Oxygen Based Technologies

Steam-methane reforming (SMR) has been the conventional route for hydrogen and carbon monoxide production from natural gas feedstocks. However, several alternative technologies are currently finding favor for an 

SMR/O2R Steam-Methane Reforming combined with Oxygen Secondary 

A POX is similar to an ATR except that it does not contain a catalyst and does not require steam in the feed. It is fed directly with a natural gas stream, which is mixed directly with oxygen from a burner located near the top of the vessel. Partial oxidation and reforming reactions occur in a combustion zone below the burner. The gas exits at about 2500°F. 

The exit gas from each of the above reactors consists of hydrogen, carbon monoxide, carbon dioxide, steam, and residual methane. Small quantities of nitrogen and argon from the original feedstocks may also be present. This gas mixture is then typically processed to yield one or more of the following products  

If only hydrogen is required, the plant becomes a hydrogen plant. If only CO is required, the plant becomes a carbon monoxide plant. If both hydrogen and carbon monoxide are required as separate streams, the plant is typically known as a HYCO plant. If only a hydrogen/carbon monoxide mixture is required, the plant is typically known as a synthesis gas (or syngas) plant. If all three products are required, the plant is considered a combination (hydrogen/carbon monoxide/syngas) plant. 

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The largest difference in production costs between the two processes, however, is in the return on investment. The lower capital cost for the oxygen-based technology provides a significant advantage. It accounts for nearly 0.03/lb. or about 10% of the total production cost. 

For the following discussion, the SMR and SMR/O2R are called SMR-based technologies because the SMR is the dominant component. And the ATR and POX are called oxygen-based technologies because the partial oxidation reactor is the dominant component. 

From Table 8, note that the natural gas requirements for the SMR-based technologies are about the same. Note also that the natural gas requirements for the oxygen-based technologies are about the same. But also note that the oxygen-based technologies require only about 70 percent as much natural gas as the SMR-based technologies. 

The natural gas requirement is lower for the oxygen-based technologies because most of the oxygen in the feed reacts with carbon in the natural gas to form carbon monoxide. The oxidation reaction is therefore more efficient for the formation of carbon monoxide, which is the desired product for the referenced plant. 

Another reason for the lower natural gas requirement is that for the oxygen-based technologies, the heat required for the reaction is applied directly to the process gas in the reactor vessel. This is more energy efficient than the SMR-based technologies, which require a temperature driving force between the combustion gas and the intube process gas. 

The oxygen price can be less than 25 per ton in large industrial sites where a large air separation plant already exists or can be economically installed to serve the needs of the area. Hence, in such cases the oxygen-based technologies merit serious consideration. 

Process Technology Considerations. Innumerable complex and interacting factors ultimately determine the success or failure of a given ethylene oxide process. Those aspects of process technology that are common to both the air- and oxygen-based systems are reviewed below, along with some of the primary differences. 

Fig. 10.9. Oxygen-based direct oxidation process for ethylene oxide. (Encyclopedia of Chemical Technology, Kirk and Othmer, Web site ed., ethylene oxide, manufacture, 2002. Copyright by John Wiley Sons, Inc. and reproduced by permission of the copyright owner.)...

Oxygen sensing technologies based on luminescence quenching are also a relatively new commercial... 

Coal is poised to eventually replace oil as the primary industrial feedstock [862a], In the way that oil is cracked to produce ethylene, coal (or other organic material, such as natural gas) may be converted to synthesis gas. A large number of oxygenates are derivable from synthesis gas, some of which (such as ethanoic acid and methanol) are already in full commercial production. In conventional (ethylene-based) technology, dichlorine is normally... 

The Sabic acetic acid technology is characterized by a novel catalyst (a Mo-V-Nb mixed oxide [335]) and a novel oxidation reactor design, which is different from the conventional methanol-based technology. In the process ethane is mixed with oxygen and compressed, then passed over the catalyst to produce acetic acid and some ethylene, which is then separated and purified for use as a feedstock in other associated plants. 

A paper by the China Petrochemical Dev Co [3h] reported that the use of pure oxygen for cyclohexane oxidation leads to an increased yield and selectivity to Ol/One with respect to the traditional air-based technology, under inherently safe conditions. The latter are achieved by the addition of water, which avoids the formation of flammable mixtures in the overhead vapor space and in the vapor bubbles. In fact, cyclohexane and water form a minimum-boiling azeotrope, the vapor pressure of which is higher than that of cyclohexane. The increased vapor pressure acts as an inert component. 

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