H2/CO ratio

Synthesis Gas Chemicals. Hydrocarbons are used to generate synthesis gas, a mixture of carbon monoxide and hydrogen, for conversion to other chemicals. The primary chemical made from synthesis gas is methanol, though acetic acid and acetic anhydride are also made by this route. Carbon monoxide (qv) is produced by partial oxidation of hydrocarbons or by the catalytic steam reforming of natural gas. About 96% of synthesis gas is made by steam reforming, followed by the water gas shift reaction to give the desired H2 /CO ratio. 

As the molecular weight of the hydrocarbon increases (lower H/C feed ratio), the H2/CO product ratio decreases. The H2/CO product ratio is approximately 3 for methane, 2.5 for ethane, 2.1 for heptane, and less than 2 for heavier hydrocarbons. Noncatalytic partial oxidation of hydrocarbons is also used to produce synthesis gas, but the H2/CO ratio is lower than from steam reforming ... 

A slurry bed reactor is in a pilot stage investigation. This type is characterized by having the catalyst in the form of a slurry. The feed gas mixture is bubbled through the catalyst suspension. Temperature control is easier than the other two reactor types. An added advantage to slurry-bed reactor is that it can accept a synthesis gas with a lower H2/CO ratio than either the fixed-bed or the fluid-bed reactors. 

Allyl acetate is a precursor for 1,4-butanediol via a hydrocarbonylation route, which produces 4-acetoxybutanal. The reaction proceeds with a Co(CO)g catalyst in benzene solution at approximately 125°C and 3,000 pounds per square inch. The typical mole H2/CO ratio is 2 1. The reaction is exothermic, and the reactor temperature may reach 180°C during the course of the reaction. Selectivity to 4-acetoxybutanal is approximately 65% at 100% allyl acetate conversion. ... 

Figure 6. Effect of H2 CO ratio in feed gas on heating value and H2 content of product gas at 20 atm and 371°C...

Steam-Moderated Process. The basic idea behind this approach is to limit the extent of conversion of the methanation reaction, Reaction 1, by adding steam to the feed gases. This process simultaneously provides for (46) elimination of the CO shift, Reaction 2, to get a 3 1 H2 CO ratio from the make-up gas ratio of about 1.5 1 and avoidance of carbon laydown by operation under conditions in which carbon is not a thermodynamically stable phase (see Chemistry and Thermodynamics section above). 

Interesting features of this process include the potential for one-stage methanation to completion without the need for gas recycle. This feature was cited by Chem Systems, but, according to Rheinpruessen-Koppers work on the Fischer-Tropsch (52, 53), gas recycle was necessary with high H2 CO ratios. Drawbacks include such factors as catalyst attrition (48, 50), and low volume productivities of the methanator (less than one-tenth that reported for fixed bed adiabatic reactors) (48, 50, 52, 53, 61). 

The effect of synthesis gas composition on conversion, catalyst life, carbon black formation, etc. was determined in numerous tests. Characteristic variables in the synthesis gas composition are the H2/CO ratio, residual C02 content, and content of trace components in the form of higher hydrocarbons and catalyst poisons. 

H2/CO Ratio. In a commercial shift conversion plant, a change in throughput and conversion must be taken into account since it will affect... 

Finally, it can be stated that variation in the H2/CO ratio will not affect operability of an SNG plant using a recycle system for methana-tion as demonstrated in the SASOL plant. 

A significant feature of the operation of the two plants is that only a small deviation in feed gas composition is tolerable when using a stoichiometric gas. Greater deviations in the H2/CO ratio and in the residual C02 content of the feed gas will cause serious problems regarding SNG specifications. Thus, methanation of a stoichiometric synthesis gas is reasonable only when there are no stringent requirements for SNG specification. 

These tests were performed to establish the limits in flexibility and operability of a methanation scheme. The two demonstration plants have been operated in order to determine the optimum design parameters as well as the possible variation range which can be tolerated without an effect on catalyst life and SNG specification. Using a recycle methanation system, the requirements for the synthesis gas concerning H2/CO ratio, C02 content, and higher hydrocarbon content are not fixed to a small range only the content of poisons should be kept to a minimum. The catalyst has proved thermostability and resistance to high steam content with a resultant expected life of more than 16,000 hrs. 

The catalytic partial oxidation of methane for the production of synthesis gas is an interesting alternative to steam reforming which is currently practiced in industry [1]. Significant research efforts have been exerted worldwide in recent years to develop a viable process based on the partial oxidation route [2-9]. This process would offer many advantages over steam reforming, namely (a) the formation of a suitable H2/CO ratio for use in the Fischer-Tropsch synthesis network, (b) the requirement of less energy input due to its exothermic nature, (c) high activity and selectivity for synthesis gas formation. 

Partial oxidation of methane to syngas over Ni and Co catalysts was effected by use of microwave irradiation, and compared with conventional heating [73]. Although the same conversion levels and H2/CO ratio (2.0 0.2) were observed, the temperature of the catalyst bed was much lower (200 K) when microwave irradiation was used than with conventional heating. Under both activation modes the Ni-based... 

H2 CO ratio in the resulting syngas is about 1.7. However, due to the relatively high content of CO in the syngas, carbon deposition may still be a problem, especially for Ni-based catalysts widely used for steam reforming. 

Johnson et al.67 studied CO hydrogenation on bimetallic catalysts consisting of cobalt overlayers on W (100) and (110) single crystals at 200°C, 1 bar at a H2/ CO ratio of 2. AES spectra showed the postreaction Co/W surfaces to have high coverages of both carbon and oxygen, with carbon line shapes characteristic of bulk carbidic carbon.67 The catalytic activity apparently could not be correlated with surface carbon level.67... 

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