Space velocity reforming

C, 0.356—1.069 m H2/L (2000—6000 fU/bbl) of Hquid feed, and a space velocity (wt feed per wt catalyst) of 1—5 h. Operation of reformers at low pressure, high temperature, and low hydrogen recycle rates favors the kinetics and the thermodynamics for aromatics production and reduces operating costs. However, all three of these factors, which tend to increase coking, increase the deactivation rate of the catalyst therefore, operating conditions are a compromise. More detailed treatment of the catalysis and chemistry of catalytic reforming is available (33—35). Typical reformate compositions are shown in Table 6. 

Reforming Conditions. The main process variables are pressure, 450—3550 kPa (50—500 psig), temperature (470—530°C), space velocity, and the catalyst employed. An excess of hydrogen (2—8 moles per mole of feed) is usually employed. Depending on feed and processing conditions, net hydrogen production is usually in the range of 140—210 m /m feed (800—1200 SCF/bbl). The C —products are recovered and normally used as fuels. 

Normally, catalytic reformers operate at approximately 500-525°C and 100-300 psig, and a liquid hourly space velocity range of 2-4 hr" Liquid hourly space velocity (LHSV) is an important operation parameter expressed as the volume of hydrocarbon feed per hour per unit volume of the catalyst. Operating at lower LHSV gives the feed more contact with the catalyst. 

For the n-Cq reforming and n-C[2 isomerization reactions the catalysts were run in a fixed bed micro reactor equipped with on-line GC analysis. The catalyst, together with a quartz powder diluent, was added to a 6 inch reactor bed. A thermocouple was inserted into the center of the bed. The catalysts were calcined at 350-500°C immediately prior to use and reduced in H2 at 350-500°C for 1 hour. n-Heptane or dodecane (Fluka, puriss grade) were introduced via a liquid feed pump. The mns were made at 100-175 psi with a H2/n-heptane (or n-Ci2) feed ratio of 7 and a weight hourly space velocity of 6-11. 

Recently, Ruckenstein and Wang (264-266) also successfully developed excellent CoO/MgO solid-solution catalysts for C02 reforming of methane. They reported that Co/MgO exhibited a good catalytic performance with a CO yield of 93% and a H2 yield of 90% at the high space velocity of 60,000 mL (g catalysts)-1 h-1 and 1163 K, which remained unchanged during 50 h of investigation (264). In contrast, Co/CaO, Co/SrO, and Co/BaO each provided low CO yields, and Co/CaO also had a low stability. The results indicate that the CoO/MgO catalysts are characterized by performances similar to those of NiO/MgO. 

The reformate gas contains up to 12% CO for SR and 6 to 8% CO for ATR, which can be converted to H2 through the WGS reaction. The shift reactions are thermodynamically favored at low temperatures. The equilibrium CO conversion is 100% at temperatures below 200°C. However, the kinetics is very slow, requiring space velocities less than 2000 hr1. The commercial Fe-Cr high-temperature shift (HTS) and Cu-Zn low-temperature shift (LTS) catalysts are pyrophoric and therefore impractical and dangerous for fuel cell applications. A Cu/CeOz catalyst was demonstrated to have better thermal stability than the commercial Cu-Zn LTS catalyst [37], However, it had lower activity and had to be operated at higher temperature. New catalysts are needed that will have higher activity and tolerance to flooding and sulfur. 

Phenol methylation to 2,6-xylenol has been widely studied for the past few deeades owing to the room for improvisation from the viewpoint of product selectivity. Generally during phenol methylation to 2,6-xylenol, occurs via sequential methylation of phenol to o-cresol to 2,6-xylenol, various reaction parameters mediate the selectivity between the two. For instance, when the reaetants stoichiometry of methanol to phenol molar ratio > 2, and significant residence time of o-cresol may favor 2,6-xylenol selectivity. However, excess methanol is often used, sinee some amount of methanol tend to undergo oxidation into various reformate produets [71] under vapor phase condition. Similarly, reaction temperature, catalyst acid-base property, and space velocity of the reaetant are the parameters that govern the selectivity to 2,6-xylenol. 

The severe working conditions often encountered in an H2 production process, such as high temperature and high space velocity, combined with the necessity for a long catalyst lifetime, impose the development of an appropriate synthetic procedure to stabilize the catalyst. The reforming activity and product distribution over supported metal catalysts depend on the choice of metal and its content, the presence of promoters, the type of support and method of catalyst preparation. 

But most of the issues involve the catalyst system itself. The catalyst must be active and selective for the fuel of choice, stable, and resistant to poisoning and attrition while subjected to variations in flow, temperature, and pressure." For successful operation at commercial scale, the reforming process must be able to achieve high conversion of the hydrocarbon feedstock at high space velocities, as well as high H2 and CO selectivities. The reforming catalyst has to meet performance targets (see Table 1) as identified by U.S. DOE before it becomes feasible for use in the fuel reformers of transportation fuel cell... 

A direct comparison of Al203-supported Pt, Pd, and Ru suggests that Ru is the most active metal for diesel reforming, at least on this support. Berry et al studied diesel reforming at a temperature range of 750 to 850°C and GHSVs of 25,000 to 200,000 h Activity increased in the order Pd < Pt < Ru. Complete conversion of diesel was obtained at 850°C and space velocity of 50,000 h from the ATR of diesel over a y-alumina supported Ru catalyst. 

Reactivity of Hydrocarbons. - Each homologous series in a liquid fuel can exhibit different kinetics upon reforming under similar reaction conditions. For example, aromatic compounds are the most difficult to reform and require higher temperatures and lower space velocities. Aromatics also contribute significantly to carbon formation, compared to paraffins and naphthenes. At the same reaction conditions, the H2 production rates are typically in the order aromatics naphthenes. ° The relative reactivities of various higher hydrocarbons are summarized in Table 12. 

Note Typically in reformer design, liquid hourly space velocity (LHSV) is defined as fresh liquid charge volumetric flow rate divided by catalyst volume. Catalyst volume includes the void fraction and is defined by WJpp( — e).]... 

CO, reforming reaction was conducted at 500-750°C, reactants mole ratio of CH3 CO, He = 1 1 3, and space velocity = 20000-80000 1/kg/h. Methane oxidation was conducted at 150-550 °C using 1 % CH in air mixture (2 ml/min CH4 198 ml/min air) at space velocity = 60000 1/kg/h, and MIBK (4000 ppm in 150 ml/min air introduced by a syringe pump) combustion at 100-500°C and space velocity of 10000-30000 h 1. Catalytic reactions were conducted in a conventional flow reactor at atmospheric pressure. The catalyst sample, 0.1-0.3g was placed in the middle of a 0.5 inch I.D. quartz reactor and heated in a furnace controlled by a temperature programmer. Reaction products were analyzed by a gas chromatography (TCD/FID) equipped with Molecular Sieves 5A. Porapak Q, and 15m polar C BP 20 capillary column. 

Catforming a process for reforming naphtha using a platinum-silica-alumina catalyst which permits relatively high space velocities and results in the production of high-purity hydrogen. 

A commercial Cu0/Zn0/Al203 catalyst was coated on quartz and fused silica capillaries by Bravo et al. [29] for methanol steam reforming and compared with packed-bed catalysts. The coatings had a thickness of 25 pm and showed 97% conversion and 97% selectivity towards carbon dioxide at 230 °C reaction temperature, a water/methanol molar feed composition of 1.1 and a space velocity of 45 kgcat s moh1 (methanol). 

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