On-Line Process Chromatographs Optimize Fine Chemicals Production

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The heart of today’s highly integrated plant is the cracker which converts light virgin naphtha (LVN) or liquefied petroleum gas (LPG) from local refineries first into a raw gas mixture and then into individual components:

in a fraction of a second, temperatures of 1,200–2,500 °C from an oxy-fuel flame crack the feedstock into low-molecular-weight products including ethylene, propylene, 1,2- and 1,3-butadiene, benzene, toluene, hydrogen, methane and acetylene;

the raw gas is quenched by water injection, and heavy impurities such as coke and tar are separated. The gas is then compressed to 14 bar and passed on to the scrubbing and separating stages;

an ammonia scrubber absorbs acidic gases including carbon dioxide. Surplus CO₂ is treated with activated carbon and converted into food-grade liquid CO₂;

acetylene is removed by a selective solvent and purified by fractionation;

the remaining cracked gas is cooled in three steps (–40 °C, –100 °C and –200 °C) and distilled using a Linde process to create fractions with different carbon numbers.

This unique technology, with the fact that the plant makes good use of all the components of the cracked gas, allows the Visp cracker to operate economically despite its comparatively small size (approximately 50,000 t/y). Most of the ethylene goes to produce niacin (vitamin B3). while the acetylene is used to make precursors of vitamins A and E, for fragrances, and with ethylene to produce acetaldehyde, an intermediate in the production of niacin.

The Visp site makes increasing use of online analyzers.

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On-Line Process Chromatographs Optimize Fine Chemicals Production