Solvent deasphalting is a process that separates heavy hydrocarbon oil into two phases, an asphalt phase, which contains substances of relatively low hydrogen to carbon ratio often called asphaltene type materials and a deasphalted oil phase, which contains paraffinic type material substances of relatively high hydrogen to carbon ratio often called Deasphalted Oil (DAO). Therefore, it may be said that solvent deasphalting is possible because different compounds have different solution affinity for each other and some combination are completely miscible while other combinations are almost immiscible. The ability of solvent to distinguish between high carbon to hydrogen asphaltene type and low carbon to hydrogen paraffinic type materials is termed as selectivity.
Solvent deasphalting of heavy residual hydrocarbon oils using solvents to remove contaminant such as asphaltenes, metals and sulphur constituents has long been a standard processing practice in the petroleum refining industry. In the era of high crude oil prices, refiners prefer to process cheaper heavier crude. The large residue generated from heavy crude can be upgraded through solvent deasphalting process to produce DAO for secondary processes.
Solvent deasphalting of short residue is primarily being employed for LOBS production. However, the process also employed to produce more feedstock for secondary conversion processes such as Fluid Catalytic Cracking (FCC) and hydrocracking so as to upgrade bottom of the barrel and improve distillate yield.
Conventionally, Propane deasphalting is predominantly used for production of LOBS feedstock and slightly heavier paraffinic solvents are used for production of feedstock for conversion process. Propane deasphalting produces high quality DAO suitable for LOBS production with limited DAO yield while use of heavier solvent say, C5 hydrocarbons results in increased DAO yield at the cost of quality. Thus, the choice of solvent for deasphalting is made based on the requirement of DAO yield and rejection level of contaminants leading to requirement of two different processing units.
The use of light hydrocarbon to upgrade heavy hydrocarbon oils is the subject of many patents, for instance U.S. Pat. No. 4,502,944, U.S. Pat. No. 4,747,936, U.S. Pat. No. 4,191,639 U.S. Pat. No. 3,975,396, U.S. Pat. No. 3,627,675, U.S. Pat. No. 2,729,589 which are incorporated herein by reference. Use of mixture of propane, CO2, H2S is reported in U.S. Pat. No. 4,191,639 and an increase in DAO yield for same quality is also reported.
In U.S. Pat. No. 3,975,396, deasphalting with 3 carbon atom solvent such as propylene and acetone is reported.
U.S. Pat. No. 2,729,589 reports that lowering of solvent molecular weight by inclusion of methane and ethane resulted in poorer plant performance. It is also found that optimum plant performance, in term of entrainment of asphaltene in deasphalted oil and color of deasphalted oil, is with 14% butane deasphalting solvent. U.S. Pat. No. 5,346,615 reports a process for deasphalting and demetalization of crude and its fraction with organic carbonates in liquid phase. The above described prior arts deal with multiple solvents.
A contacting apparatus for introducing high molecular weight solvent at the top and lower molecular weight solvent at the bottom and feed in between with agitation is reported in U.S. Pat. No. 3,627,675.
U.S. Pat. No. 4,747,936 describes an improved deasphalting and demetalization of heavy oil to produce Demetalised Oil (DMO) as feedstock for secondary cracking processes such as hydrocracking or Fluid catalytic cracking processes and not intended to produce LOBS which requires high selectivity.
U.S. Pat. No. 4,502,944 describes mixing of process material with solvent and introducing into first separator where separation of asphaltene-rich heavy first fraction and a resin-rich intermediate fraction separated by first interface is achieved. In the same separator, a first light faction separated from the intermediate fraction by second interface is formed. The first light fraction from the first separator is introduced into a second separator maintained at a temperature above the critical temperature of the solvent to separate second heavy fraction rich in oil and second light fraction rich in solvent, which is recycled to mixing zone.
In U.S. Pat. No. 3,998,726, concurrent extraction is described in which a third stream is withdrawn between top and bottom streams and the stream is heated and introduced between third and top streams.
Separation of paraffinic oil fraction, resin fraction and asphalt fraction in two stage solvent extraction is reported in U.S. Pat. No. 4,101,415.
Integration of deasphalting with catalytic conversion has also been subject of several patents, U.S. Pat. No. 6,303,842, U.S. Pat. No. 4,396,493, U.S. Pat. No. 5,024,750, etc. These prior arts deal with specific single mode operation either LOBS mode or fuel mode operation, thus lacking flexibility.
The above prior arts for deasphalting heavy hydrocarbon oils are found to be either using multiple and rather costly solvents or require complex units. Further, the methods are set to produce feedstocks for either secondary cracking process or lubricant oil base stock production but not both. Further, the said prior arts do not deal with any variation of DAO yield with quality as per requirement. Thus, there is a genuine need to develop an improved deasphalting method which does not suffer from the above problems.