Production process of cocamidopropyl betaine (CAB-35)

Cocamidopropyl Betaine (CAB-35) is an amphoteric surfactant with excellent foaming, thickening, conditioning, gentle cleaning and other properties, widely used in personal care products such as shampoo, shower gel, hand sanitizer, and industrial cleaning agents. Its production process involves multiple steps such as raw material preparation, chemical synthesis, separation and purification, and finished product testing and packaging, each of which is critical.

Part I: Raw Material Preparation

1. Raw material selection

The key raw materials for the production of CAB-35 include:

Cocamide :
Cocamide is prepared by the reaction of fatty acids from coconut oil with ethanolamine, providing hydrophobic groups that give the product surface-active properties.

Fatty acid chains are typically C12-C14 in length, which is the main component of coconut oil and provides a moderate hydrophilic/hydrophobic balance.
The use of high-quality coconut oil raw materials can improve the purity of the product.

Aminopropylamine:**
This is the core part of the formation of zwitterionic in the CAB-35 structure, which provides a hydrophilic group for the betaine structure.
Chloroacetic Acid (Chloroacetic Acid) :**
It is used to react with amine compounds to form beet base groups.
Alkaline catalyst (e.g. sodium hydroxide NaOH) :**
It provides the alkaline environment required in the synthesis process, regulates the reaction speed and improves the generation efficiency.
Solvent (deionized water or other suitable solvent) :
A homogeneous reaction medium is provided so that the reactants can be well mixed.

2. Raw material handling

Before synthesis, all raw materials need to go through the following treatments:

Dehydration Treatment:
Moisture can affect the efficiency of subsequent reactions, so all liquid feedstocks, such as cocamide and propionic acid, need to be dehydrated, usually by vacuum dehydration or heated at low temperatures.
Purity Check:
Gas chromatography (GC) or liquid chromatography (HPLC) is used to test the purity of raw materials to ensure they meet production standards.
Dissolve Treatment:
Monochloroacetic acid and sodium hydroxide usually need to be pre-dissolved to ensure that they can be quickly dispersed during the reaction.

Part II: Main Synthesis Reactions

The synthesis of CAB-35 can be divided into two main steps: the reaction of cocamide with propionic acid, followed by the production process of betanitinization.

1. Reaction of cocamide with propionic acid

Chemical Reaction Principle:**
The carboxyl group (-COOH) in cocamide undergoes an amide reaction with the amino group (-NH2) of propionic acid to form cocamidopropylmine.

Chemical Equation:
[
RCOOH H_2NCH_2CH_2CH_2NH_2 \rightarrow RCONHCH_2CH_2CH_2NH_2 H_2O
]

Reaction conditions:

Temperature: 80-100°C.
pH: Maintain a weak alkaline (pH 8-9) to facilitate the reaction.
Catalysts: Alkaline catalysts such as sodium hydroxide or potassium carbonate can be selected to increase the reaction rate.

Operation process:

Cocamide and propionic acid are added to the reaction kettle in proportion.
Add an appropriate amount of solvent (such as deionized water) to improve the solubility of the reactants.
Heat and stir to maintain the reaction temperature, and the reaction time is 2-4 hours.
Infrared spectroscopy (FTIR) is used to detect the reaction process to ensure the formation of cocamidopropylmine.

2. Betanitinization reaction

Chemical Reaction Principle:**
Cocamidopropylamine reacts with monochloroacetic acid under alkaline conditions to form a betaine structure, i.e., cocamidopropyl betaine.

Chemical Equation:
[
RCONHCH_2CH_2CH_2NH_2 ClCH_2COOH NaOH \rightarrow RCONHCH_2CH_2CH_2N^ CH_2COO^- NaCl H_2O
]

Reaction conditions:

Temperature: 60-80°C.
pH: Maintains alkaline (pH 8-9).
Reaction time: 1-2 hours.

Operation process:

Cocamidopropylamine and dissolved monochloroacetic acid are added to the reactor.
Add an alkaline catalyst (e.g., sodium hydroxide) to adjust the pH.
Stir well, raise the temperature to 60-80°C and maintain the reaction time.
Monitor betaine production by liquid chromatography (HPLC).

Part III: Product Separation and Purification

1. Separation process

After the reaction is complete, the reaction may contain unreacted raw materials, by-products (e.g., sodium chloride), and solvent residues. Separation needs to be done with the following steps:

Filtration: Removes insoluble impurities and by-products.
Centrifugation: Use a high-speed centrifuge to remove tiny particles and impurities.
Washing: Wash the reaction solution with deionized water to further remove dissolved impurities.

2. Concentration process

A vacuum concentrator is used to concentrate the product solution to the target concentration (CAB-35 is typically 35% solids). The advantage of vacuum concentration is that it lowers the boiling point and avoids degradation of the product by high temperatures.

Part IV: Quality Control

Test Items

Appearance: The product should be a light yellow transparent liquid with no precipitation.
pH: 6-8 (meets the requirements for use).
Solids: 35% or so.
Impurity content: By-products such as sodium chloride should be below the specified range.
Purity Testing: Betaine purity is tested by HPLC or FTIR.

Quality Inspection Standards

Comply with ISO or industry standards.
Content and characteristics to meet customer needs.

Part V: Packaging & Storage

Put the qualified products into anti-corrosion plastic drums or stainless steel storage tanks, and store them in a cool, dry environment to avoid light and moisture.

Part 6: Environmental and Safety Considerations

Eco-friendly: CAB-35 is biodegradable and environmentally friendly.
Safety: During the production process, protective gear should be worn and direct contact with the skin and eyes should be avoided.

Product Isolation & Purification Section Detailed Extension

Specific removal method of impurities

Selection and accuracy of filter media:
In the production of CAB-35, incompletely reacted feedstocks (e.g., cocamide) and by-products (e.g., salt impurities) may be mixed into the reaction products. In order to improve product purity, it is critical to choose the right filter media.

Commonly used filter media:
- Polypropylene membrane filtration: Efficiently removes fine solid particles and insoluble impurities from solution with filtration ratings ranging from 0.2–5 microns.
- Activated Carbon Filtration: Removes organic impurities and odors from the solution for high purity requirements.
- Diatomaceous earth filtration: Suitable for the initial filtration stage with a large number of impurities, the filtration accuracy is low.
Selection of filtration accuracy: **
- In the coarse filtration stage, a filter medium of 10–50 microns can be used to remove large impurities; In the fine filtration stage, a 0.2–1 micron medium is used to ensure that the solution is pure.

Washing times and the impact of detergent:

Number of washes:**
Some of the reaction catalyst and by-products may remain in the reaction product after the reaction, and these impurities can be significantly reduced by multiple washes. Experiments have shown that it usually takes 3–5 washes to reduce the residual salt impurities in the product to less than 0.01%.
Detergent type:**
- Deionized water: It is often used to dissolve salt impurities and avoid sodium and chloride residues.
- Dilute acids (e.g. dilute hydrochloric acid): Good removal effect on metal ion impurities.
- Ethanol or isopropanol: Effectively removes organic impurities while speeding up the drying process of the product.
Optimization method: Select the appropriate detergent according to the characteristics of the reaction products. For example, for oily residues, dilute ethanol is best mixed with deionized water in a 1:2 ratio.

Possible degradation problems during concentration

Thermal decomposition phenomenon in vacuum concentration:**

Causes of thermal decomposition phenomenon:**
During the vacuum concentration process, the backbone of CAB-35 may be partially broken due to high temperature conditions, resulting in abnormal molecular weight distribution and reduced performance of the product.
Common presentations:
- Color change: The product may change from pale yellow to dark brown.
- Decreased activity: Significant reduction in surface activity, especially foaming ability.

Ways to avoid thermal decomposition:

Temperature control:
The concentration temperature is controlled in the range of 60–80°C, and the pressure is gradually reduced at this temperature to avoid local high temperatures.
Vacuum System Optimization:
A multi-stage vacuum pump is used to achieve smoother pressure control and prevent the solvent from evaporating too quickly and causing an instantaneous increase in temperature.
Add stabilizer:**
The addition of antioxidants (e.g., vitamin E) and heat stabilizers (e.g., phosphate esters) prior to concentration can effectively slow down the thermal decomposition process.

Quality inspection section is extended in detail

Comparison of multiple detection methods

Infrared Spectroscopy (FTIR) :*

Use:
It is used to verify the presence of amine, carboxyl and betane groups in the CAB-35 molecule.
Method features:
- Quickly detect how well the reaction is complete.
- Ability to distinguish the main groups in the product, but not to accurately determine the molecular weight.

Nuclear Magnetic Resonance (NMR) :*

Use:
Accurately elucidate the molecular structure of CAB-35 and confirm the chemical environment of the main and side chains.
Pros:
- Qualitative and quantitative performance to analyze the proportion of impurities.
Cons:
- Complex operation and expensive instrumentation required.

Liquid chromatography-mass spectrometry (LC-MS) :**

Use:
Accurately detect the molecular weight distribution of CAB-35 and its polymerization range.
Features:
- High sensitivity for the separation and analysis of complex mixtures.
- Can be used to monitor by-product and residue levels.

Gas chromatography-mass spectrometry (GC-MS) :*

Use:
Analyze products for low-boiling impurities or unreacted raw materials.
Features:
- Suitable for the detection of volatile and semi-volatile components.

Quality Control Standardization Process

ISO 9001 Quality Management System:

Raw material acceptance criteria:**
- All raw materials (cocamide, chloroacetic acid, betaine, etc.) are tested for purity, water content and impurity content at the time of storage.
- The purity standard is generally required to be above 98% and the moisture content is less than 0.5%.

Production process control:

Key parameter monitoring:
- Real-time monitoring of temperature, pressure and pH in the reactor to ensure the stability of reaction conditions through in-line sensors.
Semi-finished product inspection:**
- Rapid analysis of the integrity of the main functional groups in semi-finished products using infrared spectroscopy to ensure adequate reactions.

Finished product testing:**

Appearance:
- The finished product should be a light yellow to colorless transparent liquid, with no obvious mechanical impurities or suspended particles.
Content determination:
- The active content of betaine should be higher than 35% and the chloride ion content should be less than 0.1%.
Foam performance test:**
- Test the foaming height and foam stability of the product at a certain concentration, the foam height is generally not less than 80mm, and the stability is not less than 90%.

Packaging & Storage Testing:**

Packaging Integrity:
- The product should be sealed in a high-density polyethylene drum to prevent moisture or air from entering.
Storage Environment:
- The product should be stored in a dry, cool place, away from high temperatures and direct sunlight.