6. REMOVAL OF ORGANIC SULFUR FROM GASES (FEINREINIGUNG)
The previously discussed iron oxide purification process removes only the inorganic or H2S sulfur from the gas. The organic sulphur compounds are untouched. If they are present, and must be removed, it is necessary to subject the gases to further purification.
In Germany organic sulfur in synthesis gas is ordinarily removed by a process called "Feinreinigung". After the gas has passed through the final H2S removal it goes to this "Feinreinigung" process at approximately atmospheric temperature and presssure. Here it passes through the tubes of a heat exchanger and of a direct fired preheater to raise the temperature to 150-300ºC, this temperature increasing with the age of the catalyst. The gas then goes to the catalyst chamber where it passes from the center of the chamber to the outside through an annular bed of catalyst at a velocity of about 0.25 meters per second, from the chamber through the shell side of the heat exchanger mentioned above, then through one or two more catalyst chambers similar to the first.
The catalyst, is composed of 60-70% crude iron oxide and 30-40% sodium carbonate. The organic sulfur in the gas is cracked to H2S and reacts with the oxygen present in the inlet gas, (or oxygen added before the catalyst chambers) to form Na2SO4, FeSO4, and some elementary sulfur.
A new method of catalyst manufacture produces a much lighter, more porous mass. The method of preparation for a small batch based on 100kg of Lautamasse is as follows:
100 Kg of Lautamasse with 2% alkali content and 50% water is divided into two parts. One portion is dried, mixed with 5 Kg of Na2CO3, and then added to the reminder of the charge. The mixture containing 25% water is then wetted with a fine spray to proper consistency, is pressed to the desired grain size and dried. The drying is carried out first at 60-80ºC until the mass is hard and then is completed at a temperature over 100ºC. The resulting product is compared to the older catalyst in the table below:
| OLD | NEW | |
| Apparent Specific Gravity, Kg/ liter | 0.7 | 0.5 |
| Grain strength, Kg/ cm2 | 6-7 | 3-4 |
| Na2CO3 content % | 30 | 15 |
| Fe2O3, % | 36 | 44 |
| Porosity, % | 50 | 70 |
| To fill chambers, tons | 100.8 | 76 |
| Alkali in chambers, tons | 29.5 | 12.5 |
| Iron in chambers, tons | 36.7 | 33.8 |
| Organic Sulfur Loss, g/100m3 | 1.0 | 0.1 |
| Organic sulfur conversion, % | 70 | 96.8 |
The catalyst grains should be course (8-10mm) and all dust should be removed. The catalyst dust cannot be reworked as it reduces the porosity of the finished catalyst.
A gas volume of 100,000 Nm3/ hr with 12-15 mg total sulfur in the gas entering the unit will use an average of about 4.8 tons per day of catalyst. Each unit will process 10,000 to 22,000 cbm/hr of gas depending on the age of the catalyst, and contains about 65 tons of catalyst in two chambers. Typical operating conditions for this process are as follows:
| Inlet Gas | 20,000 m3/hr |
| H2S in Inlet Gas | 0.3g/100Nm3 |
| H2S in Outlet Gas | nil |
| Organic S in inlet | 15.0 g/100 Nm3 |
| Organic S in outlet | 0.20 g/100 Nm3 |
| Temp in 1st chamber | 230ºC |
| " out 1st " | 220ºC |
| " in 2nd " | 190ºC |
| " out 2nd " | 180ºC |
Several operating difficulties are encountered in this process. The worst difficulty is the formation of resinous coatings on the catalyst. This is prevented by the installation of an activated carbon absorption process before the unit to remove the resin-forming materials. Excessive H2S in the inlet gas overloads the unit and permits sulfur to break through. This is usually traced to poor operation of the previous H2S removal unit. Excessive temperature sinters the catalyst. Poor catalyst sizing or charging causes unequal distribution of the gas or excessive pressure drop, and also causes sulfur to break through and appear in the outlet gas.
In spite of these difficulties the "Feinreiningung" process is almost without competition in Germany for general use in the removal of organic sulfur from gas.