WO2012104858A1

WO2012104858A1 - Online analysis method for crude oils using spectroscopy

Info

Publication number: WO2012104858A1
Application number: PCT/IN2011/000222
Authority: WO
Inventors: Bisht HARENDER; Preschilla NISHA; Saravanan CHANDRA; Mandal SUKUMAR; Das ASIT
Original assignee: Reliance Industries Ltd
Current assignee: Reliance Industries Ltd
Priority date: 2011-02-01
Filing date: 2011-03-30
Publication date: 2012-08-09
Anticipated expiration: 2013-08-01

Abstract

An improved method for online IR analysis of hydrocarbon mixture, particularly crude oil is provided for determining its several physico-chemical properties, wherein the oil sample is diluted with IR transparent solvent, particularly carbon tetrachloride and IR absorption is evaluated. The invention uses a method wherein sample cells of less than 0.2mm can be utilized and full IR spectrum from 800 cm^-1 to 400 cm^-1 can be used for predicting the properties of oil.

Description

ONLINE ANALYSIS METHOD FOR CRUDE OILS USING

SPECTROSCOPY

FIELD OF THE INVENTION:

The present invention relates to simple and accurate method for online analysis of oil samples.

In particular, the invention relates to an improved method for online IR analysis of cirude oil by diluting the crude oil with IR transparent solvent.

BACKGROUND OF THE INVENTION:

Online analysis of crude by NIR or IR spectroscopic technique has tremendous potential for determining several physico-chemical properties of crude oil in real time that are crucial for smooth refinery operation and profit maximization.

A major problem in evaluating crude oil through online analysis method of the state of art is high viscosity of the crude oil which makes it difficult to flow through the online sample cell for accurate analysis. Another major difficulty, particularly in the mid IR analysis, is the complete absorption of IR radiation in the region 2800 to 3100cm^"1 and 1100 to 1400 cm^"1. Due to complete absorption no useful information can be retrieved from these regions (Figure 1).

Existing Knowledge:

US6662116 B2 teaches to determine the properties of unknown materials by IR analysis. However, this patent does not teach how to analyze the crude oil online. US3996785 describes measurement of boiling point properties of crude by help of IR analysis, kinematic viscosity measurement and S analysis. This patent uses data from multiple sources to predict the boiling point properties of crude oil.

l US5656810 describes composition evaluation of oil samples by comparison of spectral differences in luminescence, excitation, light scattering and absorption spectra in the near UV, visible and near IR regions.

US6490027 Bl teaches how to practice the automatic analysis of crude oil using near IR spectroscopy.

WO2008135411A1 describes IR analysis method in batch mode using ATR technique. However, it does not indicate any dilution of crude oil and any corresponding online system for that.

US6087662 discloses an online process for determining asphaltene concentration in an asphaltene-containing hydrocarbon mixture using infrared spectroscopy and a multiple variable regression analysis. The Asphaltene content is predicted by Mid IR analysis using NaCl plates and Tunnel ATR cell in batch manner. Employing this method to an online and continuous system is seemingly non-feasible. Therefore, the proposed invention is distinct from the said process.

JP58037543A discloses a method for performing quantitative analysis by an infrared spectrophotometry to measure the amount of a curing agent in an epoxy resin using 0.05mmKBr cell and diluting the sample with chloroform (CHC1₃).

None of the aforesaid patent or any other state of art method discloses mid IR spectroscopy as an online tool for predicting various properties of crude oil.

Infact, it could not be practiced due to several practical difficulties such as crude oil being very viscous, needs IR sample cell with significant widths through which it could flow. But if the path length is increased the sample becomes opaque to IR radiation. Previous patent data shows that some of the regions are completely opaque to IR radiation therefore no useful information could be retrieved from these regions. Another important difficulty is to clean the sample cell such that the results are representative to the actual sample passing through the cell at that particular instance. In view of foregoing, there is a need for an improved method to overcome these aforesaid problems for online IR analysis of crude oil. OBJECTS OF THE INVENTION:

Accordingly, the objects of the present invention are as follows:

An object of present invention is to provide an improved method for accurate analysis of crude oil for determining several physico-chemical properties of crude oil in real time.

Another object of the invention is to reduce the viscosity of the crude oil in order to allow better flow through the IR sample cell.

Another object of the invention is to perform IR analysis of crude oil using smaller IR sample cell than a typical IR sample cell.

Still another object of the invention is to utilize full IR spectrum from 4000 cm^"1 to 400 cm^"1 for predicting the properties of crude under examination by adding an inert solvent, particularly Carbon tetrachloride.

Still another object of the invention is to perform contamination free analysis by making the IR sample cell free of any residual crude oil with little cleaning effort.

Yet another object of the invention is to use Carbon tetrachloride as cleaning solution for IR sample cell in order to quickly clean the cell.

SUMMARY OF THE INVENTION:

In accordance with the present invention there is provided an improved method for online IR analysis of crude oil, wherein, the crude oil is diluted with CC1₄ and the IR analysis of this diluted crude solution is done online.

The said method Comprises the steps of:

(a) obtaining a sample of hydrocarbon mixture; (b) diluting the said sample with a solvent to obtain a diluted hydrocarbon mixture solution;

(c) maintaining the homogeneity of said hydrocarbon mixture solution and;

(d) allowing the said solution to the past IR absorption cells of an infrared spectrometer and evaluating the absorbance.

The intensity of strong absorption bands of 2800-3200 cm^'1 and 1100-1500cm^"1 is significantly reduced due to dilution of the crude oil therefore these peaks can also be used in the chemometric analysis which was not possible for pure crude samples. The viscosity of diluted crude solution is significantly lower than pure crude oil therefore the flow of sample through the online cell is much easier as compared to the pure crude oil. Another advantage with the method of the invention is that the cleaning of the cell is better therefore the analysis is more accurate and contamination of online IR cell with previously analyzed crude sample is minimized.

BRIEF DESCRIPTION OF DRAWINGS:

The invention will now be described with reference to accompanying drawing.

Figure 1: shows the graphical representation of wave numbers on X-axis along with IR absorbance on Y-axis in the prior art in which the region 2800 to 3200cm^"1 (C-H stretching vibrations) and 1100 to 1500 cm^"1 is completely opaque to IR radiation and no information can be retrieved from these regions for as such crude samples (US6662116 B2);

Figure 2: shows that Carbon tetra chloride (CC1₄) is almost transparent to IR radiation except 750 to 800 cm^"1 region;

Figure 3: shows the IR spectra of pure crude vis a vis crude diluted with CC14 in ATR mode;

Figure 4: shows the IR spectra of pure and CC1₄ diluted crude in 0.05mm KBr cell; and Figure 5: shows the difference in absorption intensity of pure and CC14 dilutes crude in 2800 - 3100 cm^"1 band in 0.05mm KBr cell.

DETAILED DESCRIPTION OF THE INVENTION:

The present invention provides an improved method for online IR analysis of crude oil, wherein, the dilution of crude oil is done with IR transparent solvent, particularly Carbon tetrachloride and the IR analysis of this diluted crude solution is done online. The said method comprises the steps of:

(a) obtaining a sample of hydrocarbon mixture;

(b) diluting the said sample with a solvent to obtain a diluted hydrocarbon mixture solution;

(c) maintaining the homogeneity of said hydrocarbon mixture solution and;

The intensity of strong absorption bands of 2800-3200 cm^"1 and 1100-1500cm^"1 is significantly reduced due to dilution of the crude oil therefore these peaks can also be used in the chemometric analysis which was not possible for pure crude samples.

Typically IR sample cells have a path length in the range of 0.2mm - 0.5 mm. Even at the lower limit of path length i.e. 0.2mm, two regions i.e. 2800-3100 cm^"1 and 1100- 1500 cm^"1) show 100% absorption of IR radiation (US patent 6662116 B2), due to which, no information can be retrieved from these regions for as such crude samples. There is no state of art method available, wherein, an online sample cell of 0.05 mm path length is used.

Further, IR sample cells with smaller path length (<0.2 mm) could not be used due to following two reasons:

(a) There is a difficulty in passing the crude through the IR sample cell.

(b) Efficient cleaning of the sample cell for accurate analysis becomes a problem. IR cells with larger path length, although could solve the problems associated with flow of crude oil and cleaning of IR sample cell, but the problem of 100% absorption of IR radiation still persists.

This difficulty is addressed in accordance with this invention by dissolving Crude oil in a solvent which reduces its viscosity. Crude oil has good solubility (>50 wt %) in Carbon tetra chloride. The IR spectrum of Carbon tetra chloride (CC1₄) as presented in Figure 2 having wave number on X-axis and % Transmittance on Y-axis, clearly shows that the carbon tetrachloride is almost transparent to IR radiation except at 750 cm^"1 to 800 cm^"1 region.

Other than Carbon tetrachloride, solvents selected from the group consisting of halogenated CI to C 3 hydrocarbons including l,2-dibromo-l,l,2,2-tetrachloroethane (C₂Br₂Cl₄) and Hexachloroethane (C₂C1₆) can also be used. Similar to carbon tetrachloride solution, these two solvents l,2-dibromo-l,l,2,2-tetrachloroethane and Hexachloroethane are also transparent to the region of interest of IR radiation except at 600 cm^"1 to 800 cm^"1.

Crude oil diluted in CC1 is found to have considerably lower viscosity and it can smoothly flow through the online IR sample cell.

Furthermore, the absorption intensity is significantly lower for the diluted crude oil so more information can be retrieved from the 2800 to 3100 cm^"1 (CH stretching) and 1100 to 1500 cm^"1 (CH bending) region, which was never hitherto possible for pure crude oil.

The present invention therefore provides a solution to the longstanding problem of crude oil analysis by providing the following improvements:

In accordance with an aspect of the invention, the viscosity of diluted crude solution is significantly reduced therefore the flow of sample through the online cell is much easier as compared to the pure crude oil. As a result, sample cells of less than 0.2mm (e.g. 0.05mm) can be used. In accordance with another aspect of the invention, the absorbance intensity of crude oil in regions 2800 cm^"1 -3100 cm^"1 and 1100 cm^"1 -1500cm^"1 is reduced considerably therefore full IR spectrum from 4000 cm^"1 to 400 cm^"1 is used for predicting the properties of crude under examination.

In accordance with another aspect of the invention, the cleaning of the cell is better therefore the analysis is more accurate and contamination of online IR cell with previously analyzed crude sample is minimized.

The further figures accompanying the invention are described below:

Figure 3 shows the IR spectra of pure crude vis a vis crude diluted with CC14 in ATR mode. The red line represents the IR absorption by pure crude and the brown line represents the IR absorption by 9 % crude in CC1₄ (Figure 3). The IR absorption intensity in 2800 cm^"1 - 3100 cm^"1 and 1100cm^"1 - 1500cm^"1 ranges has decreased by >50% and >85% for 9% crude in CC1₄ respectively.

Figure 4 shows the IR spectra of pure and CC1₄ diluted crude in 0.05mm KBr cell. The absorbance band at 2800-3100 cm^"1 is fully saturated (100% absorbance) and the band at 1400 - 1450 cm^"1 is also approaching saturation (-100% absorbance). Since it is not , possible to determine the decrease in absorption by 0.05 mm KBr cell, the decrease was estimated from the ATR measurement.

The actual online IR sample cells have a typical path length of 0.2 to 0.5 mm therefore the absorbance of these two bands (2800 - 3100 cm^"1 & 1100 - 1500 cm^"1) will be always 100% for pure crude. However, there is significant decrease in the absorption intensity for diluted crude in 0.05 mm KBr cell.

Figure 5 shows the difference in absorption intensity of pure and CC1₄ diluted crude in 2800- 3100 cm^"1 band in 0.05mm KBr cell. It is clearly evident that no information can be retrieved from the IR spectra of pure crude due to 100% absorbance whereas, the diluted crude shows distinct peak patterns with 50 to 91%dilutions. The reduction in absorbance with dilution using the method in accordance with this invention is tabulated in Table No. 1 and Table No. 2.

Table 1:

The diluted crude solution prepared in accordance with the method of the invention was examined under optical microscope to check if there is sedimentation or precipitation of CC1₄ insoluble components. The optical microscope images showed no aggregates and/or precipitates with 50 to 91% dilution of crude oil by CC1₄. Therefore the homogeneity of crude oil is maintained after dilution with CC1₄.

Technical advancement;

The method in accordance with the present invention has several advantages such as:

(a) Accurate analysis of crude oil can be done for determining several physico- chemical properties of crude oil in real time.

(b) Viscosity of the crude oil is significantly reduced in order to allow better flow through the IR sample cell.

(c) IR analysis of crude oil can be performed using smaller IR sample cell than a typical IR sample cell.

(d) By adding an inert solvent, particularly Carbon tetrachloride, full IR spectrum can be utilized from 4000 to 400 cm^"1 for predicting the properties of crude under examination.

(e) Contamination free analysis can be performed by making the IR sample cell free of any residual crude oil with little cleaning effort.

(f) Carbon tetrachloride used as a cleaning solution for IR sample cell in order to quickly clean the cell.

"Whenever a range of values is specified, a value up to 10 % below and above the lowest and highest numerical value respectively, of the specified range, is included in the scope of the invention".

While considerable emphasis has been placed herein on the various components of the preferred embodiment, it will be appreciated that many alterations can be made and that many modifications can be made in the preferred embodiment without departing from the principles of the invention. These and other changes in the preferred embodiment as well as other embodiments of the invention will be apparent to those skilled in the art from the disclosure herein, whereby it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the invention and not as a limitation.

Claims

CLAIMS:

1. A method for online analysis of hydrocarbon mixture, using spectroscopy, for evaluating physico-chemical properties of hydrocarbon mixture, the said method comprising the steps of:

(a) obtaining a sample of hydrocarbon mixture;

(b) diluting said sample with a solvent to obtain a diluted hydrocarbon mixture solution;

(c) maintaining the homogeneity of said hydrocarbon mixture solution;

(d) allowing said solution to the pass IR sample cells of an infrared spectrometer and evaluating the absorbance; and

(e) cleaning the sample cells after one or more passes.

2. A method as claimed in claim 1, wherein the hydrocarbon mixture is crude oil.

3. A method as claimed in claim 1, wherein the solvent is IR transparent ,.

4. A method as claimed in claim 1, wherein in step (b), the solvent is an IR transparent solvent selected from a group consisting of halogenated Q to C₃ hydrocarbons including carbon tetrachloride, Hexachloroethane and 1 ,2-Dibromo- 1 , 1 ,2,2-tetrachloroethane..

5. A method as claimed in claim 4, wherein the solvent is carbon tetrachloride.

6. A method as claimed in claim 1, wherein in step (b), the said sample is diluted in the range of 1% to 99% with a solvent.

7. A method as claimed in claim 6, wherein the sample is diluted in the range of 50% to 91% with a solvent.

8. A method as claimed in claim 1, wherein in step (c) the homogeneity of crude oil is maintained by preventing sedimentation or precipitation of insoluble components.

9. A method as claimed in claim 1, wherein in step (d), the path length of IR absorption cells is in the range of 0.02 mm to 0.75mm,preferably is in the range of 0.05mm to 0.2mm ,

10. A method as claimed in claim 1, wherein in step (d)^ IR absorption cells are KBr cells.

11. A method as claimed in any of the claims 1-12, wherein absorption is measured over the full IR spectrum of 4000 cm^"1 to 400 cm^"1 or a portion thereof.

12. A method as claimed in any of the preceding claims 1-14, wherein the absorption in the IR range of 2800 cm^"1 - 3100 cm^'1 is reduced by >50%.

13. A method as claimed in any of the claims 1-14, wherein the absorption in the

range of 1100 cm^"1 -1400 cm^"1 is reduced by >80%.

14. A method as substantially herein described with reference to accompanying

figures.