Composition of concentrates of heterocyclic petroleum compounds isolated by complex-formation with titanium tetrachloride

Petrol. Chem.U.S.S.R. Vol. 23. No. 3. vo. 186-192.1981 Printed in Poland

0031--6458/83 $10.00 +.00 ~ 1985 Pergamon PressLtd.

COMPOSITION OF CONCENTRATES OF HETEROCYCLIC PETROLEUM C O M P O U N D S ISOLATED BY COMPLEXFORMATION WITH TITANIUM TETRACHLORIDE* V. I. NESTERENKO, A. P. ALEKSEYEVand A. N. PLYUSNIN Institute of Petroleum Chemistry,U.S.S.R. Academyof Sciences, Tomsk

(Received 25 February 1982)

PREVIOUSwork [1, 2] dealt with methods of separating resin-asphalthene substances (RAS) and other heterocyclic compounds (HC) from petroleums of Romashkino and Soviet (Tomsk region) deposits, which are based on complex-formation with titanium tetrachloride. Methods are also described,for the decomposition of the complex and preliminary separation of concentrates to form RAS and HC of lower molar mass. (Previous work [2] denotes these as. compounds of group A). Sulphur Compounds and aromatic hydrocarbons predominate among the last named. The composition of compounds separated from petroleums with TiCI4 are described below. EXPERIMENTAL

Concentrates of heterocyclic compounds were prepared from lower chalky Mesozoic petroleums of Soviet (well 641) and Fedorov (wells 73 and 129) deposits of West Siberia, containing respectively (wt. ~o) 1.47; 0.56 and 2.20 total sulphur, 0-48, 0.26 and 1.40 sulphide sulphur, 0.047; 0.028 and 0.033 basic nitrogen (Nba,lc). The total sulphflr content of the crude oils decreased by 32; 2.3 and 24 rel. ~o and the sulphide sulphur content by 46; 57-7 and 65 rel. ~o respectively after treatment with TiCI4. Nitrous bases (NB) were extracted by 25 ~o sulphuric acid solution [2] from a concentrate diluted with pentane (1 : 50 by volume). 2 g (well 641); 3-2 g (well 73) and 4.2 g (well 129) nitrous bases were extracted from 100 g of concentrate Separated from each petroleum. (Well number only will appear in the text for convenience of presentation). The extent of separation of NB from petroleums is 100~o, while from concentrates it is 71,70 and 74~o, respcctiyely. The.basic nitrogen content of NB is 4'0 to 4.6 Yo. A modification of the well-known method [3] used for the separation of nitrogen compounds from petroleum products was applied to free NB concentrates from aromatic sulphur compound impurities. A distinctive feature of this modification is the replacement of kaolin by 7A12Oz 1,2-dichloroethane as eluent replaced stepwise by (a) n-pentane, (b) pentane-benzene (1 : 1), (c) benzene and (d) ethanol. *

Ncftekhimiya 23, N o . 5, 604-609, 1983.

186

Composition of concentrates ot heterocyclicpetroleum compounds

18~

Tlae y-alumina was impregnated with ferric chloride in the same way as was kaolin. Further purification effected when nitrous compounds form strong complexes with FeCI3 and are ehitcd in'the form of coloured complexes, these were subsequently dissociated by heating with 1 0 ~ NaOH solution, the ligands were extracted with chloroform. NB fractions were combined before afialysis on the basis of identity of UV spectra. After separation of the nitrous bases the concentrate was fractionated on ASK silica gel using a hexane-benzene mixture as desorbent. Concentrates and their chromatographic fractions were analysed using a mass-spectrometer (model MKh-1303 accelerating voltage 2 kV) at 70 eV with direct introduction of the sample into the compartment. The MS composition of NB was calculated by methods previously described and the composition of aromatic sulphur concentrates, followed another study [5]. -: " RESULTS

Figure 1 shows one of the U V spectra of NBfr0m petroleum (well 641). The spectrum is due to the superpositionof all components, xievertheless it follows that cyclo'aromatic nitrogen compounds predominate. Absorpti0n bands with maxima at 212, 7t~nm 200

250 ?

.\

I

I

I

|

I~ ,I

300 I

!

I

350

I I I I I

to

' . ~ 2 l -I w v t t v ~ v ~ T ~ 48 ,44 4'0 2G, 32 ~.10~cm -I

Fz~. 1. UV spectra of the concentrate of nitrous bases of Soviet petroleum (well 641) obtained using ethanol (1) and ethanol in the presence of HCi (2). ~235 and 257 nm are observed in the UV spectrum of the concentrate in ethyl alcohol (spectrum 1). The diffuse maximum at 257 nm usually corresponds to ~z~z* transitions in the hetero-aromatic ring of pyridine derivatives and the maximum within the range of 200 to 235 nm may correspond to n~n* and n:-+n*-transitions of bicyclie compounds, particularly quinoline and the quinoline ion, bands of xvhich iisua!ly overlap [6]. A shift in absorption bands and further resolution of the spect r u m 0 f N B obtained in'C2HsOH with HCI additives (spectrum 2) confirms t h e presence of fi quinolinium ion in the mixture 0.m~.:=313 and 274 to 276 nm).

188

V . I . NvSTE~N~o et al.

Results of MS determination of molecular and characteristic ions indicate that homologous series are characterized in each case by compunds with-molecular formulae ranging from C,,H2n_sN to C.H2._21N (Table 1). Some compounds contain both nitrogen and sulphur atoms in the molecule and these rang from C.H2._gNS to C,,H2._llNS. Molecular formulae C.H2._sN and. CnH2._TN correspond to b

% mole Vo

8

4L

1

9

8 a

!

I

(

I2 14 16 I8 20 22 2q 2G Nc Numbep of capbon aloms in the molecule FIG. 2

2 3 q

1 2 3 4 56 Numbep o f finch'on

7 8

. FiG. 3

FIO. 2. b,lolar mass distribution according to the number of carbon atoms in the molecule of various compound series of the concentrate obtained from nitrous bases of Soviet petroleum: 1 - C . H z n _ s N , C.H2.-19N; 2 - C . H z . _ t T N ; 3 - C n H ~ . - I s N ; 4-C.Hzn-TN; C.H2._zIN; 5 - C.H.._ aaN; 6 - C.H2,- xaN; 7-- C~H2._ 9N. FIG. 3. Distribution of main types of aromatic hydrocarbon and sulphur compound (~o) in fractions of adsorption separation of aromatic sulphur concentrates. Adsorbent-silica gel (ASK); a: • -phenylparaffins; A-phenanthrcnes; []-acenaphthenes; 9 II-fluorenes; b: Ak-thiophenes, +-benzthiophenes; ID--thioindanes; c: ID-thiacycloparaffins; O-thiatricycloparaffins; V-thiatetracycloparaffins; Ak-thiabicycloparafl]ns; + cycloalkylthioparaffins.

pyridine and naphtheno-pyridine derivatives. The C,,H:,,_gN series may contain indole derivatives, as well as pyridine derivatives. C,,H2._xIN and C.H2._IaN series indicate the presence ofquinolines and naphthenoquinolines, while the CrH:._ 1~N series may incorporate carbazoles, as well as naphthene quinolines. However, indole and carbazole concentration of indoles and carbazoles should be low, since the overall nitrogen content in the concentrates agrees approximately with the content of basic nitrogen. Series ranging from C.H2._ 17N to CnH2._2~N are typicaI of benzoquinones and acridines, which cannot be distinguished in the mass-spec!rum and have practically identical thermodynamic stability. Therefore. the presence of each type

Composition of concentrates of heterocyci~c petroleum compounds

189

o f compound is equally probable. Bearing in mind the high extent of separation of NB with TiCI,~ it may be assumed that pyridine (CnH2,_ sN to C , H : , _ 9N) and quinoline (CnH2,-a~N to C, H2~-IsN) derivatives with alkyl substituents and naphthene rings predominate. The content of the former among NB varies within the range of 28.3 to 32"8Yo, and the l a t t e r - b e t w e e n 50 and 60yo. The rest is benzoquinolines and

TABLE 1. GROUP COMPOSITION OF NITROUS BASES SEPARATED FROM PETROLEUMS OF SOVIET AND FEDOROV DEPOSITS

Gross formula C.H2.-sN C-..H2._vN C.Hz._gN C,,H~._ atN CnH~._,3N C.H..-tsN

Content, mol. Yo well 73 I well 129 Iwell 641 17.1 15.9 13.1 1"3 4"3 10.4 9.9 6.8 9.3 31"9 33.1 12.9 27.2 19.7 13.4 0 2.4 13.6

Gross formula C,,H2,_ xTN C, H2,_IgN C, H2,-21N CnH2n-gNS C, H2,_ 1INS

Content, mol. Yo well 73 I well 129 Iwell 641 3.3 3.0 13.5 0 2"4 0 0 0.7 1"6 8"8 6.7 6.1 0 0 0'9

compounds with both sulphur and nitrogen in the molecule. Therefore, the most stable structures containing aromatic heterocycles predominate a m o n g NB of native petroleums. Similar results were obtained when studying NB of petroleums of South Uzbekistan and Sakhalin [7-9].

TABLE 2. GROUP COMPOSITION OF AROMATIC SULPHUR CONCENTRATES

SEPARATED WITH

TiCI4

FROM PETROLEMUS OF SOVIET AND FEDOROV DEPOSITS

Concentrate content, mol. Yo Type of Soviet Fedorov structure deposit, deposit, well 641 well 73 Sulphur compounds Thiophenes 14.4 2.5 Thiaindanes 6.4 8.5 Benzothiophenes 6-6 8.8 Dibenzothiophenes 3.6 4.0 Thiaparafiins 1.5 0-7 Cycloalkylthiaparatfins 9-1 4.7 Thiacycloparaffins 2.5 2-8 4.6 Thiabicycloparatiins 3'9 5.0 Thiatricycloparaffins 4.9 4.6 Thiat etracycloparaffins 4.2 0 Thiapentacycloparaffins 1.6 1.2 5.8 Phenylthiaparaffins 18.2 21.9 Other sulphur compounds

Concentrate content, mol. ~o Type of Soviet Fedorov structure deposit, deposit, well 641 well 73 Aromatic hydrocarbons Indanes 0 0'8 Dic~,cloallovlbenzcnes 1.2 1-5 Acenaphthenes 3.3 5.2 Fluorenes 4"6 3"8 Cycloalkylphenan0 1"8 threnes Phenylparattins 3.8 3"3 Naphthalenes 4.9 4.6 Phenanthrenes 3.6 3"6 Pyrenes 0:9 0-8 Chrysenes 0 0-3

|~

~. i. NEs~i~E~,ncoet aL

Figure 2 shows curves of molar mass distribution according to the number of (~arbon atoms in the molecule of various compound series comained in the overall concentrate of NB of a Soviet petroleum. The distribution curves show a maximum for molecules at C19-C2~, whilst the molar masses of all compound types vary within the mass range 170 to 310. The highest number of carbon atoms in the molecules of individual NB is 26 to 27, which corresponds with maxium molar mass of about 350. Compounds with higher molar mass are practically absent and the remaining proportion of basic nitrogen is concentrated in the petroleum resin/asphaltene portions. The composition of the aromatic sulphur concentrates (ASC) was studied, to reveal the basic compound types separated by complex-formationwith titanium tetrachloride. Table 2 shows MS analytical data of ASC separated from petroleums (wells 641 and 73). The tabulated data indicate that compounds with two or more aromatic rings (ranging from naphthalenes to phenanthrenes) dominate the aromatic hydrocarbons separated. The overall content of various sulphides in ASC is 23.7 70 (well 641) and 24"270 (well 73). Saturated sulphides of varying cyclic structure predominate among them (from 1 to 5 rings). Unsaturated sulphur compounds are represented by thiophene homologues (thiophenes, benzo- and dibenzothiophenes), the overall content of which (without thioindanes) is 22.2 and 15"47o, respectively. It follows from a comparison of the data that the ASC of the petroleums indicated is characterized not only by the same range of homologues, but also by a similar content of compound types (particularly sulphide content). The predominance of thiacycloparaffins among the sulphides is not influenced by complex-formation with TIC14, but reflects their ratio in petroleums, influenced perhaps by stress energy since this function of five-and six-membered rings is at a minimum [10]. Previous work [I 1] showed that the efficiency of separating sulphur compounds by complexformation with TiCI4 is independent of molar mass and is comparable with the efficiency of separation by the sulphuric acid method. Figure 3 shows distribution according to fractions from adsorption separation of the main types of aromatic hydrocarbon and sulphur compound (distribution diagram). A general regularity is observed when ACS are separated: aromatic hydrocarbons are concentrated together with certain thiophene homologues (fractions 1 to 4) in the initial fractions eluted with n-paraffins; sulphides are elutcd after the aromatic hydrocarbons have been removed, it is therefore possible to obtain fractions consisting mainly of sulphur compounds. The presence of nitrous bases and sulphides in concentrates may be regarded as regular since complexes of these compound classes are characterized by fairly high stability constants [12] and due to strong polarization of the donor-acceptor bond are apparently not readily soluble in hydrocarbon mixtures. Complexes of thiophene derivatives with TiCI4 (like those of aromatic hydrocarbons) are of low stability and their stability increases in step with increased condensation of the aromatic nuclei. Concentrates therefore contain only traces of phenylparaffins. Since the TIC14 complexes with thiophene derivatives and with aromatic hydrocarbons readily dissolve

Composition of concentrates of heterocyclic petroleum compounds

: 191

in hydrocarbons, their presence in concentrates is, probably, due to molecular interactions and the formation of mixed complexes, in which the coordination bond is localized up on n and n-donors, for example

O

•

X=S orN. The hydrogen bond has a particularly significant effect on .the separation selectivity of heterocyclic compounds. Previous work [13] summarizes hydrogen bond . behaviour; the work suggest that practically all classes of petroleum heteroc~clics are able to hydrogen bond. Methods based on complex:formation are attractive since compounds eomplexing through hydrogen bonding may separate.without breakdown, since this bond is formed via a mobile proton, while the donor-acceptor b.ond i s via a hetero-atom.-The following system illustrates the situation. R:

\

/ NH.;.O

/!

R2 "TiCl.~

R3

\ R4

Because of molecular interactions low molar mass heterocyclies may also be concentrated and separate with polyfunctional, higher molecular weight ligands, such as RAS. The theory of mixed complexes has been discussed previously [14]. If the coorchnation number of the electron acceptor is greater than one and the system contains two (A and ]3) or more different ligands, it is always possible to form mixed complexes of general type MAIBj. Calculations, show that the formation of mixed complexes is even more advantageous than the formation of simple MAn and MBn type complexes. Unfortunately the molecular interaction role in the formation of mixed complexes with electron acceptors during the separation of petroleum heterocyclics has not been studied in practice, although a better understanding of such systems could result in a fundamentally new approach to the separation of complex petro-. leum mixtures. SUMMARY

1. The group composition of nitrous bases and aromatic sulphur compounds isolated by complex-formation with titanium tetrachloride from Soviet and West Siberian (Fedorov) crude oils was studied. 2. Homologous series of nitrous bases are characterized by practically identical compounds ranging from CnH2n_sN to CnH2n_2tN. Pyridine and quinoline derivatives with alkyl substituents and naphthene rings predominate. 3. Thiacycloparaffins with a number of naphthene rings in the molecule of 1 to 5 predominate among saturated sulphur compounds. Unsaturated sulphur compounds are represented mainly by homologues of thiophene, benzo- and dibenzothiophene.

192

V. I, NES~RENKO et al. REFERENCES

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