Thermal Cracking Of Vacuum Residue Research Articles

In-situ Formation of Sulphur-Trapped Petroleum Coke via Thermal Cracking of Vacuum Residue: A Practical Approach to Reduce Environmental Pollution

Environmental regulations restrict the use of high-sulphur petroleum coke as a solid fuel due to the emission of a substantial amount of sulphur oxides (SOx) upon combustion. Therefore, the free sulphur present in petroleum coke needs to be reduced to achieve lower SOx emissions. This paper describes a novel and efficient method for the trapping of free sulphur in petroleum coke during its formation from vacuum residue in the presence of an additive. Among the various additives tested, calcium oxide (10 wt%) was found to be most effective for maximum trapping of free sulphur in petroleum coke. This sulphur-trapped petroleum coke reduces SO2 emissions by 67% upon combustion; hence, it can be used as a better fuel than regular high-sulphur petroleum coke. Thus, by replacing regular petroleum coke with this newly developed sulphur-trapped petroleum coke, environmental pollution can be reduced significantly.

Experimental investigation of sulfur distribution and yields of liquid fuel and petroleum coke produced by thermal cracking of vacuum residues

In the present work, an experimental study was conducted to investigate the sulfur distribution in the products during thermal degradation of vacuum residues at different operating conditions. In this regard, three vacuum residues with different sulfur contents were selected. The effects of main operating conditions such as pressure and temperature on products yields and properties were studied. The results show that for sulfur distribution, which is indicated as the ratio of the amount of sulfur in each product to the initial mass of sulfur in the feed, increasing temperature will be followed by increased sulfur distribution in liquid fuel and reduced sulfur distribution in petroleum coke. Furthermore, effects of reaction temperature on yields of light coker gasoil (150–350 °C) as well as heavy coker gasoil (350–500 °C), as the dominant fractions of thermal cracking products, were evaluated using simulated distillation method.

Relationship between olefins and coking propensity of heavy residual oil derived from vacuum residue thermal cracking products

Olefins, especially olefinic-bond-containing aromatics (OAH) may have a significant effect on the coking propensity of heavy residual oil (RO) derived from vacuum residue (VR) thermal cracking products in the further deep processing. However, this has been rarely studied in the past. In this work, the structure of RO (boiling point > 500 °C distillate) products and their SARA fractions derived from thermal cracking of VR under different conditions were systematically characterized by 1H nuclear magnetic resonance (1H NMR) and Fourier transform infrared (FT-IR) spectroscopy to investigate the occurrence pattern of olefins. The coking propensity of RO in the further processing was evaluated by thermal gravimetric (TG) and coking factor analysis, and the effect of different olefins on the coking propensity of RO in further processing was revealed. The results showed that the thermal cracking led to the occurrence of olefins, especially OAHs in resins (Re) and asphaltenes (Asp). The highest olefinic hydrogen contents of RO and its SARA fractions were detected at the thermal cracking condition of 415 °C for 40 min, which were 2.9 %, 4.0 %, 3.4 %, 2.8 %, and 2.4 %, respectively. Interestingly, RO obtained at the thermal cracking condition of 415 °C for 40 min also had the highest content of TG carbon residue (11.2 wt%) and the largest value of coking factor (5.33 %). Significantly, the TG carbon residue content and coking factor value of RO linearly increased with the total olefinic hydrogen content of RO, suggesting that the occurrence of olefins during thermal cracking significantly contributed to a greater coking propensity of RO in further deep processing. More importantly, an in-depth investigation by adding different olefin model compounds to the original VR thermal reaction system revealed that the olefinic-bond-containing aromatics in Asp may confer the greatest contribution to the increasing coking propensity of RO, followed by the olefinic-bond-containing aromatics in Re.

Study on the formation of olefinic-bond-containing asphaltenes during thermal cracking of vacuum residue

In this study, the occurrence of olefinic bonds in asphaltenes separated from vacuum residue (VR) during thermal cracking was explored. Also, the effect of various thermal cracking conditions on the nature of olefinic bonds was discussed. The results showed that olefinic bonds were formed in asphaltenes during VR thermal cracking. The olefinic structure of asphaltenes detected by Fourier transform infrared (FTIR) and 1H nuclear magnetic resonance (1H NMR) spectroscopy was mainly in the type of R–CH = CH–R′. An in-depth investigation revealed that increasing the severity of thermal cracking promoted the formation of more olefinic-bond-containing asphaltenes; the percentage of olefinic hydrogen in asphaltenes peaked at cracking under 420 °C for 40 min, was 2.7%. Meanwhile, the olefinic-bond-containing asphaltenes of high concentration consequently became precursors for the formation of coke by increasing the instability of the liquid system. Consequently, further prolongation of the cracking time led to a drastic decline of olefins content accompanying a sharp leap of coke yield. Finally, the hypothetical average molecular structures of the olefinic-bond-containing asphaltenes during VR thermal cracking were proposed based on the modified Brown-Ladner empirical formulas with improvement. They serve as intuitive insights into the existing olefinic bonds in asphaltenes.

NMR Characterization of Asphaltene Derived from Residual Oils and Their Thermal Decomposition

The main objective of this work is to determine the effect of thermal cracking on asphaltene molecular structure by using nuclear magnetic resonance (NMR). The NMR is used to identify and quantify the structural parameters and the functional groups, which subsequently helped in deriving a hypothetical average structure for the asphaltene molecules. The NMR analysis revealed a number of valuable findings and developed a better understanding about the nature of structural changes that asphaltene molecules undergo during the thermal cracking of vacuum residues (VRs). For instance, the polyaromatic structure of asphaltene in the parent VRs consists of peri-condensed cores interlinked through aliphatic bridges. This peri-condensed polyaromatic core converts to cata-condensed polyaromatic as the reaction severity increases. The NMR analysis confirmed that the observed reduction in the average molecular weight of asphaltene molecules, as reaction severity increases, is mainly due to cracking of the saturated par...

Reactivity study on thermal cracking of vacuum residues

This study focused on the process reactivity of thermal cracking of vacuum residues from crude oils mixtures. The thermal cracking experiments were carried out under a nitrogen atmosphere at 120psi between 430 to 500°C for 20 minutes. Temperature conditions were established considering the maximum fractional conversion reported in tests of thermogravimetry performed in the temperature range of 25 to 600°C, with a constant heating rate of 5°C/min and a nitrogen flow rate of 50ml/min. The obtained products were separated in to gases, distillates and coke. The results indicate that the behaviour of thermal reactivity over the chemical composition is most prominent for the vacuum residues with higher content of asphaltenes, aromatics, and resins. Finally some correlations were obtained in order to predict the weight percentage of products from its physical and chemical properties such as CCR, SARA (saturates, aromatics, resins, asphaltenes) and density. The results provide new knowledge of the effect of temperature and the properties of vacuum residues in thermal conversion processes.

Kinetic Modeling of Vacuum Residue Thermal Cracking in the Visbreaking Process Using Multiobjective Optimization

AbstractA discrete six‐lump kinetic model for the thermal cracking of vacuum residue in the visbreaking process has been developed, and the time‐dependent behavior of each individual lump has been determined. A combination of the heuristic method and gradient‐based method (hybrid method) has been taken into account to optimize the parameters of the model. A new concept of objective functions has been presented and applied for optimization, so more acceptable results have been obtained. Such an approach has not been presented before. A number of 60 parameters was considered primarily, which has been reduced to 36 with the aim of flash calculation information, and optimized. The obtained results are in good agreement with experimental data. The analysis of the estimated rate constants showed that the cracking of vacuum residue to lighter products was the more dominant reaction pathway during the visbreaking process over the temperature range of 400–430 °C.

Kinetic Modeling of the Thermal Cracking of a Brazilian Vacuum Residue

The thermal cracking of a vacuum residue from a Brazilian refinery was studied in a continuous pilot plant. Reaction runs were carried out at 440–520 °C, 446–1825 kPa, and space times of 23–69 s. Reaction products were lumped into gas, naphtha, light gas oil (LGO), and heavy gas oil (HGO). The increase of the reaction pressure increased the residue conversion and the product yields. A power law kinetic modeling of the experimental data was performed, comprising first-order irreversible reactions. Two reaction schemes were evaluated: the first scheme consisted of four parallel reactions (one for each product lump), and the second scheme included the consecutive conversion of HGO in LGO. Kinetic parameters were estimated taking into account the experimental error. In the parallel-reaction scheme, almost all estimated parameters were statistically significant (except for the small gas formation at the highest pressure). The LGO and HGO formation reactions presented lower activation energies and higher rate constants. Inclusion of the consecutive reaction led to parameters without statistical significance for all reaction conditions. Furthermore, empirical correlations from the literature were fitted to the product yield data as a function of the process severity. The severity index was modified to include the effect of pressure explicitly, providing a slight improvement of the correlations.

Binary cracking kinetics for thermal cracking of vacuum residues in Eureka process

A discrete lumped kinetic model for thermal cracking of Kuwaiti vacuum residues such as Ratawi–Burgan vacuum residue (RB-VR), Lower-Fars vacuum residue (LF-VR) and Eocene vacuum residue (EC-VR) in the Eureka process is presented. The discrete lumps considered for kinetic modeling of thermal cracking reactions are: (i) off-gases (<423K), (ii) cracked light oil (423–643K), (iii) cracked heavy oil (643–811K), (iv) demister oil (>811K) and (v) vacuum residue (VR-CCR). In kinetic modeling, the binary thermal cracking reactions between the lumps and reactions which occur within the lumps are considered to determine the time dependent behavior of cracked products. A combination of dynamic global and local combined particle swarm optimization and fourth order Levenberg–Marquardt algorithm is applied to estimate the twenty kinetic parameters included in the kinetic model. The discrete lumped model presented for thermal cracking of vacuum residues in the Eureka process shows good agreement with the experimental data available in the literature for RB-VR, LF-VR and EC-VR. Furthermore, the model validation reveals that the cracking reactions which occur within VR-CCR lump is significant as a result of estimated activation energies in thermal cracking of Kuwaiti vacuum residues over the range of temperature from 673 to 703K.

Changes in asphaltenes during thermal cracking of residual oils

This study attempts to understand how asphaltene molecules change under thermal stress. Asphaltene samples were precipitated from three crude oils and their atmospheric residues, vacuum residues, and pitch, using n-heptane. The pitch samples were obtained from the thermal cracking of vacuum residues at three operating temperatures (400, 415, and 430°C) and three reaction times (30, 50, and 60min). Asphaltene samples were characterized using gel permeation chromatography (GPC), ultraviolet spectroscopy (UV), metal content (Ni and V) analyses, and elemental analysis of C, H, N, and S. The experimental observations suggest that thermal cracking conditions influence the structure and the properties of asphaltene. An increase in cracking severity resulted in a notable decrease in the molecular size of asphaltene; a significant increase in aromaticity; a reduction in the H/S ratio, which indicates the presence of sulfur as a disulfide (–C–S–C–) and not as thiophenol or HS groups; and the concentration of metals in the core of smaller polyaromatic asphaltene molecules.

Thermal cracking kinetics of Kuwaiti vacuum residues in Eureka process

This work presents the development of a kinetic model for the thermal cracking of vacuum residues in a pilot-scale semi-batch reactor, which simulates the cracking operation performed in the Eureka process. The vacuum residues were derived from three Kuwaiti crude oils, both conventional and heavy. Experimental data was obtained at three cracking temperatures (400, 415, and 430°C) and three reaction times (30, 50, and 60min). The proposed thermal cracking kinetic model is based on the discrete lumping approach. The reaction scheme consisted of five lumps: the four cracked products and residual unconverted oil. The cracked products represent the product slates obtained from the commercial Eureka process, namely, the off-gases (<150°C), cracked light oil (150–370°C), cracked heavy oil (370–538°C), and demister oil (>538°C). The analysis of the results revealed that the thermal cracking of vacuum residue follows first order kinetics. The proposed model predicted the kinetic parameters for the thermal cracking of different residual feedstock and provided a good fit to the experimental data.

Modeling of mass transfer and thermal cracking during the coking of Athabasca residues

The kinetics of thermal cracking of films of vacuum residue from Athabasca bitumen in the temperature range of 457 – 530 ∘ C was modelled with liquid-phase mass transfer, reaction-dependent fluid properties, and coke formation by reaction of cracked products in the liquid phase. Previous investigations on the thermal cracking of vacuum residue in thin films showed that at low film thickness ( ∼ 20 ± 2 μ m ) the coke yield was insensitive to the temperature and heating rate for thin films of bitumen. The coke yield increased with the thickness of the initial film, in the range from 20 to 80 μ m ( ± 2 μ m ) . At the same time, the viscosity of the reacting liquid increased rapidly with time, which would slow down the diffusion of products inside the film. This coupling of transport and reaction would enhance the formation of coke by increasing the rate of recombination reactions. The concept of intrinsic coke is used in a new kinetic model to account for the minimum observed coke formation in thin films. With increasing film thickness, the increasing yield of extrinsic coke is modelled through the change in fluid properties as a function of extent of reaction, which reduces the rate of diffusion in the reacting liquid phase. The model was able to properly account for the insensitivity of coke yield in thin films to reaction temperature and the dependence of coke yield on the thickness of the liquid film.

Reaction pathways and product yields in mild thermal cracking of vacuum residues: A multi-lump kinetic model

Abstract Mild thermal cracking of vacuum residue is used in an oil refinery for ‘bottom of the barrel’ upgradation in the form of visbreaking. Lab scale studies were conducted in a batch reactor to study the cracking behavior of vacuum residues at mild severity conditions in terms of lumping of distillate fractions. Four residual feedstocks of Indian and Middle East origin, being processed in Indian refineries were studied for five different residence times between 3 and 15 min and four different temperatures ranging between 400 and 430 °C. A five lumped and seven parameter kinetic model has been developed for the prediction of yield of products. The lumping scheme chosen was based on the most value added products, i.e., gas, gasoline, light gas oil (LGO) and vacuum gas oil (VGO). Delplot analysis has been used for determining reaction pathways.

Kinetic Studies of Low Severity Visbreaking

Thermal cracking of vacuum residues and asphalts obtained from operating Indian refineries were studied in a batch reactor. The temperature was varied in the range 400-430 °C, and the batch time was varied from 0 to 15 min. The pressure was kept at a constant value of 1.2 MPa through out the experiment. The variation in the composition of the cracked gas fraction for each feed was studied by gas chromatography. The resulting visbroken products were further characterized in terms of its different industrially important boiling cuts. A five lump kinetic model, comprising of gas (C 1 -C 5 ), gasoline (IBP-150), LGO (150-350), VGO (350-500), and VR (500+) has been developed. The variation in the kinetic parameters with change in the feed properties has been discussed. Also, an attempt has been made to seek a relationship between the feed properties with the kinetic rate parameters and the activation energies.