Continuous Ion Exchange Separation

New production technique gains foothold in lysine processing from corn.

By Ron Scarborough, Calgon Carbon Corporation

In the six years since it was introduced, continuous ion exchange separation has revolutionized the economics of lysine production. It has taken over the bulk of lysine extraction from fermentation broths.

Today, the continuous separation technique handles 70% of world lysine production. Six major lysine manufacturers currently using continuous ion exchange separation are realizing higher recovery and better process economics compared with conventional intermittent fixed-bed separation.

Advantages

In keeping with increased world demand, continuous ion exchange separation helps improve lysine yields and process economics.

Continuous separation, carried out in an ISEP^® separator developed by Calgon Carbon Corporation, sequentially performs all ion exchange steps in one unit: adsorption, adsorption wash, regeneration, and regeneration rinse. By contrast, fixed-bed ion exchange systems perform these steps one at a time in an intermittent batch process. To maintain continuity of production, they require backup units for wash cycles.

In fixed-bed ion exchange, concentration of loaded material increases rapidly to a maximum, then falls off considerably over perhaps a 12-hour cycle until the resin is regenerated. In continuous ion exchange, by contrast, the concentration of loaded material increases rapidly to a maximum and begins to fall off in a one-hour cycle. Concentration increases again as fresh resin enters the system and stripped resin departs. In such a near steady-state situation, concentration remains high.

Some plant managers report that they are recouping their investment in less than two years, even when a continuous separator initially costs more than a fixed bed.

How It Works

In operation, a carousel arrangement of 12, 20, or 30 columns of small, fixed ion exchange beds slowly rotates at a constant speed below a patented "2-in-1" distributor. The distributor directs all fluids through the exchange beds as the beds move sequentially through the normal four-step ion exchange process. After a complete revolution of the carousel, the lysine is recovered, and the resin is reused for another cycle.

Essentially, the carousel and the rotating portion of the 2-in-1 distributor are the only moving parts. They typically turn six to 12 revolutions per day. Two fractional horsepower motors provide rotation with low energy consumption. The 30 or more valves required by fixed-bed systems are replaced by a single 2-in-1 distributor.

In a typical 20-bed ISEP arrangement for lysine, three beds always remain in the adsorption wash zone, four in the desorption wash zone and three in the regeneration strip zone.

Lysine Production

In production, the ISEP continuous separator recovers lysine from any sugar or starch-based sweetener-containing fermentation broth, including corn. In the ion exchanger, lysine adsorbs on the resin beds, then ammonia strips it from the resin by replacing lysine on the resin. Once stripped and washed, the resin is again ready to absorb more lysine.

Ammonium sulfate coming off the ion exchange waste stream can be recovered. The biomass exiting from the ion exchanger can be used to make fertilizer.

The resultant lysine liquor is concentrated by evaporators, then crystallized. Ammonia is stripped from the evaporator. The final products include granulated lysine and mother liquor byproduct.

Performance

In comparing fixed-bed with ISEP continuous separation, here's the consensus experience of the six plants now in full-scale operation:

… 1% to 10% higher purity end product.
… 70% higher resin productivity (i.e., pounds of lysine recovered per cubic foot of resin).
… 50% less waste produced.
… 30% less chemical consumption.
… 50% less water consumption.
… 40% smaller footprint.

Continuous ion exchange separators also can accept the whole fermentation broth and need no ultrafilters. Fixed-bed separators, on the other hand, require an ultrafiltration stage between the fermentation reactor and separator. This advantage reduces capital cost, footprint upkeep, and processing costs.

Fixed-bed systems often need secondary treatment to treat the chemical wastes from the resin-stripping wash. The ISEP continuous separation system does not; it recycles most of the wash. This is one reason why total system costs for fixed-bed units rise above those for continuous intermittent batch separation, which needs no secondary waste treatment. Fixed-bed operating costs rise still more from using more water, more regenerant, and more resin.

Return on Investment

Average annual lysine plant capacity is 20-30 million tons, with lysine valued at $3,000 per ton in the open market. With each 1% of added recovery worth $750,000/year in plants of this size range, it typically takes less than two years to recoup the $1 million investment. That's based on higher lysine recovery, which averages 5% higher than fixed-bed ion exchange separation.

Several lysine plants have started up a second-generation continuous separator, which does the same job with 20 ports and 20 columns, through use of a proprietary indexing valve. Because of its simplicity and smaller size, it improves process economics in virtually all areas versus the earlier ISEP.

N/A, P.O. Box 717, Pittsburgh, PA 15230-0717. Tel: 800-422-7266; Fax: 412-787-4523.

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