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Feasibility of bitumen production from unconverted vacuum tower bottom from H-Oil ebullated bed residue hydrocracking Rosen Kotcev Dinkov, Kiril Kirilov, Dicho Stoyanov Stratiev, Ilshat Mirgazianovich Sharafutdinov, Dimitar Dobrev, Duc Nguyen-Hong, Stephane Chapot, Jean-François Lecoz, Aneliya Burilkova, Diana Bakalova, Dobromir Ivanov Yordanov, and Stefan Smilkov Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.7b04746 • Publication Date (Web): 17 Jan 2018 Downloaded from http://pubs.acs.org on January 17, 2018

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Industrial & Engineering Chemistry Research

Feasibility of bitumen production from unconverted vacuum tower bottom from H-Oil ebullated bed residue hydrocracking

Rosen Dinkov1*, Kiril Kirilov1, Dicho Stratiev1, Ilshat Sharafutdinov1, Dimitar Dobrev1, Duc Nguyen-Hong2, Stephane Chapot2, Jean-François Le-coz2, Aneliya Burilkova3, Diana Bakalova3, Dobromir Yordanov4, Stefan Smilkov5 1

LUKOIL Neftohim Burgas AD, 8104 Burgas, Bulgaria Axens, 89 Boulevard Franklin Roosevelt, 92500 Rueil-Malmaison, France 3 SGS Bulgaria Ltd., Laboratory Complex - Oil, Gas & Chemicals, 8104 Burgas, Bulgaria 4 UNIVERSITY "PROF. D-R ASEN ZLATAROV" - BURGAS, Bulgaria, 8010 5 UTC-Université de Technologie de Compiègne, 60203 Compiègne, France 2

*Corresponding author. Office phone +35955112636; E-mail: [email protected] Abstract In relation to constant requirement for reduction of sulphur level and low demand for fuel oil, this study presents an approach for utilization of unconverted vacuum tower bottom (UVTB) from ebullated bed hydrocracking process – H-Oil technology in bitumen production. The conducted kinetic study shows slower softening point increase for crude blend 70 % Urals and 30 % Middle Eastern than other feeds in air blowing process. Also, penetration values for straight run vacuum residue feeds decrease quicker than the increase in their softening point values. UVTB softening point increase at high temperature is faster and penetration decrease is slower than LNB SRVR. Air blowing is shown to improve penetration index of UVTB to a greater extent than SRVR one. The bottleneck of this new application of UVTB is its low resistance to hardening, determined by using a rolling thin film oven (RTFO), which limits its quantity up to 20 – 30 % in blends. Key words: bitumen, unconverted vacuum tower bottom, ebullated bed hydrocracking, air blowing, resistance to hardening, penetration, softening point 1. Introduction 1.1. Background Only a small amount of world bitumen demand comes from natural surface deposits resources, like Trinidad Lake and from the coasts of Venezuela. Other natural asphalt sources (rocks enriched with bitumen), found in Albania (area of Selenitza); Romania (Derna area) and Kazakhstan are used only occasionally in pavement construction1. However, most of the bitumens used in road pavement are produced by vacuum distillation of atmospheric residues, steam reduction or combination of both processes from appropriate crude oils but unfortunately, not all crude types are suitable. The aimed properties are sufficient quantity of vacuum residue, average asphaltene levels, balanced ratio between asphaltenes and maltenes in the vacuum residue. What’s more, paraffinic crude oils are not suited for bitumen production. The K factor indicates whether the crude oil is paraffinic (K factor: 12.5–13.0) or naphthenic-aromatic (K factor: 10.5–12.5)2. Only about 100 types of crude oils are directly suitable for manufacturing of bitumen3, 4 and can be divided mainly in three groups Middle Eastern (Arabian heavy and light, Iraq, Kuwait, etc.), Venezuelan (Boscan, Bachaquero, 1 ACS Paragon Plus Environment

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Lagotreco, Lagunillas, etc.) and Mexican. When refinery processed crude slate is unappropriated for bitumen production a technological processes and blending knowledges are available for vacuum residue enrichment. The most widely spread are solvent deasphalting and deep cut vacuum fractionation followed by blending with aromatic extracts from vacuum gasoil fractions selective treatment and thereafter oxidation via air blowing4 - 6, 7 or catalytic air blowing8, 9. However, solvent deasphalting and aromatic extraction units are typical for lube oil production oriented refinery while production of bitumen for no lube oil refinery is a greater challenge. 1.2. Objectives Modern refineries strive to squeeze bottom of the barrel producing light fuels via implementation of conversion processes like visbreaking and hydrocracking. Thus, making conversion processes and bitumen production to compete for one and the same feed - refinery residues. Residues, exiting conversion processes are mainly used for fuel oil and bunker fuel oil production. In conjunction with IMO adopted lower sulphur emissions at 0,5 % sulphur equivalent10 and also decreasing worldwide fuel oil demand, a lot of attempts for bitumen production from these conversion vacuum residues are made. Some researchers11, 12 declare suitability of visbreaking residue for bitumen production and others13, 14 point deficiency of visbreaking residue related to thermo-oxidative stability and adhesion. Process severity also influences visbreaking residue bitumen related properties15, 16. Anyway, there is scarce information about hydrocracking originated vacuum residue suitability for bitumen production. Patents17, 18 from USA reveal that unconverted vacuum tower bottom (UVTB) from ebullated bed hydrocracking process can be transformed into bitumen by blending a small quantity with both straight run vacuum residue and asphalt, and thus attaches excellent anti-stripping property. The aim of this study is to evaluate and maximize the quantity of UVTB from ebullated bed hydrocracking H-Oil process in bitumen production. 2. Experimental 1.2. Materials Straight run vacuum residue (SRVR), obtained by atmospheric and vacuum distillation of crude blend 70 % Urals and 30 % Middle Eastern as well as unconverted vacuum tower bottoms (UVTBs) from ebullated bed hydrocracking process (H-Oil technology) are air blown in a laboratory reactor in LUKOIL Neftohim Burgas AD (LNB). SRVR properties are presented in Table 1. Two UVTBs - Samples 6 and 10 from Table 1, are utilized for road paving bitumen production. Table 1 reveals that along with soft exist also hard samples of UVTBs with relative physicochemical properties. 2.2. Methods The used laboratory asphalt blowing apparatus is designed to blow about 3 kg of bitumen in a batch process with duration up to 12 h. It is charged about half full of bitumen, with the remaining volume available for vapour. A circular perforated coil is installed in the bottom of the reactor and used as an air disperser of 60 to 300 dm3/kg feed/h. A thermocouple well is installed on the reactor top. The reactor is equipped with an external jacket containing electrical coil for heating the feed and maintained it at desired temperature by a digital regulator. Spent vapours and gases left the top of the reactor, through distillate traps and condensers chilled to 15 0C by a cooling water. An outlet line in the bottom of the reactor is 2 ACS Paragon Plus Environment

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used for taking samples and for draining the reactor on completion of the run. The effluent is analysed for Penetration at 25 0C, 100g, 5s according to BDS (Bulgarian standard) EN 1426, Softening Point (Ring & Ball) as is described in BDS EN 1427, Fraass breaking point - BDS EN 12593 and durability expressed by resistance to hardening at 163 0C also known as rolling thin film oven (RTFO) which simulate short-term ageing - EN 12607-1. The latter indicates loss of volatile components and oxidation of bitumen at high temperature during conventional hot mixing (approximately 150 0C), storage laying and rolling. 3. Results and discussion 3.1. Reactivity of the processed in LNB SRVR towards oxidation. Vacuum distillation in LNB, a fuel production focused refinery yields soft vacuum residue (penetration at 25 0C of 256 dmm and softening point equal to 37,4 0C), as vacuum gasoil end boiling point (~540 0C) and coke content (~0.4 %) have to satisfy fluid catalytic cracking feed requirements. What’s more, the vacuum residue is a product from processing mainly Urals type crude oil which is considered unappropriated (for its SARA composition and mainly relatively lower resin to asphaltene ratio and also for its softness downstream vacuum tower bottom) for direct bitumen production and about 30 % alternative crude types mainly from Middle East. In order to increase the hardness, a subsequent air blowing process is applied. Oxidation kinetic of straight run vacuum residue (SRVR) and later UVTB will be expressed through increase in softening point, ring and ball method and decrease in penetration value at residence time proceeding. Determination of kinetic is important for defining the proper technological parameters (temperature, residence time - feed flow quantity, etc.) of commercial air blowing unit and also is valuable for reliable modelling of bitumen production. Once the kinetic model is developed, daily or at disturbance occurrence, corrections/adjustments of temperature and feed quantity is possible based on calculated kinetic parameters - reaction rate constants, activation energies and frequency factors (preexponential factor). Therefore, data from the pilot plant experiments and also from LNB industrial plant operation are used intending to calculate the relevant kinetic parameters. In the open literature, the presentation of air blowing (increase in softening point) kinetic is via first7-9 order rate equation for the temperature below 280 0C and beyond this temperature a thermal degradation is observed. Besides, above findings, some authors9 doubt the permanent reaction order of bitumen oxidation. That’s why, in this study, we evaluate SRVR and UVTB hardness increase for its best fit on first or second order reaction kinetic. Kinetic can be described with the power law rate differential equation 1.

& = &

&

= & &

&

&

& − + 1

&

=

|

& & − = − − + 1 − + 1

Eq.1 Eq.2

Eq.3

Eq.4

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ln " $

1

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& # = &

&

−

1

&

Eq.5

% = &

Eq.6

where is reaction rate constant at temperature T, 0C and reaction order n, in h-1, n is reaction order, [& ] is the softening point, ring and ball method in 0C, t and to=0, h defines the initial and certain time i.e. reaction or residence time. Equation 2 is the definite integrated form of equation 1 and [SPR&B]t is the softening point of vacuum residue at time t, when certain oxidation in laboratory reactor is registered. At time to, we have initial softening point [SPR&B]to of vacuum residue. Equation 4 is solution of definite integral equation 2. Equation 5 and equation 6 are solutions of definite integral equation 2 when reaction order n is 1 (first order kinetic) and 2 (second order kinetic) respectively. Softening point increase kinetic of SRVR from Barauni Refinery7, while oxidizing it at different residence times and temperatures between 160 0C and 240 0C together with SRVR from LNB, processed at 150 0C and 250 0C are presented in Figure 1. In order to compare oxidation reactivity of these feeds with the ones of residues from other type of crude oils, data from8 is also included in Table 2. Consequently, kinetic parameters are calculated assuming both reaction orders – first and second by using eq. 5 and eq. 6. The oxidation rate, expressed by softening point increase reaction rate constants, of LNB SRVR is relatively low as compared to other feeds in Table 2. The one for LNB SRVR residue aromaticity (density at 15 0C = 1016 kg/m3, asphaltene content = 9,4 % m/m and CCR = 16 % m/m) is comparable with this property characterizing Iranian mix, Arabian mix and Dubai short residues. Also, group composition (saturate content = 17 % m/m) of LNB SRVR favours slower increase of softening point as compared with the waxy nature (saturate content = 35,3 %) of Bombay High short residue. As is explained8 oxidation of bitumen proceeds into two stages: oxidation of oils to resins, and conversion of resins to asphaltenes. Temperature around 250 0C influences mainly the second step and leads to a decrease of resin content. The kinetic of LNB SRVR covers broader temperature interval (150 0C – 250 0C) and the low saturates content (main component in oils) most probably influence the rate of the first step and thus slow down the whole reaction rate of softening point increase. Activation energies Ea for softening point increase of the discussed SRVRs are obtained through solving the linearized form of Arrhenius equation:

ln ' = −

() + ln , *+

Eq.7

where Ea is activation energy in kJ/mol, R is the universal gas constant and is equal to 8,314 J/molK, A is frequency factor (pre-exponential factor). Fitting reaction rate constants with temperature (calculating Ea from the slope of this correlation) for feeds7 assuming first or second order reaction results in almost equal values for correlation coefficients, respectively 0,9896 and 0,9861 and so both reaction orders can be successfully used. Penetration decrease with oxidation duration of SRVR from Barauni Refinery7 and SRVR from LNB is presented in Figure 2. Kinetic parameters related to penetration can be calculated by equations 1 – 6, where & (softening point) is changed with penetration and 4 ACS Paragon Plus Environment

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a minus sign must be added in front of the right hand part of all equations as penetration is decreasing with oxidation time increase. For the SRVR, processed in LNB refinery, only reaction rate constants among the kinetic parameters can be calculated as penetration change during oxidation is measured only at one temperature (250 0C). This information along with calculated kinetic parameters from data for Barauni Refinery7 feed are presented in Table 3. Dependence of ln(k) (Arrhenius equation 7) from reverse value of temperature is best fitted to first order. For first and second order reaction correlation coefficient results are 0,9961 and 0,9888 respectively. For both feed LNB and Barauni Refinery, reaction rate constants for penetration possess higher values than reaction rate constants for softening point, ring and ball. It means that penetration values for these feeds decrease quicker than the increase in softening point values. Figures 1 and 2 confirm that 50-70 penetration grade paving bitumen can be produced after 8,5 h of oxidation of LNB SRVR at the conditions described in 2.2. Penetration index (PI) is calculated from penetration and softening point values as is shown1 and higher values presents lower dependence of rheology on temperature – softer bitumen at low temperature and harder at high temperature. PI of LNB SRVR during oxidation at 250 0C is calculated to increase from -0,5 to -0,1. 3.2.Characterization of UVTB as a component for bitumen production. LNB ebullated bed hydrocracking process has been run at different levels of oncethrough residue conversion floating up to 75 % since the startup. Figure 3 reveals that there is a meaningful dependence between penetration at 25 0C and softening point ring and ball of UVTB from H-Oil with the unit conversion calculated as 100 % - (% UVTB + % H2S + % NH3 + % H2O). Deeper conversion in H-Oil unit is related with harder UVTB and vice versa. Deviation from the fitted equations curves shown in Figure 3 can be attributed to changes in refinery feed diet that may include alternative crudes that differ quite significantly from Urals (REBCO). Figure 3 quantitatively presents an early finding shown in reference15 that linked the quality of cracked residue to the process severity. Characterization of several UVTBs is presented in Table 1. The obtained UVTB hardness is compared to other physicochemical properties from Table 1 and the most significant relations are presented in Figures 4 and 5. It deserves noting that by increasing hydrogen content in UVTB an increase in penetration via logarithmic trend line is observed. The behaviour of UVTB resembles straight run residues as is reported19, that is, increasing the saturate content leads to production of a softer asphalt – or a higher penetration. Just the opposite, increasing asphaltenes contribute to penetration decrease also following logarithmic equation as shown in Figure 4. With increasing conversion in H-Oil, performed by increasing the reactor temperature, the asphaltenes are concentrated and probably new are formed from maltenes in the UVTB. At 58 - 62 % residue conversion, asphaltenes concentration is in the range 6 – 8 % in UVTB and reaches 22,5 % at 75 % conversion. High asphaltenes content clearly makes a lower penetration of UVTB. The same is observed with nitrogen content. Concentration of nitrogen containing compounds in UVTB is connected with increased conversion in H-Oil unit as their very low reactivity20 makes them extremely difficult to convert. Simultaneously, Figure 3 points the dependence of penetration on conversion and nitrogen content can be correlated to penetration via conversion (due to reactor temperatures) of ebullated bed hydrocracking process. Density, nitrogen and hydrogen content also influence UVTB softening point as can be marked from Figure 5. One can observe that the relations are again logarithmic as for penetration. This can be explained by the fact that both penetration and softening point are correlated and both can be used to define UVTB hardness. 3.3.Enrichment of UVTB properties for bitumen production.



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As is noted in the previous section and Figure 3, H-Oil unit produces UVTB whose hardness varies in a wide range and thus may not be applicable constantly for direct bitumen production, but only within a narrow conversion or operating conditions window. In this study, we evaluated the possibility to involve UVTBs, obtained at 73 and 75 % conversion, in bitumen production. The conversion levels are chosen as follows: 73 % is the closest to design case (70%) and the second - 75 % is the highest conversion with prolonged stable operation of the unit. Both conversion levels are obtained due to some improvements (Middle Eastern crudes and FCC slurry) in feed mixture. 3.3.1. UVTB from H-Oil 73 % conversion 73 % conversion UVTB is characterized (Table 1 – Sample 6, Figures 3 and 6) with penetration at 25 0C of 90 dmm and softening point equal to 41,8 0C and thus it is too soft for road paving bitumen production as the most popular in Bulgaria penetration grade bitumen is 50-70. An option to increase the hardness of UVTB is to subject it to air blowing. Air blowing is used for upgrading the physical properties of residues via increasing hardness, penetration index (less susceptible to temperature variations) and ductility1. The experiment is conducted in the reactor described in point 2.2. at two temperatures – 150 0C and 250 0C. The increase in softening point and decrease in penetration versus residence time can be followed in Figure 6. It is evident that both properties of UVTB depends on blowing temperature like SRVR but the kinetic of oxidation of this residue from hydrocracking origin is different. Data from Figure 6 is used as a source for calculation of kinetic parameters by using equations from 5 to 7. We

-./ can announce that penetration decrease due to oxidation rate constants are - = -1 -1

-&./

-./ 0,015234329 h ; - = 0,046829213 h for the first order reaction and -& =

-&./ 0,000182746h-1; -& = 0,00054878 h-1 for the second one. Comparing oxidation rate constants for both first and second reaction order at 250 0C with the ones for SRVR, presented in Table 3, we can point that values for UVTB constants are lower and it means that penetration decrease is slower than penetration decrease with SRVR at the same conditions of oxidation. From rate constants we can easily calculate activation energies (Ea) of UVTB for the first order reaction 20,67 kJ/mol and 20,24 kJ/mol for the second one. Higher Ea proves slower penetration decrease for UVTB. Concerning UVTB softening point increase (Figure 6)

-./

-&./ caused by air blowing, the rate constants are - = 0,018482916 h-1; - = -1 -1

-./

-&./ 0,092737665 h for the first order reaction and -& = 0,000409096 h ; -& = -1

-&./ 0,002002951 h for the second one. values for UVTB are bigger than values from Table 2, characterizing LNB SRVR. Therefore, UVTB softening point increase at high temperature of 250 0C is faster than that of LNB SRVR. This finding confirms mentioned16 statement that cracked bitumens are more sensitive to oxidation and definitely points softening point to be the fast increasing property. Penetration index at 250 0C for UVTB is calculated to increase due to laboratory oxidation from -2,2 to 0,7. Here must be pointed that PI increase for UVTB (at the same temperature and air flow, but shorter residence time of 2,5 h against 10 h for SRVR) is greater than PI increase for SRVR. This is related to higher softening point value at the same penetration and once again confirms that the increase in SP of UVTB due to air blowing is very intensive. Thus oxidation turns low bitumen quality cracked residues15 - in this study UVTB (PI = - 2,2) into higher (PI = 0,7) performance5 bitumen than oxidized SRVR bitumen (PI = -0,1). This fulfils the requirement of EN 1427. Figure 6, together with calculated rate constants and Ea, show that UVTB from H-Oil 73 % conversion can be transformed into 50-70 grade bitumen after 16-19 h of oxidation at 150


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0

C and other conditions as in point 2.2. Air blowing at 250 0C cannot change UVTB hardness in such a way to simultaneously satisfy both requirements for penetration and softening point. Another technology for hardening heavy oil residues, shared in the open literature19, is modification of group type composition of residue by blending it with asphaltenes and resins as they both simultaneously increase softening point and decrease penetration. In this regard, a stream rich in resins and also in asphaltenes is asphalt (pitch) from deasphalting unit. As LNB is not equipped with deasphalting unit, a sample of asphalt from another refinery is blended with UVTB in order to evaluate possibility to produce 50-70 penetration grade bitumen. Asphalt is obtained from deasphalting of vacuum residue with n-butane and i-butane mixture as a solvent and had softening point = 97 0C, kinematic viscosity at 135 0C = 50000 cSt, density at 15 0C = 1096 kg/m3, CCR = 35 % m/m and sulfur content = 4,8 % m/m. The UVTB for experiment with asphalt seems to be quite soft for the level of H-Oil conversion penetration at 25 0C of 240 dmm and softening point equal to 37,6 0C as it was sampled from the H-Oil unit with some of the flushing oil for the dedicated sample point. The point here however, is whether a hardness satisfying specification 50 -70 penetration grade can be achieved. Figure 7 and 8 confirms that blending even so soft UVTB with 15 – 18 % asphalt (penetration of blend 53 -70 dmm and softening point ring and ball of 46 - 49.4 0C) covers required penetration of 50-70 dmm and softening point ring and ball of 46 -54 0C. These results show that asphalt (pitch) can be successfully applied for hardening UVTB. 3.3.2. UVTB from H-Oil 75 % conversion 75 % conversion UVTB is characterized (Table 1 – Sample 10 and Figure 3) with penetration at 25 0C of 30 dmm and softening point equal to 56,4 0C and thus it is harder than requirements of 50 -70 penetration grade bitumen specification. It is known that air blowing presents a significant advantage over simply increasing penetration index and thus the dependence of bitumen rheology on temperature is lower5. Further, as resins convert to asphaltenes and aromatics to resins during oxidation, the best diluent of UVTB prior to oxidation would contain certain amount of aromatics and resins of adequate solvating power to keep asphaltenes fully peptised with the aim to save or even increase compatibility (prevent asphaltenes from association) of blend constituents. In order to convert this type of UVTB into bitumen, fluid catalytic cracking slurry was added at quantity of 7 % and 15 % as this LNB refinery stream is the most resins rich available. FCC slurry SARA composition, determined according IFP 9305 standard is the following: saturates = 15,1 %; aromatics = 50,7 %; resins = 27,6 % asphaltenes = 3,5 % and losses = 3 %. Unfortunately, after 2 hours of oxidation of the combined feed (UVTB/FCC slurry) at 250 0C the laboratory reactor plugged and no final product was received. Most probably, violent polymerization of unsaturated species, present in slurry, and an interaction between slurry and UVTB exhibits such a negative effect during oxidation. Another approach for diluting UVTB before air blowing is using SRVR as the latter stream is softer. Having in mind the advantages of air blowing process, blends with 50 % and 75 % content of UVTB and SRVR are oxidized at 250 0C in the laboratory reactor. Hardness versus residence time is presented in Figures 8 and 9. Hardness for 50 % UVTB blend can be achieved with oxidation duration between 2,5 and 4 h while for 75 % UVTB blend, the required oxidation duration is only up to 1,5 h. Figure 9 reveals that increasing the content of UVTB in the blend results in higher slope of the straight line representing increasing of softening point due to oxidation. Accumulated data in this study for penetration and softening point of blends SRVR/UVTB allows us to evaluate shared correlations21 and fit them better to our results. 7 ACS Paragon Plus Environment


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The Supporting Information - Figure S1, compares and shows relations between calculated and measured results for penetration and softening point. Adjusted literature correlations acquire the following form:

;

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