poor separation in vacuum belt filter ( VBF )

[341961]

Hi, All

I have encountered problem in vacuum belt filter ( VBF )due to poor separation. Feed is slurry which consists of carboxy methyl cellulose ( CMC ), salt and isoprophil alcohol ( IPA ). CMC is product which has to be extracted from IPA and salt in VBF by IPA solution. It comes out from VBF must be less than 0.5 % IPA. But it is impossible that level could be achieved even though adjustment feed and IPA concentration have been conducted. It may be occured that product have low viscosity and high degree of substitution ( DS ). Does any expert can suggest me to solve this problem.

 

[Mrepp]

Please confirm if your VBF is operating to create a vacuum in your process. If this is a vacuum distillation type operation then you should verify the end vacuum pressure value. Another vacuum type check should be done on the entire system to make sure the system is air tight. The system should be sealed for vacuum service, and there are products tailored to this service (gaskets, seals, etc).

The problem could be that your system capacity is consummed pumping out air that leaks in instead of pumping out vaporized CMC. The test for leaks involves quantifying the leak rate by pumping down the system to lowest vacuum value and observing the pressure rise after the system is shut in. The system will need to be down for this test. Take the time basis and the pressure difference, total system volume (piping, vessel, etc), to calculate a volume air rate. The desired capacity for vapor plus air should then be within the pumps capacity. If not then your system is pumping the air instead of product. The need for this test can be verified if a condensing unit is downstream and the pound rate of recovered product is below required. Adequate mixing should help with viscosity problems

Hope this helps.

 

[25362]

From the technical literature we learn that at high concentrations CMC molecules overlap and coil up and can entangle and become a thermoreversible gel. Increasing ionic strength and reducing pH both decrease viscosity as they cause the polymer to become more coiled. So, you can try alkali addition.

DS can indeed alter the water-solubility and negativity of CMC, but it is largely the MW of the original starting cellulose that determines the viscosity.