Catacarb solution

I ve never told this story to anyone. Not even to Liz or my mom. It occurred in Lithuania in 2006.1 had been hired to expand the capacity of the hydrogen plant that was limiting refinery capacity. The bottleneck was the absorber that removed CO with catacarb solution from the hydrogen product. This absorber was subject to flooding as the catacarb circulation rate increased in proportion to production. That is, the solution was carried overhead with the hydrogen product. 

Figure 3.12 Restriction of the inlet distributor causes entrainment of the catacarb solution.

The plant operations chief informed me that there was already a catalyst in the Catacarb solution that would be used for start-up. It was a di-ethanol amine catalyst, not LRS-10, but still it was a catalyst. 

Figure 33.2 Circulating Catacarb solution absorbs CO from hydrogen.

As lower temperatures favor the absorption of CO by the Catacarb solution, I had expanded the capacity of the circulating Catacarb solution aerial fin-fan cooler to cool the absorber tower and thus reduce CO in the Hj product. Liz stood next to me at the panel when we started the Catacarb circulation pumps. I was totally confident. 

So when the cooled Catacarb solution began to circulate, they were overjoyed. The CO content of the hydrogen product lined out at 3.5 percent CO, well above the previous level of 2 percent, and far above my target of 0.5 percent CO in the hydrogen product. 

I increased the circulation rate of the Catacarb solution, which helped a bit. 

I shut off one of the four aerial cooler fans on the lean Catacarb solution (see Fig. 33.2), which helped a lot. 

So I shut off, one by one, over a period of days, all the aerial cooler fans. The absorber became quite hot and the CO dropped to 0.5 percent in the product. None of this made any sense. CO absorption in Catacarb solution should be favored by lower, not higher, temperatures. Equilibrium conditions for CO absorption are always improved by cooling the circulating absorption liquid. 

The lesson is, if raising reaction temperature in a reactor promoting an exothermic reaction makes the reaction proceed further, the reactor is limited by kinetics and not equilibrium. The term "exothermic" means that heat is liberated in the reaction. How can one tell if the absorption of CO in the Catacarb solution is exothermic (gives off heat), rather than endothermic (absorbs heat) Refer to Fig. 33.2. Note that both the hydrogen gas and the Catacarb liquid are being heated in the absorber. They are being heated by the heat of reaction between the COj and the potassium salt in the Catacarb solution. 

Catacarb process An extraction process used to remove carbon dioxide from process gases by scrubbing the hot gases with potassium carbonate solution containing additives which increase the hydration rate of the gas in the solution. The Vetrocoke process is similar. See Benfield process. 

Invented by H. E. Benson in 1952 and then developed with J. H. Field at the U.S. Bureau of Mines. First licensed by the Benfield Corporation of Pittsburgh, subsequently acquired by the Union Carbide Corporation, and now licensed by UOP. The current UOP version includes new solution activators and incorporates zeolites or membrane processes for complete separation of acid gases and minimal loss of product gases. More than 650 plants were operating in 1996. Variations include the Benfield HiPure process and the Benfield LoHeat process. See also Carsol, CATACARB, Giammarco-Vetrocoke, HiPure. 

Carbosolvan One of the several processes for absorbing carbon dioxide from gases, using hot potassium carbonate solution. See also Benfield, Carsol, CATACARB, Giammarco-Vetrocoke, Hi-Pure. 

CATACARB [Catalyzed removal of carbon dioxide] A process for removing carbon dioxide and hydrogen sulfide from gas streams by absorption in hot potassium carbonate solution containing a proprietary catalyst. Developed and licensed by Eickmeyer and Associates, KS, based on work at the U.S. Bureau of Mines in the 1950s. More than a hundred plants were operating in 1997. See also Benfield, Carsol, Hi-pure, Giammarco-Vetrocoke. 

HiPure A variation on the Benfield process, using two stages of scrubbing by hot potassium carbonate solution in order to reduce the carbon dioxide contents of gases to very low levels. See also Carsol, CATACARB, Giammarco-Vetrocoke. 

Catacarb Aqueous Potassium Carbonate with Borate Additive Blocks pores of catalyst by evaporation of K2CO3 solution. 

Catacarb Process [667], [681], [682]. This process was introduced about 30 years ago. A modified potassium salt solution is used, containing various stable and non toxic catalysts and corrosion inhibitors. The process is very versatile and allows the process and mechanical configuration to be tailored to a wide range of C02 partial pressures. Figure 68 showes a Catacarb single-stage low heat design. 

A minor variant to the amine scrubbing process described above is the Sulfinol process, which still uses an alkanolamine base, diisopropanolamine (35%), but in a solvent consisting of a mixture of sulfolane (40%), tetramethy-lene sulfone (CH2)4S02, a good hydrogen sulfide solvent) and water [29]. Other processes are based on hydrogen sulfide absorption in aqueous alkaline carbonate solutions, such as the Catacarb and Benfield systems (Eqs. 9.16 and 9.17). 

The process for CO absorption is the same as shown in Fig. 33.1. The only difference is that a potassium salt solution is used instead of the amine solution to absorb the COj from the hydrogen product. The potassium salt solution is called Catacarb, as shown in Fig. 33.2. 

The Catacarb process, which was disclosed by Eickmeyer (1962), is licensed by Eickmey-er and Associates of Prairie Village, Kansas. For most applications the Catacarb process utilizes a catalyzed hot potassium carbonate solution however, potassium borate solutions are used for the removal of hydrogen sulfide in the absence of carbon dioxide (Gangriwala and Chao, 1985). The solutions contain undisclosed additives that catalyze absorption and desorption of acid gases, particularly carbon dioxide. The additives, which include a corrosion inhibitor, are claimed to have no effect on reformer or methanation catalysts that the purified gas may pass through downstream of the Catacarb absorber (Morse, 1968). 

Figure 5-29. Effect of Catacarb catalyst concentration on relative solution activity for CO2 absorption. Activities are based on observed overall liquid film absorption coefficient [Eickmeyer, 1962j. Reprinted widi permission from Chemicai Engineering Progress, copyright 1962, American institute of Chemicai Engineering...

Comparative operating data for two plants using solutions with and without Catacarb catalyst are shown in Table 5-7 (Eickmeyer, 1962). Plant A operated at an absorption pressure of 360 psig with single stage, uncooled absorption. Plant B used split-stream absorption at 300 psig with cooling of the smaller liquid stream. For Runs 1 and 2 in Plant A these data show that catalyst addition resulted in increased capacity and appreciably lower steam consumption for the same treated gas carbon dioxide concentration. In Runs 3 and 4 in Plant A and in Runs 5 and 6 in Plant B, use of the catalyzed solution appreciably improved the treated gas purity and heat economy,... 

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