MTO process

Mobil MTG and MTO Process. Methanol from any source can be converted to gasoline range hydrocarbons using the Mobil MTG process. This process takes advantage of the shape selective activity of ZSM-5 zeoHte catalyst to limit the size of hydrocarbons in the product. The pore size and cavity dimensions favor the production of C-5—C-10 hydrocarbons. The first step in the conversion is the acid-catalyzed dehydration of methanol to form dimethyl ether. The ether subsequendy is converted to light olefins, then heavier olefins, paraffins, and aromatics. In practice the ether formation and hydrocarbon formation reactions may be performed in separate stages to faciHtate heat removal. 

The MTO process employs a turbulent fluid-bed reactor system and typical conversions exceed 99.9%. The coked catalyst is continuously withdrawn from the reactor and burned in a regenerator. Coke yield and catalyst circulation are an order of magnitude lower than in fluid catalytic cracking (FCC). The MTO process was first scaled up in a 0.64 m /d (4 bbl/d) pilot plant and a successfiil 15.9 m /d (100 bbl/d) demonstration plant was operated in Germany with U.S. and German government support. 

A variation of this process is Mobil s methanol-to-olefins (MTO) process, in which up to 80% C2—olefins are produced over ZSM-5 of reduced acidity and at much higher temperatures. 

UOP FCC unit, 11 700-702 UOP/HYDRO MTO process, 18 568 UOP Olex olefin separation process, 17 724 Up-and-Down Method, 25 217 U/Pb decay schemes, 25 393-394 Updraft sintering, 26 565 Upflow anaerobic sludge blanket (UASB) in biological waste treatment, 25 902 Upgraded slag (UGS), 25 12, 33 Upland Cotton, U.S., 8 13 U-Polymer, 20 189 Upper critical solution temperature (UCST), 20 320, 322 Upper explosive limit (UEL), 22 840 Upper flammability limit, 23 115 Upper flammable limit (UFL), 22 840 Upper Freeport (MVB) coal... 

Chen, J.Q., Bozzano, A., Glover, B., Fuglerud, T., and Kvisle, S. (2005) Recent advancements in ethylene and propylene production using the UOP/ hydro MTO process. Catal. Today, 106, 103-107. 

This paper describes the initial scale-up of the MTO process from a micro-fluid-bed reactor (1-10 grams of catalyst) to a large pilot unit (10-25 kilograms of catalyst). 

Experimental work to date confirms that the MTO process, which is an extension of fluid-bed MTG technology, has been scaled up successfully in a 4 BPD fluid-bed pilot plant at Mobil s Paulsboro Laboratory. Product yields and catalyst performance were nearly identical to those of bench top microunits. The process is currently being demonstrated in the 100 BPD fluid-bed semi-works plant in Germany. The plant was started up February, 1985 after completing modifications required to enable extended operation at MTO conditions. 

The main reactions of the MTG/MTO process can be summarized as follows the first is the dehydration of methanol to DME on acidic zeolite catalysts. The equilibrium mixture of methanol, DME, and water is then converted to light alkenes, which react further to form higher alkenes, n- and Ao-alkanes, aromatics, and naphthenes by hydrogen transfer, alkylation, polycondensation, isomerization, and other secondary reactions. 

Until now, the detailed mechanism involved in the MTG/MTO process has been a matter of debate. Two key aspects considered in mechanistic investigations are the following the first is the mechanism of the dehydration of methanol to DME. It has been a matter of discussion whether surface methoxy species formed from methanol at acidic bridging OH groups act as reactive intermediates in this conversion. The second is the initial C—C bond formation from the Ci reactants. More than 20 possible mechanistic proposals have been reported for the first C-C bond formation in the MTO process. Some of these are based on roles of surface-bound alkoxy species, oxonium ylides, carbenes, carbocations, or free radicals as intermediates (210). 

Various NMR spectroscopic techniques have been applied to investigate the conversion of methanol on acidic zeolites in the low-temperature (r<523K) formation of DME and the high-temperature (T>523 K) formation of alkenes and gasoline. Techniques successfully applied were the stop-and-go method under batch reaction conditions 258,259), the pulse-quench method 113), and various flow techniques 46,49,74.207,260 263). This section is a summary of the recent progress in investigations of the mechanism of the MTO process by NMR techniques. 

The reactivity of surface methoxy species was further investigated with various probe molecules that were thought to possibly be involved in the MTO process, including water, toluene (representing aromatics), and cyclohexane (representing saturated hydrocarbons) (263). It was found that surface methoxy species react at room temperature with water to form methanol, which indicates the occurrence of a chemical equilibrium between these species at low reaction temperatures (Scheme 15) (263). 

B. Investigation of the MTO Process Under Steady-State Conditions... 

In an attempt to identify the catalytic role of the hydrocarbon pool, the MTO process was further studied by C CF MAS NMR spectroscopy with an alternating flow of CH3OH and After the conversion of V-II3OII under steady-... 

The goal of the MTO process is to convert methanol to light olefins, in particular ethylene, propylene and butenes. The key by-products of the reaction include the co-product water, C5+ hydrocarbons such as aromatics and heavier olefins, coke that remains on the catalyst at process conditions and light paraffins that are the primary sink for hydrogen lost during aromatic formation. Small amounts of H2 and COx are also typically observed in the MTO product, although these by-products could arise from feed and product decomposition on the reactor walls and internals at the temperatures that are typically used. 

UOP and Norsk Hydro have jointly developed and demonstrated a new MTO process utilizing a SAPO-34 containing catalyst that provides up to 80% yield of ethylene and propylene at near-complete methanol conversion. Some of the key aspects of the work have included the selection of reactor design for the MTO process and determination of the effects of process conditions on product yield. Evaluation of the suitability of the MTO light olefin product as an olefin polymerization feedstock and demonstration of the stability of the MTO-lOO catalyst have also been determined during the development of this process. 

The use of a fluidized-bed reactor has a number of advantages in the MTO process. The moving bed of catalyst allows the continuous movement of a portion of used catalyst to a separate regeneration vessel for removal of coke deposits by burning with air. Thus, a constant catalyst activity and product composition can be maintained in the MTO reactor. Figure 12.10 demonstrates the stability of a 90 day operation in the fluidized-bed MTO demonstration unit at the Norsk Hydro Research Center in Porsgrunn, Norway. A fluidized-bed reactor also allows for... 

Because of the high olefin yields and low light ends make, the MTO process does not require the high cost separation equipment of a conventional ethylene recovery unit. Figure 12.12 shows the overall process design, including product... 

Economics The MTO process competes favorably with conventional liquid crackers due to lower capital investment. It is also an ideal vehicle to debottleneck existing ethylene plants and, unlike conventional steam crackers, the MTO process is a continuous reactor system with no fired heaters. 

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