You work in a facility that produces about 100,000 tonne/y of methyl tertiary butyl ether (MTBE). MTBE is an oxygenated fuel additive that is blended with gasoline to promote CO2 formation over CO formation during combustion. The facility manufactures MTBE from methanol and isobutylene. Isobutylene is obtained from a refinery cut, and it also contains 1butene and 2-butene, bothof which do not react with methanol.
The process flow diagram is shown in Figure 1. Methanol and the mixed butylenes feed is pumped and heated to reaction conditions. Both the methanol and the mixed butylenes are made in on-site units, and are sent to this unit at the desired conditions. The reactor operates in the vicinity of 30 bar, to ensure that the reaction occurs inthe liquid phase. The reaction is reversible. The feed temperature to the reactor is usually maintained below 90°C to obtain favorable equilibrium behavior. Any side reactions involving 1-butene and 2-butene form small amounts of products with similar fuel blending characteristics, so side reactions are assumed to be unimportant. Other side reactions are minimized by keeping the methanol present inexcess. The reactor effluent is distilled, with MTBE as the bottom product. Methanol is recovered from the mixed butylenes in a water scrubber, and the methanol is subsequently separated from water so that unreacted methanol can be recycled. Unreacted butylenes are sent back to the refinery for further processing. The MTBE product is further purified (not shown), mostly to remove the trace amountsof water. The product stream from Unit 900 must contain at least 94 mol % MTBE, with the MTBE portion of the stream flowrate at specifications. Tables 1 and 2 contain the stream and utility flows for the process as designed. Table 3 contains an equipment list. Other pertinent information and calculations are contained in the appendix.
Possibility of Changing Process Feed Conditions
This plantreceives the mixed butylenes feed from a neighboring refinery, which has recently changed ownership. The new owners are planning to implement changes based on their proprietary technology. The changes will occur after a regularly scheduled plant shut down (for both plants) within the next six months. The effect on our plant is that they have proposed that the mixed butylenes feed that we receivewill contain 23 wt% isobutylene (isobutene), 20 wt% 1butene, and 57 wt% 2-butene. Our current contract for mixed butylenes expires at the next plant shut down, so we are in the process of negotiating a new contract with the new owners. An additional complication is that MTBE is in the process of being phased out as a fuel additive because of ground water contamination from leaky gasoline storagetanks.
R-901 T-901 V-901 P-901 A/B E-901 MTBE MTBE Methanol Feed Pump Feed Preheater Reactor Tower Feed Vessel
E-902 MTBE Tower Reboiler
E-903 MTBE Tower Condenser
V-902 MTBE Tower Reflux Drum
P-902 A/B MTBE Tower Reflux Pump
T-902 Methanol Absorber
P-903 A/B MTBE Tower Feed Pump
T-903 Methanol Recovery Tower
E-904 Methanol Tower Reboiler
E-905 Methanol TowerCondenser
V-903 Methanol Tower Reflux Drum
P-904 A/B MTBE Tower Reflux Pump
waste butylenes E-901
P-901 A/B V-901 methanol R-901
P-904 A/B P-903 A/B
P-902 A/B E-904
Figure 1: Unit 900 - MTBEProduction Facility
Table 1 Stream Tables for Unit 900
Stream No Temp °C Pres kPa Vapor fraction Total kg/h Total kmol/h Component kmol/h Methanol i-Butene 1-Butene Trans-2-Butene MTBE Water Stream No. Temp °C Pres kPa Vapor fraction Total kmol/h Total kg/h Component kmol/h Methanol i-Butene 1-Butene Trans-2-Butene MTBE Water Stream No. Temp °C Pres kPa Vapor fraction Total kg/h...