DD269296A3 - METHOD FOR CONTINUOUS PRODUCTION OF POLYALKYLENEPEPHTHALATE - Google Patents

Abstract

The invention relates to a process for the continuous production of polyalkylene terephthalate. The invention relates to the esterification of dicarboxylic acids and diols, preferably of terephthalic acid and ethylene glycol or butylene glycol. The process is applicable in the chemical industry in the production of polyethylene terephthalate or polybutylene terephthalate. By adjusting the reaction parameters according to the invention in the esterification of terephthalic acid with ethylene glycol, the water output from the esterification phase is decisively promoted, so that esterification products are obtained both with a high degree of conversion and with a high average degree of polycondensation, resulting in polycondensates with low equipment, materialoekonomischen and energy costs can be further processed.

Description

Field of application of the invention

The invention relates to the esterification in the preparation of polyalkylene terephthalate from dicarboxylic acids and diols, preferably from terephthalic acid and ethylene glycol or butylene glycol. The process is applicable in the chemical industry in the production of polyethylene terephthalate or polybutylene terephthalate.

Characteristic of the known technical Löc Jngen

In the production of polyesters, it is known to achieve high degrees of esterification esterification under Dn ckabsenkung (DE-OS 2711331, DE-OS 2338824, DE-OS 2414122) and temperature increase (DD-PS 206558) or under pressure increase (DE-OS 2403607 ).

While in the esterification untor pressure increase products are obtained with high degrees of esterification, the average degree of polycondensation after completion of the esterification is low, whereby increased equipment and energy costs in the subsequent condensation stages are necessary.

The known procedures for esterification under pressure reduction with simultaneous temperature increase have no optimal conditions, which are suitable to obtain both products with high degree of esterification and high average Polykondonsationsgrad already after esterification.

This objective is to be achieved by a combined esterification and polycondensation by controlling the unbound alkanediol in the esterification product (DD-PS 235458).

To optimize the esterification reaction in the batchwise preparation of polyesters, it has been proposed to carry out the esterification under ambient temperature influence as a function of the degree of esterification (EP-PA 104815), to carry out the removal of the reaction by-products as a function of the reaction time in accordance with a predetermined model (EP-PA 104814) ) and to adjust the water content in the esterification product to a maximum of 100 ppm (EP-PA 104813). However, this procedure is practicable only in the discontinuous regime and not transferable to the continuous esterification process. In addition, long esterification times (EP-PA 104814, Example 1) and high energy and equipment expenses (EP-PA 104813) are required.

Object of the invention

The aim of the invention is the production of esterification products having a high degree of esterification and a high average degree of polycondensation already after the esterification for an improved course of the polycondensation reaction.

Explanation of the essence of the invention

The object of the invention is to shift the reaction step in the esterification phase in favor of the polyesterification reaction.

According to the invention, this object is achieved by the fact that in the continuous production of polyalkylene terephthalate from dicarboxylic acids and alkanediols by esterification in the temperature range from T ₀ = 533KbisT ₍ = 548Kundim pressure range from po = 0.25MPa (Cl) to p, = 0.04MPa ( U) from the first to the last esterification stage, the water content in the esterification between 0.01 and 0.08Ma .-% and in the vapor phase to the 500- to 50-fold, based on the

Concentration in the esterification product, is set. This happens because in a reeakiorxaskade stepwise temperature increases in a difference range | ΔΤ | = 3-15K with pressure reducer in a difference range | Ap | = 0.1-0.21 MPa are inversely proportional combined so that the quotient of the absolute values

JM

_{30 to 70} JL _b .

MPa

_{= = 30 to 70}

| Δρ | Ipo-PiI MPa,

T ₀ is the product temperature in the first and T ₁ in the last and p ₀ the system pressure in the erston and pi in dor last Veresterungsstufp. The hydroxyl-bonded groups bound in the esterification product reach a maximum value of 1600 μ eq / g. The Reaction time in the esterification is at least 30 and at most 50%, based on the total reaction time. Due to the adjustment of the reaction parameters according to the invention, the heat output in the esterification becomes crucial

favors so that esterification products are both high-conversion as well as high average Polykondensationsgraderhülten that can work with little apparatus, matorial-economical and energy costs to Polykondensatenweite- work.

embodiment

Terephthalic acid and ethylene glycol were continuously esterified in a molar ratio of 1: 1.67 with the addition of antimony trioxide as the polycondensation catalyst in a two-stage esterification cascade. In this case, after the first esterification stage, a water content of 0.08% by weight and, after the second esterification stage, of 0.03% by mass in the esterification product were established. The adjustment of the water content was carried out by the application of a stepwise, inversely proportional increase in temperature in relation to the Druckerniodngung of 47.6 K / MPe from the first to the second esterification stage according to the following relationship:

| ΔΤ | ₌ IT ₀ -TiI ₌ J536K-546K | | 10K | K

| Δρ | Ipo-PiI (0.25MPa (U) -0.04MPa (U)] | 0.21MPaf "" MPa,

where T _{0 is} the product temperature in the first and Ti in the second and p ₀ the system pressure in the first and p, in the second

Represent esterification stage. With the applied ratio of temperature increase to depressurization at the same time in the vapor phase Water content of 0.37 g / g esterification product, d. H. 463 times, based on the water concentration in the Esterification product, discontinued in the first esterification stage. In the second esterification stage, the water content was in

the vapor phase 0.017 g / g esterification product, which was 57 times the water concentration in the esterification product.

The hydroxyl end groups bound in the esterification product after esterification had on average a value of

1098uÄqu / P up.

The reaction time in the esterification cascade was 180 minutes, which corresponds to a proportion of the esterification, based on the Total reaction time, including polycondensation of 47% corresponded. With the targeted adjustment of the water content and the bound hydroxyl groups in the esterification by the Application of the described temperature increase and pressure gradation was an esterification product with a Turnover of 97% and an average degree of polycondensation of Pn = 7.1 obtained in the subsequent Condensation with little equipment, energetic and material-economic costs iu a high

high-grade polyethylene terephthalate weitarverarbeitan let.

Claims (1)

Process for the continuous preparation of polyalkylene terephthalate from dicarboxylic acid and alkanediols by stepwise esterification in the temperature range from T ₀ = 533K to T, = 548K and in the pressure range from Po = 0.25MPa (Ü) to P ₁ - 0.04MPa (Cl) of the first to the last stage of pre-esterification, characterized in that the water content in the esterification product is adjusted to between 0.01 and 0.08% by mass and in the vapor phase to 500 to 50 times, based on the concentration in the esterification product, in one Reactor cascade gradual temperature increases in a differential range | ΔΤ | = 3-15K with pressure decreases in a difference range | Δρ | - 0.1-0.21 MPa are inversely proportional combined so that the quotient of the absolute values T ₀ -T, = 30 to 70 ^K Po- Pi MPa in which T _{0 represents} the product temperature in the first and Ti in the last sowio p ₀ the system pressure in the first and pi in the last esterification stage, the hydroxyl end groups bound in the esterification product reach a maximum value of 1600pÄqu / g and the reaction time in the esterification at least 30% and not more than 50% of the total reaction time.