Deasphalting process for production of feedstocks for dual applications

Abstract

The invention concerns with improved and more flexible deasphalting process for production of lube oil base stock as well as feed stock for secondary processes depending on requirement from heavy residual hydrocarbon oil containing saturates, aromatics, resins and asphaltenes etc by contacting the oil with a solvent comprising of hydrocarbon containing two to six carbon atoms, preferably LPG having C3-C4 hydrocarbons and mixture thereof at predetermined deasphalting conditions wherein the yield of deasphalted oil including its quality is controlled by varying the deasphalting conditions including the operating temperature. The yield variations of 15 to 60 wt % is achieved by swinging the temperature by about 10-20° C. within the operative temperature range of 70-130° C. keeping the rest of the operating conditions including solvent to feed ratio same. The LPG solvent can be recovered using supercritical mode of operation using technology known in the art and recycled.

Claims

1. A process for deasphalting heavy residual hydrocarbon oil, resulting in dual mode operation comprising: a) subjecting the oil to solvent deasphalting with LPG as solvent, in a single extraction apparatus at predetermined deasphalting conditions to produce a deasphalted oil product phase and an asphalt product phase, b) while maintaining a deasphalting temperature in the range of 70 to 130° C., changing the deasphalting temperature between approximately 10 and 20° C. within said range, thereby obtaining said deasphalted oil product phase that includes a deasphalted oil having conradson carbon residue (CCR) of 1.5 to 2.5 wt % and having saturates to aromatics ratio from 0.4 to 0.7 and another deasphalted oil having conradson carbon residue (CCR) of 2.5 to 6.0 wt % and having saturates to aromatics ratio from 0.15 to 0.4, c) separating out the deasphalted oil product phase and the asphalt product phase, and d) using said deasphalted oil having conradson carbon residue (CCR) of 1.5 to 2.5 wt % and having saturates to aromatics ratio from 0.4 to 0.7 as lubricant oil base stock and said other deasphalted oil having conradson carbon residue (CCR) of 2.5 to 6.0 wt % and having saturates to aromatics ratio from 0.15 to 0.4 as a feedstock for secondary cracking processes.

2. A process as claimed in claim 1, wherein the deasphalting conditions include an option of the state of operating temperature.

3. A process as claimed in claim 1, wherein the yield of deasphalted oil is 15 to 60 wt % of feed.

4. A process as claimed in claim 1, wherein the solvent dosage is in the range of 200-800 vol %.

5. A process as claimed in claim 1, wherein the solvent contains hydrocarbons with 3 to 6 carbon atoms.

6. A process as claimed in claim 1, wherein the heavy residual hydrocarbon oil contains saturates, aromatics, resins, asphaltenes along with sulphur, nitrogen and metals.

7. A process as claimed in claim 1, wherein the solvent is recovered using supercritical operation and recycled after recovery.

8. A process as defined in claim 7, wherein the solvent contains hydrocarbons with 3 and 5 carbon atoms.

9. A process as defined in claim 7, wherein the solvent contains hydrocarbons with 3 and 4 carbon atoms.

10. A process as defined in claim 1, wherein the deasphalting temperature is in the range of 90-120° C.

11. A process as claimed in claim 1, wherein the solvent dosage is in the range of 300-500 vol % of feed.

Description

DETAILED DESCRIPTION OF THE INVENTION

(1) According to the present invention there is provided an improved process for deasphalting heavy residual hydrocarbon oil comprising contacting the oil with a hydrocarbon solvent containing two to six carbon atoms in a single extraction apparatus at predetermined deasphalting conditions to produce a deasphalted oil product phase (containing paraffinic type materials of relatively high hydrogen to carbon ratio) and asphalt product phase (containing substances of relatively low hydrogen to carbon ratio), separating out the deasphalted oil product phase and isolating the deasphalted oil (DAO) therefrom wherein the yield of the deasphalted oil including its quality as measured by the contaminants level present therein is controlled by varying the deasphalting conditions. The deasphalted oil may be either used as feedstock for Lube Oil Base Stock (LOBS) or as feedstock for secondary cracking processes.

(2) LOBS Feedstock:

(3) For LOBS feedstock, the deasphalting oil should have low Conradson Carbon Residue (CCR) and higher saturates to aromatics ratio, where the aromatics include resins and asphaltenes also. The CCR for LOBS feedstock of about 2 wt % and the high saturates to aromatics ratio is necessary to meet the viscosity index requirement of resulting lubricating oil.

(4) Feedstock for Secondary Cracking Processes:

(5) While the DAO suitable for LOBS can also be used as feedstock for secondary cracking processes, it is desirable to have higher yield of DAO, to get more distillates from residue through cracking processes. However, the extent of removal of contaminants essentially depends on the yield of DAO as higher DAO yield is achieved at the cost of quality of deasphalted oil, that is, lowering saturates to aromatics ratio and higher level of contaminants like CCR, metals. The yield of DAO needs to be optimized depending upon the acceptable level of quality. Since majority of metals and contaminants are removed in asphalt, the resulting Deasphalted Oil (DAO) is a better feedstock for cracking processes in terms of catalyst life and makeup.

(6) The yield of deasphalted oil in the process can be controlled by varying the deasphalting conditions while the solvent composition is kept fixed.

(7) The invented process uses readily available refinery produced solvent comprising preferably Liquified Petroleum Gas (LPG) for achieving dual process applications for obtaining feedstock with lower Conradson Carbon Residue (CCR) and high saturates to aromatics ratio suitable for lube base oil production and also feedstock with acceptable CCR and saturates to aromatics ratio for secondary cracking processes. The liquified petroleum gas solvent contains hydrocarbons with 3 to 6 carbon atoms, preferably 3 to 5 carbon atoms, more preferably with 3 and 4 carbon atoms. The deasphalting conditions include the options of the state of pressure, temperature and solvent to feed ratio. In one embodiment of the invention one of the deasphalting conditions is the option of the state of operating temperature which may be required to vary in the ranges between 70-130° C., preferably, 90-120° C. when other parameters of deasphalting conditions are fixed in order to obtain desired deasphalted oil either as a feedstock for lube base oil production or feedstock for secondary cracking processes.

(8) The yield of deasphalted oil depends on the solvent power of the solvent used in the deasphalting process. The solvent power or the solubility of the oil depends on the surface tension of the deasphalting solvent. As the surface tension of the solvent increases, the solubility of the oil increases resulting in higher yield of deasphalted oil. Propane has lower surface tension compared to higher light paraffinic hydrocarbons like, C.sub.4, C.sub.5 and LPG and hence results in lower DAO yield. The surface tension of the solvent can be manipulated either by changing the solvent or by changing the temperature. In the present invention, the surface tension of the solvent is increased by using liquefied petroleum gas to achieve higher yield of deasphalted oil in one mode of operation while with the same solvent, surface tension is countered by increasing the temperature of operation in another mode of operation to achieve low solubility of oil. In both the modes of operation, the solvent to feed ratio is lower as compared to propane process. Propane process operated at such lower solvent to feed ratio would lead to improper phase separation and very low DAO yield. Also propane process cannot be operated at higher temperature as employed in the LPG process, as it will be close or above the critical temperature of propane. However, butane and its higher homologues say, pentane, hexane, heptane can be operated at lower solvent to feed ratio as well as at higher temperature leading to higher DAO yield but production of LOBS feedstock with acceptable CCR and higher saturates to aromatics ratio is not feasible due to poor selectivity.

(9) The advantage of the present invention allows for retrofitting existing commercial equipment. An additional advantage of deasphalting with liquefied petroleum gas as solvent in the present invention is a product produced in the refinery. Hence, separation of pure solvent say, propane for use in deasphalting unit is not required leading to significant energy savings. Another advantage is that the solvent can be recovered under supercritical mode in a commercial unit. The present process gives variable yield and quality and hence improves the utility of the unit with a single solvent. For achieving higher DAO yield of about 30 to 60 wt % with propane, solvent to feed ratio or S/F ratio should be very high or the temperature should be very low. High S/F ratio will not only put severe restriction on the extractor throughput but also will increase the cost of utilities for solvent recovery. Decrease in temperature say, from the normally operating temperature of about 60-70° C. for propane, will be impractical considering the high viscosity of residue at lower temperature, which decreases the mass transfer coefficient substantially. Higher yield say, 30 to 60 wt % with acceptable CCR and saturates to aromatics ratio can be achieved with butane and pentane as solvent.

(10) According to the invention the yield of deasphalted oil can be optionally controlled at 15 to 60 wt % on feed for a fixed solvent by varying the deasphalting conditions. Relatively higher percentage of yield of deasphalted oil is obtained at a lower operating temperature or vice versa under given deasphalting conditions. In one embodiment the deasphalted oil is obtained at 15 to 30 wt % yield with lower Conradson Carbon Residue of 1.5 to 2.5 wt % and relatively higher saturates to aromatics ratio from 0.4 to 0.7 suitable for lubricant oil base stock production. In another embodiment, the deasphalted oil is obtained at 30-60 wt % yield with relatively higher but acceptable Conradson Carbon Residue of 2.5 to 6 wt % and low saturates to aromatics ration in the range of 0.15 to 0.4 suitable as a feedstock for secondary cracking processes. In a specific embodiment, the deasphalting oil with different yields and quality suitable for both the applications is achieved by varying only the operating temperature. The deasphalted oil yield variation of 15 to 60 wt % can be achieved by swinging the temperature by about 10-20° C. within the operating temperature range of 70-130° C. preferably in the range of 90-120° C. keeping rest of the deasphalting conditions including solvent to feed ratio same.

(11) The dosage of solvent used can be in the range of 200-800 vol %, preferably in the range of 300-500 vol % of feed. Another preferred embodiment of the invented deasphalting process involves recovery of the solvent from the deasphalted oil phase by supercritical mode to save energy on solvent recovery using technology known in the art. The recovered solvent can be recycled in the process. According to this invention the heavy residual hydrocarbon oil contains saturates, aromatics, resins, asphaltenes along with sulphur, nitrogen and metals. In another embodiment it is Short Residue (SR) to generate more distillates for cracking processes. The invented process can be performed in a batch or continuous counter current extraction.

DESCRIPTION OF THE INVENTION WITH REFERENCE TO THE EXAMPLES WITH PREFERRED EMBODIMENTS

Feedstock

(12) The invented process is applied to short residue as the feedstock oil. The feedstock may typically comprise hydrocarbons having initial boiling point of greater than 450° C. Typical properties of short residue are presented in Table 1. The feed has CCR of 21.5% and the metal content viz. Nickel and Vanadium are 34 and 61 ppm, respectively. The hydrocarbon components, namely, saturates, aromatics, resins and asphaltenes (SARA) is also provided.

(13) TABLE-US-00001 TABLE 1 Typical properties of Short Residue (SR) S.No Properties Result 1 Density 1.017 gm/cc 2 Conradson Carbon Residue 21.5 wt % 3 Nickel 34 ppm 4 Vanadium 61 ppm 5 Sulphur 4.8 wt % 6 Nitrogen 2510 ppm 7 Saturates 5.9 wt % 8 Aromatics 56.0 wt % 9 Resins 22.5 wt % 10 Asphaltenes 15.6 wt % 11 Saturates to Aromatics ratio 0.06

Solvent

(14) The process of the present invention involves the use of liquefied petroleum gas solvent containing component from a group of solvents viz., C3 and C4 hydrocarbon but preferably n-propane to n-pentane and its isomers. The typical composition of straight run of liquefied petroleum gas solvent is given in Table 2.

(15) TABLE-US-00002 TABLE 2 Typical Composition of Liquefied Petroleum Gas S.No. Component Wt % 1 Propane 25-35 2 Butane 65-75 3 Iso-butane 2-5 4 Pentane 0.5-1.0

Solvent Deasphalting

(16) The deasphalting experiments were carried out in the laboratory scale high pressure Liquid-liquid equilibrium set up. Known quantity of hot short residue is charged into the set up followed by known quantities of solvent (LPG) from separate bomb. The content is stirred for two hours at a constant mixing temperature maintained with the help of external circulation of heating fluid. The constant stirring of 500 rpm is maintained in all the experiments. After two hours of mixing, the stirring is stopped and contents are allowed to settle at the same temperature for three hours. The asphalt and DAO phases were carefully separated and the products were analyzed for different important properties of interest after evaporating the solvent.

Example: I

(17) For each deasphalting experiment, liquid-liquid equilibrium extraction was performed in lab scale jacketed extraction apparatus (batch). The feed (short residue) was preheated. The feed (about 300-500 g), properties of which is given in Table 1, and solvent are fed into the extraction apparatus. The temperature of the equilibrium setup is kept constant. The feed and solvent were mixed well using a stirrer. The stirrer speed is kept constant throughout the mixing time. The mixing time is kept around 120 minutes. After mixing the content, it is kept around 3 hr for complete phase separation (settling). After settling of phases, the two phases were separated accurately and collected separately. The phases were weighed accurately with precision balance to ensure material balance. The solvent free DAO and asphalt products were weighed and the DAO yield was obtained based on feed. Final DAO samples were analyzed for various properties. The results from the experimental studies are shown in the Table 3. From the table, it can be seen that the DAO is about 20 wt % with saturates content of 35.9 wt % suitable as LOBS feedstock.

(18) TABLE-US-00003 TABLE 3 Typical operating condition for a lube mode operation and properties of the deasphalted oil Deasphalting Conditions Temperature 118° C. Solvent to feed ratio 4.0 (vol./vol.) Properties of DAO Deasphalted Oil yield 20.1 wt % Conradson Carbon Residue  2.0 wt % Saturates 35.9 wt % Saturate to Aromatics Ratio 0.55

Example: II

(19) For each deasphalting experiment, liquid-liquid equilibrium extraction was performed in lab scale jacketed extraction apparatus (batch). The feed (Short residue), properties of which is given in Table 1, was preheated. The feed and the solvent whose composition is same as in Example 1 are fed into the extraction apparatus. The temperature of the equilibrium setup is kept constant. The feed and solvent were mixed well using a stirrer. The stirrer speed is kept constant throughout the mixing time. The mixing time is kept around 120 minutes. After mixing the content, it is kept around 3 hr for complete phase separation (settling). After settling of phases, the two phases were separated accurately and collected separately. The phases were weighed accurately with precision balance to ensure material balance. The solvent free DAO and asphalt products were weighed and the DAO yield was obtained based on feed. Final DAO samples were analyzed for various properties. The results from the experimental studies are shown in the Table 4. It can be seen from the table that the DAO yield is about 41 wt % and the contaminants have been reduced substantially from that of short residue. Further, the higher DAO yield have been achieved with the same solvent composition but with different temperature used in Example 1, where the DAO yield is about 20 wt %.

(20) TABLE-US-00004 TABLE 4 Typical operating condition for a fuel mode operation and properties of the deasphalted oil Deasphalting Conditions Temperature 105° C. Solvent to feed ratio 4.0 (vol/vol) Properties of DAO Deasphalted Oil yield 41 wt % Conradson Carbon Residue 6.9 wt % Nickel 3.0 ppm Vanadium 4.8 ppm Sulphur 3.4 wt % Saturates 18.1 wt %  Saturate to aromatics ratio 0.22

(21) The embodiments of the invention disclosed herein are only illustrative in nature and there can be other several possible embodiments as would be apparent from the practice of the invention. The full scope and spirit of the invention should be derived from the following appended claims.