Hydrocracking of Various Vacuum Residues

Abstract

The residue conversion processes, coking, visbreaking, and fluid catalytic cracking (FCC), have demonstrated that feedstock quality is the single factor that most affects process performance. While, for the FCC, it is known that the heavy oil conversion at a maximum gasoline yield point can vary between 50 and 85 wt. %, for the vacuum residue hydrocracking, no reports have appeared yet to reveal the dependence of conversion on the quality of vacuum residue being hydrocracked. In order to search for such a dependence, eight vacuum residues derived from medium, heavy, and extra heavy crude oils have been hydrocracked in a laboratory unit at different reaction temperatures. The current study has witnessed that the vacuum residue hydrocracking obeys the same rule as that of the other residue conversion processes, confirming that the feedstock quality has a great influence on the process performance. A conversion variation between 45 and 85 wt. % can be observed when the sediment content in the hydrocracked atmospheric residue is within the acceptable limit, guaranteeing the planned cycle length. An intercriteria analysis was performed, and it revealed that the vacuum residue conversion has negative consonances with the contents of nitrogen and metals. Correlations were developed which predict the conversion at constant operating conditions within the uncertainty of conversion measurement of 1.7 wt. % and correlation coefficient of 0.964. The conversion at constant hydrocracked atmospheric residue (HCAR) sediment content was predicted with a correlation coefficient of 0.985. The correlations developed in this work disclosed that the higher the contents of metals, nitrogen, and asphaltenes, and the lower the content of sulfur, the lower the conversion in the hydrocracking process is. It was also shown that vacuum residues, which have the same reactivity (the same conversion at identical operating conditions), can indicate significant difference in the conversion at the same HCAR sediment content due to their diverse propensity to form sediments in the process of hydrocracking.

1. Introduction

Petroleum is a mineral resource that consists of a myriad of hydrocarbons [1,2,3] and hydrocarbon derivatives, which contain sulfur [4], nitrogen [5], oxygen [6,7,8,9], and metals [10] such as vanadium, nickel [11,12], sodium, calcium, magnesium, iron [13], mercury [14], and others [13]. Transportation fuels, products of petroleum refining, make up the majority of industrial production volume and provide more than 80% of current global primary energy demand [15]. Petroleum is used as a feedstock for manufacturing many products of chemical and pharmaceutical industry [15]. Oil is extremely important for many countries, as it is needed for numerous sectors and to maintain industrial civilization in its current form. Distribution of various types of oil all over the world has shown that the conventional oils (these are the crude oils with density at 15 °C ≤ 0.932 g/cm³, which are produced by conventional methods) presents 30% of oil resources, while the unconventional oils (heavy, extra heavy oils, and bitumen) contribute to about 70% of global proven oil reserves [16,17,18]. The significantly higher share of heavy oils, which contain a higher amount of residue fraction, as a crude oil resource makes those dealing with petroleum refining to employ processes, which can convert the bottom of the barrel in high value automotive fuels and feed for petrochemistry [19,20,21,22].

Table 1. Worldwide distribution of employed residue conversion technologies [23].

Residue Conversion Technology	Per Cent of Total
Coking	32
Visbreaking	30
Fluid catalytic cracking (FCC)	19
Hydroprocessing	15
Solvent deasphalting	4

summarizes the worldwide distribution of residue conversion technologies [23].

For the residue conversion process coking, the conversion and yields of products can be calculated on the base of information about the microcarbon residue content of the residue feed [24]. For the residue, FCC Navarro et al. [25] have shown that the FCC feed conversion is best predicted from its hydrogen content. They reported that for the range of hydrogen contents in the FCC feeds from 9.6 to 14.8 wt. %, the fluctuation of conversion at the point of maximum gasoline point is between 50 and 85 wt. % [25]. The aim of the visbreaker is to reduce the residue viscosity by a mild thermal cracking and decrease in this way the quantity of distillates used as cutter stocks [26]. Stratiev et al. [27] communicated about the presence of a correlation between the viscosity of the vacuum residue feed for a commercial visbreaker and the viscosity of the visbroken residue. Thus, one may conclude that the performance of coking, visbreaking, and FCC can be predicted on the base of information about characteristics (microcarbon residue content, hydrogen content, and viscosity) of the residue feed. Prajapati et al. [28] investigated the slurry-phase hydrocracking of six vacuum residues. They compared the catalytic activities with the thermal activities for all examined feedstocks. They observed that the lightest vacuum residue MGL-VR (density at 15.6 °C of 0.9174) that has the highest saturate content (38.1 wt. %) demonstrated the maximum catalytic conversion. The results of their study suggest that the residue conversion can be predicted from the microcarbon residue content MCR in the vacuum residue feed. However, they did not report a definite quantitative relation of vacuum residue conversion to the MCR as Muñoz et al. [24] did in their research devoted to the delayed coking. To the best of this author’s knowledge, similar reports dealing with the conversion prediction in the process of ebullated bed vacuum residue hydrocracking from feed properties has not yet appeared in the literature. For this reason, the author of this study discusses the pilot plant results obtained during the ebullated bed hydrocracking of eight distinct vacuum residues obtained from medium, heavy, and extra heavy crude oils with the aim of defining these residue characteristics, which affect the conversion level in vacuum residue ebullated bed hydrocracking. Based on a rich, positive previous experience with application of the intercriteria analysis (ICrA) to define statistically meaningful relations between different properties of feeds in various heavy oil conversion processes and the operating conditions, conversions, and yields summarized in a monograph [29], a decision was made to employ ICrA in this research too. ICrA established on the foundation of intuitionistic fuzziness and index matrices as a tool to support decision making in multiobject multivariable problems found successful applications in medicine, biology, economics, physics, etc., and it can be considered a component of the artificial intelligence tool [30,31,32]. ICrA was used in this study to investigate the presence or absence of statistically meaningful relations between the vacuum residue characteristics and the conversion obtained at the same operating conditions and at the same sediment level in the hydrocracked atmospheric residue.

2. Materials and Methods

Properties of eight crude oils from which the vacuum residues were employed as feeds for the hydrocracking are presented in

Table 2. Physical and chemical properties of crude oils under study.

Crude Oil Properties	Crude Oil 1	Crude Oil 2	Crude Oil 3	Crude Oil 4	Crude Oil 5	Crude Oil 6	Crude Oil 7	Crude Oil 8
Density at 15 °C, g/cm3	0.878	0.923	0.877	0.959	0.889	1.009	0.858	0.877
Sulfur, wt. %	2.85	3.40	1.53	3.38	2.91	4.64	1.89	1.93
Total acid number, mg KOH/g	0.20	0.16	0.11	2.30	0.28	2.70	0.06	0.14
C5-asphaltenes, wt. %	6.0	19.0	4.5	12.2	14.7	17.5	3.5	3.8
C7-asphaltenes, wt. %	3.3	12.8	2.7	7.7	8.9	12.1	2.2	2.9
Pour point, °C	−36.0	−28.2	−9.0	−28.5	−36.0		−36.0	−17.1
kinematic viscosity at 40 °C, mm2/s	36.1	82.6	12.6	99.6	10.8		10.1	19.7
True boiling point distillation fraction yields, wt. %
IBP–110 °C	9.0	4.2	8.1	2.2	6.4	0.0	9.3	8.3
110–180 °C	10.1	8.3	9.5	5.0	8.6	1.0	11.6	9.7
180–240 °C	8.7	7.6	8.9	4.5	7.8	3.0	10.1	8.8
240–360 °C	19.3	16.2	22.0	23.3	18.6	11.0	21.6	21.2
IBP−360 °C	47.1	36.3	48.5	35.0	41.5	15.0	52.6	48.0
360–540 °C	24.4	23.2	27.8	32.0	24.4	31.5	24.4	26.7
˃540 °C	27.5	39.6	22.8	32.8	33.1	53.0	21.9	24.2

.

The characteristics of the eight vacuum residues being hydrocracked in this study are summarized in

Table 3. Physical and chemical properties of vacuum residues—feeds for hydrocracking.

Vacuum Residue Properties	VR 1	VR 2	VR 3	VR 4	VR 5	VR 6	VR 7	VR 8
Density at 15 °C, g/cm3	1.049	1.080	1.018	1.040	1.045	1.061	1.022	1.019
Sulfur, wt. %	6.6	6.3	2.7	3.96	5.56	6.2	4.22	3.9
Nitrogen, wt. %	0.357	0.853	0.702	0.6253	0.387	0.63	0.4011	0.56
Conradson carbon content, wt. %	26.9	33.5	20.4	19	23	22.5	19.8	18.6
Saturates, wt. %	5.0	13.4	15.00	10.5	7.2	6.5	11.6	12
Aromatics, wt. %	36.5	17	37.3	32.7	38.9	26.4	48.6	39.7
Resins, wt. %	48.0	40	39.7	43.6	37.1	47.8	32.1	41.2
C5-asphaltenes, wt. %	19.8	44.1	15.3	22.6	28.0	31.8	14.3	13.5
C7-asphaltenes., wt. %	10.5	29.6	8	13.2	16.8	19.3	7.7	7.1
Nickel, ppm	49	154	58	209	50	95	20	71.4
Vanadium, ppm	179	841	197	890	150	290	60	232.5

.

The density of the vacuum residual oils was measured indirectly from the densities of a series of solutions of vacuum residues in toluene at different concentrations, as described in [33]. Solutions of vacuum residues in toluene at concentrations up to a vacuum residue mass fraction of 6% were prepared. Sulfur content of vacuum residues was measured using energy-dispersive X-ray fluorescence spectrometry in accordance with the ASTM D 4294 method [34,35]. The asphaltene (C₇ and C₅) content was determined as heptane and pentane insolubles following the procedure described in the ASTM D 6560 standard method [35,36]. SARA composition of vacuum residue fractions was measured in accordance with the ASTM D 4124 [35,37]. The Conradson carbon content of the studied oils was measured in accordance with ASTM D 189 [35,38]. The nitrogen content of the residual oils was determined following the ASTM D 5291 [35,39] requirements. The total sediment existent content (TSE) of the hydrocracked atmospheric residue (ATB) was measured using hot filtration in accordance with the ISO 10307-1 method [35,40]. The contents of Ni and V were measured in accordance with the standard IP 501 [41].

The 540 °C+ vacuum residue conversion was calculated using Equation (1):

$$Conversion \left(\mathrm{wt}.\%\right)={\displaystyle \frac{Feed 540 °\mathrm{C}+-Product 540 °\mathrm{C}+}{Feed 540 °\mathrm{C}+}}\times 100$$

(1)

Feed 540 °C+ = mass of the VR feed fraction boiling above 540 °C determined by the high-temperature simulated distillation method, ASTM D 7169 [42,43], of the feed and multiplied by the mass of the feed;

Product 540 °C+ = mass of liquid product fraction boiling above 540 °C determined using a high-temperature simulated distillation method, ASTM D 7169 [42,43].

Details about the laboratory hydrocracking unit and the hydrocracking-operating conditions employed are presented in [44,45]. The uncertainty of the measurement of the pilot plant vacuum residue hydrocracking conversion was 1.7 wt. %. A low-sediment Ni-Mo-supported commercial catalyst was availed in this research.

The assessment of relationships between the characteristics of the vacuum residual oils and conversion level was performed by using the intercriteria analysis (IcrA) [35]. Details of the theory and application of IcrA are presented in [46]. As input data, IcrA needs an m × n table with the measurements of m objects against n criteria. As a result, it returns a n × n table with intuitionistic fuzzy pairs, determining the degrees of relation between each pair of criteria, hence the name “intercriteria”, and allows for making informed decisions, which render accounts of the inherent uncertainty that complex real-life problems exhibit. For the sake of terminological precision, in IcrA, the term “correlation” between the criteria is avoided but the terms “positive consonance”, “negative consonance”, and “dissonance” are being used instead. The IcrA approach calculates two intuitionistic fuzzy functions: μ and υ, whose values define the degree of the relationship between the criteria [35]. For μ = 0.75 ÷ 1.00 and υ = 0 ÷ 0.25, a region of statistically meaningful positive consonance is determined, while at μ = 0 ÷ 0.25 and υ = 0.75 ÷ 1.00, an area of statistically meaningful negative consonance is derived. All other cases are considered to be dissonance. A strong consonance is considered at values of μ = 0.95 ÷ 1.00, υ = 0.00 ÷ 0.05 (positive), μ = 0.00 ÷ 0.05, and υ = 0.95 ÷ 1.00 (negative), while a weak consonance is deemed at μ = 0.75 ÷ 0.85, υ = 0.15 ÷ 0.25 (positive), μ = 0.15 ÷ 0.25, and υ = 0.75 ÷ 0.85 (negative). Two software packages for IcrA were established, were freely available as open source from https://intercriteria.net/software/ (accessed on 25 April 2025), and were detailed in [47,48,49,50]. IcrA was successfully applied in the field of economy [51,52,53], biology [54,55,56], medicine [57,58,59], education [60,61], environmental protection [62,63,64], and mathematics [65,66,67].

Before IcrA evaluation, all variables are normalized using the normalization formula (Equation (2)):

$$X_{new}={\displaystyle \frac{X-X_{min}}{X_{max}-X_{min}}}$$

(2)

The decision to apply IcrA is due to the fact that it can register the presence of statistically meaningful relations that are both linear and nonlinear, while conventional correlation analysis uncovers the presence only of linear relations [22,67].

Two types of regression models, linear and nonlinear, were employed in this research. The optimal parameters of regression coefficients were established by using the nonlinear least squares method (LSM) [68]. An optimization tool, the Differential Evolution (DE) algorithm, was used to search for the best parameter values in compact subsets in parameter space [68]. The DE algorithm does not require differentiability or even continuity of the optimized function. Moreover, it is very applicable to construct some necessary bounds in the parameter space. All calculations have been realized by the use of CAS Maple 2024.2, Global Optimization Tool (method = diffevol), and verified by a simple Python script, based on differential evolution package from scipy.optimize library [68].

The methodology used in this study is summarized in Figure 1.

3. Results and Discussion

The conversion level at constant operating conditions (constant reaction temperature and liquid hourly space velocity) for the eight studied vacuum residues is shown in Figure 2.

These data indicate that reactivity of the examined vacuum residues is different, demonstrating a conversion variation between 64 and 76 wt. % at constant operating conditions.

The variation in the hydrocracked atmospheric residue (HCAR) sediment content with conversion alteration for the vacuum residues VR 2, VR 3, and VR 5 is depicted in Figure 3.

It is worth mentioning here that VR 2 and VR 3, as apparent from the data in Figure 2, have the same reactivity. However, as shown in the data of Figure 3, these two vacuum residues exhibit quite different sediment formation propensities. Considering that, the commercial ebullated bed vacuum residue hydrocracker operates at constant sediment content in the HCAR to provide a sufficient cycle length before two consecutive cleanings; the more important conversion is that at constant HCAR sediment content (Figure 4).

The data in Figure 4 show much wider variations in conversion among the vacuum residues studied (between 45 and 85 wt. %) in comparison to that at constant operating conditions. The reason for this difference lies in the diverse sediment formation affinity of the various vacuum residues. For example, VR 2, VR 3, and VR 4 demonstrate the same reactivity (conversion in the range 65–65.5 wt. % at constant operating conditions, Figure 2). While the same vacuum residues show a difference between conversions in the range 45–65 wt. % at the same HCAR sediment content (Figure 4). This implies that at commercial conditions, the vacuum residues VR 2 and VR 3 would exhibit substantial difference in conversions as opposed to their reactivity, which seems to be the same, but their sediment formation propensity is much different.

Table 4. μ—values obtained from IcrA evaluation of the data for vacuum residue properties and conversions at constant operating conditions and constant HCAR sediment content.

μ	D15	Sul	N	CCR	Sat.	Aro	Res.	C5-Asp	C7-Asp	Ni	V	Conv. at Constant Sediment Level	Conv. at Constant Op. Cond.
D15	1.00	0.89	0.50	0.79	0.25	0.21	0.64	0.86	0.86	0.61	0.64	0.46	0.43
Sul	0.89	1.00	0.39	0.82	0.21	0.32	0.68	0.75	0.75	0.50	0.54	0.57	0.54
N	0.50	0.39	1.00	0.50	0.75	0.29	0.50	0.64	0.64	0.75	0.71	0.14	0.11
CCR	0.79	0.82	0.50	1.00	0.39	0.29	0.57	0.79	0.79	0.46	0.50	0.50	0.50
Sat.	0.25	0.21	0.75	0.39	1.00	0.54	0.25	0.39	0.39	0.57	0.54	0.21	0.29
Aro	0.21	0.32	0.29	0.29	0.54	1.00	0.29	0.14	0.14	0.25	0.21	0.68	0.71
Res.	0.64	0.68	0.50	0.57	0.25	0.29	1.00	0.57	0.57	0.68	0.71	0.46	0.43
C5-asp	0.86	0.75	0.64	0.79	0.39	0.14	0.57	1.00	1.00	0.68	0.64	0.32	0.29
C7-asp	0.86	0.75	0.64	0.79	0.39	0.14	0.57	1.00	1.00	0.68	0.64	0.32	0.29
Ni	0.61	0.50	0.75	0.46	0.57	0.25	0.68	0.68	0.68	1.00	0.96	0.14	0.11
V	0.64	0.54	0.71	0.50	0.54	0.21	0.71	0.64	0.64	0.96	1.00	0.18	0.14
Conv. at constant sediment level	0.46	0.57	0.14	0.50	0.21	0.68	0.46	0.32	0.32	0.14	0.18	1.00	0.82
Conv. at constant op. cond.	0.43	0.54	0.11	0.50	0.29	0.71	0.43	0.29	0.29	0.11	0.14	0.82	1.00

and

Table 5. ν—values obtained from IcrA evaluation of the data for vacuum residue properties and conversions at constant operating conditions and constant HCAR sediment content.

ν	D15	Sul	N	CCR	Sat.	Aro	Res.	C5-Asp	C7-Asp	Ni	V	Conv. at Constant Sediment Level	Conv. at Constant Op. Cond.
D15	0.00	0.11	0.50	0.21	0.75	0.79	0.36	0.14	0.14	0.39	0.36	0.46	0.50
Sul	0.11	0.00	0.61	0.18	0.79	0.68	0.32	0.25	0.25	0.50	0.46	0.36	0.39
N	0.50	0.61	0.00	0.50	0.25	0.71	0.50	0.36	0.36	0.25	0.29	0.79	0.82
CCR	0.21	0.18	0.50	0.00	0.61	0.71	0.43	0.21	0.21	0.54	0.50	0.43	0.43
Sat.	0.75	0.79	0.25	0.61	0.00	0.46	0.75	0.61	0.61	0.43	0.46	0.71	0.64
Aro	0.79	0.68	0.71	0.71	0.46	0.00	0.71	0.86	0.86	0.75	0.79	0.25	0.21
Res.	0.36	0.32	0.50	0.43	0.75	0.71	0.00	0.43	0.43	0.32	0.29	0.46	0.50
C5-asp	0.14	0.25	0.36	0.21	0.61	0.86	0.43	0.00	0.00	0.32	0.36	0.61	0.64
C7-asp	0.14	0.25	0.36	0.21	0.61	0.86	0.43	0.00	0.00	0.32	0.36	0.61	0.64
Ni	0.39	0.50	0.25	0.54	0.43	0.75	0.32	0.32	0.32	0.00	0.04	0.79	0.82
V	0.36	0.46	0.29	0.50	0.46	0.79	0.29	0.36	0.36	0.04	0.00	0.75	0.79
Conv. at constant sediment level	0.46	0.36	0.79	0.43	0.71	0.25	0.46	0.61	0.61	0.79	0.75	0.00	0.04
Conv. at constant op. cond.	0.50	0.39	0.82	0.43	0.64	0.21	0.50	0.64	0.64	0.82	0.79	0.04	0.00

present the μ and υ values of the IcrA evaluation of the vacuum residue characteristics and both conversions (at constant operating conditions and constant HCAR sediment content). It is evident from these data that three vacuum residue characteristics (nitrogen, Ni, and V contents) have negative consonances with both conversions. Therefore, their enhancement will affect negatively conversion levels. The regression of data for vacuum residue properties (the contents of sulfur (S), nitrogen (N), C₇-asphaltenes (C₇asp), and Conradson carbon content (CCR)), density at 15 °C (D15), and conversion at constant operating conditions has led to the development of two correlations, shown as Equations (3) and (4):

$$\begin{gathered} VR conversio{n}^{constant operating conditions}=2.060268\times S-7.9594\times N-0.2955\times C_{7}asp-{\displaystyle \frac{4.1493}{CCR}}+67.6589 \\ R=0.964, st. error=0.87 wt. \% \end{gathered}$$

(3)

$$\begin{gathered} VR conversio{n}^{constant operating conditions}=1.1843\times S-12.7763\times N-0.2461\times C_{7}asp-{\displaystyle \frac{54.1008}{D_{15}}}+125.817 \\ R=0.947, st. error=1.12 wt. \% \end{gathered}$$

(4)

Equations (3) and (4) suggest that the reactivity of a vacuum residue in the hydrocracking process increases with the enhancement of sulfur content, increasing Conradson carbon content (CCR) or density, and decreasing nitrogen and asphaltene contents. The positive effect of sulfur on vacuum residue reactivity may be a result of the decomposition of the reactive sulfur species and increasing the rates of the initiation and propagation steps during the chain reaction mechanism of vacuum residue hydrocracking [69]. The positive effect of sulfur on the conversion in the vacuum residue hydrocracking has also been reported by Chang et al. [70]. According to the free radical chain reaction mechanism for liquid-phase cracking, in order to maximize residue conversion, maximizing the initiation and propagation steps and minimizing the termination step are required [69]. Increasing the content of free radical initiators in the vacuum residue has been shown to enhance conversion during hydrocracking [71]. It deserves mentioning that the increase in density (Conradson carbon content) has a positive effect on the vacuum residue hydrocracking reactivity. These findings are in line with the results reported by Fortain [72], who showed that the vacuum residue with higher density (higher Conradson carbon content, respectively, lower saturate content) have a higher reactivity during catalytic hydrocracking. The aromatic species containing in the vacuum residues examined in this work seem to improve the rates of the initiation and propagation steps and decrease the rates of the termination step. A possible explanation for their higher reactivity could lie in their higher content of sulfur, as shown in an earlier study [73], and this higher sulfur content should be more reactive. Nitrogen has been shown to act as an inhibitor in the residue hydroprocessing [74]. The nitrogen in the residual oils is included in the polycyclic aromatic structure of the higher-boiling-point material [69]. These polycyclic aromatic nitrogen-containing structures may form stable radicals during their thermal conversion and as such to result in a decrease in the rate of cracking of the residue and an increase in the rate of termination reactions [69]. The asphaltenes, the most aromatic and polar fraction in the vacuum residue, may also form stable radicals during their thermal conversion and decrease the rate of cracking of the residue and increase the rate of termination reactions. Asphaltenes have been reported to be the most refractive fraction to process during hydroconversion [75,76,77]. Equations (3) and (4) are in line with the findings of these studies.

Figure 5a,b illustrate the agreement between measured and calculated conversions at constant operating conditions.

The regression of data for vacuum residue properties (the contents of sulfur (S), nitrogen (N), C₇-asphaltenes (C₇ asp), and Conradson carbon content (CCR)) and conversion at constant HCAR sediment content has led to the development of the correlation, which is shown as Equation (5):

$$\begin{gathered} VR conversio{n}^{constant HCAR sediment}=87.1306-0.01306\times \left(V+Ni\right)-13.3068\times N-0.92045\times CCR+5.9613\times S-0.83468\times C_{7}asp \\ \mathrm{R}=0.985, \mathrm{st}. \mathrm{error}=3.8 \mathrm{wt}. \% \end{gathered}$$

(5)

Figure 6 exhibits the agreement between conversions measured and calculated using Equation (5) at a constant HCAR sediment content.

The formation of coke-like sediments in the vacuum residue hydrocracking is believed to follow the mechanism of free radical recombination and polymerization, where unsaturated hydrocarbons react to form higher-molecular-weight components [78]. Equation (5) suggests that asphaltenes, metals, nitrogen, and heavy polynuclear aromatic components expressed by the Conradson carbon content promote this mechanism. The role of asphaltenes on the sedimentation is well documented [75,79]. The negative effect of nitrogen on sedimentation is also known [75]. Metals deactivate the catalyst by plugging the internal micro- and meso-structures and impair the catalyst function that inhibits the reactions of radical recombinations and polymerization [80,81]. A higher polynuclear aromatic structure content (CCR), that, as observed from the data in Table 4 and Table 5, has positive consonance with asphaltenes (μ = 0.79; υ = 0.21), seems to also promote the free radical recombination and polymerization, probably by the concentration effect of the species, which are more reactive in these reactions. In other words, Equation (5) indicates that the vacuum residues which have high asphaltene, CCR, nitrogen, and metal contents seem to have higher propensity to form coke-like sediments and therefore would exhibit a lower conversion level in a commercial ebullated bed vacuum residue hydrocracker.

4. Conclusions

The ebullated bed vacuum residue hydrocracking similar to the other residue conversion processes, such as coking, FCC, and visbreaker, demonstrated that the feed properties have a tremendous impact on process performance. Conversion variation between 45 and 85 wt. % is feasible for the hydrocracking of various vacuum residues. The difference in vacuum residue conversion at constant operating conditions, which is an indicator for vacuum residue reactivity, is not as big as that between conversions obtained at the same hydrocracked atmospheric residue sediment content, which is due to the different sedimentation propensity of the various vacuum residues. The performed intercriteria analysis revealed that vacuum residue conversion has negative consonances with the contents of nitrogen and metals. Correlations were developed, showing that metals, nitrogen, and asphaltenes are inhibitors, while sulfur turns out to be a promotor during the vacuum residue hydrocracking process.