Aqua Conversion 1

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SUMMARY

Selective Catalytic Steam Cracking (SCSC), better known as Aquaconversion

technology, is a process that combines thermal cracking and catalytic water dissociation

reaction to upgrade heavy crude oils and vacuum residues by increasing API gravity [1].

Product characterization studies of model molecules and real feedstocks have shown that

some of the chemical changes that occur during SCSC, involve dealkylation of side chains

from alkylaromatic moieties [1-2]. However, to get a better understanding of the structural

transformations experimented by high molecular weight fractions, spectroscopic techniques

and Ruthenium ion catalyzed oxidation (RICO) reaction have been used as characterization

tools.

The purpose of this work is try to predict from spectroscopic data and RICO information

the processability potential of two feedstocks under SCSC conditions. Thus, structural

quality parameter (SQP), defined from spectroscopic data, was found to be helpful to

describe feedstock behavior under AQC conditions. At the same time, RICO procedures

gave valuable information about aliphatic group distributions that was in agreement with

the calculated SQP values. Additionally, RICO results gave some insights related to the

reactivity of the identified aliphatic groups and about their contribution to the conversion

values achieved by the studied vacuum residues.

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1. INTRODUCTION

Selective Catalytic Steam Cracking (SCSC), better known as Aquaconversion

technology, is a process that combines thermal cracking and catalytic water dissociation

reaction to upgrade heavy crude oils and vacuum residues by increasing API gravity [1].

During this moderate conversion process, water molecules are catalytically dissociated to

form hydrogen free radicals. These radicals saturate hydrocarbon free radicals formed by

thermal cracking of feedstock components (Figure 1). By this way, condensation reactions

are quenched in such extension that coke formation is considerably reduced. As a result,

lighter hydrocarbon products are formed at higher conversion values than those achieved by

traditional thermal cracking processes at a similar product (vacuum residue) stability level

[1-2].

Previous works related to the Aquaconversion chemistry [3-5] have pointed out that

dealkylation of side chain from alkylaromatic structures is one of the chemical changes that

occur during the process. According to these works, water and the catalyst seem to have a

preference for breaking CSp3-CSp2 bonds located in -position from the aromatic ring.

Consequently, aromatic entities rich in alkyl substituents are expected to give higher

conversion levels than less alkylsubstituted aromatic ones [1-5]. Considering SARA

constituents of feedstocks, aromatic, resin, and asphaltene fractions are the most affected

because alkylaromatic moieties are concentrated in such fractions [4-5]. These observations

are an indicative of the influence of the carbon type distribution on the SCSC conversion

level.

It is important to keep in mind that aliphatic carbons are distributed among several

substituents in alkylaromatic structures. For instance, normal alkyl chains, branched alkyl

chains, polymethylene bridges and naphthenic functionalities are presented in complex

fractions as resins and asphaltenes. Consequently, it is difficult to study aliphatic

substituent distributions based only on the structural average information given by 13C and 1H NMR techniques.

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Figure 1: SCSC Reaction Sequence

To get a more detailed and accurate molecular description it is necessary to adopt

complementary characterization procedures. Chemical methods have been used extensively

for this purpose.

Some chemical methods have the property of breaking C-S, C-O, and Caliphatic-Caromatic bonds

with high selectivity [6-8]. The analysis of resulting products gives invaluable detailed

information on the structural elements, structural units and molecular architecture of resins

and asphaltenes. The selective cleavage of Caliphatic-Caromatic bond has become the most

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Water Dissociation

Thermal Cleavage

Hydrogen Addition

R Rn´

R Rn´+

Oxidation

+ Rn´R Rn´ Rn´ R R+

Condensation

H2O H OH+ Catalyst

R Rn´ R H Rn H+ 2H + + Catalyst

Rn´ + 2OH Rn'-1 + CO2 + H2

Catalyst

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popular chemical method. One of the procedures used for this purpose involves Ruthenium

ions and it is known as Ruthenium Ion Catalyzed Oxidation (RICO) reaction.

RICO reaction does not cleavage directly the Caliphatic-Caromatic bond. This reaction is able to

convert aromatic carbons selectively to carbon dioxide and/or carboxylic groups while

leaving aliphatic structures essentially unaffected [9-21]. The reaction pattern is very

simple and has been studied using model compounds [9-17]. Thus, alkylsubstituted

aromatic molecules are oxidized to CO2 except at the site of the alkyl attachment, which is

converted to a carboxylic group anchored to the alkyl chain, with the subsequent formation

of an alkanoic acid [9-21]. This situation is showed in scheme 1:

Scheme 1

When the aliphatic chain is between two aromatic carbons, a dicarboxylic acid results:

Scheme 2

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R

RICO CHO R

O

+ CO2

1

2

3

4

RICOHOOC

HOOC

(CH2)n

O

HO (CH2)nRICO

O

OH

RICOHOOC

HOOC

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In this case, ,-dicarboxylic acids are formed by the oxidation of naphthenic structures as

1,2,3,4-tetrahydronapftalene (3) or cyclopropylbenzene (4) derivatives cannot be

distinguished from those ones formed by the oxidation of , diphenylalkanes (2) [9-21].

However, Nomura et al [15-17] have pointed out that more complex naphthenic

(Hydroaromatic) structures can be easily inferred by the analysis of alkane polycarboxylic

acids formed during RICO reaction:

Scheme 3

If this kind of structures is presented in resins and asphaltenes, alkane polycarboxylic acids

are expected to be form during RICO reaction.

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7

HOHO

O

O HO

O

5

6

9

10

8

HO

HO

HO O

O

O

11

HOOCCOOH

COOH

COOH

12

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Another feature of RICO reaction is that aromatic rings are not completely oxidized to CO2

and some of them remain as benzene di, tri, tetra and less abundant penta and

hexacarboxylic acids [18]. Commonly, polyaromatic structures yield this kind of products.

For example, when one of the aromatic rings of such structures is oxidized, a carboxylic

group is formed on the adjacent aromatic ring. The deactivating effect of the carboxylic

group avoids the subsequent oxidation of the second ring. As a consequence, the latter

remains as a benzene carboxylic acid in the RICO product mixture [18] (Scheme 4)

Scheme 4

In contrast, alkyl groups on the benzene ring have an activating effect. Therefore (with the

exception of the methyl group) the alkyl-substituted ring is oxidized to CO2 . Additionally,

the position of the alkylsubstitution determines whether one or both rings will be oxidized.

If the alkyl substituent is in a position where a carboxylic group might form by the

oxidation of the host ring, the unsubstituted ring will also be oxidized [18] (Scheme 5):

Scheme 5

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RICOCO2 +

COOH

COOH

13

R

RICOCO2 + RHOOC

RRICO

CO2 + RHOOC +

COOH

COOH14

15

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Most condensed aromatic molecules would give more than one acid. Thus, for example,

pyrene can yield the 1,2,3-triacid and the 1,2,3,4 tetracid:

Scheme 6

Table 1 lists common benzene polycarboxylic acids found in RICO product mixture and

their possible aromatic system precursors [15-18].

As can be seen, the analysis of benzene polycarboxylic acids provides invaluable insight

into the mode of condensation and possible structures of aromatic systems contained in

resin and asphaltene fractions.

Thus, the analysis of RICO products together with the information provided by

spectroscopic techniques can give important structural details of the most affected SARA

fractions during SCSC process (i.e., Aromatics, Resins and Asphaltenes). The scope of the

present work is to use chemical and spectroscopic methods for the characterization of two

vacuum residues: Arabian light and Cerro Negro, in order to study and predict their

behavior under SCSC (Aquaconversion) conditions.

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HOOC

HOOC

COOH

HOOC

HOOC

COOH

COOH

16

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Table 1. Possible precursors of benzene carboxylic acids

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Benzene carboxylic acidPrecursor

Possible Precursors

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2. EXPERIMENTAL

2.1 SARA Fractionation

Asphaltenes from two vacuum residues (Arabian Light (AL) and Cerro Negro (CN) were

obtained by precipitation with n-heptane (HPLC grade, J.T Baker) [22]. The resulting

maltene portion was fractionated into Saturates, Aromatics and Resins by preparative

HPLC as indicated in reference [23]. SARA fractions were further characterized by

elemental analysis (Carbon (C), Hydrogen (H), Oxygen (O), Sulfur (S), Nitrogen (N)),

Vapor Phase Osmometry (VPO), and Nuclear Magnetic Resonance spectroscopy (1H NMR

and 13C NMR).

2.2 Elemental Analysis and Molecular weight Determination.

C, H, and O were determined in a LECO Analyzer, model CHSN-932. Sulfur was

determined in a LECO Analyzer, model IR 432 and Nitrogen, in a Dorhman Analyzer,

model 1000. Average molecular weight was determinated in a Knauer Osmometer using

CH2Cl2 and CHCl3 as solvents. Benzil was used as a reference material.

2.3 1H NMR Spectroscopy and Average Molecular Parameter Calculation.

NMR analyses were performed in a Bruker Spectrometer ACP-400. 1H NMR spectra were

acquired at 400 MHz with a 12 ppm window and a flip angle of 45º. The recycle time was 5

seconds and TMS was used as reference. Sample concentration was 25 mg/mL in CH 2Cl2/

CS2 1:1.

1H NMR data, carbon and hydrogen content determined by elemental analysis, and VPO

molecular weight were used as input data to calculate Average Molecular Parameters

(AMP) by the methodology reported in reference [24].

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2.4 13C NMR Spectroscopy.

13C NMR analyses were performed at 100.614 MHz. About 400 mg of the sample were

dissolved in a Cr (III) acetylacetonate / deuterated chlorofom solution (0.01 M). 13C NMR

spectra were acquired using a single pulse technique (30º pulse ) with a period of 5 second

between each pulse. 8000 pulses were accumulated in 12 hours.

2.5 RICO Reaction Procedure and CO2 Measurement.

Aromatic, resin and asphaltene fractions from AL and CN vacuum residues were submitted

to RICO reaction as follow:

About 200.0 mg of sample, 12.0 mg of RuCl2.3H2O, and 4.0 g of NaIO4, were placed into a

250 mL flat bottom glass reactor prototype, designed to measure the pressure of CO2

evolved during the reaction, (Figure 2). Air contained in the reactor was evacuated using

vacuum and replaced by N2. With a N2 positive pressure and using a glass funnel, 6.0 mL of

CCl4, 6.0 mL of CH3CN and 10 mL of H2O were added. Then, the reactor was closed

hermetically and filled with N2 up to reach a pressure of 3.0 psi.

The heterogeneous mixture was magnetically stirred for 24 hours at room temperature,

during which the initial dark brown color changed to yellow pale. At this point the reaction

was stopped and the final pressure was measured.

Concentration of the evolved CO2 was measured by using the GASTEC colorimetric

method. GASTEC No. 2H Carbon Dioxide detector tube with a measuring range of 1-10 %

v/v (Gastec Corporation) was connected to the reactor N2 inlet and to the GASTEC pump

for the other end. Then, 50.0 mL of the gas contained in the reactor were taken by suction

of the GASTEC pump. CO2 was absorbed on the package as the gas passed through the

GASTEC detector tube. A color response was generated indicating CO2 concentration

level.

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Figure 2. RICO Reactor prototype

After CO2 measurement, the reaction mixture was filtered trough a 0.2 m pore size

Nylon-66 filters and the precipitate was washed with diethylether. The aqueous and the

organic phases were separated and the former was further extracted with 10x2 mL of

CH2Cl2. Washings were combined with the original organic layer. About 150 mL of a

0.1mM NaOH in methanol solution were added to the aqueous layer to neutralize acidic

products and to induce the precipitation of the NaIO4 excess. After standing for a 24 h

period, aqueous and organic phases were filtered. Aqueous phase was evaporated at 70°C

to dryness. Organic phased was joined to the evaporated aqueous phase and concentrated

using a N2 stream.

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N2

Vacuum

Pressure Gauge

Magnetic Stirrier

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2.6 Esterification Procedure.

Esterification of RICO products was carried out by adding 5,0 mL of a 14% solution of BF 3

in methanol (Pierce Chemical) to the product solution. The resulting mixture was stirred at

room temperature for 12 hours. After adding the esterifier reagent, the yellow pale color of

the product solution changed to red because of iodine liberation. To eliminate this

interference, about 100 mg of Zinc powder was added to reduce I2 to I- [21]. Then, the

mixture was dried over Na2SO4, filtrated, and concentrated to 1.0 mL by rotary evaporation

at 30ºC and N2 stream. The methylester solution was further analyzed by GC-MS.

2.7 GC-MS Analysis.

GC-MS analyses were performed in a HP5890 Serie II Gas Chromatograph equipped with

a split injector and a BD-1701 capillary column (30m x 0.25mm coated with 0.5m DB-1)

connected to a HP5970 mass detector. Helium gas used as carrier gas. Typically operating

chromatographic conditions are listed in Table 2

Table 2: Operating chromatographic conditions in GC-MS analysis

Initial T (ºC) Final T (ºC) T Ramp (ºC/min)

Injector 250 250 0

Column 35 300

300

7

n/ Final T

2.8. Pilot Plant Tests.

Pilot plant tests were performed in a one barrel/day capacity pilot plant operated at a fixed

temperature and fed with the Arabian Light or the Cerro Negro vacuum residue, steam,

and the catalyst. The reaction was stopped when products reached a critical P-value of 1.20

(P-value was determined as indicated in reference [25]).

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3. RESULTS

The following partial results correspond to the characterization of Arabian Light and Cerro

Negro vacuum residues used as AQC and Viscoreduction feedstocks. In a second issue,

characterization of AQC and Visbreaking products will be presented.

3.1 Elemental Analysis and Selected Properties.

As a first characterization step, selected properties of Arabian light and Cerro Negro

residues were determined. These results are presented in Table 3.

Table 3: Selected Properties of Residues.

Property Arabian Light

Residue

Cerro Negro

Residue

API Gravity 7.0 3.8

Kinematic viscosity cSt, 210 ºF 1034 40269

Kinematic viscosity cSt, 275 ºF 153 2030

Conradson Carbon Residue, % wt. 19.9 22.0

Asphaltenes (n-heptane insolubles), % wt 7.5 18.7

Elemental Composition, % wt

C

H

N

O

S

84.7

10.61

0.32

0.52

4.10

83.84

10.22

0.93

0.86

4.23

Metals, ppm

Nickel

Vanadium

Potassium

20.03

76.00

1.62

145.20

619.50

3.05

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According to API gravity values, Cerro Negro residue (CN) resulted heavier than the

Arabian Light residue (AL) (3.8 º API and 7,0 º API respectively). This tendency is a

reflect of the higher content of asphaltenes, heteroatoms and metals, together with the lower

content of paraffins, carbon and hydrogen present in Cerro Negro residue.

On the other hand, CN residue has a higher Conradson carbon value than AL residue.

Conradson carbon residue is considered as a parameter to evaluate coke formation

tendencies of crude oils and their derivatives [26]. According to this, CN residue could

potentially form higher coke amounts than AL residue.

Table 4 shows atomic ratios of the studied residues. CN presented a lower H/C ratio and

higher N/C, O/C, and S/C ratios compared to the AL residue. These results are in

agreement with the low API value showed by this residue.

Table 4: Atomic ratios of Arabian Light and Cerro Negro residues

Residue H/C N/C x 10-3 O/C x 10-3 S/C x 10-2

AL 1.50 3.24 4.60 1.82

CN 1.46 9.50 7.69 1.89

Even though the miscellaneous properties determined give important information about

physicochemical features of residues, they are insufficient to describe them in a structural

fashion and to predict their behavior under SCSC conditions. Consequently, alternative

characterization strategies, based upon SARA fractionation and spectroscopy techniques,

were adopted to reach this goal.

3.2. SARA Distributions.

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Figure 3 shows SARA distribution of AL and CN residues. AL residue has a major

content of saturates (14.7 % wt) than CN residue (6.1% wt). According to the suggested

mechanism for SCSC, AL residue has a 85,3 % wt (aromatics+resins+asphaltenes) that can

be converted, whereas CN residue has a 93,9 % wt. (8,3% higher). As a first

approximation, it seems that CN residue could show a higher conversion value because it

has a major yield of the mainly affected fractions in SCSC.

Figure 3: SARA distribution of AL and CN residues.

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14,76,1

53,9

38,7

23,9

36,5

7,518,7

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

Arabian Light

% W

t

Saturates

Aromatics

Resins

Asphaltenes

Cerro Negro

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As stated before, aromatics, resins and asphaltenes suffer the most important chemical

changes in SCSC [4-5]. Among them, the aromatic fraction was that affected the most. As

observed in Figure 3, AL residue is richer in aromatic fraction, whereas CN residue is in

polars (resins+ asphaltenes). Even though AL residue presents a higher content in aromatic

fraction, this is not a guarantee to ensure high conversion levels, because in SCSC,

transformations could be associated not only to weight yields of SARA fractions, but also

to the structural characteristics of them [5]. In consequence, it is difficult to establish from

SARA distributions, which of the studied residues will show the highest conversion level.

3.3 Structural Quality of SARA fractions: 13C NMR Analysis.

It has been discussed how SARA distributions do not give enough information to predict

relative conversion levels in SCSC. In consequence, other parameters must be found to

improve such predictions.

It is believed that alkyl substituents in aromatic structures can have a significant influence

on the conversion value [1-5], Therefore, it is necessary to evaluate their relative abundance

in order to establish this influence. Thus, the ratio alkyl substituent/aromatic ring can be

used as a parameter to estimate the structural quality of a SCSC feedstock and to predict its

behavior under SCSC conditions. 13C NMR data gives information about carbon type

distributions (aromatic and aliphatic carbons) of SARA fractions that can be used to

estimate this parameter.

Figures 4 and 5 show 13C NMR spectra of fractions of AL and CN residues respectively.

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31

.4

89

68

.5

11

In

te

gr

al

37

.0

54

83

2.

70

01

31

.9

05

72

9.

68

86

27

.0

59

9

22

.6

83

51

9.

69

37

14

.1

47

4

( p p m )

01 02 03 04 05 06 07 08 09 01 0 01 1 01 2 01 3 01 4 01 5 01 6 01 7 0

45

.1

19

54

.8

81

In

te

gr

al

37

.0

76

5

31

.9

05

72

9.

68

86

22

.6

90

81

9.

69

37

14

.1

54

6

( p p m )

01 02 03 04 05 06 07 08 09 01 0 01 1 01 2 01 3 01 4 01 5 01 6 01 7 0

61

.2

37

38

.7

63

In

te

gr

al

37

.1

41

5

31

.9

99

62

9.

71

03

22

.7

26

91

9.

79

48

14

.1

69

1

( p p m )

01 02 03 04 05 06 07 08 09 01 0 01 1 01 2 01 3 01 4 01 5 01 6 01 7 0

Figure 4: 13C NMR spectra of fractions from AL residue

33

.3

00

66

.7

00

In

te

gr

al

13

9.

33

66

12

6.

71

29

37

.3

50

93

2.

71

46

31

.9

12

92

9.

68

86

22

.6

90

81

9.

70

10

14

.1

54

61

1.

43

20

-0

.0

00

0

( p p m )

02 04 06 08 01 0 01 2 01 4 01 6 01 8 0

34

.3

20

65

.6

80

In

te

gr

al

37

.3

50

93

2.

69

29

31

.8

91

32

9.

67

42

22

.6

69

11

9.

69

37

14

.1

47

4

( p p m )

01 02 03 04 05 06 07 08 09 01 0 01 1 01 2 01 3 01 4 01 5 01 6 01 7 0

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Aromatics

fa = 0.315

Resins

fa = 0.451

Asphaltenes

fa = 0.612

Aromatics

fa = 0.333

Resins

fa = 0.343

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52

.7

42

47

.2

58

In

te

gr

al

( p p m )

01 02 03 04 05 06 07 08 09 01 0 01 1 01 2 01 3 01 4 01 5 01 6 01 7 0

Figure 5: 13C NMR spectra of fractions from CN residue

According to these results, AL resin and asphaltene fractions have a major aromatic

character than the same CN fractions because of their higher aromaticity factor (fa) value.

Figure 6 shows aromatic and aliphatic carbon distribution (expressed as type of C/total C)

in aromatic, resin and asphaltene fractions from both residues. From this distribution, a

Structural Quality Parameter (SQP), defined as Caplihatic/Caromatic ratio, was calculated for

each fraction. Results are summarized in Table 5.

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Asphaltenes

fa = 0.527

68,51

66,70

65,68

38,76

47,26

31,49

33,30

45,12

34,32

61,24

52,74

54,88

0

10

20

30

40

50

60

70

80

90

100

AL

% W

t

C Aromatic

C Aliphatic

Aromatics Resins Asphaltenes

AL AL CN CN CN

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Figure 6: Aliphatic and aromatic carbon distributions of SARA fractions from AL and CN residues obtained by 13C NMR analysis.

Table 5: Structural Quality Parameters (SQP) of Aromatics, Resins and Asphaltenes of AL

and CN Residues

Vacuum Residue

SQP= Caplihatic/Caromatic


AL 2.18 1.21 0.63

CN 2.00 1.91 0.90

A small difference between SQP values of aromatic fractions is observed. This means that

such fractions have some features that make them similar from a structural point of view.

Consequently, both aromatic fractions are expected to be chemically transformed at a

similar extension under SCSC conditions.

SQP values of resins and asphaltenes were higher in CN residue, compared to those

calculated for AL fractions. This indicates a better structural quality of resins and

asphaltenes for the SCSC process. Differences of 0.70 and 0.33 in SQP values for resins

and asphaltenes are observed respectively. According to these results, resins and

asphaltenes from CN residue show a noticeable difference in alkyl substituents that could

have a marked influence on the conversion value. Therefore, these fractions are expected to

have a more important contribution to the conversion of CN residue than in the case of AL

residue.

Total alkyl substituents and total aromatic structures contained in each residue can be

estimated too. To do this, it is necessary to consider aromatic, resin and asphaltene yields

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(from SARA separations) together with carbon content of each fraction (from elemental

analysis), and 13C NMR data. The results are plotted in Figure 7.

Figure 7: Weight contribution of aliphatic and aromatic carbons in the combined (aromatic, resin and

asphaltene) fractions to the total carbon content in AL and CN residues.

Thus, CN residue presents a 93,3 % wt of structures that can potentially be converted under

SCSC conditions (Aromatics+Resins+Asphaltenes). This convertible portion has a total

carbon content of 78,07 %, distributed as follow: 48,72% as aliphatic carbon and 29,35% as

aromatic carbon. On the other hand, AL residue has 85,3 % wt of these structures, where

carbon represents 71.46 % wt comprising 44.36% aliphatic and 27.10% aromatic carbons.

In Table 6, the carbon type distributions among aromatics, resins, and asphaltenes are

listed.

Table 6: Total carbon type distribution in AL and CN residues and the individual

contribution of main SARA fractions converted during the SCSC process.

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27,10

44,36

29,35

48,72

0

10

20

30

40

50

60

% C aromatic % C Aliphatic

% wt (C/sample wt.)

AL

CN

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AL Residue CN Residue

% CTotal %C Aliphatic %CAromatic % CTotal %C Aliphatic %CAromatic

Aromatics 45.26 31.01 14.25 32.40 21.61 10.79

Resins 19.85 10.89 8.96 29.99 19.70 10.29

Asphaltenes 6.35 2.46 3.89 15.68 7.41 8.27

Total 71.46 44.36 27.10 78.07 48.72 29.35

Considering these results, a Total Structural Quality Parameter (TSQP) was calculated for

each residue considering total aliphatic and aromatic carbon content in Aromatic, Resin and

Asphaltene fractions ((Caliphatic)/(Caromatic)). Results are listed in Table 7.

Table 7: Total Structural Quality Parameter Calculated for AL and CN Residues.

Residue TSQP= (Caliphatic)/(Caromatic).

AL 1.64

CN 1.66

Thus, a subtle difference in TSQP values was observed: CN residue TSQP value is a little

bit higher compared to the one obtained for AL residue.

To explain this result, we have to consider that TSQP value has two main components: A

quality component and a mass yield component. Quality component is related to the

individual SQP value of the mainly affected SARA fractions, while the mass yield

component is related to the relative weight percentage of them. Each component will have

and important contribution to the TSQP value. For instance, mass yield of the aromatic

fraction of AL residue will have a more important contribution than the one corresponding

to resins and asphaltenes. In contrast, mass yield of resins and asphaltenes from CN residue

will have a significant contribution to the TSQP value than the aromatic one. Depending on

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the contribution of each component to TSQP, the resulting difference between two TSQP

values will be bigger or smaller. In this case, the difference was small. In consequence, it is

difficult to make a prediction based only on this parameter. Individual SQP values should

be considered instead.

As stated before, the aromatic fractions in both residues are expected to undergo chemical

changes at the same extension because they have almost the same SQP value. However,

resins and asphaltenes in CN residue should be more affected than the same fractions in AL

residue. The global effect is that CN residue should experience more chemical changes

than residue AL residue SCSC conditions.

3.4 Structural Quality Parameters Calculated from 1H NMR Data.

Average molecular parameters were calculated using information from 1H NMR spectra,

VPO molecular weight, and total carbon content as indicated in reference [24]. Aliphatic

and aromatic carbon content of aromatic, resin and asphaltene fractions were determined

among these parameters. Additionally, SQP values were calculated too. Results are

summarized in Table 8.

Table 8: SQP values Calculated from 1H NMR Data

Residue


%

Caliphatic

% Caromatic

SQP%

Caliphatic

% Caromatic

SQP%

Caliphatic

% Caromatic

SQP

AL 72.18 27.82 2.59 54.71 45.29 1.21 60.01 39.96 1.50

CN 72.10 27.90 2.58 58.99 41.01 1.44 61.73 38.26 1.61

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As can be seen, SQP values determined from 1H NMR data, differs from those calculated

from 13C NMR data. The difference is attributed to the considerations made during average

molecular parameter (AMP) calculation. However, the tendency is the same: Higher SQP

value for resins and asphaltenes from CN residue and almost the same SQP value for the

aromatic fraction of both residues. Therefore, predictions made upon 13C NMR data are

reinforced by 1H NMR results. Less demanding analytical requirements of 1H NMR suggest

this option as a better alternative for routine analysis.

3.5 Pilot Plant tests.

Predictions were confirmed during SCSC pilot plant test. These tests were performed using

AL and CN residues as feedstocks. The reaction was stopped at the conversion level where

products showed a minimal P-value of 1.20. In this case, P-value was used as a product

stability criterion (a P-value under 1.15 indicates that products are unstable and solid

deposition (asphaltenes) can occur [1]).

Table 9 shows results obtained from pilot plant tests. As predicted, at the same critical

product stability level (P-value of 1.20), CN residue showed higher conversion level than

AL residue. Surprisingly, CN residue showed a difference in conversion of 13.2 % respect

to AL residue, which was unexpected considering general properties of the total structural

quality parameters (TSQP). This remarkable result is believed to depend on the structural

quality of resins and asphaltenes of this residue. The fact that aromatic fractions of AL and

CN residues have almost the same structural quality implies that they should be converted

at the same extension. On the other hand, SQP values of resins and asphaltenes from CN

residue predicted higher conversions for these fractions. Therefore, they are believed to be

the main responsible for the conversion value achieved by this residue.

Table 9: Results from Pilot Plant Tests.

PDVSA-INTEVEP

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INT-8989, 2001

Feedstock Product P-value Conversion (%)

AL 1.20 19.5

CN 1.20 32.7

3.6 Structural Details of Aliphatic Substituents in SARA Fractions. RICO Product

Analysis.

To get a deeper knowledge about aliphatic distribution in aromatic, resin and asphaltene

fractions from the studied residues, RICO reaction was performed. Four kinds of aliphatic

substituents were identified: Normal alkyl side chains, branched alkyl side chains,

polymethylene bridges and hydroaromatic (naphthenic) structures. Remarks about these

results are discussed as follow:

3.6.1. Normal Alkyl Side Chains.

Alkyl side chains attached to aromatic carbons in aromatic, resin and asphaltene molecules

can be converted to alkanoic acids by RICO as shown is scheme 1 [9-21]. If the R groups

are normal alkyl groups, then the resultant acids form a series of n-alkanoic acids. These

products were quantified by GC-MS in the form of methylesters by the m/z 74 fragment

ion. Authors have reported length of the n-alkyl side chains from C2 to C28 and up to C33

[14-21]. However, shorter chains (from C2 to C5) are difficult to analyze as ester

derivatives because of their high volatility, they are lost during the evaporation procedure

performed as a previous step to the GC-MS analysis[11-21]. Ion Chromatographic

technique has been used to solve this problem [15-20]. Unfortunately, this methodology

was not adopted in the present work, so the information related to these specific

substituents was lost. As a consequence, normal and branched alkyl chains distributions

start in C6 component for all fractions analyzed.

3.6.1.1 Normal Alkyl Chains in Aromatic Fractions.

PDVSA-INTEVEP

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INT-8989, 2001

RICO oxidation has been successfully used in the characterization of resins and

asphaltenes [9-21]. Works related to the characterization of aromatic fractions by this

chemical method has not been reported up to now. It is important to point out that this is

the first work done on this fraction. Results are discussed in the next paragraphs.

Figure 8 shows n-alkyl chain distribution in the aromatic fraction of AL and CN residues.

A bimodal distribution was observed in both cases, which declines with increasing length

of the alkyl chain. For AL residue, n-alkyl chain distribution starts in C6 and ends in C27,

maximizing at C9, C16 (the most abundant) and C18 components.

Figure 8: Normal-alkyl chain distribution in the aromatic fraction of AL and CN residues

In the case of CN residue, distribution begins in C6 and ends in C25; showing picks at C8

(most abundant) and C16. In this latter case, distribution declines almost monotonically and

it is observed enrichment in shorter chains (C6 to C11). In contrast, AL aromatic molecules

are enriched in longer but less abundant n-alkyl chains.

3.6.1.2 Normal Alkyl Chains in Resin Fractions.

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0

2

4

6

8

10

12

C6

C7

C8

C9

C10

C11

C12

C13

C14

C15

C16

C17

C18

C19

C20

C21

C22

C23

C24

C25

C26

C27

Rela

tive A

rea (

%)

AL CN

INT-8989, 2001

Figure 9 shows distributions of normal alkyl side chains in the resin fractions sutied. It is

observed a multimodal distribution that starts in C6 and ends in C25 for the AL case and in

C26 for the CN case. Higher picks are reached at C9, C14, C16 and C18 components in both

fractions. However, AL resin molecules exhibit a small enrichment in almost all

components, except in C6, C9, C16 and the less abundant but longer C22 to C26 substituents.

Figure 9: Normal alkyl chain distributions in AL and CN resin fractions.

3.6.1.3 Normal Alkyl Chains in Asphaltene Fractions.

PDVSA-INTEVEP

25

0

2

4

6

8

10

12

14

16

C6

C7

C8

C9

C10

C11

C12

C13

C14

C15

C16

C17

C18

C19

C20

C21

C22

C23

C24

C25

C26

Rela

tive A

rea (

%)

AL CN

INT-8989, 2001

Alkyl chain distributions in asphaltene fractions were quite different in both residues

(Figure 10). AL asphaltene molecules exhibit a gaussian n-alkyl chain distribution which

begins in C6 and ends in C25 reaching the highest pick at C16, whereas CN asphaltene

molecules have a multimodal distribution from C6 to C25 with higher picks located at C9 and

C16 respectively. Additionally, CN asphaltenes are enriched in shorter alkyl chains (from C6

to C11), but AL asphaltenes are in longer components ( from C13 to C24).

Figure 10: Normal alkyl chain distribution in AL and CN asphaltene fractions

3.6.2 Branched Alkyl Side Chains.

Branched alkyl chains form branched alkanoic acids under RICO conditions [9-21]

(Scheme 1). However, authors point out that they are present in resins and asphaltene

molecules in low concentrations [9-21]. Strausz and co-workers [18] have identify four

families of -branched n-alkyl substituents, where the -pedant groups were methyl, ethyl,

n-propyl and n-butyl functionalities. These families derive from -branched alkyl aromatic

structures presented in resin and asphaltene fractions (Figure 11). And are quantified as

methylesters by the m/z= 88 fragment ion for -methyl derivatives, m/z =102 -ethyl

derivatives, m/z= 116 for -propyl derivatives, and m/z= 130 for -butyl derivatives.

Isoprenoid substituents were identified too.

PDVSA-INTEVEP

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0

2

4

6

8

10

12

14

16

18

20

C6

C7

C8

C9

C10

C11

C12

C13

C14

C15

C16

C17

C18

C19

C20

C21

C22

C23

C24

C25

C26

Rela

tive A

rea (

%)

AL CN

INT-8989, 2001

Figure 11: Precursor structures of -methyl, -ethyl, -n-propyl and -n-butyl alkyl chains.

In the present work, only -methyl alkyl chains were identified, the other families were in

such low concentrations that it was impossible to analyze them under the used instrumental

conditions.

3.6.2.1 Branched Alkyl Side Chains in Aromatic Fractions.

Figure 12 shows -methyl alkyl chain distributions obtained under RICO oxidation of the

studied aromatic fractions. It is observed a bimodal distribution for CN aromatic fraction

that starts in C6 and ends in C17. Higher picks are reached at C8 and C13. In contrast, -

methyl alkyl chain distribution for AL aromatics is longer than the one observed in CN

(from C6 to C25), but it declines smoothly with length chain. Higher picks are observed at C7

and C13. Additionally, molecules form AL aromatic fraction are enriched in longer but less

abundant branched substituents (C14-C25); whereas the corresponding CN aromatic fraction

molecules are in shorter but more abundant ones (from C6 to C13).

PDVSA-INTEVEP

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( )n n( )

n( ) n( )

17 18

18 19

INT-8989, 2001

Figure 12: -methyl alkyl chain distributions of AL and CN aromatic fractions

3.6.2.2 Branched Alkyl Side Chains in Resin Fractions.

In the case of resin fractions, AL residue showed an almost aussian distribution extended

from C6 to C22. Distribution in CN resin fraction is bimodal and the same includes C6 to C24

substituents. Another feature observed is that AL resin fraction molecules are enriched in

almost all its components in comparison with CN homologues except in C7, C8 and C13

substituents (Figure 13).

Figure 13: -methyl alkyl chain distributions of AL and CN resin fractions

PDVSA-INTEVEP

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0

2

4

6

8

10

12

14

16

18

MeC6

MeC7

MeC8

MeC9

MeC10

MeC11

MeC12

MeC13

MeC14

MeC15

MeC16

MeC17

MeC18

MeC19

MeC20

MeC21

MeC22

MeC23

MeC24

MeC25

Are

a R

ela

tiva (

%)

AL CN

0

2

4

6

8

10

12

14

16

MeC6

MeC7

MeC8

MeC9

MeC10

MeC11

MeC12

MeC13

MeC14

MeC15

MeC16

MeC17

MeC18

MeC19

MeC20

MeC21

MeC22

MeC23

MeC24

MeC25

Are

a R

ela

tiva (

%)

AL CN

INT-8989, 2001

3.6.2.3 Branched Alkyl Side Chains in Asphaltene Fractions

More dramatic differences were observed in the -methyl alkyl chain distributions of

asphaltene fractions (Figure 14). Monomodal distribution of branched chains in AL

asphaltenes molecules is concentrated in the C12-C20 region. In other hand, branched chain

multimodal distribution of CN asphaltene fraction spreads from C6 to C22. As a remark, AL

asphaltene fraction is enriched in all its -methyl alkyl chain substituents compared to the

corresponding CN fraction.

Figure 13: -methyl alkyl chain distributions of AL and CN Asphaltene fractions

3.6.3 Polymethylene Bridges

Polymethylene bridges connected to two aromatic systems are oxidized to , -

dicarboxylic acids under RICO conditions. However, C4-C6 diacids can arise from

naphthenic structures as shown in scheme 2 [9-20]. Strausz and co-workers have reported

distributions of polymethylene bridges ranging from C4 to C33. C2 and C3 diacids are

unstable under RICO conditions and they are further oxidized to CO2 [13,16]. In the

present work, dicarboxylic acids (polymethylene bridges) were analyzed by GC-MS as

PDVSA-INTEVEP

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0

2

4

6

8

10

12

14

16

18

20

MeC6

MeC7

MeC8

MeC9

MeC10

MeC11

MeC12

MeC13

MeC14

MeC15

MeC16

MeC17

MeC18

MeC19

MeC20

MeC21

MeC22

Are

a R

ela

tiva (

%)

AL CN

INT-8989, 2001

methyl-ester using m/z = 59 fragment ion to the shorter components (C4-C9) and m/z= 98

fragment ion for longer components (C10-C20). Distributions were split because of the

decreasing intensity of m/z = 59 fragment ion with length chain. In longer chains, m/z= 98

fragment ion signal became more intense.

3.6.3.1 Polymethylene Bridges in Aromatic Fractions.

Figure 15 shows polymethylene bridge distributions for the aromatic fractions studied.

Figure 15: Polymethylene bridge distribution in AL and CN aromatic fractions

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0

5

10

15

20

25

30

35

40

45

50

C4 C5 C6 C7 C8 C9

Rela

tive A

rea (

%)

AL CN

0

5

10

15

20

25

C10 C11 C12 C13 C14 C15 C16 C17 C18 C19

Rela

tive A

rea

(%

)

AL CN

Shorter Chains (C4-C9)

Longer Chains (C10-C19)

INT-8989, 2001

In both aromatic fractions, short polymethylenic chain distributions showed a monomodal

shape that declines smoothly with increasing length chain. A similar trend is observed in

longer polymethylenic substituents. In the case of AL residue, aromatic fraction molecules

exhibit a total distribution from C4 to C19, with higher picks located at C5, C11 and C12

substituents. Similar higher picks are observed in CN aromatic fraction molecules.

However, the distribution extends up to C17.

Concerning to the relative abundance, CN aromatic molecules are enriched in C5, C7, C8

shorter components and in almost all the longer substituents with the exception of C12, C16

and C17 chains.

3.6.3.2 Polymethylene Bridges in Resins Fractions.

Similar monomodal shapes were found in polymethylene bridge distributions of resins

fractions from AL and CN residues (Figure 16). AL resin fraction exhibits a distribution

ranging from C4 to C17 with higher picks at C5 and C11; whereas distribution in CN resin

fraction is spread up to C19 with prominent picks at C5 and C12 respectively.

In terms of relative abundance, enrichment in C4, C5, C7, C12, C15, and C17-C19 components

was observed in the CN resin fraction in comparison with the same AL fraction.

PDVSA-INTEVEP

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INT-8989, 2001

Figure 16: Polymethylene bridge distribution in AL and CN resin fractions

3.6.3.3 Polymethylene Bridges in Asphaltene Fractions.

Polymethylenic bridges in asphaltene fractions showed the same monomodal patterns

observed in aromatic and resin fractions. Figure 17 shows the results obtained. Prominent

picks are reached at C5 and C12 components as well as in aromatics and resins.

Nevertheless, differences in relative abundance and length chain were observed. Thus,

polymethylenic bridge distribution in AL asphaltenes ranged from C4 to C18, where the C5

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0

5

10

15

20

25

30

35

40

C4 C5 C6 C7 C8 C9

Rela

tive A

rea (

%)

AL CN


0

5

10

15

20

25

C10 C11 C12 C13 C14 C15 C16 C17 C18 C19

Rela

tiv

e A

rea

(%

)

AL CN


INT-8989, 2001

and C12 components were the most important. Enrichment in C6-C9 and C13, C14, C17 and C18

substituents was observed in contrast with the same components in CN asphaltenes.

Polymethylenic bridge distribution in CN asphaltenes is not so extended as in AL

homologue fraction. It ends at C16 with higher picks in C5 and C12 and a significant

abundance in C4, C5, C10-C12 and C15-C16 substituents.

Figure 17: Polymethylene bridge distribution in AL and CN asphaltene fractions

PDVSA-INTEVEP

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0

5

10

15

20

25

30

35

40

C4 C5 C6 C7 C8 C9

Rela

tive A

rea(%

)

AL CN

0

5

10

15

20

25

30

C10 C11 C12 C13 C14 C15 C16 C17 C18

Rela

tive A

rea (

%)

AL CN



INT-8989, 2001

3.6.4 Hydroaromatic Structures.

During RICO reaction experiences, Nomura and co-workers [15-17] identified some alkyl

polycarboxylic acids as possible products of the oxidation of three or more aryl-substituted

alkyl bridges and the oxidation of partially saturated condensed structures (Scheme 3). It is

believe with high probability that these products arise from the latter precursors

(hydroaromatic structures). Thus, 1,2,3-tricarboxy propane (C3 triacid), 1,2,4-tricarboxy-

butane (C4 triacid) and 1,2,3,4- tetracarboxy-butane (C4-tetraacid) were successfully

identified by GC-MS as methylesters.

In the present work, only C3 and C4 triacids were identified by the m/z =127 fragment ion.

C4 tetraacid was not observed in all the studied cases.

3.6.4.1 Hydroaromatic Structures in Aromatic and Resin Fractions

Trends in hydroaromatic structures distribution in aromatic and resin fractions of both

residue were very similar (Figure 18). In these fractions, CN residue showed higher

contents in C3-triacid products compared to the C4 homologue. This result is a reflect of the

high concentration of hydroaromatic fragments in aromatic and resin fraction of CN residue

that are similar to the structures 5, 6, and 7 showed in Scheme 3.

Related to the AL aromatic and resin fractions, an enrichment in C4 triacid was found,

which means that structures as 8, 9, and 10 (Scheme 3) dominate in these fractions.

PDVSA-INTEVEP

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Resins

INT-8989, 2001

Figure 18: Distribution of C3 and C4 tricabcoxylic acids as representative products of hydroaromatic

structures in AL and CN aromatic and resin fractions

3.6.4.2 Hydroaromatic Structures in Asphaltene Fractions

Hydroaromatic distribution in asphaltene fractions was different than those observed in

aromatics and resins (Figure 19). In this case, the relative abundance C3-triacid/ C4-triacid

ratio changed in both residue. Thus, AL asphaltene molecules showed a higher content in

hydroaromatic portions similar to the 5, 6, and 7 structures (Scheme 3). This conclusion is

supported by the higher concentration of C3-triacid observed in this asphaltenic fraction.

PDVSA-INTEVEP

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0

10

20

30

40

50

60

70

80

C3 C4

Rela

tive A

rea (

%)

CN AL

45

46

47

48

49

50

51

52

53

54

55

C3 C4

Rela

tive A

rea (

%)

CN AL

Aromatics

Resins

INT-8989, 2001

In the other hand, CN asphaltenes showed a higher content in C4 triacid, which means that

in this fraction structures 8, 9 and 10 predominate over structures 5, 6, and 7 (Scheme 3).

The opposite result was obtained in aromatic and resin fractions of both residues.

Figure 19: Distribution of C3 and C4 tricarboxylic acids as representative products of hydroaromatic

structures in AL and CN asphaltene fractions

3.7 Group Distributions

To get a better knowledge of the influence of aliphatic groups to the conversion value of

SCSC process, global distributions were considered in each studied fraction. Figure 20

shows these results.

As can be seen, in all fractions normal alkyl chains are the most abundant aliphatic group,

followed by polymetylene bridges, and the less abundant branched alkyl chains and

hydroaromatic structures.

PDVSA-INTEVEP

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42

44

46

48

50

52

54

56

C3 C4

Rela

tive A

rea (

%)

CN AL

Asphaltenes

INT-8989, 2001

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0

10

20

30

40

50

60

70

80

n-alkyl chains Bridges Branched Chains Hydroaromatics

Rela

tive A

rea (

%)

CN ALAsphaltenes

0

10

20

30

40

50

60

70

80

90

100

n-alkyl chains Bridges BranchedChains

Hydroaromatics

Rela

tive A

rea (

%) CN ALAromatics

0

10

20

30

40

50

60

70

80

n-alkyl chains Bridges Branched Chains Hydroaromatics

Rela

tive A

rea (

%) CN ALResins

INT-8989, 2001

Figure 20: Aliphatic Group Contributions in aromatic, resin and asphaltene fractions from AL and CN

residues

The first observation that arises from these results is that aromatic, resin and asphaltene

fractions from CN residue are enriched in polymethylenic bridges and branched chains

compared to the same fractions in AL residue. However, in the case of n-alkyl chains, AL

aromatic fraction showed higher abundance than the corresponding CN fraction. In

contrast, CN resins and asphaltenes exhibit a major content in this kind of substituents.

Concerning to hydroaromatic structures, aromatic fractions presented a very low abundance

in comparison with resin and asphaltene fractions. However, in resin fraction relative

concentration was almost the same in both residues. A noticeable difference was observed

in asphaltenes: AL asphaltenes were more enriched in this components than the CN

homologue fraction.

The global effect is that aromatic fractions from both residues have almost the same content

of aliphatic structures, whereas, resins and asphaltenes from CN residue are more enriched

in such structures than the same fractions in AL residue. These trends can be observed in

Figure 21 and they are in agreement with the SQP values calculated from spectroscopic

data.

PDVSA-INTEVEP

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80

85

90

95

100

105

110


Rela

tive A

rea (

%) CN AL

INT-8989, 2001

Figure 21: Total aliphatic group content in aromatic, resin and asphaltene fractions from AL and CN residues

estimated from RICO results.

3.8 Group Contributions

According to the SCSC pilot plant test results and to the RICO information, we can

speculate about reactivity trends for each aliphatic group and its contribution to the

conversion value. Thus, normal alkyl chains are believed to contribute the most to the

conversion together with polymethylene bridges and branched alkyl chains (in less

extension). Polymethylene bridges are believed to be the most reactive group among these

substituents because they have two possible points of attack (Figure 22). Hydroaromatic

structures are thought to have a lower contribution because they can either experiment

dealkylation to form lighter hydrocarbon products or dehydrogenation to form more

condensed aromatic systems that could be responsible for coke formation (Figure 22).

PDVSA-INTEVEP

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INT-8989, 2001

Figure 22: Possible alkyl group contribution to the conversion of SCSC process

4. CONCLUSION

Structural characterization of SARA fractions from vacuum residues is a useful predictive

tool for Selective Catalytic Steam Cracking (SCSC). It has been demonstrated that SCSC

conversion levels are influenced not only by the abundance of SARA fractions rich in

alkylaromatic structures, but also by the quality of them in terms of Caliphatic/Caromatic ratios.

Based upon 13C and 1H NMR data, a structural quality parameter (SQP) was defined. This

parameter could be used to predict feedstock behavior under SCSC conditions. However,

SQP values, calculated from 13C NMR data, are more accurate than those calculated from 1H NMR, since no assumptions for AMP calculations are required. 1H NMR parameters are

a viable alternative for routine analysis due to the less analytical demands involved.

Related to the structural details of aliphatic substituents, RICO reaction gave valuable

information about distributions of such substituents. Thus, normal alkyl chains and

polymethylene bridges were the most abundant alkyl substituents, whereas, branched alkyl

chains and hydroaromatic structures showed lower concentration in all the studied

fractions.

RICO results reinforced the spectroscopic information obtained, because resins and

asphaltenes from CN residue were richer in aliphatic structures than the same AL fractions,

which is in agreement with the SQP values calculated from RMN data. Additionally, RICO

product analysis gave some insight about reactivity of aliphatic groups that could explain

the observed behavior of the studied residues under SCSC conditions.

PDVSA-INTEVEP

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INT-8989, 2001

5. FINAL COMENTS.

As stated at the beginning of the result discussion, the information presented in this work

corresponds to the partial characterization of SCSC feedstocks. In this issue, we have only

discussed aliphatic substituent distributions. Information regarding to the condensation

modes of aromatic systems and the mass balance that includes CO2 measurements

(complementary RICO information) are in progress and will be presented in a second issue

together with characterization of visbreaking and Aquaconversion products.

PDVSA-INTEVEP

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INT-8989, 2001

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