Reactors dehydration

The feed is vaporized by reactor effluent heat-exchange and enters into the dehydration reactor. The dehydration reactor effluent is mixed with preheated recycle gas and enters the conversion reactors. Although Figure 10 shows four parallel or "swing conversion reactors, a lesser or greater number of reactors may be used depending upon the feed rate and regeneration frequency desired. 

We have found that to efficiently recover the high heat content in the reactor effluent it is desirable to split the stream into two parts. The majority of the effluent from a particular reactor is used to heat the recycle gas to that reactor. The excess hot effluents from all the reactors are combined and used for generating steam and heating the methanol feed to the dehydration reactor. After these services, the reactor effluents are combined and cooled by cooling water before entering the product separator. 

Prior to entering the MPC dehydration step, the EB, MPC, and MPK stream from the PO recovery unit is washed and EB is removed by distillation. The MPC and MPK are sent to the dehydration reactors, where MPC is dehydrated to styrene using one of the commercially available catalysts. 

C7 by-products derive from reactions in oxidation, and, to a lesser extent, epoxidation, with the radical decomposition of EBHP to benzaldehyde being the major route. Benzaldehyde, like phenol, is an undesirable component in the recycle EB to oxidation. Most of the benzaldehyde enters the dehydration reactors with the MPC and is removed from styrene by distillation. 

Part of the benzaldehyde stream undergoes hydrogenation to benzyl alcohol (parallel to MPK —> MPC), which is returned to the dehydration reactor. Benzyl alcohol is partially consumed by phenol alkylation and other reactions over the alumina catalyst. As is also the case for BPEA, the rather low conversion leads to a significant benzyl alcohol recycle in dehydration and hydrogenation. 

Dehydration Reactor Inlet Dehydration Reactor Outlet Conversion Reactor Inlet Conversion Reactor Outlet Pressure (kPa abs), psig Recycle Ratio, mol/mol of Charge Conversion Reactor WHSV, kg Charge/kg... 

The fixed-bed reactor system was comprised of two reactors. The first reactor was a methanol dehydration reactor where a methanol/dimethyl ether/ water mixture was produced, and the second reactor was a hydrocarbonforming reactor which converted this mixture over ZSM-5 catalyst to a gasoline-range hydrocarbon product. As noted earlier, the conversion of methanol... 

Description A heated mixture of ethanol vapor and steam is fed to an adiabatic dehydration reactor (1). The steam provides heat for the endothermic reaction and pushes the reaction to 99-"% conversion of ethanol with 99-"% selectivity to ethylene. Recovered H O is stripped of light ends (2) and recycled as process steam. Product ethylene is compressed and put through a water wash (3) before passing to the ethylene oxide reactor section. 

In the peroxidation reactor ethylbenzene is converted with air at 146 °C and 2 bar to form a 12-14 wt% solution of ethylbenzene hydroperoxide in ethylbenzene. The reaction takes place in the liquid phase and conversion is limited to 10% for safety reasons. The reactor is a bubble tray reactor with nine separate reaction zones. To avoid decomposition of the formed peroxide the temperature is reduced from 146 °C to 132 °C over the trays. In the epoxidation reactor the reaction solution is mixed with a homogeneous molybdenum naphthenate catalyst. Epoxidation of propylene in the liquid phase is carried out at 100-130 °C and 1-35 bar. The crude product stream (containing PO, unreacted propylene, a-phenylethanol, acetophenone, and other impurities) is sent to the recycle column to remove propylene. The catalyst can be removed by an aqueous alkali wash and phase separation. The crude PO, obtained as head stream in the crude PO column, is purified by distillations. The unconverted reactant ethylbenzene can be recycled in the second recycle column. The bottom stream containing a-phenylethanol is sent to the dehydration reactor. The vapor-phase dehydration of a-phenylethanol to styrene takes place over a titanium/alumina oxide catalyst at 200-280 °C and 0.35 bar (conversion 85%, selectivity 95%). 

The process technology of ethanol-to-ethylene has also been developed. Braskem filed a patent in 2007 where substantial improvements are claimed [29]. The most important is an improved process design to maximize the energy recovery Irom the outgoing stream of the dehydration reactor. Apart from decreased operational cost, this also leads to a reduction in the amount of equipment needed, leading to decreased capital cost. 

The production of ethylene by dehydration of ethanol is a proven technology and was demonstrated and implanented on large scale (Winter, 1976). Braskem started a full-scale plant in Brazil in 2010 (Braskem, 2012). The process consists of a dehydration reactor and several subsequent purification steps in order to obtain polymer-grade ethylene (composition 99.95 wt% ethylene, 0.05 wt% ethane, 5ppm CO and lOppm CO (Kochar et al., 1981)). Figure 4.6 iUustrates the ethanol dehydration process investigated in this study and lists the input data used for process simulation. 

Ethanol can be dehvered in gaseous phase to the ethylene reactors in the combined process. Thereby, the cooling demand in the rectifier column is decreased by approximately 14.3 MW, while the demand for preheating the ethanol feed to the dehydration reactor (approx. 4.3 MW) is eliminated, and the heating demand in the furnace of the ethylene plant is decreased by approximately 8.7 MW. Detailed stream data of the combined process is given in Table 4.A.3. 

---