Claus trial

Sulfur produced by the Claus process in Alberta is waiting to be shipped in the port of Vancouver .

The Claus process is a process for the industrial production of sulfur from hydrogen sulfide . Hydrogen sulfide is a component of so-called sour natural gas ( " sour gas "), which for example in Northern Germany with Oldenburg , in the Canadian province of Alberta in Calgary is promoted as well as in the Chinese province of Sichuan. However, hydrogen sulphide is mainly produced during the large-scale hydrogenation desulphurisation of crude oil in practically all refineries worldwide. In refineries, considerable amounts of hydrogen sulphide are also produced in conversion processes that do not require hydrogen, for example cracking in steam crackers .

Sour natural gas consists of natural gas (mainly CH ₄ and other hydrocarbons) and H ₂ S , as well as other components such as H ₂ O , CO ₂ , thiols as well as COS and CS ₂ . Since the Claus process requires a relatively high H ₂ S content of the gas (> 40%), the H ₂ S is first selectively scrubbed out of the natural gas (e.g. with methyldiethanolamine , MDEA, or diisopropylamine ) and then released from the washing solution by heating ( amine washing ).

history

The Claus process was originally patented in 1883 by the German-British chemist Carl Friedrich Claus , both in Germany and in England. It was originally used to recover sulfur from calcium sulfide in the production of sodium carbonate from plants.

Nowadays only the modified Claus process is carried out, which was developed in the early 1930s by the German IG Farben . Around 52.8 million t of sulfur were produced worldwide in 2014, distributed across many countries as follows (data in million t): China (10.5), USA (9.6), Russia (7.3), Canada (5.9), Germany (3.8), Japan (3.3), Saudi Arabia (3.3), India (2.8), Kazakhstan (2.7), Iran (2.1), United Arab Emirates (1.9), Mexico (1.8), Chile (1.7), South Korea (1.4), Poland (1.1), followed by France, Australia, Venezuela, Kuwait and others. For 2015, global sulfur production was estimated at over 70 million t, most of which is generated during the desulfurization of natural gas and crude oil ("Claus sulfur").

Procedure

The basic chemical process can be described by the following three equations, whereby the specified reaction enthalpies apply to gaseous reactants at 1 bar pressure and 298 K:

The hydrogen sulfide separated off in the amine wash is driven out of the wash solution. One third of this hydrogen sulfide gas is burned in the Claus furnace with process air to form sulfur dioxide by adding enough oxygen in the form of air or oxygen-enriched air that the following stoichiometry is met:

(I) ${\displaystyle \mathrm {H_{2}S\ +\ 3/2\ O_{2}\longrightarrow SO_{2}+\ H_{2}O} \qquad \Delta H^{0}=-518.0\ {\frac {\mathrm {kJ} }{\mathrm {mol} }}}$

Part of the remaining hydrogen sulphide reacts with the SO _{2 formed} by comproportioning to elemental sulfur with the molecular size of S ₂ :

(II) ${\displaystyle \mathrm {2\ H_{2}S\ +\ SO_{2}\longrightarrow 3/2\ S_{2}+\ 2\ H_{2}O} \qquad \Delta H^{0}=+47.3\ {\frac {\mathrm {kJ} }{\mathrm {mol} }}}$

The remaining hydrogen sulfide is catalytically converted with the remaining SO ₂ at a lower temperature to form elemental sulfur (mainly S ₈ ):

(III) ${\displaystyle \mathrm {2\ H_{2}S\ +\ SO_{2}\longrightarrow 3/8\ S_{8}+\ 2\ H_{2}O} \qquad \Delta H^{0}=-107.2\ {\frac {\mathrm {kJ} }{\mathrm {mol} }}}$

The technical process therefore consists of three stages:

1st thermal stage : The required amount of SO _{2 is} generated in a Claus furnace by partially burning the H ₂ S with air or a mixture of air and pure oxygen (reaction I; approx. 950–1200 ° C). The central part of the furnace is the burner, which optimally mixes the reaction gases (F1; see Fig. 1). The resulting SO ₂ already partially reacts in the Claus furnace with the H ₂ S present to form elemental sulfur, which due to the high temperature is initially obtained as S ₂ (reaction II). Behind the Claus furnace, the gas mixture is cooled to approx. 300 ° C in a heat exchanger with boiler feed water (KSW), with steam being generated. As a result of the cooling, the sulfur produced is deposited in liquid form, the S ₂ molecules oligomerizing to form a mixture of ring molecules such as S ₈ , S ₇ and S ₆ . About 60-70% of the maximum possible amount of sulfur is already obtained here, provided the H ₂ S content of the feed gas is sufficiently high. After the first sulfur separator, the gas then mainly consists of nitrogen, water vapor, H ₂ S and SO ₂ .

Flow diagram of a Claus plant for the production of elemental sulfur (SRE: Sulfur Recovery Efficiency)

2. Catalytic stages : In two or three successive catalytic stages, further sulfur is obtained after reaction III. This exothermic gas phase reaction is an equilibrium process, with the equilibrium at low temperatures lying furthest on the side of elemental sulfur. Synthetic aluminum oxide or titanium dioxide is used as a catalyst to accelerate the establishment of equilibrium. The outlet temperatures of the catalytic reactors are set high enough to reliably avoid condensation of sulfur vapor on the catalyst material and thus its deactivation. In order to achieve maximum yield with an acceptable reaction time at the same time, the temperature in the first reactor R is 305-350 ° C, in the second about 225 ° C and in the third at 180-200 ° C. Behind each reactor, the sulfur produced is separated in liquid form by cooling the gas mixture (K1 to K3), after which the remaining gas must be heated up to the required reaction temperature in a preheating stage (W1 to W3), provided that another reactor is connected.

The first catalytic reactor also has the function of hydrolytically decomposing carbon disulfide and carbonyl sulfide, for which the highest possible temperature is required:

(IV) ${\displaystyle \mathrm {CS_{2}\ +\ 2\ H_{2}O\longrightarrow 2\ H_{2}S\ +\ CO_{2}} }$

(V) ${\displaystyle \mathrm {COS\ +\ H_{2}O\longrightarrow \ H_{2}S\ +\ CO_{2}} }$

The total sulfur yield is approx. 95% in two catalytic stages, while up to 98% of the sulfur can be obtained in three stages. The liquid sulfur produced and freed from dissolved H ₂ S is stored and transported in steam-heated containers; it is so pure that it can be used without further cleaning. B. can be used directly for the production of sulfuric acid. Overall, a Claus system generates more energy (in the form of steam) than it consumes itself.

3. In the Claus tail gas after the last catalytic stage there are not only N ₂ , water vapor, hydrogen, CO and CO _{2 but} also traces of sulfur vapor and SO ₂ , COS, CS ₂ and H ₂ S, which have to be removed to avoid unpleasant odors and to minimize environmental damage (the odor threshold for H ₂ S is only 0.1 ppm). There are more than a dozen different types of fine desulphurisation in use. In the meantime, a fine desulfurization process based on the hydrogenating conversion of all sulfur components into H ₂ S has become widely accepted . The latter is selectively washed out in a downstream washing stage with the aid of an amine solution (typically water-containing MDEA) and thus obtained as a concentrated H ₂ S stream which is fed into the Claus furnace. This means that sulfur recovery rates of over 99.8% can be achieved, i.e. top values ​​compared to other fine desulphurization processes (such as catalytic H ₂ S oxidation with the aid of air or SO ₂ ). However, this performance in terms of minimizing SO ₂ emissions must be bought at the expense of relatively high equipment and energy costs. Since even after the fine desulfurization with low concentrations of sulfur compounds such. B. H ₂ S is to be expected in the process gas, this is finally subjected to a catalytic or (more often) thermal air oxidation, so that practically all sulfur components are converted to SO ₂ , which is then finally emitted.

literature

• R. Steudel: Elemental Sulfur and Sulfur-Rich Compounds. Top. Curr. Chem., Vol. 230, Springer, Berlin, 2003, ISBN 3-540-40191-1 .
• FP Springer, On Sulfur and Hydrogen Sulphide - The History of These Components of Natural Gases. Erdöl-Erdgas-Kohl, 2011, Issue 10, pp. 382–388.
• Linde brochure Sulfur Process Technology. 2012. ( PDF. )

See also

• Frasch process

Individual evidence

1. ↑ ^{a b} Bernhard Schreiner: The Claus process. Rich in years and more important than ever . In: Chemistry in Our Time . tape 42 , no. 6 , December 2008, pp. 378–392 , doi : 10.1002 / ciuz.200800461 .
2. ↑ Ralf Steudel, Lorraine West, Vita of Carl Friedrich Claus - inventor of the Claus process for production of sulfur from hydrogen sulfide , online document from 2015, available on the ResearchGate.net platform
3. ↑ Hans Baehr, Gas Purification by the Alkacid Process and Sulfur Recovery by the IG Claus Process , Refiner & Natural Gasoline Manufacturer, 1938, Vol. 17 (6), p. 237-244.
4. ^ Mineral Commodity Summary 2016
5. ^ Ralf Steudel: Chemistry of the non-metals. de Gruyter, Berlin, 2013, ISBN 978-3-11-030439-8 , pp. 465-466.
6. ↑ Calculated from the enthalpy data in the NIST database