Adsorptive Treatment of Residues on Macroporous Adsorbent for Marine Fuel Production Scheme on Refinery

Abstract

Adsorptive treatment using granulated macroporous Al₂O₃-SiO₂ adsorbent is proposed as a preliminary stage for residue pretreatment in refineries. The study evaluates the adsorptive treatment of atmospheric and visbreaking residue at 485–510 °C and 1 h⁻¹ feed rate, resulting in a total liquid product yield of about 73.0–75.0 wt%, coke on the sorbent of 12.6–18.3 wt%, demetallization exceeding 98%, and a reduction in carbon residue of 65–72%. The paper also discusses the role of feed dilution with light gasoil, process temperature, and feed rate in optimizing the adsorptive treatment process. The high coke content on the adsorbent necessitates its regeneration, which is shown to be complete at temperatures up to 750 °C. Regeneration decreases macropore size and volume but does not significantly impact demetallization. The pretreated residual product has low viscosity and is further processed through hydrotreatment in a fixed-bed unit to produce low-sulfur marine fuel. The hydrotreated atmospheric residue meets the requirements for RMA 10 fuel, with a sulfur content lower than 0.1 wt%.

1. Introduction

Atmospheric residue consumption in Russia began to grow in the 2010s [1], which could be explained by the start of its use as a marine fuel for international ships. However, since 2020, the International Convention for the Prevention of Pollution from Ships (MARPOL) has limited the use of marine fuels with sulfur content exceeding 0.5 wt% [2]. The International Maritime Organization (IMO) has also identified Special Environmental Control Areas (SECAs) where the requirements for ship operation are even more stringent: since 1 January 2015, the sulfur content limit is 0.1% wt. Such ECAs include the Baltic and North Seas, as well as some coastal areas of the United States and Canada [3]. Various non-petroleum fuels such as liquefied natural gas, alcohol-based fuels, hydrogen, ammonia, biofuels, and solar power have been suggested to reduce sulfur content in marine fuels to meet the IMO requirements. The advantages and disadvantages of each of these alternatives are also being considered [4]. However, only a limited amount of residues is involved in marine fuel production, and the proportion of vacuum distillates or even middle distillates for ultra-low sulfur marine fuel is significant [3].

Therefore, there are two factors stimulating the need for flexible technologies for deeper refining of residues. Firstly, as the consumption of residues for marine fuel production has dramatically decreased, the demand for light crudes may not be satisfied for long due to the depletion of light oil reserves [5]. Secondly, an increase in heavy crude and natural bitumen refining is observed [6], resulting in higher amounts of heavy petroleum residues. Processing these residues is not effective enough or is very difficult and requires significant investment [7].

The main limitation of affordable thermal processing of residues (delayed coking, visbreaking) [8] is a large amount of low-value by-products. Known catalytic technologies (catalytic cracking, hydrocracking, hydrotreating) have their own limitations on the carbon and metal content in the feedstock [9]. Any residue pretreating is supposed to deal with these limiting factors.

Solvent deasphalting with individual selective solvents such as toluene, hexane, heptane, and benzene is used as a stage for residue processing, in which viscosity, density, and carbon residue of the feed or recycle stream are reduced, as well as the content of metals [10]. Solvent processes are characterized by high energy consumption, capital costs, and lead to heavier by-product formation than vacuum residue. Further, the efficiency of resin removal from residues with solvents is low in terms of low sulfur marine fuel production [11].

Therefore, as a solution to the problem of residue refining, thermal adsorption processes, especially adsorptive treatment [8], were considered as a pretreatment stage before hydrotreating. The process is designed for residual feed demetallization and deasphalting, and partial reduction of sulfur content.

The adsorptive treatment is the selective evaporation of lighter components of the feed in the reactor over a solid adsorbent with simultaneous asphaltenes deposition on its surface. Those asphaltenes are selectively cracked with the formation of an additional amount of liquid products and coke.

Commercial modifications of the adsorptive treatment process are designed for demetallization and deasphalting of residual oil feedstock [12]. It can serve as feed pretreatment for catalytic cracking or hydrotreating for obtaining low-sulfur marine fuel. Process modifications on granular fixed-bed or moving-bed adsorbent could demonstrate greater stability than lift modifications with microspherical adsorbent [12].

Natural kaolin (Al₂O₃∙2SiO₂∙2H₂O), powdered petroleum coke, iron ore pellets, ceramics [12], and other materials [13,14] have been tested as adsorbents, each with its own advantages and disadvantages. Petroleum coke has low strength and porosity, and can not be regenerated, while iron ore pellets have almost no porosity [15], which leads to diffusion difficulties and rapid deactivation of the adsorbent due to surface coking [16]. Therefore, adsorbents for residue processing require a large macropore volume (diameter not less than 50 nm) [17].

It is advisable to use macroporous adsorbents for the adsorptive removal of metals and non-volatile components from residues. Such materials can be synthesized in various ways, with template synthesis [18,19,20,21] being the most accessible. A granulated macroporous adsorbent based on kaolin and pseudoboehmite (60 wt% and 40 wt%, respectively) [22] has a high specific surface area, high adsorption capacity, and affinity for coke and metals. Previous research has focused on creating a macroporous structure using templates such as guar gum and wax emulsion. The wax template adsorbent had a larger pore volume and showed high efficiency in the adsorptive treatment of residues.

The aim of this study is to investigate adsorptive treatment of atmospheric residue and visbreaking residue as the primary residual feedstocks over novel macroporous adsorbents. The study will assess the impact of diluent use on the efficiency of the process and evaluate the regeneration of the adsorbent. In addition, the study will examine the hydrotreating of the process product to determine its potential for use in the production of low-sulfur marine fuel. The results of the research will allow an evaluation of the potential integration of the adsorptive treatment into the technological scheme of oil refining, with several pathways for low-sulfur marine fuel production.

2. Materials and Methods

The selection of the adsorbent for the adsorptive treatment process was carried out in the paper [22]. An adsorbent based on kaolin (60 wt%), pseudoboehmite (40 wt%), with the addition of 15% (by weight of the prepared adsorbent) wax was chosen. The characteristics of the adsorbent are presented in

Table 1. Characteristics of adsorbent.

Properties	Values
Average pellet diameter, mm	3.0–6.0
Loss on ignition at 800 ± 10 °C, %	≤5.0
Bulk density, g/cc	0.85–0.95
Specific surface area, m2/g	≥25.0
Pore volume (including macropore) 1, cc/g	0.32
Mechanical strength, kg/mm	3.42
Macropore volume 2 (diameter > 50 cc/g)	0.25

¹ Evaluated by water absorption. ² Evaluated by mercury porosimetry.

.

The process feed and products were analyzed using the following methods: liquid chromatography (HPLC) to determine the hydrocarbon-type content, simulated distillation (SimDis) for naphtha paraffins, isoparaffins, olefins, naphthenes, and aromatics content (PIONA) by capillary gas chromatography; carbon, CHNS-analysis by pyrolysis-GC; sulfur and metals content by X-ray fluorescence analysis. Standard methods were used to determine the density, kinematic viscosity, and iodine number.

The adsorptive treatment process was conducted in a fixed-bed flow-type reactor, as shown in Figure 1.

To address the high viscosity and carbon residue of the feed, particularly the visbreaking residue (VisR), a diluent was used during the adsorptive treatment process. Recirculating light gasoil from the own cycle oil helped maintain stability in the fixed-bed adsorbent system. Without recirculation, reactor coking was observed periodically.

As diluents, straight-run diesel fraction (SRGO) and light coker gasoil (LCG) were utilized. LCG is produced through a thermo-destructive process, which mimics gasoil from the adsorptive treatment process the best.

Table 2. Characteristics of the feed for adsorptive treatment.

Properties	Values
	AtmR	VisR	AtmR (70 vol%) + SRGO (30 vol%)	VisR (70 vol%) + SRGO (30 vol%)	AtmR (70 vol%) + LCG (30 vol%)	VisR (70 vol%) + LCG (30 vol%)
Density at 20 °C, kg/m3	992	1010	955	980	970	996
Kinematic viscosity at 100 °C, mm2/s	52.50	112.90	17.20	20.11	18.13	20.24
Carbon residue, wt%	16.9	18.9	12.3	13.2	12.6	15.4
Asphaltenes, wt%	10.98	12.9	7.69	9.05	8.01	9.80
Sulfur content, wt%	2.30	2.64	1.68	1.85	1.71	2.04
Metals content (Ni+V+Fe), ppm	257	281	180	197	217	217
Fraction yield1, wt%: IBP-195 °C 195–350 °C >350 °C, including: 350–540 °C >540 °C	2.0 12.0 86.0 21.9 64.1	1.8 7.2 91.0 19.1 71.9	2.6 32.8 64.6 20.6 44.0	2.5 32.6 64.9 17.9 47.0	1.6 28.6 69.8 25.5 44.3	1.3 25.9 72.8 23.4 49.4

¹ SimDis (ASTM D 5307).

presents the characteristics of the feed for the adsorptive removal process.

The adsorptive treatment was performed in downflow reactor with an adsorbent loading of about 50 cc. The conversion experiments were carried out within a temperature range of 485–510 °C, a liquid hourly space velocity (LHSV) of 1.0 h⁻¹, an adsorbent volume of 50 cc, and a feed injection time of 1 h. To completely remove the liquid products after the reaction, the reactor and separator were purged with an inert gas (nitrogen) for 1 h, so the average feed and adsorbent contact time was considered to be 1 h.

The adsorbent’s efficiency should be evaluated in terms of feed conversion and feed purification. The difference in sulfur content, metals (Ni+V+Fe), the content of the fraction boiling over 350 °C, and non-volatile residue boiling over 540 °C of the feed and products were used as indicators of adsorbent efficiency:

$$\mathrm{X}=\left(1-\frac{A_{product}}{A_{feed}}\right)\times 100\%,$$

(1)

where A_product, A_feed—content of the fraction boiling over 350 °C, or non-volatile residue boiling over 540 °C, or sulfur, or metals (Ni+V+Fe) in liquid product and feed, respectively.

The sorbent was unloaded and washed with n-hexane in a Soxhlet extractor for at least 1.5 h after each experiment. The coke content was determined for washed and dried sorbent samples using a PerkinElmer 2400 Series II CHNS/O analyzer (Waltham, MA, USA).

Sorbent regeneration was studied with NETZSCH STA 449 F5 Jupiter (Selb, Germany). Preparative sorbent regeneration was carried out in an oven at 750 °C with air.

For hydrotreating, a conventional FCC pretreatment catalyst with 5.7 wt% NiO and 24.7 wt% MoO₃ content was used. The same reactor was loaded with 15 cc of Ni-Mo catalyst (0.25–0.5 mm fraction) diluted with silicon carbide in a ratio of 1:1. Hydrotreating was carried out at 360–400 °C, 15 MPa, and 1500–2000 H2/feed ratio.

3. Results and Discussion

3.1. Adsorptive Treatment of Different Feedstock

Characteristics of products obtained by adsorptive treatment of various residual feed are presented in

Table 3. Characteristics of the adsorptive treatment process of residual feed at 485 °C.

Properties	Values for Feed
	AtmR	AtmR (70 vol%) + SRGO (30 vol%)	VisR (70 vol%) + SRGO (30 vol%)	AtmR (70 vol%) + LCG (30 vol%)	VisR (70 vol%) + LCG (30 vol%)
Total liquid product
Density at 20 °C, kg/m3	903	884	919	889	920
Sulfur content, wt%	1.86	1.32	1.50	1.41	1.72
Carbon residue, wt%	4.25	3.79	3.19	4.58	3.52
Metals content (Ni+V+Fe), ppm	19	14	4	4	4
Fraction yield 1, wt%: IBP-195 °C 195–350 °C >350 °C, including: 350–540 °C >540 °C	11.6 36.2 52.2 37.1 15.1	11.7 51.3 37.0 28.9 8.1	10.1 50.2 39.7 28.2 11.5	4.8 45.3 49.9 38.6 11.3	5.0 42.2 52.8 40.5 12.3
Fractions yield calculated to residue without diluent, wt %
Gas Liquid product, including: IBP-195 °C 195–350 °C >350 °C, including: 350–540 °C >540 °C Coke	12.2 79.5 9.2 28.8 41.5 29.5 12.0 8.3	16.6 76.0 13.9 31.0 31.1 21.5 9.6 7.4	11.1 72.9 11.7 28.1 33.1 19.8 13.3 16.0	13.0 74.4 5.6 23.1 45.7 32.4 13.3 12.6	8.0 73.7 5.8 19.2 48.7 34.4 14.3 18.3
Feed conversion and purification
Conversion, %, of: fraction > 350 °C fraction > 540 °C	39.3 76.4	42.7 81.6	38.8 75.5	28.5 74.5	27.5 75.1
Demetallization, %	92.6	92.2	98.0	98.2	98.2
Desulfurization, %	19.2	21.4	18.9	17.5	15.7

¹ SimDis (ASTM D 5307).

.

Table 3 shows that liquid products of adsorptive treatment have a significantly lower carbon residue, with a decrease of 63–65% in carbon residue for AtmR/LCG conversion product and VisR/LCG conversion product of 70–72%. Additionally, the products contain a much lower amount of nickel and vanadium, proving the high efficiency of the adsorbent in residue upgrading. Furthermore, it should be noted that the non-volatile fraction, in which the main amount of asphaltenic compounds is concentrated, reached a conversion of 82% in the performed adsorptive treatment of AtmR.

Despite achieving a high non-volatile residue conversion in the process of adsorptive treatment of atmospheric residue, processing it in a laboratory unit on a fixed-bed adsorbent led to reactor coking, making the process unstable.

The characteristics of adsorptive treatment of atmospheric residue and product fractions yield are almost the same for both diesel and LCG diluents. However, the sulfur content for feed with straight-run diesel fraction decreased by 21.4% compared to 17.5% for feed with LCG, which might be caused by the greater stability of sulfur compounds in LCG.

The synthesized adsorbent provided high feed demetallization in the process with both diluents. In the case of of AtmR/LCG feed, vacuum gasoil (VGO) fraction and non-volatile residue (> 540 °C) content in the liquid product were higher by 9.0–9.5 wt%.

Considering that visbreaking residue (VisR) has a higher viscosity and carbon residue and cases of reactor coking during some experiments with atmospheric residue, the adsorptive treatment of VisR feed was carried out only with diluents. The comparable yield of non-volatile residue was obtained for atmospheric and visbreaking residues with delayed coking gasoil as a diluent. At the same time, the amount of coke increased by 1.5 times for VisR+LCG adsorptive treatment due to higher asphaltenic compounds and metals content in visbreaking residue.

The adsorptive treatment of VisR+SRGO, in comparison with the use of LCG as a diluent, shows a larger yield of gases with almost the same yield of the liquid product. Moreover, the yield of the light gasoil fraction (195–350 °C) is higher than for VisR/LCG by more than 9 wt%.

In the case of using a mixture with straight-run diesel fraction, the conversion of the >350 °C fraction was higher, leading to a lower content of coke on the adsorbent. The obtained results could be explained by higher aromatics content in LCG compared to SRGO (aromatics content is 44.3 and 25.9 wt%, respectively). On the one hand, higher aromatics content contributes to better dissolution of asphaltenes, and on the other hand, it increases the tendency to coke formation [23]. The results in Table 3 make it possible to suggest the use of own gasoil as a diluent or others depending on the refinery flowchart.

3.2. Temperature and Feed Rate Influence on Products Yield and Quality

Increasing the temperature to 510 °C, as shown in Figure 2, caused an expected increase in light distillate yield (the yield of fractions > 350 °C decreased by 10.0%), while non-volatile residue yield dropped by a third.

However, increasing the temperature enhanced coke formation, which interfered with the even feed passage through the fixed-bed adsorbent. Acceleration of thermal destruction led to the increased formation of unsaturated structures and fragments of hydrocarbons inclined to polycondensation or polymerization [24]. It can be concluded that raising the temperature to 510 °C is unreasonable due to the instability of the process and insignificant advantages.

At temperatures below 485 °C, experiments with high-viscosity VisR were not carried out (as in [25]), since this leads to adsorbent coking [26], which, however, can be avoided by using higher pressure and volumetric hourly space velocity [27].

Adsorptive treatment gases have a significant share of C1–C2 gas (about 40 vol%), the propane-propylene fraction (PPF) is about 25 vol%, butane-butylene is about 17 vol%, and about 1.0 vol% hydrogen sulfide (H2S).

Low-viscosity feed (AtmR (70 vol%) + SRGO (30 vol%)) was chosen for experiments to determine the optimal feed space velocity. Characteristics of the adsorptive treatment products obtained at 1.0–1.7 h⁻¹ are presented in

Table 4. Characteristics of the total liquid product of adsorptive treatment at 485 °C (Feed—AtmR (70 vol%) + SRGO (30 vol%)).

Properties	Values for Feed
	Feed Space Velocity, h−1
	1.0	1.5	1.7
Total liquid product
Density at 20°C, kg/m3	884	892	894
Sulfur content, wt%	1.32	1.44	1.50
Carbon residue, wt%	3.79	3.98	4.10
Metals content (Ni+V+Fe), ppm	14	13	2
Fractions yield calculated to residue without diluent, wt %
Gas Liquid product, including: IBP-195 °C 195–350 °C >350 °C, including: 350–540 °C >540 °C Coke	16.6 76.0 13.9 31.0 31.1 21.5 9.6 7.4	14.1 77.9 12.7 28.4 36.8 26.4 10.4 8.0	13.6 79.7 12.4 28.5 38.9 27.5 11.4 6.7
Feed conversion and purification
Conversion, %, of: fraction > 350 °C fraction > 540 °C	42.7 81.6	36.4 80.5	34.7 78.9
Demetallization, %	92.2	92.8	93.0
Desulfurization, %	21.4	14.3	10.7

.

As shown in Table 4, at 485 °C, increasing feed space velocity from 1.0 to 1.7 h⁻¹ caused a slight increase in liquid product yield (1.9–3.7% wt.) with lower gas and coke yield. At the same time, the >350 °C fraction yield simultaneously increased with feed space velocity increasing due to IBP-350 °C yield decrease, which was caused by the reduction in contact time of feed and adsorbent. Demetallization was 92–93% wt., desulfurization decreased by 2 times.

3.3. Spent Adsorbent Analysis and Regeneration

After the extraction of liquid hydrocarbons with hexane, the content of carbon, nitrogen, and sulfur in spent adsorbent was determined. The total coke content in spent adsorbent after one cycle of AtmR treating was 11.2 wt%, with coke elemental composition: C—88 wt%, H—4 wt%, N—2 wt%, S—6 wt%.

Adsorbent regeneration parameters were evaluated by synchronous thermal analysis (thermogravimetric/differential thermal analysis (TG/DTA)): heat release from coke 1388 J/g spent adsorbent; specific heat release of coke burning 12,437.3 J/g, the temperature of complete regeneration—no more than 749 °C (Figure 3). The temperature is lower than sorbent calcination temperature, so such regeneration does not cause sorbent destruction, and it is not uncommon. For example, FCC regenerators are operated at a similar temperature.

The regenerated adsorbent was colored red, indicating iron deposition on the surface. As mentioned earlier, Ni and V, along with Fe, deposited on the adsorbent and could act as catalysts for some reactions in the treatment process.

Pore characteristics and pore size distribution of fresh and regenerated adsorbents presented in Figure 4.

After the first regeneration, the volume of pores with a diameter > 100 nm decreased by about 2 times, and after three regenerations, pores > 100 nm were almost absent. The decrease of macropore volume may be due to their blocking by metals. This assumption is supported by the red tint of the regenerated samples, indicating Fe deposition on the adsorbent surface. However, demetallization of the regenerated adsorbent only slightly decreased (by 3% and 5%, respectively), while remaining above 86%. The decrease of macropores > 100 nm was accompanied by an increase of macropores with a diameter of 50–100 nm, and their volume is sufficient for consistently efficient metal removal. To ensure stable adsorptive removal of metals, sulfur, and non-volatile components from the feed, a portion of fresh adsorbent can be added to the regenerated adsorbent during reactor reloading or to the moving bed after the regenerator.

3.4. Products of Adsorptive Treatment Characterization

Table 5. Characteristics of adsorptive treatment liquid products (T = 485 °C).

Properties	Values
	AR (70 vol%) + LGO (30 vol%)	VisR (70 vol%) + LGO (30 vol%)
Naphta (IBP-195 °C)
Density at 20 °C, kg/m3	764	770
Sulfur content, wt%	0.65	0.60
Hydrocarbon content, wt%. Paraffins Isoparaffins Aromatics Naphthenes Olefins	18.3 20.5 27.4 13.6 20.3	16.0 18.9 19.1 13.5 32.5
Iodine number, g iodine/100 g of sample	48.5	79.9
Light gasoil (195–350 °C)
Density at 20 °C, kg m−3	863	879
Sulfur content, wt%	0.92	1.08
Aromatics content, wt%, including: Monoaromatics Diaromatics Polyaromatics	33.5 19.0 11.3 3.2	41.1 19.7 18.4 3.0
Iodine number, g iodine/ 100 g of sample	9.8	36.6
Olefins content, wt%.	8.0	33.1
Pour point, °C	−23	−24
Atmospheric residue (350 °C+)
Metals content (Ni+V+Fe), ppm	2	2
Kinematic viscosity at 100 °C, mm2 s−1	5.65	6.27
Density at 20 °C, kg m−3	953	961
Sulfur content, wt%	1.79	2.00
Carbon residue, wt%	3.65	4.25
Saturates, wt%: Aromatics, wt%: Polar (I), wt%: Polar (II), wt%:	31.2 55.3 12.4 1.1	33.0 50.7 14.6 1.7

presents the characteristics of liquid product fractions. The process feed is atmospheric residue/visbreaking residue with 30 vol% light gasoil.

Naphtha and light gasoil of adsorptive treatment obtained from the atmospheric residue (AtmR) contained fewer unsaturated hydrocarbons compared to products from visbreaking residue (VisR). This could be due to lower thermal stability and a higher tendency to crack VisR. Meanwhile, naphtha of atmospheric residue treating contains more monoaromatic hydrocarbons, while visbreaking residue treating gasoil contains significantly more diaromatic hydrocarbons, which is also associated with different molecular weights of compounds in the processed feed.

Naphtha and gasoil from the adsorptive treatment require further upgrading, for example, as part of conventional hydrotreating feedstock. The wide gasoil fraction and residue (>350 °C) of the process with reduced metals and coke content could be hydrotreated in a fixed-bed reactor to obtain low-sulfur marine fuels. The cold-flow properties of marine fuel components (such as light gasoil) could also be improved by using depressant and depressant-dispersing additives [28].

The sulfur content of the residue of adsorptive treatment (AtmR/LCG feed) is slightly higher than in the feedstock, which is probably caused by a significant sulfur decrease of distillate products and the concentration of sulfur-containing compounds in the atmospheric residue of treating process. The deposition of resins and asphaltenes on the adsorbent surface caused a high decrease of the carbon residue (almost 3 times) in both adsorptive treatment residues (for AtmR and VisR feed). Therefore, periodic adsorbent regeneration is inevitable.

The properties of unconverted adsorptive treatment residues are significantly different from the feedstock (AtmR or VisR). Process residues have significantly lower viscosity (more than 3 times) and a low metal content, which greatly expands the possibilities of their use and further processing, and even allows hydrotreating with a fixed bed. After hydrotreating, atmospheric residue can be used to produce marine fuels with low viscosity and ultra-low sulfur content.

The adsorptive treatment residue can also be returned to atmospheric/vacuum distillation to derive the vacuum gasoil fraction, which can then be hydrotreated to obtain catalytic cracking feedstock or low sulfur marine fuel as shown in Figure 5.

3.5. Hydrotreating of Adsorptive Treatment Residue

The atmospheric residue of the adsorptive treatment of AtmR was processed on a conventional hydrotreating catalyst of FCC pretreating. Hydrotreated fuel oil with sulfur content lower than 0.5 wt% was obtained at 360 °C, 15 MPa, and 1500 H₂/feed ratio. Obtaining a product with sulfur content lower than 0.1 wt% was possible at 380 °C, 15 MPa, and 2000 H₂/feed ratio. Products of adsorptive treatment residue hydrotreating are characterized by low viscosity, density, and carbon residue. In the context of marine fuels, these characteristics must satisfy specific numerical limits that vary according to the blend in question. Obtained low-viscosity components can be involved in almost any blend in varying proportions to achieve the desired characteristics.

Table 6. Characteristics of hydrotreated adsorptive treatment atmospheric residue.

Property	Requirements for Marine Fuel Type		Obtained Sample
	RMA 10	RMB 30
Kinematic viscosity at 50 °C, mm²/s, max	10.00	30.00	20.17
Density at 15 °C, kg/m³, max	920.0	960.0	899.6
Calculation aromatization index SSAI, max	850.0	860.0	800.0
Mass fraction of sulfur %, max.	Depends on region (less than 0.5 wt% or 0.1wt% )		0.097
Flash point in a closed crucible, °C, min	61.0	61.0	72.0
Acid number, mg KHO/g, max	2.5	2.5	0.09
Total sediment after aging, wt%, max	0.10	0.10	0.01
Carbon residue (micromethod), wt%, max	2.50	10.00	2.0
Flow temperature, °C, not higher:	–	–	minus 6
winter	0	0
summer	6	6
Water content, % vol, max	0.30	0.50	absence
As content, %, max	0.040	0.070	absence
Vanadium content, mg/kg, max	50	150	0.5
Sodium content, mg/kg, max	50	100	absence
Aluminum and silicon (total) ∑, mg/kg, max	25	40	absence

shows characteristics of obtained samples with requirements for RMA 10 fuel (at 400 °C due to partial hydrocracking) and RMB 30 (obtained at 360 °C).

4. Conclusions

Adsorptive treatment can be used to remove metals, sulfur, and non-volatile components from petroleum residual feed, making it a possible preparatory stage for obtaining catalytic cracking or hydrotreatment feed to increase refinery efficiency produce low-viscosity marine fuel components.

To ensure a stable process, feed dilution with gasoil can be used, up to 30% by volume, to eliminate the negative consequences associated with the high viscosity and carbon residue of heavy oil feedstock. Light gasoil of own production or gasoil from other thermal processes can be used for this purpose.

Adsorptive treatment from both atmospheric residue and visbreaking residue proceeds with high efficiency. At a temperature of 485 °C and a feed rate of 1.0 h⁻¹, the resulting product has the following content: C₁–C₄ gas—8.0–13.0 wt%, liquid product—73.0–75.0 wt% (including gasoline—5.5–6.0 wt%, light gasoil—19.2–23.1 wt%, vacuum gasoil—32.4–34.4 wt%, vacuum residue 13.3–14.3 wt%), and coke—12.6–18.3 wt%. Demetallization was more than 98%. The liquid product from the adsorptive treatment contained 65–72% lower carbon residue and 15–17% lower sulfur content. Increasing the temperature up to 510 °C led to an increase in coke yield and process instability, while feed space velocity higher than 1.0 h⁻¹ led to a lower quality liquid product. A reduction in feed adsorbent contact time led to a >350 °C fraction yield increase (up to 20.0%). The adsorptive treatment on a macroporous sorbent demonstrates industrially insignificant sulfur removal, and increasing desulfurization could be an aim of further research.

The high coke content on the adsorbent determines the necessity for its permanent regeneration. According to the results of synchronous thermal analysis, the adsorbent regeneration temperature (coke content 11.2 wt%) was set at 749 °C. Pore characteristics analysis of three times regenerated adsorbent showed that there are practically no macropores, which is caused by clogging with metals from the feedstock. Demetallization was above 85%. In the context of environmental concerns, adsorbent regeneration technology should be revised significantly, for example, wet regeneration to obtain fuel gas or synthesis gas should be considered as a research subject.

The properties of unconverted adsorptive treatment residues are significantly different from the feedstock, with 10 times lower viscosity and a low total content of Ni and V of about 2 ppm, which greatly expands the possibilities of further processing, including hydrotreating with a fixed bed. The samples obtained after hydrotreating over a fixed-bed commercial NiMo catalyst had sulfur content of 0.097 wt%. Other characteristics met the requirements for RMA 10 and RMB 30 marine fuels.

The adsorptive treatment residue can be used to produce marine fuels with low viscosity and ultra-low sulfur content. It can also be returned to atmospheric/vacuum distillation to derive the vacuum gasoil fraction, which can then be hydrotreated to obtain catalytic cracking or hydrocracking feedstock or low-sulfur marine fuel components.