Basic nitrogen compounds identification

in a blend of Libyan crudes and in its

middle distillates and Residue

Youssef A. Al Mestiri and Abeer A. Al Shiki

Ras Lanuf Oil and Gas Processing CompanyTechnical Services Department

Laboratory SectionP.O.Box 1971

Benghazi – Libyayelmisteri@yahoo.com

Abstract

Basic nitrogen content in naphtha, kerosene, light and heavy gas oils (LGO

and HGO) produced by Ras Lanuf Refinery from a blend of Libyan crudes as

well as the physical and the chemical properties of this crude blend and its

LGO, HGO and residue were determined. Basic nitrogen compounds from this

crude blend and from its LGO, HGO and residue were extracted by

hydrochloric acid, the extracted basic nitrogen compounds were

accompanied with some non basic nitrogen compounds. Separation and

identification of these compounds were achieved by a GC-MS technique. The

basic nitrogen content in naphtha and kerosene is zero ppm whilst in LGO,

and HGO is 13 and 88 ppm respectively, the identified basic nitrogen

compounds are quinoline, isoquinoline, and acridine derivatives and the

accompanied non basic nitrogen compounds are indole derivatives.

Introduction

It has been realized for a long time. The deleterious effect of nitrogen

compounds that naturally occurring in petroleum and distributed in

petroleum distillates.

Environmentally nitrogen compounds are extremely harmful since they

contribute nitrogen oxides emissions and are known to be carcinogenic and

mutagenic in humans and animals [1-3]. Industrially both basic and non-basic

nitrogen compounds reduce the stability and storage stability of petroleum

distillates, by darkening the colour, sediment and odour formation[1,2,4,5],

moreover basic nitrogen compounds are strong inhibitors in various

petroleum processes; cracking, hydrocracking reforming processes and

hydrodesulfurization (HDS) reactions by interacting with the acidic sites of

the catalyst employed causing catalyst poisoning: in this reaction basic

nitrogen compounds are electron pair donor whilst catalyst is electron pair

acceptor [2,5-8]. Non-basic nitrogen compounds inhibition in HDS reactions

has been observed and reported; hydrogenation reduction reaction of these

compounds that take place in HDS and reaction process leading to the

formation of basic nitrogen compounds [8-11] or by a strong adsorption of

non-basic nitrogen compounds over the support surface of the catalyst

[8,12,13].

The aims of this work is to assess quantitatively basic nitrogen content in

naphtha, kerosene, LGO and HGO produced from a blend of Libyan crudes

and extraction, separation and identification of these compounds by GC-MS

technique [14-26].

Experimental

The properties of Libyan crude blend; a 50% Sarir/50% Mesla crudes blend

and its LGO, HGO and residue were attained following ASTM standard

methods whilst the total basic nitrogen content in naphtha and kerosene was

determined following UOP-312 plant control test method and in LGO and HGO

by applying UOP-313 standard method. All the samples were taken from the

Ras Lanuf Refinery.

The extraction of basic nitrogen compounds was performed by a slight

modification of the Hartung and Jewell separation scheme [1].

Prior basic nitrogen compounds extraction; the samples were diluted or

dissolved in the proper solvent as follow, 2.4L raw sample of Libyan

crudes blend were diluted with 600 ml n-heptane, 2L LGO was used

without dilution, 2L HGO sample was dissolved and diluted with 500 ml n-

heptane and 1L of residue was dissolved and diluted with 2L 1:1

toluene/xylene mixture.

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Basic nitrogen compounds were extracted; from the Libyan crudes blend

sample with 6 x 500 ml 0.1M HCl acid, from each LGO and HGO sample with

5 x 500 ml 0.1M HCl acid and from the residue extracted with 6 x 250 ml

0.1M HCl acid, the acid extract of each sample was extracted with n-heptane

followed by benzene and the resulting acidic aqueous solution was reacted

with concentrated NaOH in presence of 50 ml dichloromethane with vigorous

shaking to raise the pH to 12-13, the liberated basic nitrogen compounds

were extracted from the NaOH solution with 650 ml dichloromethane. The

light-yellow dichloromethane basic nitrogen compounds solution was

evaporated to about 1-2 ml for GC-MS separation and identification of basic

nitrogen compounds.

Basic nitrogen compounds were separated and identified by GC-MS (Thermo

Finnigan Trace GC and Trace DSQ). 2-4 µl of each basic nitrogen compounds

mixture was injected onto the GC fitted with a 30 m, 0.25 mm id, 0.25 μm df

capillary column (5% diphenyl-95% dimethyl polysiloxane), coupled directly

to MS spectrometer detector; operating in electron impact mode at 70 eV,

mass detector gain 1.00 KV, ionization current 100 μA, full scan 40-300 μ.

GC operating temperature was as follows initial temperature was set at 85оC

for 1 min, ramped 5оC/min up to 200оC at which it was held for 20 min and

finally ramped 5оC/min up to 270оC at which it was held for 5 min.

Injector temperature was 280оC at constant temperature split mode, carrier

gas was helium flow rate 1.0 ml/min; at constant flow. Both MS transfer line

and the ion source temperatures were 250оC. The nitrogen compounds in

each sample were identified by means of a computer matching method,

comparing their spectra with those of the NIST library of mass spectral Data.

Result and Discussions

It is obvious that large volumes of samples and reagent were used to achieve

separation of basic nitrogen compounds from the samples that is to obtain a

rather concentrated basic nitrogen compounds mixture suitable for a GC-MS

analysis.

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The samples solvents treatment prior basic nitrogen compounds extraction

is; to dilute, to dissolve and to reduce the density of the samples which

facilitate the extraction of basic nitrogen compounds from each sample.

The physical and some of the chemical properties of Libyan crude blend,

LGO, HGO and residue are presented in table 1.

From table 1; the sulfur content increases as the boiling point of the Libyan

crudes blend distillates increases and attain its highest content in residue.

Also basic nitrogen content increases as the boiling point of the distillates

increases; as naphtha and kerosene contain zero ppm of basic nitrogen HGO

contains the highest basic nitrogen content.

GC-MS technique revealed that the extracted basic nitrogen compounds

contain some non-basic nitrogen compounds due to the strong adsorption of

these non-basic nitrogen compounds to the acid. No further attempts were

made to separate the basic nitrogen compounds from the non-basic nitrogen

compounds. The identified basic nitrogen compounds in LGO, HGO and

residue produced from this crudes oil blend do not show any structure

alteration or rearrangement from those identified in the raw crudes blend oil.

All the identified basic nitrogen compounds and the accompanied non-basic

nitrogen compounds are presented in table 2.

Total ion chromatograms of the separated basic nitrogen compounds from

the Libyan crudes blend and its LGO, HGO and residue are shown in figures 1,

2, 3 and 4; the numbers associated with the peaks refer to the identified

basic and non-basic nitrogen compounds in each distillate.

Table 1 Properties of Libyan crude blend, LGO, HGO and residue

Property Method LCB* LGO HGO Residue

Specific gravity @15.6 °C ASTM D-1298 0.8340 0.8192 0.8480 0.9104

Density @15.6 °C ASTM D-1298 0.8336 0.8188 0.8476 0.9099

API gravity (°C) ASTM D-1298 38 41 35 24

Initial boiling point (°C) ASTM D-86 - 207 279 -

Final boiling point (°C) ASTM D-86 - 338 - -

Flash point (°C) ASTM D-93 - 89 - 124

Pour point (°C) ASTM D-97 18 -9 27 41

Cloud point (°C) ASTM D-2500 - -3 - -

Aniline point (°C) ASTM D-611 - 81 94 -

Total Aromatic (wt %) - 9.27 9.30 -

Cetane index ASTM D-976 - 59 - -

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Total sulfur (wt %) ASTM D-4294 0.1393 0.0414 0.1372 0.2532

Basic nitrogen (wppm) UOP-313 ND 13 88 ND ND = not determined *Libyan crudes blend

Table 2 Basic and non basic nitrogen compounds identified in Libyan crude blend, LGO, HGO and residue

Peak No m/z Identified compounds RT. Min Fraction

1 157 Dimethyl quinoline 12.09 LCB, LGO

2 171 Ethyl-methyl quinoline 13.57 LCB, LGO

3 171 Trimethyl quinoline 14.61 LCB, LGO, HGO

4 159 Trimethyl indole 16.44 LCB, HGO

5 173 Tetramethyl indole 17.07 LCB, HGO, R

6 185 1,2-Dimethyl-5,6-dihydro-4H-pyrrolo[3,2,1-ij]quinoline

17.56 LCB, LGO, HGO

7 187 Pentamethyl indole 18.52 LCB, LGO, HGO

8 211 7-ethyl-1,2,3,4-tetrahydroacridine 21.45 LCB, LGO

9 213 6-methyl-2-(2-thienyl)-1H-indole 24.83 LCB, LGO

10 207 Ethyl acridine 26.35 all

11 221 Trimethyl benzoisoquinoline 30.01 all

12 251 1,2,3,4,7,8,9,10-octahydro-12-methyl benzoacridine

31.49 LCB, HGO

13 251 1,2,3,4,8,9,10,11-octahydro-7-methyl benzoacridine

34.17 LCB, HGO

14 221 2,3,4-trimethyl benzoquinoline 34.83 LCB, HGOR = Residue RT. Min = Retention time in minutes

Figure 1. Total ion chromatogram of nitrogen compounds in crude blend

Figure 2. Total ion chromatogram of nitrogen compounds in LGO

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Figure 3. Total ion chromatogram of nitrogen compounds in HGO

Figure 4. Total ion chromatogram of nitrogen compounds in the residue

The identified basic nitrogen compounds in Libyan crudes blend and in its

LGO, HGO and residue were C2- to C3-methyl quinolines, ethyl-methyl

quinoline, ethyl acridine, ethyl hydroacridine, C1-alkyl benzohydroacridine, C2-

alkyl dihydro pyrrolo-quinoline, C3-methyl benzoquinoline and C3-methyl

benzoisoquinoline. The non-basic nitrogen compounds accompanied the

extracted basic nitrogen compounds were indole derivatives; C3- to C5-methyl

indoles and 6-methyl-2-(2-thienyl)-1H-indole.

Figures 5-8 are reproduced mass spectra of C2-methyl, ethyl-methyl and

C3-methyl quinolines and 1,2-dimethyl-5,6-dihydro-4H-pyrrolo[3,2,1-

ij]quinoline; molecular ion peaks of these quinoline derivatives appear at m/z

157, 171, 171 and 185 whilst the base ion peaks appear at m/z 157, 170, 171

and 185 respectively.

Figure 5. Dimethyl quinoline mass spectrum

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Figure 6. Ethyl-methyl quinoline mass spectrum

Figure 7. Trimethyl quinoline mass spectrum

Figure 8. 1,2-dimethyl-5,6-dihydro-4H-pyrrol[3,2,1-ij]quinoline mass spectrum

Figures 9, 10, 11 and 12 are reproduced mass spectra of substituted alkyl

hydroacridine and alky acridine; these are 7-ethyl-1,2,3,4-tetrahydroacridine,

ethyl acridine, 1,2,3,4,7,8,9,10 - Octahydro - 12- methylbenzoacridine and

1,2,3,4,8,9,10,11- Octahydro -7- methylbenzoacridine; molecular ion peaks

of these hydroacridine and acridine derivatives appear at m/z 211, 207, 251

and 251 whilst the base ion peaks appear at m/z 196, 206, 251 and 251

respectively.

Figure 9. 7-ethyl-1,2,3,4-tetrahydroacridine mass spectrum

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Figure 10. Ethyl acridine mass spectrum

Figure 11. 1,2,3,4,7,8,9,10-Octahydro-12-methylbenzoacridine mass spectrum

Figure 12. 1,2,3,4,8,9,10,11-Octahydro-7-methylbenzoacridine mass spectrum

Figures 13 and 14 are reproduced mass spectra of both

trimethylbenzoisoquinoline and 2,3,4-trimethylbenzoquinoline the molecular

ion peaks of these two compounds appear at m/z 221 whilst the base ion

peaks appears at m/z 221 for trimethylbenzoisoquinoline and 220 for 2,3,4-

trimethylbenzoquinoline.

Figure 13. Trimethyl benzoisoquinoline mass spectrum

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Figure 14. 2,3,4-trimethyl benzoquinoline mass spectrum

Non-basic nitrogen compounds are shown in figures 15, 16, 17 and 18 these

are C3, C4 and C5 methyl indole and 6-methyl-2-(2-thienyl)-1H-indole (a non-

basic nitrogen compound containing sulfur), the molecular ion peaks of these

indole derivatives appear at m/z 159, 173, 187 and 213 and the base ion

peaks appear at m/z 158, 173, 186 and 213 respectively.

The mass spectrum of 6-methyl-2-(2-thienyl)-1H-indole shows an M + 2 ion

peak of about 4% of the abundance of the main molecular ion peak that is a

typical of 32S containing compound.

Figure 15. Trimethyl indole mass spectrum

Figure 16. Tetramethyl indole mass spectrum

Figure 17. Pentamethyl indole mass spectrum

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Figure 18. 6-methyl-2-(2-thienyl)-1H-indole mass spectrum

The mass spectra of these compounds show a loss of the stable HCN (m/z 27)

neutral molecule; a typical fragmentation pattern of nitrogen compounds.

Conclusion

Basic nitrogen compounds accompanied with some non-basic nitrogen from

Libyan crudes blend and from its LGO, HGO and residue were successfully

separated and identified as well the basic nitrogen content in naphtha,

kerosene, LGO and HGO were quantitatively determined.

The identified basic nitrogen compounds are quinoline, isoquinoline,

benzoquinoline, benzoisoquinoline, acridine, benzohydroacridine and

hydroacridine derivatives and the identified non-basic nitrogen compounds

are indole derivatives.

The identified basic and non-basic nitrogen compounds are thermally

stable through the refining processes of the Libyan crudes blend.

The nitrogen compounds which identified in residue are only trapped

basic nitrogen molecules.

Acknowledgement

We are grateful to Ras Lanuf refinery operation staff for collecting and

providing the samples. The preparation of the reagent by the special analysis

lab of Ras Lanuf is gratefully acknowledged.

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