Hydrogen-containing light hydrocarbon gas mixtures are widely found in the tail gas of petroleum refineries and ethylene plants. The economic recovery of hydrogen from such gas mixtures is of industrial significance. The H2-content in the refinery tail gases varies significantly with specific refining processes. For example, in the tail gas of hydrogenation process is usually quite high (> 60 mol%), while it is quite low in the refinery dry gas (> 20 mol%). The conventional techniques used for hydrogen recovery include adsorption, chemical absorption, membrane separation and deep cooling, however, those techniques are not economically attractive for low H2-content gas mixtures. The new H2-separation technique proposed in this work is based on the fact that hydrogen is a hydrate non-former while methane and some other light hydrocarbons are capable of forming hydrates. By keeping suitable temperature and pressure conditions in a reactor, most light hydrocarbons could be clathrated in the solid hydrate phase (which is subsequently dissociated in a separate vessel), while hydrogen content in the gas phase is thus enriched. The principle flow diagram is shown in Figure 1.

The key factors influencing the practicability of this new separation technique are the pressure / temperature conditions and the rate of hydrate formation / decomposition processes. For exploring the feasibility of the process, in this work we have systematically studied the following aspects: Figure 1: Schematic of the proposed separation process A- -CH4-hydrate formation column, B- -CH4-hydrate dissociation tank BLOCK 2 - - FORUM 12 487

A STUDY ON THE RECOVERY OF HYDROGEN FROM REFINERY (HYDROGEN & METHANE) GAS MIXTURES USING HYDRATES TECHNOLOGY

  • Optimum pressure and temperature conditions for separating (H2 + CH4) feed mixtures containing various H2-content (20–90 mol%).

  • Maximum H2 enrichment could be achieved and the yield of H2.

  • Suitable promoter (additive) and its optimum concentration to be used for lowering the hydrate formation pressure (Promoter A) / enhancing the rate of hydrate formation / dissociation process (Promoter B).

  • Kinetic behavior of the formation/dissociation of methane-hydrates.

The schematic diagrams of the bench scale separation unit, the apparatus for measuring phase equilibrium conditions and the circulating flow system for studying the kinetic behavior of hydrate formation / dissociation and flow properties are shown in Figures 2 to 4, respectively.

Typical experimental results are presented in Tables 1-3. The kinetic data measured on the rate of hydra

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