GT-BTX is an aromatics recovery technology that uses extractive distillation to remove benzene, toluene and xylene (BTX) from refinery, petrochemical or coke oven aromatics streams such as catalytic reformate, pyrolysis gasoline or coke oven light oil (COLO). With lower capital and operating costs, simplicity of operation, a wider range of feedstock and solvent performance, extractive distillation is superior to conventional liquid-liquid extraction processes. Flexibility of design allows use for grassroots aromatics recovery units, debottlenecking, or expansion of conventional extraction systems.
Sulzer GTC’s GT-BTX process is a result of extensive testing of extractive distillation solvents and blends. Our experience indicates that certain combinations of solvent components enhance extraction performance. Co-solvents also provide an additional parameter for the optimization of unit performance (e.g., stability, mass transfer efficiency). GT-BTX utilizes the Techtiv-100℠ extractive distillation solvent which provides optimum extractive distillation performance. GT-BTX has no special feed preparation requirements and is capable of handling a wide-range (BTX) feedstock while producing very high aromatics purities (99.99 wt.% plus) at high recoveries (99.9 % plus).
The flow scheme of the GT-BTX process consists of two columns: an extractive distillation column (EDC) and a solvent recovery column (SRC).
Since the basic separation in the GT-BTX process is achieved by distillation, the operation of the unit is very simple and intuitive. Control of the main process parameters are achieved in a manner similar to that of a regular distillation column.
Hydrocarbon feed is preheated with hot circulating solvent and fed at a mid-point into the EDC. Lean solvent is fed at an upper point and selectively extracts the aromatics into the tower bottoms in a vapor/liquid distillation operation. The non-aromatics hydrocarbons exit from the top of the column. A portion of the overhead stream is returned to the top of the column as reflux, which washes back any entrained solvent.
Rich solvent from the bottom of the EDC is routed to the SRC, where the aromatics are stripped overhead. The SRC is operated under a vacuum to reduce the boiling point at the bottom of the column.
Lean solvent from the bottom of the SRC is passed through a heat exchanger before returning to the EDC. A small portion of the lean circulating solvent is processed in a solvent regeneration step to remove heavy decomposition products.
The SRC overhead mixed aromatics product is routed to the purification section, where it is fractionated to produce chemical-grade benzene, toluene and xylenes.
The benefits of extractive distillation, particularly those highlighted by GT-BTX technology, may be summarized as follows:
- Simple two-column ED system which requires 30-40 percent lower capital cost than conventional liquid-liquid extraction systems
- Carbon steel construction throughout
- Smaller plot requirement than other systems
- Lower solvent inventory that further reduces investment requirement
- Solvent blend exhibits highest selectivity among all others in commercial use. Solvent properties allow wide boiling range materials (C5- C9) to be fed into unit, with varying aromatics content
- A short time is required to stabilize unit (few hours vs. few days with liquid-liquid extraction systems)
- Lowest specific energy consumption (20-30 percent less than others)
- Very low solvent consumption and circulation rates
- Higher product purity and aromatic recovery
- Insignificant fouling compared to liquid-liquid contactors
- The benzene product from GT-BTX is nitrogen free. Unlike some competing solvents, Sulzer GTC’s solvent is free of basic nitrogen containing components, which permanently poison the catalyst in many benzene consuming units