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A Comparitive Study: Effect of SCH2O & Catalysts on

Heavy Oil Upgrading Compared to Delayed Cokers

Ramazan Oğuz Canıaza,b

, Can Erkeya,c,

* Serhat Arcab

a. Koç University TÜPRAŞ Energy Center (KÜTEM), Koç University, 34450 Sarıyer, Istanbul, Turkey

b. Turkish Petroleum Refineries Corporation, R&D Product Development Department, Izmit 41780

Turkey

c. Department of Chemical and Biological Engineering, Koç University, 34450 Sarıyer, Istanbul, Turkey

* Corresponding authoer at Department of Chemical and Biological Engineering, Koc¸

University, 34450 Sarıyer, Istanbul, Turkey.Tel.: +90 212 338 18 66; fax: +90 212 338 15

48.E-mail address: cerkey@ku.edu.tr (C. Erkey).

Exploiting already existing heavy & unconventional hydrocarbon resources has become more

important than ever because of the continuously increasing energy demand. Regarding the

feasibility and processibility of these unconventional resources, the state-of-the-art upgrading

technologies such as delayed cokers are not always convenient for these types of feedstocks.

Supercritical fluids (SCFs), on the other hand, possess tunable solvent properties and might

provide processing alternatives for refining operations. Supercritical water (SCH2O) among

other SCFs is the most suitable one for heavy oil upgrading purposes. Under supercritical

conditions, the properties of water start to resemble that of hydrocarbons making it an

excellent solvent for organic compounds. As for the hydrogen donation behavior, increased

ionic product of water leads to an increasing [H3O+] concentration and thus promotes the

reactions requiring the addition of an acid. Modified dielectric constant & accompanying

solvation power enables the extraction of lighter compounds while increased hydronium ion

concentration makes the reactive extractions of heavy hydrocarbons possible. In addition to

that, SCH2O can form layers between asphaltene micelles and suppress the formations of

coke, an undesired by product of refineries’ upgrading units. Unlike the delayed cokers,

SCH2O also helps the removal of heteroatoms and when combined with other advantageous

properties it opens up new alternatives for process intensification studies. In this study, 50/70

pen-grade bitumen has been used as heavy oil feedstock and its detailed characterization was

performed by elemental analysis, molecular weight analysis (Gel Permeation Chromotograpy,

GPC), Proton Nuclear Magnetic Resonance (H-NMR), Differential Scanning Calorimetry

(DSC), Thermal Gravimetric Analysis (TGA), Fourier Transform Infrared

Spectroscopy (FTIR), X-Ray Diffraction (XRD), and GC-Simulated Distillation. Subgroups

of saturates, aromatics, resins and asphaltene content were also measured. Supercritical water

upgrading experiments were performed at 440 °C, 30MPa for 2 hours with oil/water ratio of 2

and oil/catalyst ratio of 20:1 in a home-made 10 cm3, SS316, bomb reactor coupled with

pressure and temperature indicators. Experiments were performed at the same conditions

without water as well to mimic the delayed coking processes by MCR (Micro Carbon

Residue) tests. Coke-liquid-gas yields were determined and breakdown of liquid products

were analyzed by GC-Simdist. By product of aluminum industry (red mud), sulfided forms of

the iron based catalysts, spent FCC (Fluid Catalytic Cracking Unit) catalysts and entrainers

with pre-determined silica/alumina ratios were used. DSC analysis of the catalysts under

reaction temperatures was performed. While the coke yield of industrial cokers generally vary

between %16-28, the supercritical water upgrading experiments enabled to decrease the coke

yield down to %9 and %3,7 with SCH2O and SCH2O+FeSO4, respectively. %70 liquid

products yield, %85 of which can be treated as a hydrocracker feed is obtained. Even without

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the use of SCH2O, FeSO4 addition comparatively decreases the coke yield by 5% for DCU

applications. To improve the conversion and selectivity, mixes of additives

(SCH2O+2,5%FeSO4+%2.5FCC Spent) are also prepared. The least amount of HVGO and

highest H.Diesel is obtained. However, the capability to suppress coke formation during

upgrading reactions is lost when binary additives are preferred. Varying metal deposition

tendencies and coke types were obtained. The studies concluded that depending on the desired

conversion and selectivity, one might choose or design & synthesize additives accordingly.

INTRODUCTION

Increasing energy demand of rapidly growing world requires making use of all available

heavy oil resources. The complicated representative structure of heavy oil is given in The

Figure 1 [1]. At the state of the art, there are some commercially available energy conversion

technologies such as delayed coker units (DCU) or hydrocrackers (HYC). However, large

percentage of feed is rejected as coke, an undesired by-product, in DCU while HYC requires

expensive and quite sensitive catalysts together with extensive hydrogen consumption having

an associated cost. Thereby alternative technologies need to be developed. Supercritical

fluids, especially SCH2O with its unique physicochemical properties is a promising candidate

to be an alternative for the upgrading of heavy oils towards lighter compounds. Figure 2

illustrates the P-T diagram of water indicating the supercritical region. When reached to the

critical region, water becomes a hydrogen donor and also losses its polarity together with a

sharp decrease in its dielectric constant

making it a good solvent for

hydrocarbons. A recent study [2] of

Hosseinpour et al. showed by isotope

labeling technique that supercritical

water behaves like a hydrogen-donor

solvent thereby SCH2O shows chemical

reactivity together with its unique

solvation and dispersion effects. In

addition to the SCH2O, some catalytic

additives as entrainers might be

introduced to the heavy oils during

upgrading reactions to further suppress

the undesired coke yield and improve the

selectivity of the upgraded products.

Activated carbon catalysts in a bench-scale plug flow reactor in the presence of hydrogen gas

& hydrogen rich solvents in a supercritical state is used [3] and promising results are obtained

at ~7 MPa and 673–723 K. The liquid product conversion of 82–88 wt% and 6–8 wt% coke

and pitch formations were found.

Water-activated (3 wt% of feed) natural zeolites (chabazites and clinoptilolites) were shown

[4] to be quite active for the integrated extraction and low severity upgrading of oil sands

bitumen at 573 and 623 K. Quite high liquid yields, up to 96%, with comparatively lower

viscosity, boiling point distribution, and average molecular weight as compared to raw

bitumen together with reduced concentrations of heteroatoms were obtained. It was suggested

that the decreased viscosity of the products may lead to a reduction in pumping costs for

transportation.

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The use of catalysts has been shown to be

beneficial for reservoir applications as well

[5]. Catalytic emulsions consisting of Ni-W-

Mo were used for catalytic upgrading of heavy

oil and bitumen in a batch reactor at 3.45 MPa

and temperatures ranging from 593 to 653 K.

Large excess hydrogen was used to avoid the

coke formation. It was concluded that ultra-

dispersed catalytic upgrading in a batch reactor

provides residue conversion products with

high yield.

There are also patented technologies

combining the use of catalysts with SCH2O for

heavy oil upgrading in slurry-phase flow

reactors [6, 7].

The use of iron based catalysts for oxidative cracking / upgrading of heavy oil in SCH2O was

also reported [8] at 420 °C & 20 Mpa with catalyst:oil ratio of 4:1 and benzene as a solvent in

the feed, containing 30 % bitumen at most and water:feed ratio of 3:1. Though proposed

process is unlikely to be used in industry, it is reported that heavy hydrocarbon fractions are

converted to lighter ones. In another study [9], it was proposed that coke formation can

successfully be decreased down to 5,46% by mass when silica supported Fe2O3 are used with

water:oil ratio of 80:3 and oil:catalyst ratio of 3:1 at 450 °C for 60 minutes reaction time. The

drawback of this study is the consumption of huge amount of water and catalysts in batch

process for the upgrading purposes.

This study, on the other hand, is conducted to reveal the potential of both acidic and metallic

(in their oxide and sulfided forms) additives on SCH2O assisted heavy oil upgrading

experiments with low water:oil and catalysts:oil ratios where byproducts of several industries

have been benefited. Entrainers with predetermined Si/Al ratios and spent FCC catalysts with

some cracking additives (CAs) are used to check for the effect of acidity on the conversion

and selectivity. By product of aluminum industry (red mud) having both acidic parts for

cracking and metal oxides for hydrogenation/dehydrogenation functions is also used. Main

group in the red mud is iron based metal oxides. Thereby iron oxide alone and also the

sulfided forms (FeSO4.7H2O) of the iron as compared to oxide forms are used.

MATERIALS AND METHODS

Upgrading experiments are carried at 440 °C & ~30 Mpa with water/oil ratio of 2 and

oil/catalyst ratio of 20:1 for 120 min in a home-made 10 cm3, bomb reactor made from

SS316. DCU experiments for comparison of the coke yield as compared to SCH2O upgrading

experiments are simulated by MCR (ASTMD4530). Bitumen from TUPRAS Izmit Refinery,

Iron(III)Sulfate(heptahydrate), iron (III) oxide, domestic red mud samples, spent FCC

catalysts, acidic cracking additives (CAs) and entrainers (AL-SI) with predetermined Si:Al

ratios are used (Al2O3:SiO2 ratio is ~60:40). The feed, catalysts and the products are analyzed

in details by means of XRF, XRD, elemental analysis, SEM, SARA fractionations, TS

EN12591, GC-Simdist, NMR, TGA, DSC, GPC according to their related EN/ASTM

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standards. SARA fractionation is carried out according to the solvent-sequence protocol

which makes use of the solubility differences of the sub-fractions of bitumen like heavy oils.

RESULTS

Physical properties of the bitumen, which is a bottom product of the vacuum distillation unit

that fractionates the crude oil by means of temperature and pressure gradients via the

distillation column, are determined according to EN12591. The feed is found to be in a 50/70

penetration grade (See Table 1).

Knowing the fact that heavy oils

are composed of ~10,000

molecules with varying

molecular weights (MW) and

chain lengths, they can be treated

as polymeric materials as well.

Thereby MW analysis of the feed

is done by HPLC-GPC and a

number average MW (Mn) is

found as 762. Similar analyses has been done to SARA (Saturates, Aromatics, Resins,

Asphaltenes) sub-fractions of the bitumen feed which is a generally accepted classification

methodology for bitumen like heavy oils based on solubility differences (See Table 2).

However, chemical structure of the feed has a huge impact on the upgrading efficiency as

well. Heteroatoms and elemental ingredient may also affect the catalytic additives’

(entrainers’) performance on a great extent. Thereby more detailed chemical analyses of the

feed are done by SARA, elemental analysis and NMR. The results are given in Table 2 and

Figure 3. NMR spectrums of sub-fractions are not provided here for space limitations, but the

results are already given in Table 2.

H/C ratio of 1,44

together with 1,71 wt %

sulfur in the feed is

detected by elemental

analysis. SARA

fractionation has been

performed with 99%

efficiency. When GPC

value of feed is

estimated by means of

the SARA % values and

GPC values of each sub-

fraction, 781,1 is found which is quite close to the measured value of 762 giving an error of

only ~2,5%. Such an agreement indicates / confirms the high efficiency of SARA

fractionation (solvent sequence) protocol.

In the NMR analysis of saturates fractions of feed, 24,80 % methyl hydrogen indicates the

existence of short chain isoparaffins in high amounts. 69,56% methylene hydrogen formation

suggests the existence of partially saturated hydro aromatics and their branched forms. The

fact that aromatic formations in saturates is observed in small amounts do mean that together

with the solvent used, slight portion of the aromatics are purged throughout the column and

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removed by the saturates. As for the aromatic

fraction: 16,56 % methyl side chains and 54.84%

methylene branches indicates the existence of

isoparaffins at a molecular form and of both short and

long side-chain paraffins in aromatic fractions. In

addition to aromatic formations, hydroaromatic

formations are observed to commonly exist as well.

19,40 % alfa-hydrogens are detected suggesting the

highly branched aromatic structures. Resin fraction’s

NMR analysis on the other hand reveals 18,08%

methyl groups and 66,66% methylene chains

suggesting the fact that resins have long-side chains in

paraffinic forms. Moreover, it is interesting to note

that hydrogen of 2 or 3 rings aromatics and diphenyl

methane bridges between aromatic rings do exist. NMR analysis of the heaviest and darkest

portion of feed, asphaltene fraction, points out the fact that it can be understood from the

methyl groups’ low amounts, i.e. 3,92%, that asphaltene fractions contains almost no

branched like structure but only some long chain ones. 72,8 % of asphaltenes are formed of

saturated and hydroaromatic rings. The fact that 16,03% hydrogen belonging to alfa aromatic

and biphenyl bridges is found suggests that core aromatic portion having side chains actually

forms connections among ring like structures via biphenyl bridges.

As for the thermal properties, 85,4 %

mass loss is observed on feed via

TGA analysis with a delta Cp and Tg

values of 0,184 J/g*°C and -19,19 °C

on DSC (See Figure 4).

The characterization of the red mud

which is a by-product of an

aluminum industry is done by XRD

and XRF. Bayerite, Hematite,

Gibssite and Sinnerite formations are

observed on XRD (See Figure 5). Fe2O3, Al2O3, SiO2, and Na2O are found to exist at ratios of

41, 21.9, 15.3, and 10.8 % by mass respectively, on XRF (See Table 3).

Figure 5: XRD Analysis of Red Mud Samples. XRD Diffractogram (on the left) and pie

chart (on the right) showing the estimated % existence of bayerite, hematite, gibbsite and

sinnerite like formations are given.

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Gas products are measured in terms of their

mass after upgrading experiments. Mass of

solid products is found by toluene solubility

tests according to EN12592. Liquid products

on the other hand, after being recovered from

the reactor by rinsing with excess toluene are

characterized according to their TBP values

by GC-Simdist and all the results are given in

Figure 6.

Figure 6: The solid-liquid-gas products’ mass percentages values together with

corresponding breakdown analysis of liquid products obtained by GC-Heavy Simdist are

shown in the Figure. Compositional analysis of feed is also provided as a reference data.

The coke yield of industrial cokers may theoretically vary

between %16-28 by mass depending on the properties of the

feed. Similar experiments are performed by a simulated test

method, MCR (Micro Carbon Residue), to mimic delayed

cooking conditions. 5% by mass catalytic entrainers are

introduced as well. However coke yield could only be

comparatively reduced by 5,46% when FeSO4 is added

during coker simulation experiments without SCH2O (See

Table 4). The supercritical water upgrading experiments on

the other hand enabled to decrease the coke yield down to

%9 and %3,7 when SCH2O and SCH2O+FeSO4 are introduced into the reactor, respectively.

Up to %70 liquid products yield, %85 of which can be treated as a hydrocracker feed, is

obtained with SCH2O+5%FeSO4 addition. Although the lowest coke yield is achieved with

FeSO4 addition, the highest L.disesel yield is obtained with FCC spent. Thereby, to study the

synergistic effects and to couple the desired optimum properties of additives, mixes are

prepared. Though a mix of 2,5%FeSO4 + 2,5%FCC Spent has maximized the H.diesel yield,

selectivity is disturbed and coke yield is increased in that case.

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Morphological

examination of the

solid products, coke

samples, is done by

SEM, EDX and XRD.

Depending on the

properties of the feed,

chosen additive and the

focused area of the

beam, EDX and SEM

results confirmed both

sponge type (Figure 7-

left) coke formations,

together with sulfur-

heavy trace metal

accumulations (Figure

7-right). Honey comp

structures of iron based

formations (Figure 8-

left) when red mud is used as entrainer and even trace amount of silver accumulation in a rod

structure (Figure 8-right) are detected. EDX results of the corresponding measurements are

provided at the bottom of the SEM images. When combined with the results given in Figure 6

and 7, use of FCC spent provided the highest amount of L. Diesel which can be attributed to

the high acidity of the catalysts triggering the cracking of heavy-long chain hydrocarbons.

This thinner fraction can boil more easily during upgrading / pyrolysis and thereby provide

sponge like structures as can be shown on SEM images.

Amorphous XRD

profile of solid,

coke samples are

given in Figure 9.

Two broad peaks

are located at 26°

and 44° 2𝜃

corresponding to

(002) and (100)

reflections of

graphite micro-

crystals,

respectively. The

sharpness of peak

at 26° 2𝜃 reveals

the number of

similarly

orientated graphite

micro-crystals. The broad nature of the peak can be attributed to a low lattice order [10].

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CONCLUSION

Introduction of SCH2O into pyrolysis – upgrading

reactions of heavy oil enabled to decrease the

coke yield and improve the liquid yield with

better selectivity. Best results are obtained with

SCH2O + 5%FeSO4 addition, probably due to the

high resistance of the sulfided forms of the metals

against the poisoning effect of sulfur compounds

existing in the feed.

MCR experiments revealed that even without

SCH2O, FeSO4 addition can decrease the coke

yield by more than 5%. Knowing the fact that

coke is an undesired side product as compared to middle distillates, these improvements even

without the use of SCH2O are of paramount importance for oil refineries to improve their

profit.

More detailed characterization of the entrainers can be done to have a keen knowledge on the

effect of those additives on SCH2O upgrading reactions’ mechanism. This is quite important

in a sense that based on the feed properties and desired products yield and selectivity, one

should be able to design and synthesize the best catalytic additives.

As for the future studies, the use of flow reactor systems having a higher inner volume for the

collection of enough products for more detailed characterization, together with acid treated

red mud catalysts exhibiting higher BET values and with the addition of H2 and CO like

entrainers and varying reaction times for higher conversion or better selectivity can be done as

a part of a complementary study. Moreover, gas content, H/C ratio, SARA and elemental

analysis of products might be performed to reveal the upgrading mechanism.

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