In the production process of the chemical industry, alkaline solutions (such as sodium hydroxide and potassium hydroxide solutions) serve as core raw materials or process media, and their concentration stability directly affects product quality, reaction efficiency, and production safety. The refractive index based online alkali concentration meter, based on the critical angle refraction principle of borrowed light, has become the mainstream solution for monitoring alkali concentration in the chemical industry with technical advantages such as high accuracy, real-time response, and strong anti-interference. It is widely suitable for multi scene process needs such as chlor alkali production, fine chemical industry, and wastewater treatment, and provides key data support for production automation control. Here is a detailed introduction:

1、 Core application scenarios and technological adaptability

（1） Chlor alkali industry: concentration monitoring of the entire process of caustic soda production

The chlor alkali industry, as a fundamental chemical industry, directly determines the energy consumption and product purity of subsequent evaporation and solid alkali manufacturing in the production of caustic soda using ion membrane and diaphragm methods. The concentration of caustic soda at the outlet of the electrolytic cell (usually controlled at 30% -50% NaOH) is crucial. Traditional manual sampling titration has hysteresis (a single measurement takes 5-10 minutes), which can easily lead to concentration fluctuations exceeding the process threshold and increase the risk of equipment corrosion. The refractive index online alkali concentration meter is installed through a pipeline to capture the concentration changes at the outlet of the electrolytic cell and the inlet and outlet of the evaporator in real time. The response speed is less than 1 second, and the measurement accuracy reaches ± 0.05%. Combined with a multi-point temperature compensation algorithm (suitable for process temperatures of 5-100 ℃), it can accurately correct the influence of temperature on concentration measurement. The 4-20mA signal output by the instrument is directly connected to the DCS system to achieve automatic adjustment of caustic soda concentration, controlling the concentration fluctuation range within ± 0.1%, reducing energy consumption in the evaporation process by 10% -15%, and reducing safety hazards caused by manual sampling.

（2） Fine Chemicals: Reaction Process and Concentration Control of Raw Material Preparation

In the field of fine chemicals (such as synthetic detergents, pharmaceutical intermediates, and coating additives), alkaline solution is used as a neutralizing agent, catalyst, or raw material, and its concentration accuracy directly affects the reaction conversion rate and product performance. For example, in the synthesis process of sodium fatty acid, the concentration of NaOH needs to be strictly controlled at 25% -30%. If the concentration is too high, it can easily lead to the formation of side reactions, while if it is too low, the reaction will be insufficient. The refractive index online alkali concentration meter can be installed at the raw material preparation tank, reaction kettle inlet and outlet to monitor in real-time whether the alkali concentration meets the process set value. Its sapphire prism (9 Mohs hardness) is resistant to strong alkali corrosion and is not affected by solution color, turbidity, or trace solid particles. Even in systems containing small amounts of catalyst impurities, it can maintain stable measurement. By linking with the PLC system, when the concentration deviates from the threshold, the raw material replenishment or dilution process is automatically triggered, which increases the reaction conversion rate by 3% -5% and the product qualification rate from 95% to over 99%.

（3） Chemical wastewater treatment: precise control of alkali solution addition

In the treatment of wastewater in chemical enterprises, NaOH and KOH solutions are often added to adjust the pH value (usually controlled at 6-9), or used for chemical precipitation treatment of wastewater containing heavy metal ions. Traditional manual adjustment relies on experience to determine the dosage, which can easily lead to excessive alkaline solution causing the pH of the effluent to exceed the standard, or insufficient dosage failing to achieve the treatment effect. This not only increases the cost of chemical consumption, but also may cause environmental compliance risks. The refractive index online alkali concentration meter is installed in the wastewater treatment tank feeding pipeline to monitor the concentration of alkali solution (0-20% NaOH/KOH) in real time. Combined with water quality pH sensor data, the dosage is automatically calculated through the DCS system to achieve closed-loop control of alkali solution feeding. Practice has shown that this scheme can reduce alkali consumption by 8% -12%, stabilize the effluent pH compliance rate at over 98%, reduce sludge production, and lower subsequent sludge treatment costs.

（4） New Energy Chemical Industry: Real time Monitoring of Electrolyte Concentration

In the field of new energy chemical industry such as hydrogen production through electrolysis of water and production of lithium battery materials, alkaline solution (such as 30% -40% KOH solution) is used as the electrolyte, and its concentration stability directly affects the electrolysis efficiency and product performance. For example, in the process of electrolyzing water to produce hydrogen, a low concentration of KOH can lead to an increase in the internal resistance of the electrolytic cell and an increase in energy consumption; If the concentration is too high, it is easy to crystallize and block the pipeline. The refractive index online alkali concentration meter, with its wide range measurement capability (0-50% KOH) and high stability (light source life>100000 hours), can adapt to the concentration monitoring needs of electrolytic cell inlet and outlet and circulation pipelines. Its explosion-proof design (Ex d IIC T6Gb) meets the safety requirements of new energy chemical workshops, and real-time monitoring data helps operators optimize electrolysis process parameters, reducing hydrogen production energy consumption by 5% -8% and extending the operating life of electrolysis cells by 1-2 years.

2、 Core values applied in the chemical industry

The application of refractive index online alkali concentration meter in the chemical industry has solved the pain points of traditional monitoring methods (manual titration, specific gravity method) such as "lag, large error, and complex maintenance". Its value is mainly reflected in three aspects: firstly, it realizes real-time concentration monitoring and automatic control, reduces human intervention, and improves production process stability; The second is to reduce drug consumption, energy consumption, and labor costs, helping enterprises achieve cost reduction and efficiency improvement; The third is to avoid risks such as equipment corrosion and product scrapping caused by abnormal concentration through precise monitoring, ensuring production safety and environmental compliance.

3、 Key points of application selection

The working conditions in the chemical industry are complex (high temperature, high pressure, strong corrosion, explosion-proof requirements), and when selecting, special attention should be paid to: medium adaptability (clearly measuring NaOH, KOH or mixed alkali solutions, matching exclusive calibration curves), range range (selecting corresponding ranges such as 0-30% and 0-55% according to process requirements), protection and explosion-proof level (IP68 sensors are preferred for corrosive environments, and explosion-proof areas must comply with Ex d IIC T6Gb standards), installation method (pipeline type adaptation to continuous processes, flow pool type adaptation to high viscosity or alkali solutions containing small amounts of impurities), and at the same time, it is necessary to confirm that the signal output types supported by the instrument (4-20mA, RS485) are compatible with existing control systems.

Summary: The refractive index online alkali concentration meter has become a key equipment for achieving refined production and green development in the chemical industry through technological innovation and deep adaptation to different scenarios. It helps enterprises improve market competitiveness while ensuring product quality and production safety.