Glycerin is a valuable product that can be obtained from natural or synthetic sources. Natural glycerin is produced as a by-product of soap production or biodiesel production, while synthetic glycerin is produced from petroleum or sugar. The production of glycerin involves different steps depending on the source and the desired purity. Some of the common steps are:

- Transesterification: This is the process of converting vegetable oils or animal fats into fatty acid methyl esters (FAME) and glycerol. This is the main source of natural glycerin from biodiesel production.

- Saponification: This is the process of reacting fats or oils with a strong base such as sodium hydroxide or potassium hydroxide to produce soap and glycerol. This is the main source of natural glycerin from soap production.

- Hydrolysis: This is the process of breaking down fats or oils with water and heat to produce fatty acids and glycerol. This is an alternative method of producing natural glycerin from fats or oils.

- Hydrogenolysis: This is the process of converting sugars into glycerol and other products by using hydrogen and a catalyst. This is one of the methods of producing synthetic glycerol from sugar.

- Chlorination: This is the process of reacting propylene with chlorine to produce allyl chloride, which is then hydrolyzed to produce glycerol and hydrochloric acid. This is one of the methods of producing synthetic glycerol from petroleum.

After these steps, the crude glycerol obtained contains water and other impurities such as salts, methanol, soap, fatty acids, etc. The crude glycerol needs to be purified further to obtain refined glycerol with a high concentration and quality. The purification steps may include:

- Neutralization: This is the process of removing excess alkali or acid from the crude glycerol by adding an acid or a base respectively. This also helps to separate soap and fatty acids from the glycerol phase.

- Settling: This is the process of allowing the crude glycerol to settle in a tank or a vessel for some time so that the heavier impurities can sink to the bottom and the lighter impurities can rise to the top. The middle layer containing glycerol can then be separated from the top and bottom layers.

- Filtration: This is the process of passing the crude glycerol through a filter or a membrane to remove solid particles such as salts, dirt, etc.

- Evaporation: This is the process of heating the crude glycerol under a vacuum to remove water and other volatile impurities such as methanol, acetone, etc. This also helps to increase the concentration of glycerol in the solution.

- Distillation: This is the process of separating glycerol from other non-volatile impurities such as organic acids, aldehydes, ketones, etc. by using different boiling points. This also helps to further increase the concentration and purity of glycerol in the solution.

- Ion exchange: This is the process of passing the crude glycerol through a resin that can exchange ions with the impurities in the solution. This helps to remove ionic impurities such as chlorides, sulfates, nitrates, etc.

- Bleaching: This is the process of adding a bleaching agent such as activated carbon or hydrogen peroxide to the crude glycerol to remove color and odor-causing impurities such as phenols, aldehydes, ketones, etc.

The final product obtained after these purification steps is refined glycerol with a concentration above 99%. However, depending on the application and specification, different grades of refined glycerol may be required. For example, pharmaceutical grade glycerol requires a concentration above 99.5% and a very low level of impurities such as heavy metals, chlorides, sulfates, etc.

The question asked in this request is about why after treatment of different steps and selection of different CG (glyceryl acrylate/acrylic acid copolymer), concentration of glycerin is not rising above from 98.5%. CG is a product that contains glycerin, water, propylene glycol and other ingredients that are used for personal care applications such as moisturizers, lotions, gels, etc. CG has a lower concentration of glycerin than refined glycerol because it contains other components that dilute it. Therefore, even after treating it with different steps such as neutralization, filtration, evaporation, etc.