Convex bent ramp

One of the predictions to emerge from the model is that improved Cr(VI) conversion should result from a "convex bent ramp," usually represented as just a "bent ramp." The object is to accelerate the heat-up process while the temperatures are low, because the Cr(VI) is least sensitive to water vapor in this temperature range. Then, at high temperatures when the sensitivity is greatest, the heat-up rate is slowed so that water is not released as fast. Thus, the catalyst is exposed to a lower water vapor concentration during the most critical period, and the conversion to Cr(VI) is consequently improved. The result is improved conversion to Cr(VI) with no loss in heat-up time, compared with the standard linear thermal ramp. 

Each of the three ramp profiles took the same time to reach 800 °C, but there was a major difference in the conversion to Cr(VI). The "convex bent ramp" led to the release of water vapor slowly as the highest temperature was reached, which produced higher Cr(VI) levels. The improvement in conversion resulting from the "convex bent ramp" has been confirmed in commercial operations in many manufacturing plants where it has now been adopted. 

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