[Physical and chemical properties] Morpholine is also known as morpholine; p-oxoazido has been ring; 1,4-oxoazido hexacyclic. Colorless absorbent oily liquid. Relative density 1.0005, melting point -4.76℃, boiling point 128.3℃, flash point 37.6℃(open cup), vapor pressure 879.9Pa, auto-ignition temperature 310℃, dipole distance 1.58, viscosity 0.00223Pa-s(20℃), surface tension 0.0375N/m(20℃), explosion limit 1.4%~11.20%, refractive index 1.4540(20℃).

Ammonia odor, strong alkaline, soluble in water and most organic solvents, can evaporate with water vapor, and form azeotropic mixture with water, can be decomposed by high heat to produce CO, CO2, NOx and ammonia toxic fumes. Keep in a cool, dry and ventilated place. Protect from sunlight and moisture, and keep away from fire and heat source. It should not be stored in large quantities or for a long time, and should be stored separately from oxidizing agents. Packed tightly in glass bottles or ceramic jars with wooden barrels. When handling, lightly load and unload to avoid package breakage. Store and transport according to the regulations of toxic chemicals.

[At present, the main methods of producing morpholine are diethylene glycol (DEG) catalyzed ammonia cyclization and diethanolamine (DEA) strong acid dehydration cyclization. Among them, diethylene glycol-catalyzed aminolysis cyclization is the main synthetic method used at home and abroad.

(1) Diethanolamine (DEA) strong acid dehydration cyclization method

The mixture of 95% sulfuric acid and diethanolamine solution is mixed in a certain ratio, and the mixture is heated at 160°C for a certain period of time, neutralized with a quantitative concentrated sodium hydroxide solution after cooling, and the sodium sulfate is removed by filtration, and the aqueous morpholine solution is obtained by distillation and fractionation, and then the morpholine with 97% content is obtained by distillation. 1889 morpholine was discovered by heating diethanolamine in concentrated hydrochloric acid to above 1500°C. Later, concentrated sulfuric acid was found to be more effective as a dehydrating agent, and the method was once used on a large scale in industry. At present, this method is still used by Dow Chemical Company and Union Carbide Company in the United States, Osaka Organic Chemical Company in Japan, and Shenyang New Life Chemical Plant and Shanghai Changjiang Chemical Plant in China.

Diethanolamine strong acid dehydration method for the production of morpholine has many defects, mainly: First, the price of diethanolamine is high; Second, the quality of the product is not up for a long time, hovering at the content of 95% to 97%, limiting the widespread use of morpholine products; Third, due to the production process using strong acid, alkali media, resulting in serious corrosion of equipment, equipment maintenance costs are high; Fourth, environmental pollution is heavy. Therefore the process is now rarely used.

(2) Diethylene glycol (DEG) method

Diethylene glycol (DEG) method is to diethylene glycol and hydrogen as raw materials in the role of hydrogenation catalyst, at a certain temperature and pressure range, with liquid ammonia or ammonia, while completing the role of ammonolysis and cyclization reaction and the production of morpholine. According to the different reaction pressure, it can be divided into high-pressure liquid-phase method, low-pressure gas-liquid-phase contact method and atmospheric pressure gas-phase method, and the reaction equations are as follows.

①High-pressure liquid-phase method High-pressure liquid-phase reaction is usually carried out under pressure conditions (preferably 6.5 to 22.5 MPa) that keep diethylene glycol as the liquid phase. Since the raw material diethylene glycol and the reaction intermediate diethylene glycolamine remain essentially in the liquid phase at higher pressure, the catalyst particles are practically submerged in the reaction solution. When the reaction product morpholine overflows from the above liquid phase, the resistance is higher, so it not only inhibits the conversion of diethylene glycolamine to morpholine, but also promotes the condensation reaction of morpholine and diethylene glycol more easily, so that the yields of intermediate diethylene glycolamine and by-products monomorpholine-based diethylene glycol and di-morpholine-based diethylene glycol are increased. The main disadvantages of this method are: high pressure equipment, short catalyst life and low yield of morpholine.

②Low pressure vapor-liquid phase contact methodLow pressure vapor-liquid phase contact reaction pressure is in the range of 0.5~4.2 MPa, the diethylene glycol is in the gas-liquid mixed-phase state, and the pressure is favorable for the synthesis reaction of morpholine. At the same time, the content of the reaction solution intermediate diethylene glycol amine is greatly reduced. If a highly active and selective catalyst is used, as well as optimized reaction conditions (reaction temperature, reaction pressure and the feed ratio of diethylene glycol, ammonia and hydrogen in the raw material), the content of morpholine in the reaction solution can be increased significantly. According to the literature, the yield of low-pressure synthesis of morpholine is generally above 70%, which shows that the key to low-pressure synthesis of morpholine is still the activity, selectivity and service life of the catalyst.

③Atmospheric pressure method atmospheric pressure gas phase reaction pressure is less than 0.5MPa, in the temperature range to maintain the basic diethylene glycol gas phase reaction. The main advantages of this method are no pressure equipment, simple process, safe operation, low investment, fast results, and easy to achieve industrialization. For small and medium-sized morpholine production plants, the atmospheric pressure synthesis method is an optional technical route, but its disadvantages are that the selectivity is not as high as the liquid phase method, the catalyst life is not long, and the yield cannot catch up with the low-pressure vapor-liquid phase contact method.

[Technical specifications]

[Application] Morpholine has moderate toxicity, in a cool, dry, ventilated place. Protect from sunlight and moisture, keep away from fire and heat source. It should not be stored in large quantities or for a long time, and should be stored separately from oxidizing agents. When using, the operator should pay great attention to protect the eyes and skin, wear closed glasses, gloves, etc.

Morpholine is usually used as boiler feedwater pH adjuster. When morpholine is added to the feed water, it can neutralize the free carbon dioxide and high temperature acidic oxide reaction in the water and improve the pH of boiler feed water to slow down the corrosion of carbon dioxide by using the alkaline nature of morpholine dissolved in water. However, morpholine does not inhibit the corrosion caused by oxygen, so strengthen the thermal deoxidation of feedwater is an important step to ensure the effect of morpholine treatment, to be noted.

The amount of morpholine in feed water is related to the pH value of feed water. When the pH value of feed water rises to 7.0, the amount of morpholine required to neutralize the required CO2 is 1.6mg/L, and when the pH value of feed water is kept at 9.0, 4mg/L of morpholine is required.

Morpholine is an intermediate for the preparation of many chemical products with secondary amine group, and the most important application with secondary amine group is the production of rubber additives. Also widely used as corrosion inhibitor and scale inhibitor for steam boilers. Bis-morpholine-based polysulfide, N-N alkylidene-bis-morpholine, etc. are used as lubricant preservatives. Morpholine aqueous solution can be used to remove gas CO2, H2S or HCN. methyl morpholine and ethyl morpholine can be used as a foaming agent for polyurethane foam. In addition, morpholine can also be used in the manufacture of surfactants, pesticides, synthetic fluorescent whitening agents, catalysts, gas absorbers and herbicides.

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