Deacon process developed by Henry Deacon in 1868 [11].
4HCl + O2 2Cl2 + 2H2O
(i) Direct oxidation around 425 to 475°C [11] in presence of copper catalyst. (ii) Exothermic process has intermediate reactions resulting in sluggish reaction kinetics.
(i) Lower yields because of low conversion and catalyst activity [12]. (ii) Construction is expensive due to highly corrosive [11] intermediates.
(i) Single pass conversions around 60% to 80%. (ii) Catalyst activity decreases above 402°C because of volatilization [9]. (iii) Never been put to commercial use [12, 13].
(i) Oxidation using nitrogen oxides as the catalyst and sulphuric acid as circulating medium [7].
(i) Needs expensive plant design and safety features because of many intermediate reaction steps [7, 11], making it only possible for large-scale plants.
(i) Needs extensive downstream processing to get pure chlorine. (ii) DuPont started 200,000 ton/year plant in 1974, but it is not operating at present [7].
(i) Oxidation in fluidized bed process at 300 to 425°C. (ii) Catalyst is composed of copper, chloride, rare earth materials, and others at determined ratio [15].
(i) High catalyst activity because of low volatilization. (ii) Corrosion is also less [15].
(i) Conversion of 80% can be achieved [15]. (ii) Shell operated a facility of 30,000 t/yr in the 1970s [13], but operation was eventually shut down.
UHDE diaphragm process developed by Bayer Material Science & Uhdenora.
Anode: 2Cl− 2Cl2 + 2e− Cathode: 2H+ + 2e− H2
(i) Aqueous electrolysis process using PVC/PVDF diaphragm at 65 to 70°C [2]. (ii) Graphite electrodes are used. Water transfer (osmatic drag) is present.
(i) Gas purity is limited because the diaphragm cannot impede gas diffusion completely [3]. (ii) Minimum HCl concentrations should be maintained to avoid oxygen evolution [3].
(i) The conversion is 25% (23 to 17 wt%). (ii) Power consumption is 1670 kWht−1 Cl2 at 5 kAm−2 [2]. (iii) In Germany in 1995 20% of the HCl produced was recycled this way [3].
(i) Similar to CEM electrolysis process but occurs in gas phase through gas diffusion type membranes. (ii) The electrolyser is operated at 450–550 kPa and 70–90°C.
(i) No HCL absorption step. (ii) Simple downstream process is sufficient for purification because feed is anhydrous [14]. (iii) Water transport (osmatic drag) is present.
(i) HCl conversion ratio up to 85% [7] can be achieved because of high diffusion coefficients (gas phase) [14]. (ii) Power consumption at 5 kAm−2 is roughly 1120 kWh/tCl2 [14].
Sumitomo process by Sumitomo Chemical Co., Ltd. developed in 2000 [13].
4HCl + O2 2Cl2 + 2H2O
(i) Oxidation process in fixed bed reactor using RuO2/TiO2 (rutile) catalyst. Can be operated as low as 250°C. (ii) This process has higher conversions because of fixed bed reactor.
(i) This catalyst has higher activity and thermal stability than the ones discussed above [13]. (ii) Since 2003 a plant having production capacity of 100,000 t/y is operating smoothly.
(i) Conversions up to 95% are possible [13]. (ii) Power consumption is 165 kWht−1 Cl2 [13] which is very less in comparison to Bayer-DE Nora Process, but no comparisons for capital costs are reported.
(i) Similar to CEM electrolysis process, but hydrogen generation is suppressed by water formation resulting in 30% savings in electric consumption and voltage less than 1 V [2].
(i) Water transport is present from anode to cathode. (ii) Many plants lately licensing this technology; for example, Bayer started operating a commercial plant of 215,000 t/yr [7].
(i) The power consumption is 1070 kWht−1 Cl2 at 5 kAm−2 that is less than diaphragm process, but the capital costs for the same are not reported.
