Ron R Chevalier

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  • Topic: Alkylation, Acid, Alkene
  • Pages : 13 (3892 words )
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  • Published : December 13, 2012
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ACID CONSUMPTION AND ACID RUNAWAY IN A SULFURIC ACID ALKYLATION UNIT Presented By Sarah Hoelzle Process Engineer

DuPont™ STRATCO® Clean Fuel Technologies 11350 Tomahawk Creek Parkway Suite 200 Leawood, KS 66211

September 2007

Copyright 2007 DuPont™ STRATCO® Clean Fuel Technologies

Table of Contents

Page Number I. ACID CONSUMPTION FUNDAMENTALS.....................................................................1 Figure 1 - Diluent Production vs. Acid Strength- 40/60 C3=/C4= .........................................2 II. MINIMUM ACID CONSUMPTION ...................................................................................2 Figure 2 - Acid Consumption vs. Spending Strength - 40/60 C3=/C4= ..................................3 Figure 3 - Acid Consumption vs. Spending Strength – Butlyene Feed .................................3 Figure 4 - Acid Consumption vs. Spending Strength – Butlyene Feed .................................4 Figure 5 - Acid Consumption vs. Spending Strength –C5= Feed ..........................................4 Figure 6 - Acid Consumption vs. Spending Strength – 80/20 C3=/C4= .................................5 Figure 7 - Relative Acid Consumption in Different Stages – 80/20 C3=/C4= ........................5 Figure 8 - Acid Consumption vs. Spending Strength – Separate Processing .......................6 Table 1 - Stage Consumption from Operating Data 40/60 C3=/C4= .....................................6 III. OPTIMUM SPENDING STRENGTH .................................................................................7 Table 2 - Acid Consumption and True Alkylate Properties versus Spending Strength ...........................................................................................................................8 IV. V. VI. ACID RUNAWAY RECOGNITION ...................................................................................8 ACID RUNAWAY RESPONSE ..........................................................................................9 HANDLING OF RUNAWAY ACID .................................................................................10

Acid Consumption and Acid Runaway in a Sulfuric Acid Alkylation Unit

Page 1

ACID CONSUMPTION AND ACID RUNAWAY IN A SULFURIC ACID ALKYLATION UNIT DuPont is frequently asked what can be done to lower an alkylation unit’s fresh acid consumption. Literature on alkylation implies that lowering the target spending strength is one way to lower acid consumption. The same literature may mention the risk of acid runaway if the spending strength is too low. Acid runaway can be described as very high acid consumption that occurs if the acid strength gets too low. How are these two statements reconciled? What is the optimum spending strength for your alkylation unit? In this paper, acid consumption will be shown to reach a minimum as a function of spending strength. Reducing acid consumption by lowering spending strength is only effective above the minimum acid consumption strength. Near the minimum, acid consumption is insensitive to changes in spending strength. At spending strengths below the minimum, acid consumption is higher. Acid runaway is an extrapolation of that trend. At some lower than normal acid strength, acid consumption exceeds the hydraulic capacity of the acid delivery system. Acid strength then drops uncontrollably or “runs away”. There is also a perception that the type of olefin feed (propylene, butylene, amylene) determines the optimum spending strength and strength at which an acid runaway begins. It will be shown that the type of olefin feed does have an impact on the optimum and acid runaway strength but only in context with operating conditions and the hydraulic capacity of the acid delivery system. I. ACID CONSUMPTION FUNDAMENTALS

The alkylation reaction can be considered as occurring in three steps: First the olefin absorbs into the acid forming an alkyl sulfate or cation intermediate (olefin absorption). Second,...
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