Rectisol scrubbing

Benzene. Benzene is ordinarily scrubbed out by a Rectisol system before the methanators. However, if a different H2S removal system were used, benzene could pass through the system and then hydrogenate, plug up the catalyst pores, or reform. Benzene was therefore included in this poison study. 

The raw gas is purified in the Lurgi Rectisol process (cold methanol scrubbing) where various by-products (eg tar naphthas) and impurities (eg CO2 and H2S) are removed. 

In the gasifiers the sulphur present in the coal is converted to H S which is scrubbed out, together with the C0 in the downstre Rectisol unit. The effluent stream from this unit (typically 1.5 % HpS in CO2) is treated in a homogeneous catalytic process in which tne H S is converted to high grade elemental sulphur. The catalytic liquor consists essentially of an alkaline vanadium solution. In the... 

The shift reaction is carried out by commercially available sulfur-tolerant catalyst thus, the CO content of the gas is reduced to about 1%. The next step is removal of CO2 and H2S by a scrubbing process such as Rectisol or Selexol. The H2S is recovered separately eind sent to a Claus process unit for conversion to elemental sulfur. The CO2 is of adequate purity for urea production. 

In the case of sulphur containing synthesis gases from a partial oxidation, amine scrubbing processes can be apphed as well in which the sulphuric components H2S and COS are scrubbed out together with CO2. In the case of higher sulphur contents (coal and heavy oil gasification) the sulphur components have to be removed selectively. A physical scrubhing process such as the so-called Rectisol... 

The hydrogen stream is water scrubbed to remove solids, ammonia and hydrogen chloride and to saturate it with water vapor. The CO converts to H2 via the shift reaction, and the Rectisol process selectively removes the sour gases (H2S and CO2). Pressure Swing Adsorption (PSA) removes residual impurities (CO, nitrogen, etc.) to produce H2 with a purity of 99.85%. 

The synthesis gas stream from the radiant cooler undergoes further cooling in a convection cooler to generate an additional 700 psi saturated steam. The gas is then water scrubbed, and the Rectisol process selectively removes sour gases to prepare the oxosynthesis gas stream. Adding part of the H2 stream adjusts the H2/CO ratio. 

If the gas contains large amounts of sulfur, it is quite often the practice to remove this sulfur before the carbon monoxide-shift operation. There are a number of sulfur removal processes, namely, amine scrubbing, hot potassium carbonate scrubbing, and the Rectisol process. Ash removal and carbon removal usually are carried out before the gas is treated for sulfur or carbon dioxide removal and before the shift operation. 

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