Partial Oxidation purification

If tars are formed (which happened in the trial with mixed PVC waste), it is necessary to apply a partial oxidation to convert these tars into gaseous products. Via a quench, HCl is recovered from the product stream which consists of fuel gas and HCl. After purification the HCl can be used for producing ethylene dichloride (EDC) via oxychlorination. The recovery of CI2 is more then 90%, in general 94%-97%. Inert materials in the feed, such as the chalk and metal stabilisers present in a PVC-formulation, are separated from the flue gas as fly ash or will be set free as a bleed from the circulating sand. 

Gas purification Solid hydrocarbons such as coal are partially oxidized without a catalyst in the process. 

Hydrogen production from carbonaceous feedstocks requires multiple catalytic reaction steps For the production of high-purity hydrogen, the reforming of fuels is followed by two water-gas shift reaction steps, a final carbon monoxide purification and carbon dioxide removal. Steam reforming, partial oxidation and autothermal reforming of methane are well-developed processes for the production of hydro-... 

Small reformers R D areas include compact and low cost reformers (1-5 kW) to convert fossil fuels (natural gas, gasoline) or biomass fuels (ethanol) to hydrogen via different processes (steam reforming, partial oxidation, auto-thermal, non catalytic hybrid steam reforming). Improvements in reformer efficiency, capacities and response times, and integration of purification unit are also being studied. Examples of projects include ... 

Catalytic gas purification of reformate containing significantly more than 1% of carbon monoxide is performed by the water-gas shift reaction. Frequently, especially in the case of partial oxidation reactions, water is added to the reformate to shift the equilibrium of the reaction in the desired direction ... 

Figure 5.3 is a simplified diagram that shows the basic steps in the different processes that are used to produce synthesis gas. Note that the Sulfur Removal step is just before Purification when Partial Oxidation and Gasification are used. Sulfur Removal is the first step when Steam Reforming is the chosen process. The reasons that the process order is as shown will be explained in the following sections of this chapter174. 

Certain catalytic systems based on the use of cobalt and molybdenum offer good resistance to sulfur. On the other hand, they cannot guarantee advanced conversioa of carbon monoxide, of which a few per cent remain in the effluent obtained. Their value resides in the simplification of the purification schemes for effluents produced by the partial oxidation of sulfiir-containing feeds. This is because they do not require prior removal of hydrogen sulfide, which can be removed subsequently in a angle add gas separation. 

In further purification, carbon dioxide, residual carbon monoxide, and sulfur compounds (only present in the synthesis gas from partial oxidation) have to be removed as they are not only a useless ballast but above all poisons for the ammonia synthesis catalyst. 

Methanation as final purification for the raw gas from partial oxidation was proposed by Topsoe [739]. In this case the shift conversion is carried out in two stages with a special sulfur-tolerant shift catalyst followed by removal of hydrogen sulfide and carbon dioxide in an acid gas removal unit. Because of the potential danger of a sulfur break-through causing poisoning, the normal copper - zinc - alumina catalyst is usually not applied, which is surprising as the same risk exists in partial oxidation based methanol plants for the similarly composed methanol catalyst. 

Cyrogenic methods are usually used for final purification of partial oxidation gases, but may be also incorporated in steam reforming plants. A prominent example for the application in a steam reforming concept is the Braun Purifier process [746]-[753]. 

Farrusseng D, Julbe A, and Guizard C. Evaluation of porous ceramic membranes as O2 distributors for the partial oxidation of alkanes in inert membrane reactors. Sep Purif Technol 2001 25 137-149. 

Figure 3.3. Schematic representation of partial oxidation (POX), autothermal reforming (ATR), and catalytic partial oxidation (CPO) reformers followed by H2 purification steps. HEX, heat exchanger.

Derivation (1) Reaction of steam with natural gas (steam reforming) and subsequent purification (2) partial oxidation of hydrocarbons to carbon monoxide and interaction of carbon monoxide and steam (3) gasification of coal (see Note 1) (4) dissociation of ammonia (5) thermal or catalytic decomposition of hydrocarbon gases (6) catalytic reforming of naphtha (7) reaction of iron and steam (8) catalytic reaction of methanol and steam (9) electrolysis of water (see Note 2). In view of the importance of hydrogen as a major energy source of the future, development of the most promising of these methods may be expected. 

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