CN1191473C - Method for measuring total active sulfur in petroleum fractions - Google Patents

Abstract

The present invention discloses a method for measuring total active sulfur in petroleum fractions. Disulfide and elemental sulfur in petroleum fractions are deoxidated by zinc powder. A mixed solution containing ammonia water and alcohol is used as a titration medium. A glass electrode is used as a reference electrode. A silver-silver sulfide electrode is used as an indicating electrode. Potentiometric titration is carried out by the alcohol solution of silver nitrate. The method can exactly measure the content of total active sulfur once.

Description

Measure the method for gross activity sulphur in the petroleum cuts

The invention relates to a kind of method of measuring the gross activity sulfur content, more precisely about a kind of method with gross activity sulfur content in the current potential titration determination petroleum cuts.

Said active sulphur is meant and can be directly the processing unit (plant) of conveyance conduit, storage facilities and the crude oil of crude oil be produced sulphur in the sulphur compound of corrosion in oil and the petrochemical industry.Elementary sulfur, sulfuretted hydrogen, mercaptan, disulfide are the existence forms of dissimilar active sulphurs in the petroleum fraction.Gross activity sulphur just is meant the total amount of these active sulphurs.The size of gross activity sulfur content can reflect corrosive size that it is potential in the petroleum fraction, by measuring the content of gross activity sulphur in the various petroleum fractions, can predict corrosive height, and helpful to the serviceable life of prediction unit material.

Measure the existing bibliographical information of method of active sulphur.

UOP 163-80, UOP Laboratory Test Methods for Petroleum and ItsProducts, 1986:Vol (I) have reported the potentiometric titration of measuring sulfuretted hydrogen and mercaptans content in the liquid hydrocarbon.The titrant that adopts in this method is the ethanolic solution of silver nitrate.But this method can not be used for the mensuration of elementary sulfur and disulfide.

UOP 202-67, UOP Laboratory Test Methods for Petroleum and ItsProducts.1986:Vol (I) have reported the method for measuring disulfide.This method is with zinc powder disulfide to be reduced to mercaptan, measures with the ethanolic solution potentiometric titration of silver nitrate again.

Petroleum refining and chemical industry, 31 (1), reported the oscilloscopic polarography of measuring element sulfur content among the 58-60 (2000).

The method that prior art obtains gross activity sulphur is to measure the content of all kinds active sulphur respectively in order to last method, and then their additions are obtained.Obviously, the method for this acquisition active sulphur total amount is loaded down with trivial details, time-consuming, and needs multiple instrument and equipment.But do not see the method for the gross activity sulfur content in the single-time measurement petroleum cuts so far.

The objective of the invention is on the basis of existing technology, provide a kind of quick, easy, but single-time measurement goes out the method for gross activity sulfur content in the petroleum cuts.

We find the disulfide in the petroleum fraction not only, and elementary sulfur also can be by zinc powder reduction, and their reduzate and mercaptan, sulfuretted hydrogen is carried out quantitative reaction with silver nitrate together, just can obtain the content of gross activity sulphur in the petroleum fraction.

Method provided by the invention is carried out according to the following step:

1, the sample dissolution that will accurately take by weighing is in 10～100: 1 the mixed solution and in the weight ratio of sample and zinc powder to be that 1～10: 1 ratio adds zinc powder in the volume ratio of methyl alcohol and glacial acetic acid, stirs after 10 minutes～2 hours and moves into titration cell;

2, be that 50～200: 1 mixed solution is the titration medium with the volume ratio of pure and mild ammoniacal liquor, glass electrode is a contrast electrode, silver-sulfide electrode is an indicator electrode, with concentration be the alcoholic solution titration step 1 of the silver nitrate of 0.005～0.05M obtain sample solution;

3, calculate the gross activity sulfur content with (i)～(iii) formula:

$S_1=\frac{16\×A\×M}{G}\×1000...............\left(i\right)$

$S_2=\frac{32\×(B-A)\×M}{G}\×1000.........\left(\mathrm{ii}\right)$

S＝S ₁+S ₂………………………(iii)

In the formula: S ₁Micrograms for the active sulphur that exists with sulfuretted hydrogen, elementary sulfur form in every gram sample; S ₂Micrograms for the active sulphur that exists with disulfide, mercaptan form in every gram sample; S is the gross activity sulphur micrograms in every gram sample; A is for arriving S ^2-The used AgNO of terminal point ₃The volume milliliter number of solution; B is for arriving the used AgNO of mercaptan terminal point ₃The volume milliliter number of solution; M is AgNO ₃The volumetric molar concentration of alcoholic solution; G is a sample quality gram number.

The principle of assay method provided by the invention is:

Zinc powder can be reduced into mercaptan with the disulfide in the petroleum fraction under certain condition:

Following reaction also can take place with zinc powder in elementary sulfur:

The zinc sulphide that generates in acid medium, dissolve go on a tour from S ^2-, elementary sulfur and disulfide have just changed into S like this ^2-And RSH.

The drop reaction formula is as follows:

In assay method provided by the invention, the purity of said zinc powder is greater than 99.99%.

The volume ratio that said titration medium is pure and mild ammoniacal liquor is 50～200: 1 mixed solution, and wherein the effect one of ammoniacal liquor is the H that is generated by precipitation reaction in order to neutralize ⁺Ion is quantitatively finished reaction, and the 2nd, can prevent halide anion, mainly be the interference of chlorion; The effect of alcohol is in order to eliminate Ag ⁺Absorption on precipitation.Said alcohol should select for use polarity little, the alcohol of good stability, preferred isopropyl alcohol.

In assay method provided by the invention,, therefore the time that sample contacts with air should be reduced as far as possible in the mensuration process because the active sulphur that exists with the mercaptan form is easy to oxidation; Alcohol in titration medium and the titrant before use preferably through purging with nitrogen gas to remove dissolved oxygen DO wherein.

In the assay method provided by the invention, two hop current potentials are arranged during titration, be respectively and arrive S ^2-With the current potential that arrives the mercaptan titration end-point, the corresponding respectively S that arrives ^2-The volume milliliter number of the liquor argenti nitratis ophthalmicus that is consumed with the mercaptan titration end-point.Numerical value 16 in step 3 formula (i) be the atomic weight of sulphur with by S ^2-Used up Ag ⁺The ratio of molal quantity, (ii) the numerical value 32 in be the atomic weight of sulphur with by the used up Ag of mercaptan ⁺The ratio of molal quantity.

Method provided by the invention is quick, easy, can accurately measure the content of gross activity sulphur in the petroleum cuts once, and measurement result precision height, good reproducibility.

The present invention is further illustrated below by embodiment, but protection scope of the present invention is not subjected to the restriction of these embodiment.

In the following example, agents useful for same is analyzes pure level.

Zinc powder is provided by Beijing Non-Fervoous Metal Inst., and purity is 99.99%

Potentiometric titrimeter is 716 DMS Titrino types of Switzerland Metrohm company.

Embodiment 1

These embodiment illustrate and adopt the mensuration of the inventive method to standard specimen.

The preparation of sulfur-bearing standard specimen:

(1) elementary sulfur standard specimen: accurately take by weighing the sublimed sulfur of 0.150g,, add white oil, accurately claim fully to shake up to 300g with a little toluene dissolving.The element sulfur content of this solution is 500 μ g/g.

(2) sulfuretted hydrogen standard specimen: with the platinum filament is anode, and silver sulfide-Yin is a negative electrode, and the phosphate aqueous solution of electrolysis 0.5M, selected steady current are 8 milliamperes, and electrolysis 5 minutes produces the sulfuretted hydrogen of 426 micrograms, adds white oil, makes the solution that hydrogen sulfide content is 100 μ g/g.

(3) hexyl mercaptan standard specimen: accurately take by weighing the hexyl mercaptan of 0.5542g, add white oil to 300g, fully shake up, being mixed with sulfur content is the hexyl mercaptan standard specimen of 500 μ g/g.

(4) two sulphur dibenzyl standard specimens: accurately take by weighing the two sulphur dibenzyls of 0.5765g, add white oil to 300g, fully shake up, being mixed with sulfur content is the two sulphur dibenzyl standard specimens of 500 μ g/g.

The standard specimen preparation that takes by weighing a certain amount of elementary sulfur, sulfuretted hydrogen, hexyl mercaptan and two sulphur dibenzyls mixes four parts of standard specimens, sees Table 1.Every part is mixed standard specimen replicate determination five times.

Table 1

Mix the standard specimen numbering	Standard specimen weighing number (gram)				Gross activity sulfur content actual value (μ g/g)
						Elementary sulfur	Sulfuretted hydrogen	Hexanol sulphur	Two sulphur dibenzyls
	1	0.025	0.150	0.200						0.200	227.5
2					0.050	0.300	0.200	0.200	255.0
	3	0.100	0.500	0.350						0.200	375.0
4					0.100	0.500	0.700	0.400	650.0

With mixing volume ratio that standard specimen adds 25mL methyl alcohol and glacial acetic acid is in 15: 1 the mixed solution, adds the 1g zinc powder again, stirring reaction 40min at room temperature, and reaction back sample is filtered in the beaker of 200mL fast.

Use the purging with nitrogen gas isopropyl alcohol, getting the isopropyl alcohol of above-mentioned processing and ammoniacal liquor, to be mixed with volume ratio be 150: 1 mixed solution 100mL and cleaning reaction bottle and filter paper.In filtrate, add magnetic stirring bar, insert glass electrode and silver-sulfide electrode and stirring, with the AgNO of 0.01M ₃Titration.

Measurement result sees Table 2.In table 2:

In the formula: n is the replicate determination number of times, x _iBe the unitary determination value, x is the arithmetic mean of n replicate determination value;

Table 2

Mix the standard specimen numbering	Gross activity sulfur content (μ g/g)							Relative standard deviation (%)	Average recovery rate %
										Actual value	This method measured value
	Five replicate determination values					Mean value
							1				227.5	228.2	224.0	221.5	221.2	229.1	224.8	1.47	98.8
2	255.0	251.4	259.1	254.3	260.0	247.7		254.5	1.82	99.8
							3				375.0	375.1	372.5	378.9	376.3	371.2	374.8	0.73	99.9
4	650.0	651.6	653.6	647.7	648.5	650.7		650.4	0.33	100.1

As can be seen from Table 2, assay method provided by the invention is accurate, precision height, good reproducibility.

Embodiment 2

These embodiment illustrate and adopt the mensuration of method provided by the invention to the gross activity sulphur in matter oil, Saudi Arabia's each cut of lightweight wet goods crude oil in Kazakhstan's oil, Iranian lightweight oil, Iranian mink cell focus, the Saudi Arabia.

In conical flask, accurately take by weighing 2 gram samples respectively, the volume ratio that adds 25mL methyl alcohol and glacial acetic acid is 25: 1 a mixed solution, add the 1g zinc powder again, stirring reaction 30min at room temperature, reaction back sample filters fast in the beaker of 250mL, is 100: 1 mixed solution cleaning reaction bottle and filter paper with about 100mL isopropyl alcohol and ammoniacal liquor volume ratio.In filtrate, add magnetic stirring bar, insert electrode and stirring, with the AgNO of 0.01M ₃Titration.

Measurement result sees Table 3.

Table 3

The crude oil kind	Boiling spread (℃)
								Initial boiling point～50	50～100	100～150	150～200	200～250	250～300	300～350
	Gross activity sulfur content (μ g/g)
								Kazakhstan's oil	2529.9	1672.3	1624.2	1537.7	1053.1	680.2	414.6
Iran's lightweight oil	97.6	128.2	209.7	213.3	123.0	79.0	48.9
								Iran's mink cell focus	210.6	264.8	295.3	293.7	102.6	43.1	41.1
Matter oil in the Saudi Arabia	57.2	100.6	132.5	139.6	64.4	52	46
								Saudi Arabia's lightweight oil	58.9	85.4	80.1	147.4	132.9	100.6	85.7

Claims (3)

1, a kind of method of measuring gross activity sulfur content in the petroleum cuts is characterized in that this method carries out according to the following step:

(1) sample dissolution that will accurately take by weighing is in 10～100: 1 the mixed solution and in the weight ratio of sample and zinc powder to be that 1～10: 1 ratio adds zinc powder in the volume ratio of methyl alcohol and glacial acetic acid, stirs after 10 minutes～2 hours and moves into titration cell;

(2) be that 50～200: 1 mixed solution is the titration medium with the volume ratio of pure and mild ammoniacal liquor, glass electrode is a contrast electrode, and silver-sulfide electrode is an indicator electrode, is the sample solution of alcoholic solution titration step (1) of the silver nitrate of 0.005～0.05M with concentration.

(3) with following various calculating gross activity sulfur content:

$S_1=\frac{16\×A\×M}{G}\×1000$

$S_2=\frac{32\×(B-A)\×M}{G}\×1000$

S＝S ₁+S ₂

In the formula: S ₁Micrograms for the active sulphur that exists with sulfuretted hydrogen, elementary sulfur form in every gram sample; S ₂Micrograms for the active sulphur that exists with disulfide, mercaptan form in every gram sample; S is the gross activity sulphur micrograms in every gram sample; A is for arriving S ^2-The used AgNO of terminal point ₃The volume milliliter number of solution;

B is for arriving the used AgNO of mercaptan terminal point ₃The volume milliliter number of solution; M is AgNO ₃The volumetric molar concentration of alcoholic solution; G is a sample quality gram number.

2, in accordance with the method for claim 1, it is characterized in that the alcohol described in the step (2) is isopropyl alcohol.

3, in accordance with the method for claim 1, the purity that it is characterized in that described zinc powder is 99.99%.