Methanol Weekly Topic: What are the quality issues with pure methanol? 2016.04.10---2016.04.17
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Methanol Weekly Topic: What are the common quality issues associated with pure methanol products? How to sort it out? 2016.04.10---2016.04.17 What are the common quality issues associated with pure methanol products? How to handle it? Answer: Common quality issues with pure methanol products include: 1) Water solubility: The product becomes turbid when water is added to it. 2) Stability: The product was tested for oxidation using prepared potassium permanganate, and it changed color before the time specified by the standards. 3) Moisture: The moisture content in the methanol product is above the specified limit. 4) Color: Compared with distilled water, pure methanol has a slightly rusty color. 5) Additionally, the pure methanol in some diol plants has a high alkalinity and a fishy odor. This is caused by the formation of methylamine from ammonia and methanol in the feed gas. Water solubility is also known as turbidity. When pure methanol contains organic impurities that are insoluble or poorly soluble in water, upon adding water, these impurities precipitate as gel-like particles, resulting in turbidity. 1) Water extraction distillation in the pre-tower is the best method for removing these impurities; the amount of water added generally should not exceed 20% of the feed volume. Adding more water certainly helps to remove organic impurities, but it reduces the production capacity of the pre-tower, so it must be done in an appropriate manner. 2) The control of the pre-tower top temperature also has a significant impact on the water solubility of the product; it is generally maintained at 30–40°C. As the catalyst in the synthesis tower is used for an extended period, the top temperature of the tower also needs to be adjusted accordingly. 3) Properly control the operation of the main tower; based on the results of sampling and analysis, it is necessary to continue removing fusel oils, thereby preventing them from ending up in the product and affecting its clarity.
Common quality issues of pure methanol products include: 1) Water solubility: Pure methanol products become cloudy when water is added to them. 2) Stability: The product was tested for oxidation using prepared potassium permanganate, and it changed color before the time specified by the standards. 3) Moisture: The moisture content in the methanol product is above the specified limit. 4) Color: Compared with distilled water, pure methanol has a slightly rusty color.
The refined methanol product becomes cloudy after adding water. Stability: The product was tested for oxidation using prepared potassium permanganate, and it changed color before the time specified by the standards. Moisture: The moisture content in the methanol product is above the specified limit. Color: Compared with distilled water, pure methanol has a slightly rusty color. Furthermore, the refined methanol in some diol production units has a high alkalinity
1) Water solubility: Precise methanol becomes turbid when mixed with water. 2) Stability: The potassium permanganate oxidation value of the pure methanol product decreases too rapidly over time. 3) Moisture: The moisture content in the pure methanol product is above the specified limit. 4) Chroma: Pure methanol has a slightly rusty color when compared to distilled water; this may be due to crude methanol as the raw material or inadequate cleaning of the distillation equipment. 5) High alkalinity may be due to the presence of ammonia in the feed gas (especially in glycol production)
Common quality issues of pure methanol products include effects related to water solubility, moisture content, color, and stability (K value). Regarding water solubility: 1. The pre-distillation tower primarily removes methanol oil through water-assisted extraction distillation. The process of water-assisted extraction distillation involves adding extraction water to form an azeotrope with methanol; the impurities whose boiling point is lower than that of methanol in this azeotrope are separated and removed. Care should be taken to control the amount of extraction water added, which generally should not exceed 20% of the feed amount. An increased amount of water used for extraction will increase the load on the main distillation tower and simultaneously raise steam consumption. The control of the overhead vent temperature in the pre-distillation tower also has a significant impact on the water solubility of the product. The vent temperature is controlled too low, causing the low-boiling compounds to be re-condensed and enter the reflux stream, which in turn makes its way into the main distillation tower; this ultimately results in the finished alcohol having unacceptable water solubility levels. We control the vent temperature of the pre-distillation column between 45–60°C, which is favorable for the removal of low-boiling compounds. 2. During the operation of the main distillation column, it is necessary to strictly control various operating conditions within the column, especially the temperature of the sensitive plates in the distillation section, in order to prevent the upward movement of heavier components. In the stripping section, it is necessary to maintain an appropriate amount of extraction of the heavy components—fusel oils, through side extraction. That is, the fusel oil is extracted to the oil-water tank at an appropriate plate side in the stripping section, which greatly helps to improve water solubility. Regarding moisture: the standard for premium-grade moisture in spirit products is less than 0.1%. Excessive moisture is mainly caused by the upward movement of heavy components. In practical operation, this is manifested as a low reflux ratio, or it occurs when changes in utility services (water, steam) disrupt the temperature and pressure equilibrium within the tower. At this point, the reflux ratio should be increased, and the temperature of the sensitive plate in the distillation section must be well controlled. Damage to the internals of the main distillation tower and a reduced separation efficiency can also lead to an increase in the moisture content of the product; in such cases, the only remedy is to increase the reflux ratio. Regarding chroma: The chroma test involves comparing the pure methanol product with distilled water; it is considered satisfactory if no slight rustish color is observed. The chroma index is ≤5# (platinum-cobalt). The formation of chroma is generally caused by poor quality of the crude methanol feedstock or inadequate cleaning of the distillation column equipment. The chromatic difference is generally caused by trace catalysts brought in by the crude methanol feedstock. This portion of impurities accumulates at the bottom of the main tower and is removed along with the residual liquid at the tower bottom. When the process conditions change, such as variations in the temperature and pressure inside the tower or the reflux ratio, the heavier components rise to the top of the main tower, and these impurities move upward along with them. Handling this situation is quite challenging; it is more difficult than dealing with water-soluble substances or moisture, and in severe cases, normal operation cannot be restored for one or two days. Even when increasing the reflux ratio or going to full reflux, if it still cannot be eliminated, the only solution is to shut down the column. After draining all the liquid inside the tower, wash the distillation tower with hot water; drain the liquid from the bottom and sides of the tower until the color of the discharged water meets the specified standards. After the distillation tower is cleaned, the next round of operation is carried out, ensuring that the color of the pure alcohol product meets the specified requirements for a certain period of time. Regarding stability (K value): By adding extraction water to the reflux collection tank of the pre-distillation column, the oil and water in the reflux liquid are separated through extraction. Observation through the sight glass of the pre-distillation column reflux collection tank revealed that the upper layer consisted of methanol oil and water; if this methanol oil and water cannot be properly removed, it will affect the stability of the refined alcohol product. A row of oil pipes is installed on the side of the sight glass in the pre-distillation column reflux collection tank to drain the oil and water from the upper layer into the oil-water collection tank. Oil drainage must be carried out consistently over the long term; otherwise, it will inevitably affect the stability of the product. When the K value in the product is low, the reflux ratio of the main distillation column can be appropriately increased to reduce the yield. However, if the reflux ratio is increased excessively, causing the light components to move downward, this can sometimes affect the oxidizing property of the pure methanol, as the number of trays above the pure methanol extraction point is no longer sufficient to remove the remaining light components. An appropriate initial fraction can be extracted from the reflux liquid, which effectively improves the stability of purified methanol.
What are the common quality issues associated with pure methanol products? ⑴. Water solubility: The pure methanol product becomes turbid when water is added to it. ⑵. Stability: When a test for oxidizing properties was conducted using prepared potassium permanganate on the pure methanol product, it changed color before reaching the time specified in the standards. ⑶. Moisture: The moisture content in the pure methanol product is above the specified limit. ⑷. Color: The pure methanol product has a slight rusty color when compared to distilled water, which is due to unclean raw methanol material or purification equipment
⑴. Water solubility: The pure methanol product becomes turbid when water is added to it. ⑵. Stability: When a test for oxidizing properties was conducted using prepared potassium permanganate on the pure methanol product, it changed color before reaching the time specified in the standards. ⑶. Moisture: The moisture content in the pure methanol product is above the specified limit. ⑷. Color: The pure methanol product has a slight rusty color when compared to distilled water; this is due to impurities in the crude methanol raw material or to inadequate cleaning of the distillation equipment. (5) Alkalinity: The pure methanol product has a high alkalinity level and exhibits a fishy odor. This is caused by the formation of methylamines (especially dimethylamine and trimethylamine) from ammonia and methanol in the feed gas.
⑴. Water solubility: The pure methanol product becomes turbid when water is added to it. ⑵. Stability: When a test for oxidizing properties was conducted using prepared potassium permanganate on the pure methanol product, it changed color before reaching the time specified in the standards. ⑶. Moisture: The moisture content in the pure methanol product is above the specified limit. ⑷. Color: The pure methanol product has a slight rusty color when compared to distilled water, which is due to unclean raw methanol material or purification equipment
1) Water solubility: The neat methanol product becomes turbid when water is added. (2) Stability: A test was conducted using the prepared potassium permanganate to determine the oxidation value; discoloration occurred before the time specified by the standards. (3) Moisture: The moisture content in the pure methanol product is above the specified limit. (4) Chroma: The refined methanol product appears slightly rusty when compared to distilled water, which is due to the equipment not being cleaned properly. (5) High alkalinity may be caused by the presence of ammonia in the feed gas (especially in glycol production)
Are there any other issues besides the four common ones?
What are the issues in the production process of high-purity methanol reagents?