3 research outputs found
Determination of Naphthenic Acid Number in Petroleum Crude Oils and Their Fractions by Mid-Fourier Transform Infrared Spectroscopy
Naphthenic acid is a generic name
used for all the organic acids
present in crude oils. The quantitative determination of naphthenic
acid number (NAN) is an essential parameter for petroleum refineries
to evaluate corrosive properties of crude oils prior to their processing.
Currently, most of the refineries are using total acid number (TAN)
as a measure of corrosivity of crudes during their selection, valuation,
and processing. Some of the organic molecules are being used as corrosion
inhibitors to reduce corrosion in refinery process units, and the
dosage of the same depends on the total acid number as it has been
understood from the studies that acid inhibitors form a protective
layer on the surface of the pipes and thus reduces the corrosion due
to acids present in crude oil. TAN measurement by titration overestimates
the acid number as each and every molecule like thiols and phenols
etc. that are titratable by alkali are also included in the calculation
and that causes the improper estimation of the addition of corrosion
inhibitors. To get a better refinery margin in the present economic
scenario, optimization of the addition of corrosion inhibitors is
very much essential and thus accurate measurement of NAN is a primary
concern. Hence, we present a quick and efficient mid-Fourier transform
infrared (FTIR) spectroscopic method for the determination of NAN
using a variable path length liquid cell with calcium fluoride windows.
Two distinct photon absorption bands in the region of 1680 to 1800
cm<sup>–1</sup> were observed during the spectral measurement
and are due to the formation of monomeric and dimeric forms of carbonyl
(Cî—»O) group of carboxylic acids, and hence both are considered
for the quantification. The method is applicable even to highly volatile
crude oils that are not measurable by the normal attenuated total
reflectance (ATR)-FTIR technique. This article also presents the effect
of solvents, hydrogen bonding, formation of monomer and dimer, etc.
Currently, this method is being applied for the determination of NAN
for crude oils and straight run vacuum gas oil (VGO) samples as they
contain either negligible or no carbonyl compounds other than carboxylic
acids that interfere in the region of interest
Simultaneous Determination of Boiling Range Distribution of Hydrocarbon, Sulfur, and Nitrogen in Petroleum Crude Oil by Gas Chromatography with Flame Ionization and Chemiluminescence Detections
We present a quick
and efficient gas chromatographic method to
simultaneously determine the boiling range distribution of hydrocarbon
(C), sulfur (S), and nitrogen (N) in crude oils by a high temperature–CNS
simulated distillation (HT-CNS SimDis) analyzer. The analyzer is a
gas chromatograph equipped with flame ionization (FID) and sulfur
and nitrogen chemiluminescence (SCD and NCD) detectors with simulated
distillation features. The hydrocarbon yield profile of crude oil
obtained by FID response was applied to calculate S and N content
in various isolated fractions such as naphtha, kerosene, diesel, and
vacuum gas oil. This method was used to analyze 10 different crude
oils of variable composition. A fraction of crude oil that boils above
the atmospheric equivalent temperature (AET) of 700 °C does not
elute fully and forms a coke inside the chromatographic column. As
a result, it is not possible to quantify total sulfur and total nitrogen
content in the high-boiling vacuum residue (VR) fraction (565 °C
and above) of crude oil by this method. However, we have addressed
this issue by calculating sulfur in the VR fraction as a difference
between total sulfur in crude oil (using X-ray fluorescence or combustion
methods) and sulfur in the rest of the fractions (using HT-CNS SimDis).
A similar technique was employed to determine nitrogen in the VR fraction
of crude oil. The <i>gas oil reference standard</i> with
known boiling range distribution was used to check the system suitability
and generate the response factor for the calculation of hydrocarbon
yield, and <i>VGO NS Reference</i> (internal nitrogen/sulfur
QC standard) was used as a calibration standard for sulfur and nitrogen
quantification. Currently, there is no single method available for
the simultaneous determination of C, S, and N present in crude oil.
This method produces detailed temperature distribution of S and N
in a crude oil sample that cannot be obtained by either total sulfur
and total nitrogen analysis or analysis of sulfur and nitrogen in
discrete distillation cuts. As a result, this technique is extremely
valuable to the refining industry for the valuation of crude oil,
plant troubleshooting, and optimization of refinery processes
Property Prediction of Diesel Fuel Based on the Composition Analysis Data by two-Dimensional Gas Chromatography
The
objective of the present study is to develop robust statistical
models for the prediction of critical diesel properties such as cloud
point, pour point, and cetane index with composition inputs such as <i>n</i>-Paraffins, Iso-paraffins, Naphthenes, and Aromatics (PINA)
obtained by flow modulated two-dimensional gas chromatography with
flame ionization detection (GC×GC-FID). A single gas chromatographic
measurement coupled with models to predict the key physical properties
is attractive for refiners to make quick decisions in optimizing diesel
blending. We present a partial least-squares (PLS) linear regression
statistical model that has been developed using 41 data sets of diesel
samples with different compositions, out of which 33 samples were
used for the calibration and eight samples for validation of the model.
The <i>R</i><sup>2</sup> values obtained for cloud point,
pour point, and cetane index were 0.92, 0.93, and 0.92 with standard
deviations of 1.20, 1.50, and 0.40, respectively. The average relative
errors for predicted values of cloud point, pour point, and cetane
index are found to be 0.86, 1.02, and 0.25, respectively. The PINA
analyses of diesel and kerosene samples were carried out using flow
modulated GC×GC with flame ionization detection (FID). The technique
adapts reverse phase gas chromatography with two capillary chromatographic
columns; the columns differ in length, diameter, stationary phase,
and film thickness to get maximum peak resolution. The gravimetric
blends of high purity reference standards of paraffins, naphthenes,
and aromatic compounds (PINA) with variable carbon numbers were used
for identification and to draw the boundaries for group types. Monoaromatic
and polyaromatic content obtained for diesel and kerosene samples
by the flow modulated GC×GC method were comparable to the results
obtained by the High Performance Liquid Chromatographic (HPLC) method
as per IP 391 or ASTM D 6591. Repeatability and reproducibility of
the GC×GC analysis were performed for several samples to validate
the method. It has been found that the HPLC method for the determination
of aromatics content using a single calibration standard for each
type, such as mono-, di-, and polyaromatics, causes a small error
in the quantification in some of the samples as the refractive indices
of all the aromatic species present in the diesel and kerosene samples
vary depending on the addition of alkyl side chains; the presence
of heteroatoms such as sulfur, nitrogen, and oxygen; etc