SVP-SCW process
Salt cake wash
Our large scale SVP® processes are all vacuum Single Vessel Processes producing solid salt cake as by-product. Therefore, it is possible to convert any SVP® process to another with only minor equipment changes.
Production of chlorine dioxide in an SVP® system can be accomplished by reducing sodium chlorate with methanol in the presence of sulfuric acid. Methanol technologies require generator acidities of about 6 N or above to achieve high reaction efficiencies. High acidities result in the production of an acidic salt cake by-product. This salt cake is sodium sesquisulfate which is an acidic version of sodium sulfate. Sodium sesquisulfate has a sulfuric acid content of about 18 wt%.
Recovery of the sulfuric acid content in sodium sesquisulfate is possible while operating Eka Engineering's SVP®-SCW system. SVP®-SCW stands for Single Vessel Process Salt Cake Wash. The SVP®-SCW process is basically an SVP-LITE® process with an additional salt cake wash stage which involves a secondary saltcake filter system.
In the SVP®-SCW process, sodium sesquisulfate is filtered from the generator solution by the first saltcake filter and transferred to a metathesis tank. Here the sodium sesquisulfate is separated into its sodium sulfate and sulfuric acid components. The metathesis tank slurry is pumped to a second salt cake filter where the sodium sulfate crystals are removed and sent to the mill's recovery system. The filtrate from the second filter, which contains the sulfuric acid to be recovered, is transferred to a filtrate tank. The filtrate tank solution is pumped back to the generator and/or to any other acid consumer in the pulp mill.
SVP®-SCW Chemistry:
In the SVP®-SCW ClO2 process, sodium chlorate (NaClO3) reacts with methanol in sulfuric acid solution (H2SO4) to produce chlorine dioxide (ClO2). The reaction by-products are formic acid (HCOOH) and acidic salt cake, sodium sesquisulfate [Na3H(SO4)2].
Equation 1:
9NaCIO3 + 2CH3OH + 6H2SO4 --> 9ClO2 + 3Na3H(SO4)2 + ½CO2 + 3/2HCOOH + 7H2
Sodium sesquisulfate is dissolved in hot water in the metathesis tank where it dissociates into sodium sulfate crystals and a weak sulfuric acid solution. The weak sulfuric acid solution is recycled to the generator.
Equation 2:
H2O + 4Na3H(SO4)2 --> 2 H2SO4 + 6Na2SO4
This process is a trademark of Eka Chemicals, registered in one or more countries.
Related Links
Chlorine dioxide process
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