Modified technique for preparing acrylic acid by propylene two-step oxygenation method

Abstract

The invention discloses an improved process of preparing acrylic acid through a propylene two-step method, which is characterized in that: the amount of propylene in raw material ratio is increased to ensure that the feed concentration of propylene is 8.0-9.88 percent (mol); washing liquid entering from the top of a washing tower is the mixture of desalted water and acrylic acid containing wastewater; the acrylic acid wastewater is the acid containing wastewater produced by an acrylic acid refining unit in an acrylic acid device; the quantity of wastewater accounts for 50-60 percent (wt) of the total amount of the washing liquid. The improvement has the advantages that: the adoption of high concentration propylene feed can raise the conversion rate of propylene as well as the yield coefficient of acrylic acid, regulate the operating point of oxidation reactant to be beyond the range of an explosion curve, ensure that the device operates in an optimal safe region, reduce the consumption of propylene raw material and raise the production capacity of the device; the adoption of the mixture of desalted water and acrylic acid containing wastewater reduces the dosage of desalted water, the treatment load of a wastewater unit of the device as well as the wastewater discharge amount of the device, and can recycle acrylic acid to the utmost extent, so as to decrease the production cost of the acrylic acid device.

Description

technical field [0001] The invention relates to a process for preparing acrylic acid. technical background [0002] Acrylic acid is produced by two-step oxygenation of propylene, mainly using propylene and air as raw materials, and a chemical reaction occurs under the condition of the presence of a catalyst. The first step is the oxidation of propylene to acrolein, and the second step is the oxidation of acrolein to acrylic acid. The reaction equation is as follows : [0003] CH 2 =CH-CH 3 +O 2 →CH 2 =CH-CHO+H 2 o [0004] CH 2 =CH-CHO+1 / 2O 2 →CH 2 =CH-COOH [0005] This process is an exothermic strong oxidation reaction, and the reaction temperature is relatively high. When the circulating tail gas method is adopted, the propylene feed concentration of the existing device is less than or equal to 8% (mol), the propylene consumption is large, and the conversion rate is low; In the process device of the circulating tail gas method, since the tail gas at the top of ...

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Problems solved by technology

[0005] This process is an exothermic strong oxidation reaction, and the reaction temperature is relatively high. When the circulating tail gas method is adopted, the propylene feed concentration of the existing device is less than or equal to 8% (mol), the propylene consumption is large, and the conversion rate is low; In the process device of the circulating tail gas method, since the tail gas at the top of the washing tower is directly recycled to the reactor, the oxidation catalyst has higher requirements on the composition of the tail gas at the top of the tower. The washing tower top of the existing equipment uses desalted water to directly absorb acrylic acid gas to ensure absorption. effect to meet the requirements of the catalyst, so a large amount of desalted water is consumed in the production unit, which increases the production cost

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