Patent GB-949412-A (GB)
Title: A method of determining the vanadium content of a hydrocarbon oil
IPC: G01N33/28
Filed: 1961-06-14
Abstract: 949,412. Gyromagnetic resonance apparatus. GULF RESEARCH & DEVELOPMENT CO. June 14,1961 [June 15, 1960], No. 21415/61. Heading G1N. [Also in Division G3] Quantitative determination of vanadium, along with other trace metals, as an impurity in crude petroleum oils or in distillates derived therefrom is effected by electron paramagnetic resonance spectrometry. It is explained that provided the viscosity of the oils is such that sufficient vanadium resonance occurs to produce a detectable signal; vanadium exhibits a characteristic spectrum which in the presence of a strong field can be detected to provide an indication of the amount of vanadium present in the oil. It is important, it is stated, that the presence of vanadium should be detected since it leads to the catalysts becoming progressively less selective for the proper treatment of the oils. Fig. 1 shows a system of electron paramagnetic resonance spectroanalysis for a test sample of oil placed in a microcavity 18. A Klystron microwave generator 2 feeds a four arm bridge 4 containing a crystal detector 6 and is associated with the cavity 18 by a wave guide 16. Opposite poles 8,10 of an electromagnet are disposed about the cavity, the power supply of the electromagnet being controlled by a scanner 14. The field is modulated by an audio sweep generator 24 connected to a phase detector 22 which is also fed from the detector 6 via an amplifier 20. The phase detector is connected to a recorder 26. An oscilloscope may also be connected to the amplifier 20 or the phase detector 22. The cavity 18 is so oriented that the microwave magnetic field of the sample is perpendicular to the field produced by the poles 8,10. The microwave bridge 4 is first balanced for zero output from the crystal detector 6 and then slightly off-balanced by a screw turner to obtain a linear output from the detector. The microwave power of the generator 2 is then adjusted for maximum power and the field of electromagnet 8,10 slowly altered by the scanner. When as a result electron resonance occurs in the sample and microwave energy is absorbed by the paramagnetic vanadium electrons, less energy is reflected to the bridge 4 and the bridge become unbalanced. An A.C. output is thus produced at the crystal 6 which is proportional to the energy absorption of the sample. These outputs after amplification in unit 20 can be plotted against change of magnetic field strength as such or as shown as the first derivative of the absorption curve. In analyzing an unknown sample the proportion of vanadium may be obtained by comparing the peak height of the absorption curve with calibration curves obtained from standard samples having known vanadium concentrations. For a comparative test of this nature the difference between the viscosity of the samples and reference standard must be substantially constant, preferably not more than 20 centistokes. The system may be employed in oil refinery processes for automatically controlling the process in accordance with the vanadium content of the oil being processed. In such an arrangement oil may be passed continuously through the cavity 18 and the final output of the system as shown in Fig. 1 converted by transducer means into a pneumatic output which by the operation of valves controls the rate of make-up of catalyst or the removal rate of spent catalyst. In this manner the desired proportion of active catalyst in the process may be maintained at the desired level in accordance with the vanadium content of the oil being treated. Alternatively and as described with reference to Fig. 5 (now shown) the flow of steam to the stripping zone and flash zone of a vacuum dis - tillation tower may be controlled in accordance with the vanadium content of the highest boiling oil side stream from the tower to maintain that content at a predetermined level. Similarly the heavy gas side stream from the tower may be varied by recycling some of the stream through the tower in dependence on the vanadium content of the stream tested.