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The contact process is the current method of producing sulfuric acid in the high concentrations needed for industrial processes. Platinum used to be the catalyst for this reaction, however as it is susceptible to reacting with arsenic impurities in the sulfur feedstock, vanadium(V) oxide (V2O5) is now preferred.〔http://www.ravensdown.co.nz/Resources/Education/History.htm〕 This process was patented in 1831 by British vinegar merchant Peregrine Phillips.〔On March 21, 1831, Peregrine Phillips, Jr., a vinegar manufacturer in Bristol, England, received British patent 6096 for "Certain improvements in manufacturing sulfuric acid, … " See: * ''The Repertory of Patent Inventions'' … , no. 72 (April 1831), (page 248 ). * (Anon.) (1832) "English patents: Specification of the patent granted to Peregrine Phillips, Jr. of Bristol, in the county of Somersetshire, Vinegar Maker, for an improvement in manufacturing Sulphuric Acid. Dated March 21, 1831." ''Journal of the Franklin Institute'', new series, vol. 9, (pages 180-182. ) * Ernest Cook (March 20, 1926) "Peregrine Phillips, the inventor of the contact process for sulphuric acid," ''Nature'', 117 (2942) : 419-421. * George Lunge, ''Theoretical and Practical Treatise on the Manufacture of Sulphuric Acid and Alkali, with the Collateral Branches'', 3rd ed., vol. 1, part 2 (London, England: Gurney and Jackson, 1903), (page 975 ).〕 In addition to being a far more economical process for producing concentrated sulfuric acid than the previous lead chamber process, the contact process also produces sulfur trioxide and oleum. ==Process== The process can be divided into five stages: # combining of sulfur and oxygen # purifying sulfur dioxide in the purification unit # adding excess of oxygen to sulfur dioxide in presence of catalyst vanadium pentoxide, with temperatures of 450 °C and pressure of 1-2 atm # sulfur trioxide formed is added to sulfuric acid which gives rise to oleum (disulfuric acid) # the oleum then is added to water to form sulfuric acid which is very concentrated. Purification of air and SO2 is necessary to avoid catalyst ''poisoning'' (i.e. removing catalytic activities). The gas is then washed with water and dried by sulfuric acid. To conserve energy, the mixture is heated by exhaust gases from the catalytic converter by heat exchangers. Sulfur dioxide and oxygen then react as follows: :2 SO2''(g)'' + O2''(g)'' ⇌ 2 SO3''(g)'' : Δ''H'' = -197 kJ·mol−1 According to the Le Chatelier's principle, a lower temperature should be used to shift the chemical equilibrium towards the right, hence increasing the percentage yield. However too low of a temperature will lower the formation rate to an uneconomical level. Hence to increase the reaction rate, high temperatures (450 °C), medium pressures (1-2 atm), and vanadium(V) oxide (V2O5) are used to ensure a 96% conversion. The catalyst only serves to increase the rate of reaction as it does not change the position of the thermodynamic equilibrium. The mechanism for the action of the catalyst comprises two steps: # Oxidation of SO2 into SO3 by V5+: #: 2SO2 + 4V5+ + 2O2− → 2SO3 + 4V4+ # Oxidation of V4+ back into V5+ by oxygen (catalyst regeneration): #: 4V4+ + O2 → 4V5+ + 2O2− Hot sulfur trioxide passes through the heat exchanger and is dissolved in concentrated H2SO4 in the absorption tower to form oleum: : H2SO4''(l)'' + SO3''(g)'' → H2S2O7''(l)'' Note that directly dissolving SO3 in water is impractical due to the highly exothermic nature of the reaction. Acidic vapor or mists are formed instead of a liquid. Oleum is reacted with water to form concentrated H2SO4. :H2S2O7''(l)'' + H2O''(l)'' → 2 H2SO4''(l)'' 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「contact process」の詳細全文を読む スポンサード リンク
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