|Title of Invention||
A FLUORIMETRIC DEVICE FOR IN ESTIMATION OF ADULTERANTS IN LIQUID PETROLEUM PRODUCTS
|Abstract||A fluorometric device for in situ estimation of adulterants in liquid petroleum products. This device comprises of a lamp and a first monochromator connected to the pc and to a sensor head through a first optical fibre. A second monochromator is also connected to the pc and to sensor head through a second optical fibre. A detector is connected to the second monochromator and to the pc. The sensor head is in contact with the sample petroleum product. The first and second optical fibres convey the excitation to and receive the emission from the sensor head respectively. The pc collects the detector signal intensity as a function of wavelength reading in the first monochromator. The intensities at appropriate wavelengths are used for estimation of adulterants.|
|Full Text||This invention relates to a fluorometric device for in situ estimation of adulterants in liquid petroleum products.
Adulteration of petrol and diesel is widely prevalent in countries of South Asia. Laboratory procedures of testing are time consuming, costly and often complicated. The common physical properties and spectroscopic techniques based methods suffer certain limitations in terms of accuracy and sensitivity in determining the adulteration level. Therefore, development of a simple and a more useful device to check adulteration is important.
Conventional methods for detection and estimation of adulteration in diesel and petrol include filter test, ASTM distillation, checking properties like density, flash point and viscosity, microprocessor based electronic method using principle of cooling on evaporation, odor based method, ultrasonic techniques, titration techniques, optical technique, furfural test and refractive index. Many of these techniques are elaborate and often not very accurate.
When fluorescence intensity is plotted against both excitation and emission wavelengths, the resultant three dimensional plot is called a total fluorescence spectrum. In principle such a spectrum contains in it all possible information obtainable from of steady state fluorimetry. The technique of synchronous fluorimetry makes it possible to travel along a diagonal of this 3-dimensional plot. In synchronous fluorescence spectroscopy both excitation wavelength and emission wavelength are synchronously scanned and the fluorescence intensity is recorded against the scan range. Under such condition the shape of intensity distribution ceases to have any relationship
with conventional spectrum. This distribution is a unique function of the scan parameters used for obtaining them.
Both diesel and petrol samples from various sources were subjected to fluorimetric analysis using synchronous and total fluorescence techniques. Conditions for which the scan parameters were optimized included concentration of sample, the wavelength ranges, the slit widths, the power level of detector, the sample geometry, scan speed and the nature and power of the lamp. A standard set of optimized conditions was arrived at for petrol and diesel this way. Working with petrol and diesel samples obtained from various sources over 2 Vz year"s period, it was observed that the optimized scan parameters remain invariant to the source of samples.
Adulterants commonly used are various industrial solvents and kerosene from free market and public distribution system. A variety of adulterants commonly available in the market: kerosene from free market & public distribution system, industrial solvents like turpentine oil, petroleum ether, hexane and cyclohexane, were used for the adulterant study. Known amounts of an adulterant were added both to petrol and diesel and the corresponding changes in the fluorescence intensity profiles were observed. Changes in three associated measurement parameters: Maxima and intensity for synchronous fluorescence and intensity of the total fluorescence spectrum were monitored as a function of the adulterant proportion in the sample. The previously adjusted scan parameters were reoptimized for maximum sensitivity of response of measurement-parameters. The procedure was tested on a wide variety of non-aromatic and aromatic hydrocarbons, their
derivatives and various forms of kerosene available in the market. The results were found to be good, with recovery within ± 10 % of the actual value.
The following forms the basis of the said device:
Petroleum products (petrol, diesel etc) contain a variety of polycyclic aromatic compounds, which are fluorescent. Fluorescence is a process in which light of a particular wavelength incident on a sample causes emission of light from the sample at wavelengths longer than the incident wavelength. For petroleum products which are multifluorophoric systems with unknown fluorophores at high concentration, conventional fluorometric techniques are not useful due to a variety of reasons like inner filter effect, fluorescence resonance energy transfer, self quenching etc. We have found that the position and width of the electronic spectral window where the absorbance of the sample reaches a cut-off limit, can be profitably used in the device proposed herein. The fluorescence intensity is a function of the choice of the incident and fluorescent light wavelengths. Simultaneous variation (scanning) of these two wavelengths over a defined interval causes a maximum in fluorescence intensity at a particular wavelength, which is characteristic of a petroleum product sample. Presence of adulterants in the sample modifies this intensity maximum and its position.
The device proposed herein will now be described with reference to the accompanying drawings which illustrates, by way of example (and not by way of limitation) one of possible embodiments of the device proposed herein.
Fig.l illustrating a layout diagram of the said embodiment and Fig. 2 illustrating a separate view of the sensor head of orthogonal geometry for the excitation and emission light path (sample compartment) with the two optical fibres
The uhraviolet-visible lamp provides light at different wave lengths 200 nm - 600 nm( the two scanning monochromators are to be used to isolate the wave length, optical fibres will transmit light to and from the sensor head detector will convert the light signal intensity to electrical signal and PC will be used for data acquisition and processing. The dip-in type senso head is specifically designed for convenient in-iitu use in liquid samples.
The instrument is to be operated as follows:
(1) the lamp will be switched on
(2) the monochromator (I) and monochromator (II) will be set at appropriate wave lengths corresponding to the analyte sample.
(3) The sensor head will be in contact with the sample (that is dipped m the sample) In the embodiment ilhistrated this is in til e form of flow-through compartment
(4) The two monochromators will be scanned stmukaneously by using the PC
(5) The detector signal (intensity) will be collected by the PC as a function of wave length readmg m monochromator (I)
(6) The mtensities at appropriate wave lengths (character»tic of the sample to be analysed) will be used for estimation of adulterants. The relative examples are found m Tables I and II.
(7) An appropriate calibration plot (step 8) from the PC data base will be used to obtain a direct read-out of adulterant concentration in the sample.
Typical calibration plots for kerosene in diesel and kerosene in petrol are ilhistrated in Tables III and IV.
The calibration plot: Calibration plot of intensity agaiast
analyte concentration will be constructed for a particular sample of interest by preparing known mixtures of the sample with adulterants and subjecting these mixture-samples of known concentration to the steps 1 to 6 listed above. The plots for various petroleum product samples and adulterants will be stored in PC data base.
The fluorometric device for in situ estimation of adulterants in liquid petroleum products, therefore comprises a UV-visible lamp; a first monochromator connected to a PC and a sensor head through a first optical fibre; a second monochromator connected to the PC and to the sensor head through a second optical fibre; a detector connected to the second monochromator and to the PC; the sensor head being in contact with the sample petroleum product, the fu-st and second optical fibres respectively conveying the excitation to, mid receiving the em ission from the sensor head, the detector signal intensity being collected by the PC as a function of wavelength reading in the first monochromator, the intensities at appropriate wavelengths being used for estimilion of adulterants, characterised in that the wavelengths of Ae two monochromators are simultaneously scanned and in that the sensor head has orthogonal geometry for the excitation and emission light path.
The device proposed herein does not require any time for sample preparation mid can be adopted to on site nalysis of petrol and diesel simply by diping Ae sensor head mto the test sample. With previously constructed calibration plots from the corresponding original samples of petroleum products, the total time required for analysis is much less compared to any other analytical method available. This being an optical method, no part of the instrument other then an the sensor head is in direct contact with the sample. The method is more operator friendly and rugged. The technique is capable of estimating adulterants at fairly low adulterant concentration
1. A fluorometric device for in situ estimation of adutteraots in liquid petroleum products comprising a UV-visible lamp; a first monochromator connected to a PC and a sensor head through a furst optical fibre; a second monochromator connected to the PC and to the sensor head through a second optical fibre; a detector connected to the second monochromator and to the PC; the sensor head being in contact with the sample petroleum product, the first and second optical fibres respectively conveymg the excitation to, and receivmg the emission from the sensor head, the detector signal intensity being collected by the PC as a function of wavelength reading in the first monochromator, the intensities at appropriate wavelengths being used for estimation of adulterants, characterised in that the wavelengths of the two monochromators are simultaneously scanned and in that the sensor head has orthogonal geometry for the excitation and emission light path.
2. A device as claimed in Claim 1 wherein the sensor head is in the form of a flow through compartment for the said sample.
3. A device as claimed m Claim 1 or Claim 2 comprising a data base storage system for obtaining a direct read-out of adulterant concentration in the said sample.
4. A fluorometric device for in
situ estimation of adulterants in liquid petroleum products substantially as herein described and illustrated with reference to the Tables and the accompanying drawings.
|Indian Patent Application Number||372/MAS/2001|
|PG Journal Number||8/2007|
|Date of Filing||09-May-2001|
|Name of Patentee||M/S. INDIAN INSTITUTE OF TECHNOLOGY|
|Applicant Address||IIT POST BOX CHENNAI 600 036,|
|PCT International Classification Number||G01N 21/00|
|PCT International Application Number||N/A|
|PCT International Filing date|