Technology Developed

• Recovery of Water with Inorganic Chemicals from Kraft Black Liquor

Patent No. (India) 189310 - "Process for the Recovery of Inorganic Chemicals from Kraft Black Liquor", P. K. Bhattacharya, S. De & Director, IIT KANPUR

A patent is obtained for a process for the recovery of water and inorganic chemicals from Kraft black liquor (BL) based on membrane separations. In the conventional process, BL (with 15% total dissolved solids) is concentrated to 60-65% and then incinerated. The molten inorganic chemicals are then causticized to recover around 85% of alkali chemicals. This process involves a huge loss of water during the concentration step in multi-effect evaporators. Also, organics burnt during incineration cause environmental pollution. Apart from this, the equipment incurs high capital investment and energy cost. Small-scale paper industries, instead of processing BL, prefer to simply discard it, causing more pollution problems while losing valuable inorganic chemicals.

A three-step process has been developed where BL is first carbonated under pressure for the release of bound alkali from organics and then ultra-filtered for the removal of bigger molecular weight compounds. Finally, permeate of the UF process is subjected to nano-filtration to recover water and inorganic chemicals. Permeate of the NF is very clear and rich in inorganic. The complete kinetics of carbonation and parametric studies on UF and NF has been studied. The scheme results in the recovery of around 80% of the inorganic present, which compares favourably with 85% recovery in the conventional process. The process developed in his laboratory, thus, not only recovers water with alkali chemicals, it is also non-destructive. Further work, relevant and required for design and process, may be taken-up upon request.

* S. De and P. K. Bhattacharya, “Recovery of water with inorganic chemicals from Kraft black liquor using membrane separation processes“, Tappi J., 79, 103-111 (1996).

* C. Bhattacharjee and P. K. Bhattacharya, “Flux decline analysis in ultrafiltration of Kraft black liquor“, J. Membrane Sci., 82, 1-14 (1993).

• Ammonia and carbon-di-oxide removal from urea plant condensate through membrane contactor

Membrane contactor was utilized to remove dissolved gases (NH₃ + CO₂) in water condensate emanating out of urea-plant using a membrane contactor having number of hydrophobic hollow fibres; utilizing both the modes of operations: liquid-liquid extraction (LLE) and sweep/vacuum (S/V). Both the modes have demonstrated the feasibility of the removal of gases through membrane contactor.

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