work, we call these materials toluene
insolubles (TI) and clarify what TIOM means. Our focus in this work
is to determine the chemical composition of the organic portion of
the TI obtained from the extraction of fouling deposits collected
from a heat exchanger unit of a refinery. Analysis of TI using thermogravimetric
analysis (TGA), optical microscopy, inductive coupling plasma (ICP),
and X-ray diffraction (XRD) showed that these materials are composed
of both organic and inorganic solids/clay minerals. Using an accelerated
solvent extraction (ASE) unit, the TI fraction was sequentially solvent-extracted
using methylene chloride/methanol (9:1, at 110 °C/1000 psi) and
acetonitrile CH3CN (ACN, at 130 °C/1000 psi). The
extracted fractions were then analyzed by using high-resolution mass
spectrometry (HRMS) and Fourier transform infrared (FTIR). The results
showed that the extracted materials were mainly organic polymers consisting
of a variety of polyethers used as chemical additives in the oil industry.
The analysis by atmospheric pressure photoionization (APPI) in positive
ion mode and electrospray ionization (ESI) in positive and negative
ion modes revealed that besides the predominant polyether polymer
in the form of ethylene oxide (EO) and propylene oxide (PO), there
are also condensed aromatics, pyridine, alkylpyridines, sulfonates,
low-carbon low-double bond equivalent (DBE) species with one heteroatom,
and acidic species. A subsequent analysis of the blank solvent obtained
from the ASE unit by HRMS showed that no polyether polymers were present,
indicating that these polymers are part of the foulant deposits. To
obtain more structural information on the organic fraction, the TI
sample was subjected to pyrolysis gas chromatography–mass spectrometry
(GC-MS) between 300 and 600 °C. Compositional analysis revealed
that the volatile organic fraction of the TI is composed mostly of
polar components with oxygen and nitrogen functionality, including
phenols, indoles, alkylpyrroles, aldehydes, and carboxylic acids.
These products are most likely from the decomposition of polyethers
as well as nonylphenols used as chemical additives. The presence of
intact nonylphenol indicates the desorption of polar molecules from
the surface of clays/minerals during pyrolysis. The results of this
work have demonstrated that fouling deposits of a heat exchanger formed
by organic molecules associated with inorganic solids are not only
derived from the original oil but also derived from chemical additives
that are used during oil production/processing.