Electro-chemical pH Sensor with Redox Copolymer
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Solution Overview
Problem
Existing electro-chemical sensors for downhole fluid analysis, particularly for pH measurement, are prone to instability and require frequent recalibration due to extreme conditions such as high temperatures and pressures, and are not suitable for measuring in oil-water mixtures.
Innovation Solution
An electro-chemical pH sensor comprising a copolymer of redox systems with peak redox reaction potentials sensitive and insensitive to pH, covalently bound to an organic polymer, which provides stability and eliminates the need for temperature calibration, using anthracene and ferrocene derivatives as pH-active and pH-inactive redox systems respectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional electro-chemical sensors are used for pH measurement in downhole conditions, then pH measurement capability is achieved, but sensor stability and reliability deteriorate due to extreme temperatures and pressures
Solution Approach 1:
The patent changes the chemical parameters of the sensor by using redox-active polymers with specific redox potentials that are insensitive to pH changes, while the reference electrode potential changes with pH. This parameter change allows the sensor to maintain reliability under extreme conditions while achieving accurate pH measurement through the potential difference between the indicator and reference electrodes.
Solution Approach 2:
The patent employs composite materials by combining redox-active polymer films (such as polyvinylferrocene or polyanthraquinone sulfonic acid) with conductive support matrices. This composite structure provides both the pH-sensitive response and the structural stability needed for reliable operation in high-temperature and high-pressure downhole environments.
2Reliability
If conventional pH sensors are deployed in downhole environments, then pH data acquisition is enabled, but measurement precision deteriorates due to temperature effects requiring constant recalibration
Solution Approach 1:
The sensor performs self-calibration by using the internal reference electrode potential as a built-in reference that automatically compensates for temperature effects. The system serves itself by measuring the potential difference between the pH-sensitive indicator electrode and the reference electrode, eliminating the need for external recalibration while maintaining measurement precision across varying temperatures.
Solution Approach 2:
The patent exploits the temperature dependence of redox potentials to create a compensation mechanism. By selecting redox systems with known and stable temperature coefficients, the sensor can distinguish between potential changes caused by pH variations and those caused by temperature changes, maintaining measurement precision without constant recalibration.
3Measurement precision
If glass electrodes are used for pH sensing, then selectivity towards pH is improved, but device complexity and maintenance requirements increase due to constant recalibration needs
Solution Approach 1:
The patent extracts the reference electrode function from a separate component and integrates it directly into the sensor film structure through the redox-active polymer. This extraction and integration simplifies the device by eliminating the need for separate reference electrode assemblies and their associated calibration procedures, while maintaining pH selectivity through the potential difference measurement approach.
Solution Approach 2:
The integrated reference electrode within the redox-active polymer film provides automatic self-calibration by serving as an internal reference that compensates for environmental variations. This self-service capability eliminates the need for external calibration equipment and procedures, reducing device complexity while maintaining measurement accuracy.
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
The sensor achieves enhanced robustness and stability, maintaining accuracy over time and across varying conditions, with results consistent with the Nernst equation, and can function as a dual pH/sulfide sensor without requiring temperature calibration.
Implementation Method 1
a monomer comprising a redox system having a peak redox reaction potential which is sensitive to pH (i.e. proton concentration)
Implementation Method 2
a second monomer comprising another redox system with a different structure to the first redox system and having a peak redox reaction potential which is essentially insensitive to pH
Implementation Method 3
with results consistent with the Nernst equation
Data Source
Figure 1~2B
Figure 3A~4B
Figure 5A~5B
AI summary
An electro-chemical sensor is described having two molecular redox systems one being sensitive the other insensitive to the species to be detected and both being covalently bound to a polymer and having a detector to detect relative shifts in the voltammograms of the two redox systems.