Starch Slurry pH Control for Propylene Chlorohydrin Reduction
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Solution Overview
Problem
The standard process for producing hydroxypropylated/crosslinked starch generates excessive propylene chlorohydrin (PCH) byproducts, exceeding regulatory limits, and requires extensive washing that leads to starch loss and increased wastewater, while existing methods to reduce PCH either fail at commercial scales or strip the crosslinking from the starch.
Innovation Solution
A method involving adjusting the pH of the hydroxypropylated or hydroxypropylated/crosslinked starch slurry to between 9 and 10.4, followed by washing and neutralization, to minimize PCH levels below 1 ppm without stripping the crosslinking, using a process that includes adding an acid to reduce the pH of the slurry, washing, and further neutralizing to reduce water usage and maintain starch stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If extensive washing is performed to remove PCH, then PCH levels are reduced, but starch loss and wastewater increase
Solution Approach 1:
The patent changes the pH parameter of the slurry from high pH (>11) to intermediate pH (9-10.4) to alter the chemical environment. This parameter change enables PCH removal through washing at intermediate pH without requiring extensive washing, thereby reducing starch loss while achieving regulatory compliance for PCH levels.
2Object-affected harmful factors
If high pH aeration is used to reduce PCH, then PCH levels decrease, but crosslinking is stripped from the starch
Solution Approach 1:
The patent changes the pH parameter from high pH (>11) to intermediate pH (9-10.4). This intermediate pH is sufficiently alkaline to enable PCH removal but not so high as to cause crosslink stripping. The controlled pH parameter change resolves the contradiction by finding the optimal balance point where PCH can be removed without compromising crosslinking stability.
3Object-affected harmful factors
If prolonged aeration is performed to reduce PCH at commercial scale, then PCH levels decrease, but processing time becomes impracticable
Solution Approach 1:
The patent changes the pH parameter to intermediate pH (9-10.4) before washing, which fundamentally alters the removal kinetics of PCH. This parameter change enables rapid PCH removal during washing without requiring prolonged aeration or holding times, making the process practical for commercial-scale production while achieving regulatory compliance.
4Object-affected harmful factors
If extensive washing is performed to remove PCH, then PCH levels are reduced, but wastewater volume increases
Solution Approach 1:
The patent changes the washing pH from high pH to intermediate pH (9-10.4). This parameter change enables effective PCH removal with reduced water consumption, thereby reducing wastewater volume while still achieving regulatory compliance for PCH levels in the final product.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This method effectively reduces PCH levels to below 1 ppm, minimizes crosslink stripping, and maintains viscosity stability, achieving compliance with regulatory standards while reducing water usage and starch loss.
Implementation Method 1
adding an acid to a slurry comprising a hydroxyproplyated or hydroxypropylated/crosslinked starch having pH greater than 11 to reduce the pH of the slurry to between 9 and 10.4
Implementation Method 2
washing the slurry
Implementation Method 3
neutralizing the washed slurry with acid to further reduce the pH of the slurry to less than 7.5
Data Source
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AI summary
A method of reducing the amount propylene chlorohydrin produced in a reaction to make a hydroxypropylated/crosslinked starch comprising removing residual propylene oxide from alkaline slurry. The residual propylene oxide is removed by the dewatering the alkaline slurry or by washing the starch in slurry at a pH of around 10. The starch is then neutralized in an acid solution and recovered from the second slurry and may or may not be washed, depending on whether the slurry while at pH around 10 to make a hydroxypropylated/crosslinked starch having less than 1 ppm propylene chlorohydrin.