CS256082B1 - Method of morpholine recovery - Google Patents

Abstract

The solution relates to a method for processing the reaction mixture and regenerating morpholine in the production of N-(3-oxa-pentamethylene)-2-benzothiazylsulfenamide, prepared by reacting 2-mercaptobenzothiazole with morpholine at a molar ratio of morpholine to 2-mercaptobenzothiazole equal to 1.5 to 8:1 and in the presence of hydrogen peroxide. The product is first separated from the mixture in the form of a solid phase and then a mixture of water and morpholine is separated from the organic resinous substances by one or more stages of distillation or rectification, which is partially or completely separated and partially returned to the reactor for reuse without separation, while the morpholine is returned to the reactor for subsequent use directly or after refining rectification.

Description

The invention provides a method for processing the reaction mixture and regenerating morpholine in the production of N-(3-oxa-pentamethylene)-2-benzothiazylsulfenamide, which achieves high efficiency of morpholine regeneration with an ecologically favorable composition of the wastewater.

N-(3-oxa-pentamethylene)-2-benzothiazylsulfenamide, commercially known as Sulfenamide M, Sulfenax MOR and the like, is one of the most important rubber vulcanization accelerators. It is prepared by various methods from benzothiazole derivatives, most often from 2-mercaptobenzothiazole (2-MBT) and morpholine in the presence of an oxidation-condensation agent, e.g. hydrogen peroxide, alkali metal hypochlorite and the like.

The reaction proceeds according to the basic equation

'S

HN _x ⁰

CH,- CH,

oh.

SN / ^CH r

CH·

CH _r CH^ however, in addition to it, a number of undesirable side oxidation-condensation reactions occur, the result of which are mainly resinous derivatives of sultanic, sulfinic and sulfonic acids, condensation products of morpholine and other hardly volatile or non-volatile substances, technologically collectively referred to as resins. Their formation is suppressed by conducting the reaction at a molar excess of morpholine to 2-MBT of 4:1 to 25:1 with careful control of the reaction temperature and with the addition of the oxidation-condensation agent according to a predetermined program.

The result of the reaction is a suspension (when using a low molar ratio of morpholine : 2-MBT) or a solution of the product (at a high molar ratio) in a water-morpholine mixture, which also contains pitches and small amounts of other impurities, such as unreacted 2-MBT, benzthiazole, etc. From this mixture, it is necessary to isolate the product at a high quality level, regenerate morpholine as a valuable raw material for reuse, and finally separate the water from the pitches, which can partly be reused in the process, partly is discharged as waste to a wastewater treatment plant. The thickened pitches leave the process for incineration or other use. However, pitches are thermolabile and, when subjected to temperature stress above 80-90 °C, they easily release odorous volatile sulfur and nitrogen compounds, which can contaminate both the product and the separated water or the regenerated morpholine.

According to NSR Offenlegungsschrift 2,726,901, an at least eight-fold, preferably 9-25-fold excess of morpholine relative to 2-MBT is used to prepare the reaction mixture, and hydrogen peroxide is chosen as the condensing agent. The reaction mixture after the reaction is finished is processed by first distilling off the solvent (a mixture of morpholine and water) down to a solvent:product mass ratio of 1:1. The reaction product is separated from the morpholine by dissolving it in an inert, water-immiscible solvent, the morpholine is extracted with water and the product is obtained by driving off the inert solvent (e.g. toluene, chlorobenzene, etc.). Another possibility according to the cited invention is that after distilling off a substantial portion of the morpholine, water is added to the solvent-product mixture, as a result of which the product precipitates as a solid phase and can be separated. The distilled morpholine is freed from water in a column and recycled, and the mother liquor is also separated into morpholine and water in a column. The organic distillation residue is discharged for incineration.

However, this method of preparing the reaction mixture and its processing is disadvantageous and, moreover, very economically demanding. Distillation of morpholine in the presence of the entire amount of product is accompanied by decomposition of the resins, the fumes of which can adversely affect the properties of the product. From an energy point of view, it is necessary to distill and regenerate a significant amount of morpholine and also the water that is added to the mixture, whether for the extraction of morpholine or for the precipitation of the product. Production costs are therefore burdened by a significant consumption of heat and the process is economically demanding, even though the yields achieved are relatively high.

A more economically advantageous result with equally high or better quality parameters of the product is achieved when the reaction mixture is prepared using such a molar ratio of morpholine:2-MBT that after the reaction is completed the product is in the form of a suspension of the solid phase in a water-morpholine solution of resins and other components. The product can be separated directly from such a mixture by filtration and, after rinsing, sent to the final treatment. Morpholine, water and resins are then separated from the mother liquors and rinsing solutions from the filtration stage. The product is not thermally stressed as in

2560 62 according to the procedure of the cited application, so there is no risk of its contamination by decomposition odorous tar products.

The linear separation of the combined filtrates tsk, that is, first the water is separated from them by rectification, then the morpholine and the pitches are discharged as a waste stream, is not advantageous. When mining at atmospheric or elevated pressure, both the water and the morpholine are contaminated with the decomposition products of the pitches. In the case of morpholine, this results in difficult-to-predict effects on the course and result of the reaction, and in the case of water, significantly increased demands on the method of its purification associated with increased investment and operating costs for the wastewater treatment plant. Separation at reduced pressure requires a very large device with high investment requirements for the entire technological node.

According to the present method, the reaction mixture in the production of N-(3-oxa-pentamethylene)-2-benzothiazylsulfenamide, prepared by the reaction of 2-mercaptobenzothiazole with morpholine in a molar excess of morpholine of 1.5.1 to 8:1 and in the presence of an aqueous solution of hydrogen peroxide, is processed and morpholine is regenerated by first separating the product in the form of a tubular phase from the processed mixture and then separating from the organic resinous substances by single- or multi-stage distillation and/or rectification, preferably under reduced pressure of 5-50 kPa, a mixture of water and morpholine, which is partially or completely separated into morpholine and water, preferably by azeotropic rectification and partially recycled for reuse without separation, wherein morpholine is recycled for reuse directly or after refining rectification.

The separation of water and morpholine from the resinous organic residue must be carried out _under mild conditions in order to suppress the decomposition of the resins as much as possible. It is therefore advantageous to work under reduced pressure so that the working temperature does not exceed 60—80 °C and to choose apparatus with a short residence time in order to shorten the thermal exposure of the solution as much as possible.

These requirements are met, for example, by a falling film evaporator, in which the average retention time is several seconds, a circulating evaporator with a flooded boiler with an economically designed volume, and a film rotor evaporator, which is particularly suitable for the final stage of processing of thickened pitches.

In addition to its ecological advantages, the process according to the present invention is also characterized by high energy efficiency. In the rectification separation of the water-morpholine mixture, steam with a high heat content is obtained at the top of the column, but at a relatively low temperature level. This heat, which would otherwise be difficult to use economically, can be partially or completely utilized in the separation of morpholine and water from the resins.

The evaporation of the entire amount of water and morpholine during their separation from the resinous residue is energy-intensive, but must take place completely or for the most part at a relatively low temperature level of 60—80 ^C C. The necessary heat for this separation can therefore be obtained by using the vapors obtained during the rectification separation of water from morpholine as the heating medium for the individual evaporators. Depending on the separation method, these vapors have a temperature of e.g. 100 ^C C (in the case of direct separation) or 92—94 °C (in the case of azeotropic separation, e.g. with butanol) and can cover the entire heat requirement of the evaporation unit. Another suitable heat source is the vapors of morpholine from its refining rectification, which can be included in the process with particularly high requirements for its purity. Depending on the operating pressure, these vapors have a temperature of 100— —130 °C and can therefore also be used for heating the evaporators. As a result, the consumption of parv in the processing of solutions and the regeneration of morpholine is significantly lower compared to processes in which these technological heat sources would not be used.

As a result of the above-mentioned treatment under very mild conditions, the reaction mixture is separated into pure substances and the thermal decomposition of the mixture is practically completely suppressed. The waste water obtained can be treated in a conventional manner and the process is therefore ecologically, energetically and economically very advantageous due to this and the use of heat.

The attached examples further illustrate! the mentioned procedure and its advantages.

Example 1 (comparative)

The reaction mixture prepared by reacting 2-mercaptobenzothiazole with morpholine in the presence of an aqueous solution of hydrogen peroxide at a molar ratio of morpholine:2-MBT equal to 3:1 contained 20.3 parts of product, 16.3 parts of morpholine, 18 parts of water and 4.9 parts of resins and other low-volatile substances.

After filtering off the product and washing it with a morpholine-water mixture (40% morpholine) and water, combined filtrates of the following composition were obtained: morpholine 27.2 wt. %, water 65.7 wt. %, pitch 7.1 wt. %/o.

In an efficient rectification column (40 theoretical plates, reflux ratio 4:1), water was separated from the solution, in another rectification column (15 theoretical plates, reflux ratio 2:1) morpholine was separated, and from a concentrated mixture of resins and morpholine in a ratio of about 1:1, the rest of the morpholine was obtained by evaporation in a film evaporator.

The efficiency of the morpholine separation was 92%, the morpholine was slightly brownish with an uncharacteristic odor and had to be purified once more by rectification before the abbot could use it. The water was clear with a slight turbidity, had a foreign odor, its COD (Cr) value was 5,706—5,726, after distillation of 50% 4,075—4,095 mg O ₂ /l; the BOD ₅ value was 945—2,100 mg O ₂ /l.

Example 2

The product was filtered off from the reaction mixture of the same composition as in Example 1 and prepared by the same method, and after washing with a water-morpholine mixture and water, filtrates of the same overall composition as in Example 1 were obtained.

In a circulating evaporator with a mean residence time of 30 minutes, the mixture was continuously concentrated to one third of the initial volume by evaporating a mixture of water and morpholine at a pressure of 50—53 kPa and a temperature of 65 °C. From the concentrated residue, further portions of water and morpholine were obtained in a film evaporator at 10—14 kPa and a temperature of 80 °C. The concentrated pitch was removed from the bottom of the evaporator, the distillate was added to the distillate from the primary evaporator and together with it was separated in a continuous rectification column (20 theoretical plates) by azeotropic rectification with butanol into water saturated with butanol and morpholine. The vapors leaving the top of the column had a temperature of 93—94 °C, the morpholine at the bottom of the column had a temperature of 128—130 °C. After subsequent distillation of butanol from the distillate, clear water without significant odor was obtained with a COD (Cr) value of 1082—1,851 after distillation of 50% 836—1,320, the BOD ₅ value was 190—620 mg O ₂ /l, the efficiency of morpholine regeneration was 96%, the morpholine was clear, clear without foreign odor, so there was no need to refine it by rectification before further use.

Claims (2)

1. A process for the recovery of morpholine in the production of N (3-oxa-pentamethylene) -2-benzothiazylsulfenamide by reacting 2-mercaptobenzothiazole with morpholine at a molar ratio of morpholine: 2-mercapenzobenzothiazole of 1.5 to 8 and in the presence of hydrogen peroxide. of the mixture, the solid phase product is first separated and then separated from the organic pitch by one or more stages of distillation and / or rectification, preferably under reduced pressure of 5 to 50 kPa, a mixture of water and morpholine which is partially or completely divided into morpholine and water, preferably by azeotropic rectification and in part, lead to reuse without disintegration, whereby morpholine is re-used directly or after refining rectification. 2. A process according to claim 1, characterized in that the heat required to separate the water and the morpholine from the organic pitches is supplied to the process mixture partly or completely by condensation of the vapors from the rectifying separation of water and morpholine and / or from the refining rectification of morpholine.