introduced to the heater or furnace. In the furnace the stream is heated to 600 °C, the reaction temperature, then introduced into the reactor.
The reactor is where the main reaction happens:
C7H8 + H2  C6H6 + CH4
This reaction is irreversible, and it requires catalyst. The catalyst consists of chromium or molybdenum oxides, platinum or platinum oxides, on silica or alumina.
The catalytic process occurs at lower temperatures and offers higher selectivity but requires frequent regeneration of the catalyst. The products are then cooled and introduced into a pair of separators that separate the unreacted hydrogen. Portion of the unreacted hydrogen is compressed and recycle back to the feed and the reactor. The products leaving the separators …show more content…
The exiting stream exits at 24.81 bar and 671 oC, it contains methane, benzene, toluene, and hydrogen. The one pass conversion is typically around 75%. The process then continues to the separator feed preparation phase. This process phase begins with introducing the stream into a cooling water heat exchanger E-2. This heat exchanger cools the product stream to 38 oC, which condenses most of the toluene and benzene in the stream.
The stream then proceeds to the final phase of the process: the separation. In this phase, the desired product is separated from the byproducts and the unreacted components. That is, benzene is separated from unreacted toluene, unreacted hydrogen and the by-product methane. This is achieved by introducing the two-phase stream containing benzene, methane, hydrogen and toluene into a high-pressure phase separator, F-1. In this flash drum the vapor and liquid are separated. In the overhead mainly hydrogen and methane exits, and in the bottom some hydrogen, methane, and mainly all the toluene and benzene exit. The overhead stream is split into two streams; one stream is compressed to 25.5 bar in compressor C-1 and is recycle back to the feed and to the reactor, the other stream is a portion of the fuel gas stream. The separation happens at a temperature of 38 oC and 23.9 bar. …show more content…
This separator is a low-pressure separator. The liquid exiting the low-pressure flash drum consist of mainly toluene and benzene and traces of dissolved hydrogen and methane. The separation is then completed by heating the stream in heat exchanger E-3, and then introducing it to a distillation column, T-1. The stream is heated to a temperature of 90 oC in E-3, low pressure steam is used for this purpose. The distillation column is used to purify the benzene product by separating all the unreacted components and the by products. This tower consists of 42 sieve trays, a reboiler E-6, a condenser E-5, a reflux drum F-3, and a reflux pump P-2. Toluene exits as a liquid in the bottom at a temperature of 112 oC and 2.43 bar. The overhead containing benzene, traces of hydrogen and methane, is condensed in E-5 at a temperature of 112 oC and a pressure 2.5 bar. Cooling water is used to condense the vapor exiting the column. A remaining hydrogen and methane are then separated in the reflux drum F-3; this vapor stream is combined with the other gases streams: the overhead of the first separator F-1, and the overhead of the second separator F-2, which are combined to form the fuel gas. The liquid stream exiting in the bottoms of the reflux drum is pumped to a discharge pressure of 3.3 bar. The pumped stream is separated in two