1. Introduction
1.1 Application
Sulfolane Aromatics Extraction (SAE) is a typical physical process to recover high purity BTX simultaneously from C6~C8 cut of reformate or hydrogenated pyrolysis gasoline. In this process, sulfolane is used as the selective solvent. Using the solvent with different solubility and selectivity to the aromatics and non-aromatics, high purity BTX can be obtained through the combination of liquid-liquid extraction and stripping distillation. After further fractionation, high purity benzene, toluene and C8 aromatics are produced.
1.2 Process Description
The principal flow diagram of SAE is shown in figure 1.
The feed from the feed tank is pumped to the lower section of the extractor. The lean solvent is sent to the top of the extractor and the aromatics reflux is fed to the bottom of the extractor. After multistage countercurrent liquid-liquid extraction, raffinate from the top of the extractor is sent to water washing column to recover the small amount of solvent. Then raffinate as the by product is sent to outside battery limit.
The first rich solvent from the bottom of the extractor is transferred to the top of the stripper after heat exchange. In the stripper, non-aromatics and an appropriate amount of aromatics are stripped overhead and condensed. The hydrocarbon phase is recycled to the bottom of the extractor as reflux and water phase is transferred to water stripper.
The second rich solvent is pumped to the middle of the recovery column. In this column, aromatics and solvent are separated. The lean solvent from bottom of the recovery column is recycled after passing through several heat exchangers. BTX cut from the top of the recovery column will be sent to fractionation to produce benzene, toluene and C8A.
The water stripper is used to strip the small amount of non-aromatics in the stripping water. The small solvent regenerator is set to remove the mechanical impurities and polymers in the solvent formed during the operation, and the bottom residue is discharged irregularly.
Fig.1 SAE Process
1.3 Main Technical Parameters
Table 1 Main Operating Parameters
| Items | Parameters |
| Extractor | |
| Top Pressure, MPa(g) | 0.5~0.6 |
| Solvent/Feed Ratio, w | 2.5~4.5 |
| Reflux/Feed Ratio, w | 0.4~0.7 |
| Stripper | |
| Top Pressure, MPa(g) | 0.10~0.25 |
| Bottom Temperature, ℃ | 165-175 |
| Recovery Column | |
| Top Pressure, MPa(g) | -0.04~-0.06 |
| Reflux Ratio, w | 0.5~0.7 |
| Stripping Water/Solvent Ratio, w | 0.015~0.025 |
2. Technical Features
2.1 Feedstock Flexibility
The feedstock of SAE can be C6~C8 cut from reformate, pyrolysis gasoline, catalytic pyrolysis gasoline and coke oven light oil.
2.2 Product Specifications and Recovery Rate
SAE is suitable to recover high purity BTX simultaneously with high recovery rate. The product specifications adopting SAE (after fractionation) are listed in Table 2 ~ Table 5. Recovery rate of the aromatics is listed in Table 6.
Table 2 Benzene Specifications
| Items | Units | Specifications |
| Benzene | w% min | 99.95 |
| Toluene | mg/kg max | 200 |
| Non-aromatics | mg/kg max | 500 |
| Total Sulphur | mg/kg max | 0.5 |
| Organic Nitrogen | mg/kg max | 0.1 |
| Solidification | ℃ min | 5.45 |
Table 3 Toluene Specifications
| Items | Units | Specifications |
| Toluene | w% min | 99.9 |
| Non-aromatics | mg/kg max | 1000 |
| Benzene and xylenes | mg/kg max | 500 |
| Total Sulphur | mg/kg max | 1 |
Table 4 C8 aromatics Specifications
| Items | Units | Specifications |
| C8A | w% min | 99.5 |
| Toluene | w% max | 0.1 |
| Non-aromatics | w% max | 0.5 |
| Total Sulphur | mg/kg max | 2 |
Table 5 Non-aromatics Specifications
| Items | Units | Specifications |
| Aromatics | w% max | 1 |
| Solvent | mg/kg max | 1 |
Table 6 Recovery Rate
| Items | Units |
| Benzene | 99.9 |
| Toluene | 99.8 |
| C8A | 99.5 |
2.3 Process Flexibility
SAE is suitable to recover BTX simultaneously and can be shifted to produce BT or benzene according to clients’ requirements.
2.4 Technical Economy
The typical utility and chemical consumptions (not including fractionation) in a SAE unit for C6~C8 cut feedstock from pyrolysis gasoline with 85 w% aromatics are listed in Table 7.
Table 7 Utility and Chemical Consumptions
| Items | Units | Consumptions |
| Cooling Water (⊿t=10℃) | t/t Feed | 4.0 |
| Steam MP (1.6MPa) | t/t Feed | 0.60 |
| Electric Power | kWh/t Feed | 10.0 |
| Sulfolane | g/t Feed | <5 |
According to practice in China, the construction investment is about 130 million RMB for a typical SAE unit with a capacity of 600kMTA in 2010.
3 Commercial Experiences
Up to now, there have been 19 commercial units put on stream with the total capacity of 7000KMTA and the maximum capacity of a single SAE unit is 1500 KMTA. In 1992, the data package for SAE process simulation was licensed to Aspen Tech in US.