Process for preparing DMT and DOTP by recycling waste printing and dyeing white mud

Abstract

The invention discloses a process for preparing DMT and DOTP by recycling waste printing and dyeing white mud. The process comprises a pretreatment unit, a methyl esterification unit, a rectification unit, a pulping unit, an ester exchange unit and a refining unit, waste printing and dyeing white mud is used for methyl esterification to prepare DMT, DMT rectification and purification, DMT transesterification to prepare DOTP and DOTP purification. According to the process, efficient esterification of the white mud and product separation can be achieved through the catalyst and the process conditions adopted in the methyl esterification stage, the obtained refined DMT can serve as a polyester monomer product and can also serve as a raw material to further react with isooctanol to prepare DOTP, and high-valued conversion and resource utilization of the white mud are achieved through the process.

Description

Technical Field

[0001] The invention relates to the technical field of liquid-solid heterogeneous reaction, homogeneous reaction and distillation separation, and in particular to a process for recovering waste printing and dyeing white mud to prepare DMT and DOTP. Background Art

[0002] After acid neutralization, the wastewater produced by the dyeing and printing alkali reduction process precipitates a solid mixture containing a large amount of crude terephthalic acid and other impurities, commonly known as dyeing and printing white mud. At present, the main treatment method for this material is landfill, which occupies a large amount of land resources and pollutes the environment. The recycling and high-value conversion of dyeing and printing white mud has obvious economic, environmental and social benefits and has broad prospects.

[0003] DOP is the most widely used traditional phthalate plasticizer, but it has certain carcinogenic and teratogenic risks. DOTP is an excellent green substitute for DOP and is widely used in PVC products with excellent plasticizing properties. At present, the commonly used production process in industry is to use terephthalic acid (PTA) and isooctyl alcohol as raw materials for direct esterification reaction. This method has high requirements on raw material purity, slow reaction rate and high energy consumption. In response to the above problems, people have proposed different improvement methods.

[0004] Prior art CN110759828A proposes "a method for preparing environmentally friendly plasticizer DOTP using waste white mud". This method reacts the acidified white mud at 200-260°C for 7-8h, and then obtains the DOTP product after neutralization, water washing, dealcoholization and decolorization. In this process, terephthalic acid PTA is insoluble in isooctyl alcohol, and the reaction involves a liquid-solid heterogeneous reaction, and the reaction is limited by diffusion control. Since the reaction temperature is much greater than the boiling point of isooctyl alcohol, a large amount of isooctyl alcohol is in a "vaporization-condensation-refilling" state, and the actual concentration of alcohol participating in the reaction in the liquid phase is low, resulting in a long reaction time and high energy consumption. In addition, the direct esterification method has high requirements for the purity of the raw materials, and the resulting DOTP product may have problems such as yellowish hue.

[0005] The prior art CN101513641A proposes a "resource treatment method for purified terephthalic acid waste residue", which is a method in which the waste residue is first distilled to obtain crude acid, and the crude acid is esterified, decolorized, neutralized, and distilled to obtain terephthalate products. Another part of the crude acid is refined by distillation, and the two parts of the distillation residues can be treated to extract rare metals such as cobalt and manganese. However, the purity of the terephthalic acid and terephthalate obtained by this method is still not high, and the treatment process is long and energy consumption is high. The prior art CN101302152A proposes a "method for recovering terephthalic acid from colored terephthalic acid residue by complex crystallization", which is a method for recovering terephthalic acid from residue by complex crystallization, wherein a complex crystallizing agent is added and stirred and mixed, and solid-liquid separation is performed after the complex crystals are precipitated. The obtained complex crystalline solid can be subjected to melting, solid-liquid separation, washing and drying to obtain terephthalic acid with high purity. However, for a residue system with a large amount of insoluble matter, it is difficult to obtain high-purity terephthalic acid by the crystallization method, so this method lacks universality.

[0006] The prior art CN105111074A proposes "a method for methyl esterification and recycling of solid residues from alkali reduction wastewater", which is a method for obtaining dimethyl terephthalate by esterification followed by refining. The residue after washing and drying is first mixed with methanol and a catalyst for slurrying, and the slurry is subjected to two methyl esterification reactions and then distilled and crystallized to obtain refined dimethyl terephthalate. The first esterification kettle and the second esterification kettle are respectively operated at 160-280°C and 200-250°C with a short residence time to achieve a higher conversion rate and DMT yield, but the subsequent separation of DMT crystallization process is long, and there is a certain loss of ester during the distillation process, which is about 1-2wt% of the recovered amount.

[0007] In summary, the recycling technology of printing and dyeing white mud needs to be further developed and optimized. The current recycling methods have problems such as low product purity, high cost, and lack of universality. Under the premise of ensuring product quality, it is urgent to develop a recycling method with good economic and environmental benefits and high industrial feasibility.

[0008] Therefore, the present invention provides a process for recycling waste printing and dyeing white mud to prepare DMT and DOTP. The present invention is a process for high-value conversion of printing and dyeing white mud. First, the pretreated solid white mud is methylated, and the product is separated by distillation to obtain refined dimethyl terephthalate DMT; the obtained refined DMT can be used as a high-value product, and can also be used as a raw material to further react with isooctyl alcohol, and the product is separated by distillation to obtain a high-performance plasticizer DOTP; the process not only realizes the resource recycling of printing and dyeing white mud, but also provides a preparation method for a green plasticizer. Summary of the invention

[0009] The purpose of the present invention is to provide a process for recycling waste printing and dyeing white mud to prepare DMT and DOTP, so as to realize the resource recycling of printing and dyeing white mud, and also provide a preparation method of a green plasticizer.

[0010] The purpose of the present invention is achieved through the following technical solutions: A process for recovering waste printing and dyeing white mud to prepare DMT and DOTP comprises the following steps: S1, pretreatment unit: the solid residue of printing and dyeing white mud obtained by the alkali reduction process is repeatedly washed with 80°C deionized water until the pH of the filtrate is 6-7, and the solid after the filtrate is dried is added into the first pulping kettle with methanol and catalyst I in proportion and stirred and mixed; S2, methyl esterification unit: the mixed slurry is sent to the primary esterification kettle for reaction, the PTA (terephthalic acid) conversion rate is maintained at more than 90%, the outlet liquid phase material is sent to the secondary esterification kettle for deep esterification, the gas phase is sent to the first distillation tower to separate MMT (monomethyl terephthalate) / DMT (dimethyl terephthalate), and then the gas phase is sent to the alcohol-water separation tower for dehydration and then the methanol is refluxed; MMT (monomethyl terephthalate) / DMT (dimethyl terephthalate) is sent to the secondary esterification kettle, the terephthalic acid conversion rate of the liquid phase outlet of the secondary esterification kettle is maintained at more than 98%, the liquid phase is sent to the distillation unit, and the gas phase is also sent to the first distillation tower for dehydration and then the methanol is refluxed; S3, distillation unit: the liquid phase obtained from the secondary esterification reactor in step S2 is sent to the second distillation tower for distillation separation and purification of DMT (dimethyl terephthalate), the top fraction of the second distillation tower is condensed and sent to the pulping unit, and the bottom fraction is separated from the residue and sent to the methyl esterification unit; S4, pulping unit: adding the product obtained from the top fraction of the second distillation tower in step S3, isooctyl alcohol and catalyst II in proportion into a second pulping kettle and stirring and mixing; S5, transesterification unit: the mixed materials are sent to the transesterification kettle, and when the conversion rate of DMT (dimethyl terephthalate) in the outlet liquid phase reaches 99%, the gas phase is sent to the methanol / isooctanol separation tower to remove methanol and then the isooctanol is refluxed; the crude DOTP (diisooctyl terephthalate) in the liquid phase is sent to the refining unit; S6, refining unit: remove isooctyl alcohol from the crude DOTP (diisooctyl terephthalate) in step S5 by vacuum distillation, neutralize with alkaline solution under heating conditions until the acid value is less than 0.1 mgKOH / g, wash repeatedly with water, stand for stratification, take the upper layer solution and send it to the stripping tower to remove residual water and isooctyl alcohol from DOTP (diisooctyl terephthalate), finally add decolorizer to the stripped DOTP (diisooctyl terephthalate), heat for decolorization, and cool to obtain the final product DOTP (diisooctyl terephthalate).

[0011] Preferably, in step S1, the mass ratio of the solid after drying the filtrate to methanol is 1:3~4; the catalyst I is selected from one or more of concentrated sulfuric acid, methylbenzenesulfonic acid, manganese acetate, cobalt acetate, antimony acetate, zinc acetate, zinc oxide, titanium sulfate, dibutyltin oxide, tetrabutyl titanate, isopropyl titanate, polymerized ferric sulfate, and solid acid catalysts, such as molecular sieve type, and the amount of the catalyst I is 0.2%~0.8% of the mass of the solid residue of printing and dyeing white mud.

[0012] Preferably, in step S1, the main components of the solid residue of printing and dyeing white mud include water, terephthalic acid, oligomer waste fiber, SiO2, TiO2, Na + 、SO4 2- , inorganic or organic impurities.

[0013] Preferably, in step S2, the reaction temperature in the primary esterification kettle is 180-240°C, the reaction pressure is 3.0-15.0 MPa, and the liquid phase residence time is 1-5 h, which is a liquid-solid heterogeneous reaction; the outlet liquid phase material is sent to the secondary esterification kettle for deep esterification at a reaction temperature of 180-240°C, a reaction pressure of 3.0-15.0 MPa, and a liquid phase residence time of 1-5 h.

[0014] Further preferably, in step S2, the reaction temperature in the primary esterification kettle is 220-240°C, the reaction pressure is 3.0-15.0 MPa, the liquid phase residence time is 1-3 h, and the outlet liquid phase esterification rate is greater than 90%, which belongs to a liquid-solid heterogeneous reaction; the outlet liquid phase material is sent to the secondary esterification kettle for deep esterification at a reaction temperature of 220-240°C, a reaction pressure of 3.0-15.0 MPa, a liquid phase residence time of 1-3 h, and an outlet liquid phase esterification rate of greater than 98%.

[0015] Preferably, in step S2, the number of theoretical plates of the first distillation tower is 2-5, the number of feed plates is 2-4, the top reflux ratio is 0.6-0.8, the absolute pressure is 100-200 kPa, the reboiler temperature is 100-150 ° C, the load is 120-180 kw, and the condenser load is 300-600 kw; the first distillation tower mainly removes low-boiling components at the top of the tower, the low-boiling components include water and methanol, the bottom of the tower is mainly DMT, the transport pipeline is insulated, and the DMT flows into the secondary esterification kettle in a molten state; the number of theoretical plates of the alcohol-water separation tower is 25-30, the feed plates are the 15th-20th, the top reflux ratio is 0.6-0.8, the absolute pressure is 100-120 kPa, the reboiler temperature is 100-120 ° C, the load is 200-350 kw, and the condenser load is 350-450 kw.

[0016] Further preferably, in step S2, the number of theoretical plates of the first distillation tower is 2 to 3, the number of feed plates is 2 to 4, the top reflux ratio is 0.6 to 0.8, the absolute pressure is 100 to 150 kPa, the reboiler temperature is 100 to 120°C, the load is 120 to 140 kw, and the condenser load is 300 to 400 kw.

[0017] Preferably, in step S3, the number of theoretical plates of the second distillation tower is 15-40, the number of feed plates is 10-30, the reflux ratio at the top of the tower is 0.6-0.8, the absolute pressure is 10-60 kPa, the reboiler temperature is 250-350 ° C, the load is 60-80 kw, the condenser load is 60-80 kw, the bottom of the tower is mainly MMT, PTA, catalyst I and insoluble impurities, after filtering the impurities, MMT and PTA can be sent to the secondary esterification kettle for further reaction, and the insoluble impurities can be incinerated to recover heat. The top of the tower is DMT with a purity greater than 99%.

[0018] Further preferably, in step S3, the number of theoretical plates of the second distillation tower is 15-20, the number of feed plates is 20-30, the reflux ratio at the top of the tower is 0.6-0.8, the absolute pressure is 10-30 kPa, the reboiler temperature is 250-300 ° C, the load is 70-80 kw, the condenser load is 70-80 kw, the bottom of the tower is mainly MMT, PTA, catalyst I and insoluble impurities, after filtering the impurities, MMT and PTA can be sent to the secondary esterification kettle for further reaction, and the insoluble impurities can be incinerated to recover heat. The top of the tower is DMT with a purity greater than 99%.

[0019] Furthermore, in the distillation unit, in order to ensure the purity of the top product, a certain amount of DMT flows out from the bottom residue of the second distillation tower, and the discharge amount is less than 0.2% of the recovery amount.

[0020] Furthermore, in the present invention, a distillation method is used to recover methanol, and the methanol recovered from the top of the tower is refluxed into the pulping kettle according to the required alcohol-acid mass ratio.

[0021] Preferably, in step S4, the molar ratio of the product obtained from the top fraction of step S3 to isooctyl alcohol is 1:2-2.5, the catalyst II is selected from one or more of sodium methoxide, isopropyl titanate, tetrabutyl titanate, stannous octoate, dibutyltin dilaurate, zinc oxide or a new catalyst, such as imidazole ionic liquids, etc., and the amount of the catalyst II is 0.2-0.8% of the product obtained from the top fraction of step S3.

[0022] Preferably, in step S5, the reaction temperature of the transesterification kettle is 90-180° C., the reaction pressure is 0.1-0.2 MPa, the liquid phase residence time is 1-3 h, and the outlet liquid phase conversion rate is greater than 99%.

[0023] Preferably, in step S6, the temperature of the reduced pressure distillation is 100-180°C, and isooctyl alcohol is removed at -0.1 MPa for 3-5 hours; the upper layer solution is sent to a stripping tower for stripping using 100°C water vapor, and the decolorizing agent is selected from one or more of powdered activated carbon, kaolin, and diatomaceous earth, and the decolorization is carried out at 60-100°C for 1-5 hours.

[0024] Preferably, in step S6, the heating temperature for the neutralization reaction using an alkaline solution under the heating conditions is 60-100°C, the alkaline solution is a NaHCO3 solution with a mass concentration of 5-10%, a Na2CO3 solution with a mass concentration of 2-5%, or a NaOH solution with a mass concentration of 1-5%, the stirring and mixing time of the neutralization reaction is 10-30 minutes, and the standing stratification time is 1-3 hours.

[0025] Due to the application of the above technical solution, the present invention has the following beneficial effects compared with the prior art: 1. In the prior art, terephthalic acid is usually extracted by distillation, crystallization and other methods for the treatment of printing and dyeing white mud waste, but the purity is low; or low-quality chemical downstream products are directly obtained by reaction, which has the problems of high cost or insufficient resource utilization; while the present invention utilizes the physical property of dimethyl terephthalate that it is easy to sublimate, and obtains dimethyl terephthalate with high purity by distillation, which can be used as polyester monomer and as raw material for preparing green plasticizer; 2. After the white mud is efficiently esterified, the present invention utilizes the mild reaction conditions of the ester exchange method to reduce the reaction temperature and time, solves the problems of high purity requirements and high energy consumption of the raw material PTA in the direct esterification method, realizes the resource utilization of waste chemicals, and provides a new way for the industrial production of DOTP, which has good commercial significance. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, some of the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be made based on these drawings without paying any creative work.

[0027] Figure 1 This is a flow chart of a device for preparing DOTP from printing and dyeing white mud in Example 1 of the present invention; Figure 2 It is a curve diagram of the change of PTA conversion rate over time at 200° C. for Comparative Examples 11 and 12 of the present invention; Figure 3 It is a curve diagram of the change of MMT yield over time at 200° C. for Comparative Examples 11 and 12 of the present invention; Figure 4 It is a curve diagram of the change of DMT yield over time at 200° C. for Comparative Examples 11 and 12 of the present invention; Figure 5 It is a curve diagram of the change of PTA conversion rate over time at 240° C. for Comparative Examples 13 and 14 of the present invention; Figure 6 It is a curve diagram of the change of MMT yield over time at 240° C. for Comparative Examples 13 and 14 of the present invention; Figure 7 It is a curve diagram of the change of DMT yield over time at 240° C. for Comparative Examples 13 and 14 of the present invention; in, Figure 1 In: 1-primary esterification kettle; 2-secondary esterification kettle; 3-first distillation tower; 4-second distillation tower; 5-alcohol-water separation tower; 6-methanol / isooctanol separation tower; 7-stripping tower; 8-ester exchange kettle; 9-first pulping kettle; 10-second pulping kettle; 11-first batching tank; 12-second batching tank; 13-flash tank; 14-alkali washing tank; 15-water washing tank; 16-decolorization tank; 17-dryer; 18-methanol tank; 19-isooctanol tank. DETAILED DESCRIPTION

[0028] In order to have a clearer understanding of the technical features, purposes and effects of the present invention, a specific implementation scheme is now described in detail.

[0029] The present invention is further described below in conjunction with the examples, but the present invention is not limited to the following examples. The implementation conditions used in the examples can be further adjusted according to the different requirements of specific use, and the implementation conditions not indicated are conventional conditions in the industry. The technical features involved in each embodiment of the present invention can be combined with each other as long as they do not conflict with each other.

[0030] Example 1 See attached Figure 1 This embodiment provides a process for recycling waste printing and dyeing white mud to prepare DMT and DOTP, comprising the following steps: S1, pretreatment unit: the solid residue of printing and dyeing white mud obtained by the alkali reduction process (the printing and dyeing white mud is treated by secondary methyl esterification, and the residue used is also the solid residue after the alkali reduction wastewater treatment of a certain enterprise) is repeatedly washed with 80°C deionized water until the pH value of the filtrate is 7, and sent to the dryer 17 for drying to ensure that the water content is less than 1%, and the solid white mud after the filtrate is dried and the methanol in the methanol tank 18 are added to the first pulping kettle 9 at a mass ratio of 1:3 and 0.4wt% of catalyst I polyferric sulfate (based on the mass of the white mud) and stirred and mixed; S2, methyl esterification unit: the mixed slurry is pressurized to 8MPa by a pump and then sent to the first batching tank 11. After the temperature is raised to 220°C by a heat exchanger, it is sent to the primary esterification kettle 1 for reaction. It is a liquid-solid heterogeneous reaction. The reaction temperature is 220°C, the reaction pressure is 7.0MPa, and the liquid phase residence time is 4h. The PTA (terephthalic acid) conversion rate is maintained at more than 90%. The outlet liquid phase material is sent to the secondary esterification kettle 2 for deep esterification. The gas phase is sent to the first distillation tower 3 to separate MMT (monomethyl terephthalate) / DMT (dimethyl terephthalate) and then the gas phase is sent to the alcohol water After dehydration from tower 5, methanol is refluxed; MMT (monomethyl terephthalate) / DMT (dimethyl terephthalate) is sent to the secondary esterification kettle for deep esterification. The reaction of the secondary esterification kettle is in the homogeneous stage, so that the unreacted terephthalic acid and monomethyl terephthalate continue to be esterified. The reaction temperature is 230°C, the reaction pressure is 6MPa, and the residence time is 2h. The esterification rate of terephthalic acid at the liquid phase outlet of the secondary esterification kettle is kept greater than 98%. The liquid phase is sent to the distillation unit, and the gas phase is also sent to the first distillation tower for dehydration treatment, and then the methanol is refluxed, and the liquid phase is sent to the second distillation tower 4; The first distillation tower has 3 theoretical plates, 4 feed plates, a top reflux ratio of 0.6, an absolute pressure of 120 kPa, a reboiler temperature of 120°C, a load of 130 kW, and a condenser load of 400 kW. The feed stream of the first distillation tower mainly comprises water, methanol, DMT and a small amount of MMT. The top fraction is water and methanol entering the alcohol-water separation tower. The bottom fraction is 87.6% DMT, 3.65% MMT, 0.03% PTA, 2.62% water and 6.1% methanol. The bottom pipeline is insulated at a temperature of above 220°C to ensure that DMT and a small amount of MMT are extracted from the bottom of the tower in a molten state and re-enter the secondary esterification kettle for reaction. Among them, the theoretical number of plates of the alcohol-water separation tower is 28, the feed plate is the 18th, the top reflux ratio is 0.6, the absolute pressure is 100kPa, the reboiler temperature is 110℃, the load is 270kw, the condenser load is 400kw, the methanol mass fraction in the feed stream is 87%, the top methanol is refluxed into the first pulping kettle, and the bottom wastewater is sent to the sewage treatment system; S3, distillation unit: the liquid phase obtained from the secondary esterification reactor in step S2 is sent to the second distillation tower for distillation separation and purification of DMT (dimethyl terephthalate), the top fraction of the second distillation tower is condensed and sent to the pulping unit, and the bottom fraction is separated from the residue and sent to the methyl esterification unit; Specifically, the second distillation tower has 15 theoretical plates, 20 feed plates, a top reflux ratio of 0.6, an absolute pressure of 20 kPa, a reboiler temperature of 280°C, a load of 70 kW, a condenser load of 70 kW, and a feed stream of the liquid phase of the secondary esterification kettle, mainly containing DMT, MMT and a small amount of PTA. The DMT is sublimated and enriched at the top of the tower by a low-pressure distillation method, and then the sublimated DMT is condensed and extracted from the top of the tower through a condenser. The DMT with a purity greater than 99.5% is sent to a pulping unit for ester exchange; the bottom fraction mainly contains 93% MMT, 2% PTA, 2% DMT and 3% other impurities. After separating the impurities, it is sent to the secondary esterification kettle for further reaction. The insoluble impurities can be incinerated to recover heat. The top of the tower is DMT with a purity greater than 99%; S4, pulping unit: add the DMT obtained from the top fraction of the second distillation tower in step S3, the isooctanol in the isooctanol tank 19 in a molar ratio of 1:2.2 and 0.6 wt% of catalyst II tetrabutyl titanate (based on the mass of DMT) into the second pulping kettle 10 and stir to mix; S5, transesterification unit: the mixed slurry is sent to the second batching tank 12, heated to 120°C by a heat exchanger, and sent to the transesterification kettle 8. When the conversion rate of DMT (dimethyl terephthalate) in the outlet liquid phase reaches 99%, the gas phase is sent to the methanol / isooctanol separation tower to remove methanol and then the isooctanol is refluxed; the crude DOTP (diisooctyl terephthalate) in the liquid phase is sent to the refining unit; Specifically, the reaction temperature of the transesterification kettle is 160°C, the reaction pressure is 0.1MPa, and the transesterification residence time is 2h, wherein the gas phase part (methanol / isooctanol) is sent to the methanol / isooctanol separation tower 6 to reflux the isooctanol, and the methanol is sent to the sewage treatment system, and the liquid phase part is sent to the flash tank 13 for vacuum distillation at a temperature of 160°C. After de-alcoholization at -0.1MPa for 3h, the crude DOTP is cooled to 80°C by a heat exchanger and sent to the alkali washing tank 14, and the isooctanol in the gas phase of the flash tank is sent to the sewage treatment system; S6, refining unit: send the crude DOTP (diisooctyl terephthalate) in step S5 into an alkaline washing tank and mix and stir with 80°C 8% NaHCO3 solution for 25 minutes for neutralization reaction, wash repeatedly with water until the acid value is less than 0.1 mgKOH / g, stand for 2 hours for separation, send the lower waste liquid to the sewage treatment system, send the upper liquid to the washing tank 15 and mix and stir with 80°C water for 2 hours, stand for 2 hours for separation, send the lower waste liquid to the sewage treatment system, and send the upper liquid to the stripping tower 7; use 100°C steam stripping, the top gas (water / isooctanol) is condensed and sent to the sewage treatment system, the bottom product is pumped into the decolorization tank 16, and the product is filtered out after decolorization for 2 hours using activated carbon and diatomaceous earth as decolorizers. The obtained diisooctyl terephthalate (DOTP) product has a purity greater than 99% and a volume resistivity of 2.1×1010 Ω·m, reaching the industrial high-quality standard.

[0031] The main components of the solid residue of printing and dyeing white mud include water, terephthalic acid, oligomer waste fiber, SiO2, TiO2, Na + 、SO4 2- , other impurities (inorganic or organic impurities); the specific composition of the solid residue is shown in Table 1.

[0032] Table 1

[0033] The liquid phase at the outlet of the secondary esterification kettle, the top of the second distillation tower, the liquid phase at the outlet of the transesterification kettle and the outlet of the decolorization tank were analyzed by HPLC. The test results of this example are shown in Table 2 below.

[0034] Table 2

[0035] Compared with the intermittent operation of the comparative example, although the PTA conversion rates of both reached more than 99%, the DMT yield under the continuous operation of Example 1 was better than that of the intermittent operation, and the DMT purity was better than that of the simple distillation of Comparative Example 10. This is because water was continuously taken out of the reactor under the continuous operation, which promoted the forward movement of the esterification reaction equilibrium. The multi-stage distillation of Example 1 improved the DMT purity compared with the simple distillation once.

[0036] Example 2 This embodiment is carried out on the basis of the above-mentioned embodiment 1, and the similarities are not repeated here.

[0037] In this embodiment: the bottom product of the first distillation tower is not sent to the secondary esterification kettle, but is directly sent to the second distillation tower for separation of DMT and MMT, wherein the bottom product of the first distillation tower is composed of 87.6% DMT, 3.65% MMT, 0.03% PTA, 2.62% water and 6.1% methanol. The liquid phase part at the outlet of the secondary esterification kettle, the top part of the second distillation tower, the liquid phase part at the outlet of the ester exchange kettle and the outlet part of the decolorization tank are also taken for HPLC analysis. The detection results of this embodiment are shown in Table 3 below.

[0038] Table 3

[0039] Compared with Example 1, the DMT yield of Example 2 is improved, but the DMT purity, DOTP yield, DOTP purity and DOTP volume resistivity are all reduced. This is because the bottom extraction stream of the first distillation tower is not recycled back to the secondary esterification kettle, which reduces the DMT content and promotes the forward movement of the esterification reaction equilibrium, but directly enters the second distillation tower, which reduces the separation efficiency of the tower and causes the top DMT purity to decrease, thereby affecting the subsequent ester exchange reaction and reducing the product performance.

[0040] Comparative Example 1 The raw materials of this comparative example are purified terephthalic acid with a purity of 99.8%, HPLC grade methanol and polyferric sulfate, the mass ratio of alcohol to acid is 1:3, the amount of purified terephthalic acid added is 8g, the amount of methanol added is 24g, and the amount of catalyst polyferric sulfate added is 0.4% of the acid mass, i.e. 0.032g. A 50ml parallel intermittent reactor is used for methyl esterification reaction. The autoclave is equipped with an electric heating and temperature control system. After the heating furnace is preheated, it is added to the reactor and the temperature is rapidly raised to 180°C. The pressure of the reactor is raised to 3MPa, the stirring rate is 200rpm, and after reacting for 0.5h, the reactor is quenched with ice water, the reaction is terminated and sampling is taken, and liquid chromatography quantitative analysis is adopted to calculate that the PTA conversion rate is 21.2%, the DMT yield is 12.9%, and the MMT yield is 8.1%. The results are compared and listed in Table 4.

[0041] Comparative Example 2 This comparative example carried out a similar methyl esterification reaction, with 8 g of purified terephthalic acid added, 24 g of methanol added, 0.4% of the acid mass, i.e. 0.032 g, of the catalyst polyferric sulfate added, the reaction temperature was 220°C, the pressure was 7.8 MPa, the esterification time was 0.5 h, and after the reaction was completed, sampling and analysis were performed, and the calculated PTA conversion rate was 70.4%, the DMT yield was 41.3%, and the MMT yield was 28.7%. The results are listed in Table 4 for comparison.

[0042] Comparative Example 3 This comparative example carried out a similar methyl esterification reaction, with 8 g of purified terephthalic acid added, 24 g of methanol added, 0.4% of the acid mass, i.e. 0.032 g, of the catalyst polyferric sulfate added, the reaction temperature was 240°C, the pressure was 12.5 MPa, the esterification time was 0.5 h, and after the reaction was completed, sampling and analysis were performed, and the calculated PTA conversion rate was 87.3%, the DMT yield was 59.2%, and the MMT yield was 25.6%. The results are listed in Table 4 for comparison.

[0043] Table 4

[0044] Comparing Comparative Example 1 with Comparative Examples 2 and 3, it can be seen that increasing the reaction temperature can effectively increase the esterification rate. Since DMT methylation is a series of reactions, the first step of generating monomethyl ester is a fast reaction, and the second step of generating dimethyl ester from monomethyl ester is a slow reaction. Increasing the temperature can accelerate both reactions at the same time. When 180°C is increased to 220°C, the PTA conversion rate and DMT yield are significantly increased, while when 220°C is increased to 240°C, the PTA conversion rate and DMT yield are not significantly increased. Therefore, 220°C is a more suitable temperature for the methylation reaction. In addition, when the reaction time is 0.5h, the PTA conversion rate is increased more significantly than the DMT yield when the temperature is increased. Therefore, increasing the temperature mainly accelerates the reaction rate of the first step in the early stage of the reaction.

[0045] Comparative Example 4 This comparative example carried out a similar methyl esterification reaction, using a 200ml intermittent reactor, 20g of purified terephthalic acid, 60g of methanol, 0.4% of the acid mass, i.e. 0.08g of tetrabutyl titanate catalyst, reaction temperature of 200°C, pressure of 5.6MPa, esterification time of 2h, sampling and analysis after the reaction, calculated PTA conversion rate of 77%, DMT yield of 50.4%, MMT yield of 26.7%, the results are compared and listed in Table 5.

[0046] Comparative Example 5 This comparative example carried out a similar methyl esterification reaction, using a 200ml intermittent reactor, 20g of purified terephthalic acid, 60g of methanol, 0.4% of the acid mass, i.e. 0.08g of zinc acetate catalyst, reaction temperature of 200°C, pressure of 5.6MPa, esterification time of 2h, sampling and analysis after the reaction, calculated PTA conversion rate of 35.7%, DMT yield of 17.6%, MMT yield of 26.7%, the results are compared and listed in Table 5.

[0047] Comparative Example 6 This comparative example carried out a similar methyl esterification reaction, using a 200ml intermittent reactor, 20g of purified terephthalic acid, 60g of methanol, 0.4% of the acid mass, i.e. 0.08g of catalyst manganese acetate, reaction temperature of 200°C, pressure of 5.6MPa, esterification time of 2h, sampling and analysis after the reaction, calculated PTA conversion rate of 72.7%, DMT yield of 65.6%, MMT yield of 18.1%, the results are compared and listed in Table 5.

[0048] Comparative Example 7 This comparative example carried out a similar methyl esterification reaction, using a 200ml intermittent reactor, 20g of purified terephthalic acid, 60g of methanol, 0.4% of the acid mass, i.e. 0.08g of cobalt acetate catalyst, reaction temperature of 200°C, pressure of 5.6MPa, esterification time of 2h, sampling and analysis after the reaction, calculated PTA conversion rate of 56.7%, DMT yield of 22.1%, MMT yield of 28.0%, the results are compared and listed in Table 5.

[0049] Comparative Example 8 This comparative example carried out a similar methyl esterification reaction, using a 200ml intermittent reactor, 20g of purified terephthalic acid, 60g of methanol, 0.4% of the acid mass, i.e. 0.08g of catalyst polyferric sulfate, reaction temperature of 200°C, pressure of 5.6MPa, esterification time of 2h, sampling and analysis after the reaction, calculated PTA conversion rate of 94.2%, DMT yield of 84.3%, MMT yield of 10.0%, the results are compared and listed in Table 5.

[0050] Table 5

[0051] Comparison of Comparative Examples 4 to 8 shows that, with the conversion rate of terephthalic acid (PTA) and the yield of dimethyl terephthalate (DMT) as the evaluation criteria, it is determined that polyferric sulfate has the best catalytic effect on the methylation reaction, followed by tetrabutyl titanate. Polyferric sulfate is less prone to hydrolysis than titanium-based catalysts, has better catalytic effect and lower cost, and has better economic efficiency. SPFS is soluble in methanol at around 80°C.

[0052] Comparative Example 9 The raw materials of this comparative example are purified terephthalic acid with a purity of 99.8%, chromatographic grade methanol and polyferric sulfate, the mass ratio of alcohol to acid is 1:3, the amount of purified terephthalic acid added is 8g, the amount of methanol added is 24g, the catalyst is polyferric sulfate, and three 50ml parallel intermittent reactors are used for methyl esterification reaction. Different masses of catalysts (0.2wt%, 0.4wt%, 0.6wt%) are added to the reactors respectively. The reaction temperature is 220℃, the reactor pressure is increased to 7.8MPa, the stirring rate is 200rpm, and after reacting for 0.5h, the reactor is quenched with ice water. After the reaction is completed, samples are taken for analysis. The reaction results are shown in Table 6. When the catalyst concentration is increased from 0.2wt% to 0.4wt%, the PTA conversion rate and The DMT yield increased significantly, but further increasing the catalyst concentration did not significantly increase the yield. This is because polyferric sulfate is a chain complex, and the esterification reaction occurs on the catalyst surface. Under the condition of excess methanol, the 0.4wt% ratio is better, and the catalyst can fully adsorb PTA. The rate is 200rpm, and after 0.5h of reaction, the reactor is quenched with ice water. After the reaction, samples are taken for analysis. The reaction results are shown in Table 6. When the catalyst concentration is increased from 0.2wt% to 0.4wt%, the PTA conversion rate and DMT yield are significantly improved, but further increasing the catalyst concentration does not significantly increase the yield. This is because polyferric sulfate is a chain complex, and the esterification reaction occurs on the catalyst surface. Under the condition of excess methanol, the 0.4wt% ratio is better, and the catalyst can fully adsorb PTA.

[0053] The reaction efficiency under different catalyst dosages is shown in Table 6.

[0054] Table 6

[0055] Comparative Example 10 The raw materials of this comparative example are the raw materials of Example 1, and the main components of the residue are shown in Table 1. Before the reaction, the residue is washed with hot water at a water temperature of more than 80°C until the pH is about 7 and then dried; A 200 ml high pressure intermittent stirring kettle was used for the reaction. First, 20 g of dry residue, 60 g of methanol and 0.08 g of polyferric sulfate were quantitatively weighed in the reactor, heated to 220°C, the reactor pressure was raised to 5 MPa, the stirring rate was 200 rpm, and the reaction was continued for 2 hours. After the temperature was lowered to room temperature, the reaction was terminated and samples were taken for analysis. The calculated PTA conversion rate was 99%, and the DMT yield was 85.7%. After the product was dried at 100°C, the dried product was placed in a sublimator and sublimated at 160°C and -0.1 MPa to obtain DMT. , DMT purity is 95% (including 5% MMT); 10g of DMT obtained by sublimation, 14.76g of isooctyl alcohol (molar ratio of 1:2.2) and 0.06g of tetrabutyl titanate (based on the mass of DMT, 0.6wt%) were taken in a flask, heated to 160°C in an oil bath, stirred at 100rpm, a certain amount of nitrogen was continuously introduced to discharge methanol and condensed and collected, reacted for 2h, and samples were taken for analysis after the reaction was completed. The yield of DOTP was 98%; the mass concentration used was The mixture was neutralized with 8% NaHCO3 solution, stirred for 25 min, and allowed to stand for 2 h until the acid value was less than 0.1 mgKOH / g, then washed with water three times, allowed to stand for 2 h, and the upper layer of liquid was put into a flask. The device was vacuumed and de-alcoholized at 160 ° C and -0.1 MPa for 2 h. After the decolorization was completed, activated carbon was added at 80 ° C for 2 h, and then filtered to obtain the final product, diisooctyl terephthalate (DOTP). The volume resistivity of the sample was 2.4×10 10 Ω·m, reaching the industrial high-quality standard.

[0056] Comparative Example 11 See attached Figure 2-4 The raw materials of this comparative example are purified terephthalic acid with a purity of 99.8%, HPLC grade methanol and polyferric sulfate, the mass ratio of alcohol to acid is 1:3, the amount of purified terephthalic acid added is 8g, the amount of methanol added is 24g, the catalyst is tetrabutyl titanate, the amount is 0.2wt% (based on the mass of PTA), six 50ml parallel intermittent reactors are used for methyl esterification reaction, and the same amount of raw materials are added to each reactor for parallel experiments. The reaction temperature is 200℃, the reactor pressure is increased to 4.5MPa, the stirring rate is 200rpm, and one reactor is taken out every 20min, and the reactor is quenched with ice water. After all six reactors are taken out and cooled, samples are taken for analysis, and the results are compared and listed in Figure 2-4 .

[0057] Comparative Example 12 See attached Figure 2-4 In this comparative example, similar methyl esterification reaction was carried out on the basis of the comparative example 10 above. The feed of purified terephthalic acid was 8g, the feed of methanol was 24g, the catalyst was polyferric sulfate, the amount was 0.2wt% (based on the mass of PTA), the reaction temperature was 200℃, the pressure of the reactor was 4.5MPa, and after the reactor was completely taken out and cooled, samples were taken for analysis. The results are listed in the table below. Figure 2-4 .

[0058] Comparative Example 13 See attached Figure 5-7 In this comparative example, similar methylation reaction was carried out on the basis of the comparative example 10 above. The feed of purified terephthalic acid was 8g, the feed of methanol was 24g, the catalyst was tetrabutyl titanate, the amount was 0.2wt% (based on the mass of PTA), the reaction temperature was 240℃, the pressure of the reactor was 7.8MPa, and after the reactor was completely taken out and cooled, samples were taken for analysis, and the results were compared and listed in Figure 5-7 .

[0059] Comparative Example 14 See attached Figure 5-7 In this comparative example, similar methyl esterification reaction was carried out on the basis of the comparative example 10 above. The feed of purified terephthalic acid was 8g, the feed of methanol was 24g, the catalyst was polyferric sulfate, the amount was 0.2wt% (based on the mass of PTA), the reaction temperature was 240℃, the pressure of the reactor was 7.8MPa, and after the reactor was completely taken out and cooled, samples were taken for analysis, and the results were compared and listed in Figure 5-7 .

[0060] The test results of Comparative Examples 11-14 are shown in Table 7.

[0061] Table 7

[0062] Comparing Comparative Examples 11 and 13 with Comparative Examples 12 and 14, it can be seen that at 200°C, in the early stage of the reaction, the DMT generation rate of the tetrabutyl titanate catalytic group is faster, and after 1 hour, the DMT generation rate is gradually lower than that of the polyferric sulfate group and the PTA consumption rate is significantly lower than that of the polyferric sulfate group. This is because the product water is not discharged immediately in the intermittent reactor, resulting in the hydrolysis and inactivation of the catalyst; at 240°C, the DMT generation rates of the two groups are significantly improved, but the polyferric sulfate group is slightly lower than the tetrabutyl titanate group, and the PTA consumption rates of the two catalyst groups are close; in addition, at 240°C. The two groups of MMT concentration maxima are close and appear in similar positions, while at 200°C, the MMT concentration maximum of the tetrabutyl titanate group appears faster and earlier, which shows that the catalyst mainly catalyzes the second step reaction; the current price of tetrabutyl titanate is about 25,000 to 30,000 yuan / ton, while the price of polyferric sulfate is about 200 to 1,200 yuan / ton. Polyferric sulfate has a greater cost advantage, so polyferric sulfate is a better choice for methylation catalyst.

[0063] The present invention adopts a high performance liquid chromatography method to analyze the composition of the product, wherein the methyl esterification reaction system mainly contains three substances: terephthalic acid (PTA), monomethyl terephthalate (MMT), and dimethyl terephthalate (DMT); the analysis adopts an external standard method, and the solvent uses dimethyl sulfoxide (DMSO) and methanol to prepare a standard solution; Taking PTA conversion rate and DMT yield as the evaluation criteria for esterification efficiency, the calculation method is: ; .

[0064] In summary, in the prior art, terephthalic acid is usually extracted by distillation, crystallization and other methods for the treatment of printing and dyeing white mud waste, but the purity is low; or low-quality chemical downstream products are directly obtained by reaction, which has the problems of high cost or insufficient resource utilization; while the present invention utilizes the physical property of dimethyl terephthalate that it is easy to sublime, and distills to obtain dimethyl terephthalate with higher purity, which can be used as a polyester monomer and as a raw material for preparing green plasticizers; after the white mud is efficiently esterified, the present invention utilizes the mild reaction conditions of the ester exchange method to reduce the reaction temperature and time, solves the problems of high purity requirements and high energy consumption of the raw material PTA in the direct esterification method, realizes the resource utilization of waste chemicals, and provides a new way for the industrial production of DOTP, which has good commercial significance.

[0065] The above-mentioned embodiments only express the preferred implementation of the present invention, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the scope of the invention patent. It should be pointed out that for ordinary technicians in this field, several modifications and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be based on the attached claims.

Claims

1. A process for recovering waste printing and dyeing white mud to prepare DMT and DOTP, characterized in that: The steps include: S1, pretreatment unit: the solid residue of printing and dyeing white mud obtained by the alkali reduction process is repeatedly washed with 80°C deionized water until the pH of the filtrate is 6-7, and the solid after the filtrate is dried is added into the first pulping kettle with methanol and catalyst I in proportion and stirred and mixed; S2, methyl esterification unit: the mixed slurry is sent to the primary esterification kettle for reaction, the PTA conversion rate is maintained at more than 90%, the outlet liquid phase material is sent to the secondary esterification kettle for deep esterification, the gas phase is sent to the first distillation tower to separate MMT / DMT, and then the gas phase is sent to the alcohol-water separation tower for dehydration and then the methanol is refluxed; MMT / DMT is sent to the secondary esterification kettle, the terephthalic acid esterification rate of the liquid phase outlet of the secondary esterification kettle is maintained at more than 98%, the liquid phase is sent to the distillation unit, and the gas phase is also sent to the first distillation tower for dehydration and then the methanol is refluxed; S3, distillation unit: the liquid phase obtained from the secondary esterification reactor in step S2 is sent to the second distillation tower for distillation separation and purification of DMT, the top fraction of the second distillation tower is condensed and sent to the pulping unit, and the bottom fraction is separated from the residue and sent to the methyl esterification unit; S4, pulping unit: adding the product obtained from the top fraction of the second distillation tower in step S3, isooctyl alcohol and catalyst II in proportion into a second pulping kettle and stirring and mixing; S5, transesterification unit: the mixed materials are sent to the transesterification kettle, and when the DMT conversion rate in the outlet liquid phase reaches 99%, the gas phase is sent to the methanol / isooctanol separation tower to remove methanol and then the isooctanol is refluxed; the crude DOTP in the liquid phase is sent to the refining unit; S6, refining unit: remove isooctyl alcohol from the crude DOTP in step S5 by vacuum distillation, neutralize with alkaline solution under heating conditions until the acid value is less than 0.1 mgKOH / g, wash repeatedly with water, stand for stratification, take the upper layer solution and send it to a stripping tower to remove residual water and isooctyl alcohol from DOTP, finally add a decolorizer to the stripped DOTP, heat for decolorization, and cool to obtain the final product DOTP.

2. A process for recovering DMT and DOTP from waste printing and dyeing white mud as claimed in claim 1, characterized in that: In step S1, the mass ratio of the solid after drying the filtrate to methanol is 1:3~4; the catalyst I is selected from one or more of concentrated sulfuric acid, methylbenzenesulfonic acid, manganese acetate, cobalt acetate, antimony acetate, zinc acetate, zinc oxide, titanium sulfate, dibutyltin oxide, tetrabutyl titanate, isopropyl titanate, polymerized ferric sulfate, and solid acid catalysts, and the amount of the catalyst I is 0.2%~0.8% of the mass of the solid residue of printing and dyeing white mud.

3. A process for recovering DMT and DOTP from waste printing and dyeing white mud as claimed in claim 1, characterized in that: In step S1, the main components of the solid residue of printing and dyeing white mud include water, terephthalic acid, oligomer waste fiber, SiO2, TiO2, Na + 、SO4 2- , inorganic or organic impurities.

4. A process for recovering DMT and DOTP from waste printing and dyeing white mud as claimed in claim 1, characterized in that: In step S2, the reaction temperature in the primary esterification kettle is 180-240°C, the reaction pressure is 3.0-15.0 MPa, and the liquid phase residence time is 1-5 h, which is a liquid-solid heterogeneous reaction; the outlet liquid phase material is sent to the secondary esterification kettle for deep esterification at a reaction temperature of 180-240°C, a reaction pressure of 3.0-15.0 MPa, and a liquid phase residence time of 1-5 h.

5. The process for recovering DMT and DOTP from waste printing and dyeing white mud as claimed in claim 1, characterized in that: In step S2, the number of theoretical plates of the first distillation tower is 2-5, the number of feed plates is 2-4, the top reflux ratio is 0.6-0.8, the absolute pressure is 100-200 kPa, the reboiler temperature is 100-150 ° C, the load is 120-180 kw, and the condenser load is 300-600 kw; the first distillation tower removes low-boiling components at the top of the tower, and the low-boiling components include water and methanol, and the bottom of the tower is DMT; the number of theoretical plates of the alcohol-water separation tower is 25-30, the feed plates are the 15th-20th, the top reflux ratio is 0.6-0.8, the absolute pressure is 100-120 kPa, the reboiler temperature is 100-120 ° C, the load is 200-350 kw, and the condenser load is 350-450 kw.

6. A process for recovering waste printing and dyeing white mud to prepare DMT and DOTP as claimed in claim 1, characterized in that: In step S3, the number of theoretical plates of the second distillation tower is 15-40, the number of feed plates is 10-30, the top reflux ratio is 0.6-0.8, the absolute pressure is 10-60 kPa, the reboiler temperature is 250-350 ° C, the load is 60-80 kw, the condenser load is 60-80 kw, the bottom of the tower is MMT, PTA, catalyst I and insoluble impurities, and the top of the tower is DMT with a purity greater than 99%.

7. The process for recovering DMT and DOTP from waste printing and dyeing white mud as claimed in claim 1, characterized in that: In step S4, the molar ratio of the product obtained from the top fraction of step S3 to isooctyl alcohol is 1:2-2.5, the catalyst II is selected from one or more of sodium methoxide, isopropyl titanate, tetrabutyl titanate, stannous octoate, dibutyltin dilaurate, zinc oxide or a new catalyst, and the amount of the catalyst II is 0.2-0.8% of the product obtained from the top fraction of step S3.

8. The process for recovering DMT and DOTP from waste printing and dyeing white mud as claimed in claim 1, characterized in that: In step S5, the reaction temperature of the transesterification kettle is 90-180° C., the reaction pressure is 0.1-0.2 MPa, the liquid phase residence time is 1-3 h, and the outlet liquid phase conversion rate is greater than 99%.

9. The process for recovering DMT and DOTP from waste printing and dyeing white mud according to claim 1, characterized in that: In step S6, the temperature of the reduced pressure distillation is 100-180°C, and isooctyl alcohol is removed at -0.1 MPa for 3-5 hours; the upper layer solution is sent to a stripping tower for stripping using 100°C water vapor, and the decolorizing agent is selected from one or more of powdered activated carbon, kaolin, and diatomaceous earth, and the decolorization is carried out at 60-100°C for 1-5 hours.

10. The process for recovering waste printing and dyeing white mud to prepare DMT and DOTP as claimed in claim 1, characterized in that: In step S6, the heating temperature of the neutralization reaction using an alkaline solution under the heating conditions is 60~100°C, the alkaline solution is a NaHCO3 solution with a mass concentration of 5~10% or a Na2CO3 solution with a mass concentration of 2~5% or a NaOH solution with a mass concentration of 1~5%, the stirring and mixing time of the neutralization reaction is 10~30min, and the standing stratification time is 1~3h.

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