Chemical Byproduct Chlorinealkali Electrolysis

A solution of salt in water is electrolytically decomposed into hydrogen and soda lye (cathode) and chlorine (anode) for the mercury process (as shown in Fig. B.4). Chlorine and caustic soda are the main products made from the chlorine-alkali electrolysis technology. Mercury is used as a negative electrode or cathode that works with a titanium anode to keep the highly reactive products involved apart when electricity is passed through brine. As mercury is extremely toxic, 100% needs to be recycled within the plant to ensure there are no dangers to the environment. The chlorine-alkali electrolysis process results in the manufacture of Cl2, H2, and NaOH caustic solution. Of these three, the primary product is Cl2. The overall process reaction is:

The plant produces NaOH, H2, and Cl2 as described above plus HCl and liquid sodium hydrosulfite. The Olin facility (USA) has a total rated output of 340 tonnes/day of Ch, 348

383 tonnes/day of NaOH, and 9 tonnes/day of H2 produced by the 60 cells in the building [96].

The chlorine-alkali water electrolysis is the only large-scale technological method to be commercialized, where the hydrogen is actually a by-product of the chlorine production and mostly used as a thermal energy source and substitute of natural gas.

Chlorine, Cl2

Figure B.4 Electrolyte chlorine (and hydrogen) production using mercury process [96] B.4 REFINERY BY-PRODUCT (CATALYTIC REFORMING)

Catalytic reforming is a conversion process in which a catalytically promoted chemical reaction converting low octane feed components into high octane products. The use of a catalyst results in much higher octane levels and yields than can be obtained in thermal reforming. In addition, significant amounts of valuable hydrogen are produced as a byproduct (Figure B.5).

Product

Regenerated catalyst Gas/Liquid stripper separator _Light Ends

Catalyst Regenerating section

Catalyst Regenerating section

Naptha/ Gasoline feed from hydrotreatment

Figure B.5 Catalytic reforming flow diagram (continuous) [214]

Reformate/High Octane Product

Hydrogen product to hydrotreatmen^

Naptha/ Gasoline feed from hydrotreatment

Figure B.5 Catalytic reforming flow diagram (continuous) [214]

Feed to the reformer (naptha, a light petroleum fraction) is mixed with recycled hydrogen gas, raised to the reaction temperature (482 - 548°C) by heat exchange and a fired heater, and is then charged to the reactor section. After proceeding through the series of reactors, effluent is cooled by air or water cooling. Gas and liquid products are then separated. Some of the gas from the separator is recycled back to the reactor section; net hydrogen produced is used elsewhere in the refinery complex (e.g., hydrocracking). The liquid effluent is then pumped to a stabilizer system where light, volatile hydrocarbons (methane, ethane, propane and butane) are fractionated off. Aromatic components are left in the stabilizer bottoms as reformate. The primary product stream (80-90%) is a high-quality gasoline blending component.

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