Process for the production of DMT-intermediate product of specific purity and pure terephthalic acid

The invention relates to a process for the production of a DMT intermediate product as well as its working up to fibregrade DMT and to medium pure and pure terephthalic acid. The DMT intermediate product is moreover produced by combined oxidation of a predominantly para-xylene (p-X) and para-toluic acid methyl ester (p-TE) containing mixture in liquid phase with an oxygen containing gas, esterification of the acids being produced with methanol, distillative or rectificative separation of the esterification products being produced into a p-TE rich fraction I, a fraction II containing more than 99% by weight DMT and its isomers and a high boiling residue fraction III as well as feeding back the p-TE fraction I into the oxidation, with the residue fraction III having a DMT content of 15 to 70% by weight and the DMT fraction II being purified by single solvent recrystallisation in methanol to form the DMT intermediate product to such an extent that the amounts of hydroxymethylbenzoic acid methyl ester (HM-BME) and terephthalic acid methyl ester (TAE) in the DMT intermediate product amount together to less than 200 ppm.

FIELD OF THE INVENTION 
The invention relates to a process for the production of DMT-intermediate 
product according to the preamble of claim I as well as its working up to 
medium pure or fibregrade dimethylterephthalate (DMT-p) and/or medium pure 
or pure terephthalic acid (MTA/PTA). 
Dimethylterephthalate (DMT) is produced in numerous large scale plants 
according to the so-called Witten-DMT-Process (cf. German Patent 
Specification 10 41 945). DMT is subsequently worked up to polyesters by 
reaction with multifunctional alcohols. Those high molecular 
compounds--also known as saturated polyesters--are worked up inter alia to 
form fibres, filaments, films or moulded parts. 
STATE OF THE ART 
According to the Witten-DMT-Process, a mixture of para-xylene (p-X) and 
para-toluic acid methylester (p-TE) is oxidised in-the liquid phase in the 
absence of solvents and of halogen compounds at a pressure of about 4 to 8 
bar and a temperature of about 140 to 180.degree. C. with atmospheric 
oxygen in the presence of dissolved heavy metal oxidation catalysts, e.g. 
in the presence of a mixture of cobalt and manganese compounds (cf. German 
Patent Specification 20 10 137). 
Subsequently to the oxidation step, the reaction mixture obtained, which 
consists predominantly of monomethyl terephthalate (MMT), p-toluic acid 
(p-TA) and terephthalic acid (TA), dissolved or suspended, resp., in 
para-toluic acid methyl ester-(pT-ester) and dimethyl terephthalate (DMT), 
is esterified with methanol at a pressure of 20 to 25 bar and a 
temperature of about 250.degree. to 280.degree. C. Higher pressures are 
technically possible but for cost reasons are not used. The esterification 
product is distillatively separated into a p-TE-fraction, a crude DMT 
fraction and a high boiling, tar-like residue. The p-TE-fraction is fed 
back into the oxidation. The high boiling, tar-like distillation residue 
contains, inter alia, all the constituents of the catalyst system, which 
according to EP-B-0 053 241 can be recovered and fed back into the 
oxidation. 
The crude DMT originating from the distillation and having a typical purity 
of 97 to 99.9% contains, besides about 0.05 to 2% of isomers of DMT 
(dimenhylortho- and dimethylisophthalate [DMO, DMI]), still partly 
interfering amounts of terephthalaldehydic acid-methylester (TAE), 
monomethylterephthalate (MMT), para-toluic acid (p-TA) and other 
impurities resulting from the p-xylene employed or from side reactions. 
For purification of the crude DMT to pure (fibregrade) DMT (DMT-p), with it 
being necessary in particular, for TAE and the isomers to be removed, it 
is known to treat the crude DMT by methanolic recrystallisation (German 
Offenlegungsschrift 20 14 012, Hydrocarbon Processing, Nov. 1983, P.91). 
For attaining a purity of the DMT (sum of impurities inclusive of the 
isomers DMO and DMI less than 100 ppm) sufficient for fibre production 
(fibregrade DMT), it has been to some extent usual to carry out the 
recrystallisation twice with intermediate washing with methanol, with the 
methanol being fed in countercurrent. In addition a final distillation of 
the DMT has still been necessary hitherto with a crude DMT of low purity. 
The filtrate residue obtained in the methanolic recrystallisation by 
filtration from the mother liquor still contains, in addition to the 
isomers DMO and DMI, large amounts of DMT and other valuable products 
(intermediate products in the pMT-process), so that the filtration residue 
was hitherto as a general rule for the largest part fed back into the 
oxidation. As a result of this feeding back of filtration residue, the 
isomers accumulate up to values of 8 to 12% by weight so that the 
antecedent reactors and especially the distillation and recrystallisation 
must have additional capacities. The feeding back of the filtration 
residue was, according to the state of the art, necessary for obtaining 
sufficiently "neutral products" for the adjustment of the melting point 
and the acid number in the oxidation and the flowability of the oxidation 
product to the esterification. 
From German Patent specification 30 11 858 and German Patent Specification 
29 16 197 it is known that the amount of terephthalaldehydic acid 
methylester (TAE) in the DMT intermediate product must be kept as small as 
possible, in particular in the working up to form fibregrade terephthalic 
acid (PTA). In German Patent Specification 30 11 858, there is proposed a 
particularly expensive rectification column, for reduction of the TAE 
content in the crude DMT, in which column the TAE content in the crude DMT 
can be reduced to values of &lt;0.01% by weight. 
In spite of this high cost, it has been shown with this process that an 
always still interfering large amount of terephthalaldehydic acid (TAS, 
4-CBA), the acid formed from the TAE in the hydrolysis, can be present in 
the end product, terephthalic acid (TA). The residual content of TAS in 
the terephthalic acid could then assume in particular inexplicably high 
values if the crude DMT had to be stored in the meanwhile before the 
working up to terephthalic acid. 
OBJECT OF THE INVENTION 
It is the object of the present invention to improve the process of the 
indicated type for the production of DMT intermediate product to the 
effect that, in the working up of the DMT intermediate product to 
fibregrade DMT, the TAE content, and in the working up to PTA, the TAS 
content, is reduced further. In particular, even with longer intermediate 
storage of the crude DMT and then working up to pure DMT or PTA 
respectively, the TAE content or the TAS content, in the end product 
should be kept as low as possible. 
Further concerns of the invention are the lowering of the cost of apparatus 
and energy in the DMT and PTA production, the increasing of yield and the 
creation of a possibility of producing DMT-p and PTA simultaneously in one 
plant. 
SUMMARY OF THE INVENTION 
This object is solved according to the invention by the features of claim 
1. 
It is an essential feature of the invention to improve and to simplify the 
purification of the crude DMT by cost effective rectification and 
subsequent single solvent recrystallisation. 
The largest part of the impurities--with exception of the isomers--is 
removed according to the invention by rectification so that the thus 
purified crude DMT (fraction II) preferably has a TAE and 
hydroxymethyl-benzoic acid methylester content (HM-BME) of together less 
than 0.2% by weight (2.000 ppm). The rectification of the ester mixture 
can be simplified, in relation to the process according to German Patent 
Specification 30 11 858 because the high boiling residue fraction III has 
a high DMT content of 15 to 70% by weight, preferably 40 to 60% by weight. 
Likewise, the p-TE rich fraction I can have a high DMT content, this lying 
preferably at 20 to 30% by weight. 
The residue fraction III can be prepared for example with a process 
according to German Patent Specification 24 27 575. According to a 
preferred embodiment of the invention, the residue fraction is however 
prepared by methanolysis in two steps, -with the DMT as well as further 
valuable products being fed back into the oxidation. In all, the DMT 
content, ,which is recovered from the residue fraction and is fed back 
into the oxidation, amounts preferably to 3 to 7% by weight related to the 
sum of all the components supplied in the liquid phase to the oxidation. 
Preferably, the D-TE fraction I is fed back in excess to the oxidation so 
that still about 5 to 30% by weight of p-TE, in particular 20 to 25% by 
weight, are obtained in the acid mixture being produced in the oxidiser. 
The adjusted p-TE excess as well as the DMT quantities recycled serve for 
increasing reaction and for melting point adjustment of the product flow 
leaving the oxidiser. Melting points of 130.degree. to 150.degree. C. with 
an acid number of 200 to 300 g KOH/kg oxidate are preferred. 
The crude DMT purified by rectification (fraction II) is then subjected to 
a single solvent recrystallisation, preferably in methanol, in order to 
remove residual amounts of TAE, HM-BME and other impurities. At the same 
time, the isomers DMO and DMI can be removed in this step. 
According to a preferred embodiment of the invention, the mother liquor 
originating from the (first) methanolic recrystallisation is concentrated 
by evaporation of methanol. The dissolved DMT with amounts of isomers and 
impurities corresponding to the solvent equilibrium are then crystallised 
out as a result of further cooling to about 20.degree. to 50.degree. C., 
preferably about 25.degree. C., filtered off and after mixing with 
methanol fed back to the (first) recrystallisation. The substances still 
dissolved in the remaining mother liquor, predominantly DMO, DMI and 
residues of DMT as well as the amounts of TAE and HM-BME not removed in 
the rectification, are concentrated by evaporation of the residual 
methanol and discharged as residue from the process or fed back into the 
oxidation. 
Insofar as is usual according to the state of the art, the p-xylene 
employed has an isomer content of above 1,000 to 5,000 ppm, according to a 
preferred embodiment of the invention, a feeding-back into the oxidation 
of the residue being deposited is completely dispensed with. A complete 
discharging of the residue is therefore not subject to uneconomical losses 
because, in the preceding rectification, the valuable products TAE and 
HM-BME have already been removed almost completely from the crude DMT. At 
the same time, a feeding back of residue--in contrast to the known 
process--is also not necessary for the adjustment of the melting point and 
the acid number in the oxidiser since the neutral product quantities 
needed for this purpose are fed back into the oxidation as DMT-proportions 
of the p-TE-fraction I and the residue fraction III. 
With p-xylene particularly clean with respect to isomers, with isomer 
amounts below 100 to 500 ppm, the entire residue can optionally also be 
fed back into the oxidation, insofar as a corresponding amount of isomers 
can be tolerated in the end product. With these small amounts of isomers 
in the p-xylene, which according to the present state of the art is 
certainly not in sufficient amounts for convenience, the amount of residue 
fed back is however relatively small, amounting to about 3 to 6% by weight 
of the amount of DMT fed back into the oxidation from the rectification. 
Indeed, depending on required end product purity and amount of isomers in 
the p-xylene, a part of the filtrate residue can also optionally be fed 
back into the oxidation, with the amount of DMT and its isomers being 
small in relation to the amounts of DMT, which are fed back into the 
oxidation from the rectification. 
It is a further essential feature of the invention to minimise also the 
amount of the impurity hydroxymethyl-benzoic acid methylester (HM-BME) 
present in the DMT intermediate product, in addition to TAE. 
It has been surprisingly shown that the amount of HM-BME in the crude DMT, 
in addition to the amount of TAE, is decisive for the TAE content in the 
fibregrade DMT or for the amount of TAS in PTA. It is supposed that HM-BME 
in the intermediate storage tank connected to the DMT production or in the 
subsequent processing steps is reacted with atmospheric oxygen to form 
TAE, with the atmospheric oxygen being able to be present in the closed 
plant as a result of unavoidable micro leakages in the distillation part, 
which is run with sub-atmospheric pressure. This relationship was unknown 
until the time of the invention. 
As a result of the process according to the invention for the production of 
DMT intermediate product, it has been possible for the first time to 
essentially simplify the subsequent processing steps for producing 
fibregrade DMT and/or PTA, without the TAE content in the pure DMT or the 
TAS content in PTA assuming higher values. Also, with longer interim 
storage of the DMT intermediate products, it can be guaranteed reliably 
that the amount of TAE or TAS in the end product does not increase 
further, so that a uniform quality is attained. 
The DMT intermediate product according to the invention with a typical 
content of isomers, TAE and HM-BME of, in total, 50 to 200 ppm can be 
worked up by a second recrystallisation in methanol with low cost in 
apparatus to fibregrade DMT with a typical purity of &gt;99,995% by weight. 
The content of impurities may be reduced, when needed, once again to 
values of &lt;10 ppm by means of an additional methanolic washing of the DMT 
intermediate product before the final recrystallisation. 
The working up of the DMT intermediate product to terephthalic acid takes 
place preferably by hydrolysis in a simple reactor, the produced methanol 
being removed together with the by-product dimethylether (DME) by feeding 
in of stripping steam. The terephthalic acid formed is discharged from the 
reactor suspended or dissolved in water and crystallised out in multiple 
stages, centrifuged and dried. Insofar as the DMT intermediate product is 
supplied to the hydrolysis directly without additional water, the medium 
pure terephthalic acid (MTA) typically contains 500 to 1,000 ppm of 
impurities. By means of a simple washing of the DMT intermediate product 
in methanol and subsequent centrifuging, the purity of the terephthalic 
acid may be increased to 100 to 150 ppm (PTA), with the impurities chiefly 
consisting of MMT. As a result of simple washing of the PTA in water, even 
the MMT content, insofar as necessary, may be further reduced so that a 
terephthalic acid with a purity hitherto hardly attainable in a large 
scale industrial plant with a sum of all impurities inclusive of MMT and 
p-TA of &lt;50 ppm can be produced (PTA-p). 
Furthermore, an essential saving of energy is achieved with the process 
according to the invention. Of especial value is the possibility of 
working up the DMT intermediate product according to the invention both to 
fibregrade DMT (DMT-p) and also to medium and pure terephthalic acid (MTA 
or PTA) with this working up being essentially simplified, for example in 
comparison to the DMT intermediate product according to German Patent 
Specification 29 16 197 and German Patent Specification 30 11 858, since 
the DMT intermediate product according to the invention has only very 
small residual contents of isomers. Finally, the process according to the 
invention opens up the possibility of producing terephthalic acid of very 
high purity (PTA-p) with, in contrast to conventional PTA, reduced amounts 
of impurities, in particular even of MMT and p-TA. 
Of special advantage is finally the possibility of producing with reduced 
additional cost of apparatus and energy at the same time pure DMT and 
fibregrade or very high purity terephthalic acid, with the proportions of 
DMT-p/PTA and PTA-p being able to be varied as desired.

WAYS OF CARRYING OUT THE INVENTION 
EXAMPLE 1 
In FIG. 1 there is shown a plant for the production of crude DMT (fraction 
II) according to the process of the invention with the main components 
oxidiser 1, esterification column 5, and crude ester rectification 7 and 
11. An analysis of the material flows 1.1 to 1.20 defined subsequently and 
shown in FIG. 1 is indicated in Table I. 
In the oxidiser 1, known per se, for example corresponding to DE-C3-28 05 
915, a liquid mixture consisting chiefly of p-xylene (material flow 1.1) 
and p-TE (material flow 1.4) is oxidised with atmospheric oxygen (material 
flow 1.2) at a temperature of about 160.degree. C. and a pressure of about 
7 bar and subject to addition of catalyst (material flow 1.3). 
The oxidation product P.sub.1 being produced contains as main components 
p-toluic acid (p-TA) (about 17% by weight), MMT (about 22% by weight), 
p-toluic acid methylester (p-TE) (about 24% by weight), DMT (about 14% by 
weight) and terephthalic acid (TA) (about 10% by weight). 
Moreover, by-products and impurities, in particular benzoic acid 
methylester (BE), TAE, HM-BME, high boiling substances etc., are to be 
found. 
In the oxidation, the oxygen contained in the air (material flow 1.2) is 
consumed up to a residual content. The otherwise remaining nitrogen is 
saturated with the substances to be found in the oxidiser 1 and leaves as 
oxidiser discharge gas (material flow 1.5) the oxidiser 1 together with 
the reaction water being formed in the oxidation, as well as high boiling 
cracking products like CO, CO.sub.2, formic acid and acetic acid. 
The xylenic mixture denoted as p-xylene (material flow 1.1) consists of 
freshly employed xylene with an isomer content of 6,000 ppm as well as the 
xylenic and organic fractions respectively recovered from the material 
flows 1.5, 1.6 and 1.10. 
The para-toluic acid methylester (p-TE) (material flow 1.4) is withdrawn 
from an intermediate tank which is not shown which is fed predominantly 
from the head produce of the crude ester rectification column 11 (material 
flow 1.12). In the exemplifying embodiment according to FIG. 1, the 
organic components of the flows 1.11, 1.16, 1.15 as well as the products 
recovered from the residue 1.14 are likewise fed into the p-TE 
intermediate tank. 
In the main, the p-TE-flow 1.12 is accordingly fed back into the oxidiser 1 
so that a closed circuit exists. 
The reaction products being produced in the oxidation have in part high 
melting points--p-TA of about 180.degree. C., MMT of about 227.degree. 
C.--or are practically not meltable (terephthalic acid) and are soluble in 
other substances only to a limited extent so that the danger of a 
crystallising out and accordingly blockage occurs. As a result of a 
relatively high amount of p-TE and DMT running in the circuit, this danger 
can be restricted. 
The p-TE-excess employed as well as the DMT quantities running in the 
circuit serve to increase reaction and adjust melting point of the product 
flow P.sub.1 leaving the oxidiser. Melting points in the region of 
140.degree. C. are preferred in this connection. 
The acid number, which is held at 200 to 300 g KOH/kg oxidation product at 
the outlet from the oxidiser, is a valid measure of the well-balanced 
ratio between high melting acids and other products improving the melting 
point and flowability. With too high acid numbers, bad flowability and 
disadvantageous melting points are to be expected and with too low acid 
numbers, that is too large amounts of circulating products, too high 
distillation cost in-the crude ester distillation columns 7 and 11. The 
p-TE-excess is so adjusted that the oxidation conditions in the oxidiser 
remain moderate, than is the temperature lies between 150.degree. and 
180.degree. C. at 5 to 8 bar. It has been established that concentrations 
of 5 to 30% by weight p-TE should be established in the final oxidation 
product. The quantitative flows shown in Table I are obtained if a small 
p-TE excess of 24% and an acid number at the outlet from the oxidiser of 
225 g KOH/kg oxidation product are maintained. 
The oxidation product produced is freed of xylene still contained therein 
in the stripper 2 by means of steam (material flow 1.7). The vapours which 
are obtained have a composition 1.6 according to Table I. 
The oxidation product flow P.sub.1 is next after increasing the pressure by 
means of the high pressure pump 3, combined with hot methanol (material 
flow 1.8) and, after heating in the heat exchanger 4.degree. to 
250.degree. C., is esterified in the esterification reactor 5.degree. at 
250.degree. C. with methanol (material flow 1.9). The methanol is supplied 
at the sump in the form of vapour. The relatively high methanol excess 
leaves the head of the column 5 (material flow 1.10) with the reaction 
water and is saturated with other compounds present at the head of the 
column 5. The esterified oxidation product, the so-called crude ester, is 
depressurized to normal pressure in the intermediate tank 6 and is 
moreover cooled to temperatures of about 200.degree. C. The methanol still 
present escapes in the form of vapour (material flow 1.11) via a vapour 
duct and is saturated with the components obtained in the reactor. 
Crude Ester Rectification 
The crude ester mixture, which still contains byproducts like TAE, BME, 
high boiling substances, HM-BME as well as the catalyst, in addition to 
DMT (about 58% by weight) and p-TE (about 33% by weight), is pumped into 
the rectification consisting of two columns 7, 11 from the intermediate 
container 6. 
The high boiler column 7 with vaporiser 8 and condenser 9 serves for 
driving off of high boiling substances contained in the crude ester 
(material flow 1.14) as sump product, which can be subsequently treated as 
"Residue A" in a separate residue working up (FIG. 2). 
In addition, the "Residue A" contains all of the catalyst as well as a high 
proportion of about 52% by weight DMT. The largest part of the HM-BME is 
likewise discharged together with the residue fraction. 
As a result of the provided high DMT content in the sump flow 1.14 of the 
high boiler column 7, the sump temperature can be held at 250.degree. C. 
and the head pressure at 0.2 bar, with a high temperature level of about 
205.degree. C. which makes possible an energetically satisfactory recovery 
of the condensation heat (condenser 9) in the form of low pressure steam 
(3.5 bar) being set at the head of the high boiler column 7. The head 
pressure of about 0.2 bar in the high boiler column 7 is maintained by a 
vacuum plant which is non shown, wherein the material flow 1.16 is 
discharged. 
The condensed head product flows from the condenser 9 in the low boiler 
column 11 with vaporiser 12 and condenser 13 in order to drive off the 
p-TE fraction. At head temperatures of about 194.degree. C., the 
condensation heat can be used to produce 3.5 bar low pressure steam. The 
DMT content in the head product is held high an about 18% by weight so 
that, inclusive of the amounts of DMT contained in the residue A (material 
flow 1.14), there is obtained a high circulating amount of DMT and 
accordingly the acid number of 225 g KOH/kg oxidation product in the 
oxidate. The relationships set in the exemplifying embodiment shown are 
obtained from Table I (material flow 1.14 and 1.12). Should relationships 
which are suitable for the process be set by the choice of the refluxes 
and amounts, the amounts of TAE and HM-BME in the crude DMT of 0.1% by 
weight for TAE and 0.05% by weight for HM-BME respectively indicated in 
Table I are attained. 
A sump temperature of 250.degree. C., a head temperature 194.degree. C. and 
a head pressure of 0.3 bar are set in the low boiler column 11. The head 
pressure is maintained by pumping off the flow 1.15 by means of a vacuum 
plant which is not shown. 
The high p-TE quantity obtained at top of column 11 assures a residual 
content of p-TE in the oxidation product P.sub.1 of 24%. The substances 
HM-BME and TAE important for the quality of crude DMT represent 
intermediate products of the p-TE oxidation to MMT and can therefore be 
fed back to the oxidiser with the p-TE distillate and the valuable 
products obtained from the residue respectively without problem. It is 
apparent from the reflux ratios or the amounts of vapour in the columns 
(7,11) that the energy necessary for the distillation is relatively low 
compared with the process according to DE-C1-30 11 558. In particular it 
is advantageous that the condensation heat of the low boiler column. 11 
can be utilised in the form of low pressure steam (3.5 bar). 
Recrystallisation 
The crude DMT (fraction II) purified according to FIG. 1 by rectification 
is further purified to the DMT intermediate product by single methanolic 
solvent recrystallisation (FIG. 3, analyses of the material flows 3.1 to 
3.5, see Table III). Moreover the crude DMT (material flow 3.1, 
correspondingly material flow 1.13 according to FIG. 1) is mixed up in the 
mixing tank 28 with methanol from the intermediate tank 39. The hot 
solution is cooled in the crystalliser 29 by means of rotary pump 30 and 
condenser 31 by release of pressure. The pump 32 conveys the crystalysate 
to the centrifuge 33 where it is separated into the Filtrate A and the 
crystalysate. The Filtrate A is fed via tank 34 and pump 35 (material flow 
3.4) to the isomer discharge system (FIG. 4 ) 
The separation as completely as possible of the crystallisation product and 
mother liquor adhering thereto is of decisive significance for the 
purification effect of the apparently expensive recrystallisation since, 
with respect to the mother liquor, this is subject to almost all the 
impurities. A methanolic washing of the crystalysate is therefore carried 
out in the illustrated exemplifying embodiment to increase the 
purification effect of the recrystallisation. Moreover, the crystalysate 
is mixed in the tank 36 with freshly distilled methanol and supplied via a 
pump 37 to the centrifuge 38. The filtrate being produced--an only 
slightly impure methanol--is supplied to the head of the melter 41, while 
the crystalysate is conducted into the melter 41. 
In the melter 41, the residual mother liquor is driven off from the 
crystalysate and the DMT melted. The vaporised methanol is condensed in 
the head of the melter 41 and fed together ,with the filtrate from the 
centrifuge 38 into the intermediate tank 39 for methanol. 
The DMT (material flow 3.5) taken from the melter 41 via the pump 42 
represents the DMT intermediate product of desired purity. It can as a 
matter of choice be worked up by hydrolysis (FIGS. 5 and 6) to 
terephthalic acid or can be worked up by a second recrystallisation to 
fibregrade DMT (DMT-p), with the combination of these possibilities, in 
particular offering surprising advantages. The DMT intermediate product 
(material flow 3.5) still contains only very little impurities of TAE and 
HM-BME, of a maximum of 100 ppm, in the indicated explanatory example of 
only 17 ppm (see Table III), as well as small amounts of the isomer DMI 
and DMO, in the illustrated exemplifying embodiment, together 67 ppm. 
Processing of filtrate 
The filtrate removed from the intermediate tank 34 (FIG. 3) via the pump 35 
(material flow 3.4, FIG. 3 =material flow 4.1, FIG. 4) is initially 
concentrated by evaporation in the vaporiser 59 with separator 60 so that 
the concentrated mixture consists of up to 2/3 of methanol and 1/3 of 
dissolved substance (DMT+impurities). The evaporation pressure is 4 bar 
and the temperature is 100.degree. C. The remaining solution is stored 
under this pressure in the tank 61 and pumped by means of a pump 62 into 
the crystalliser 63 with condenser 64, where the solution is cooled by 
evaporation cooling to about 25.degree. C. 
The corresponding suspension is supplied via pump 65 to the centrifuge 66 
and separated into a filtrate and the crystalysate. The crystalysate can, 
as shown in FIG. 4, be fed back via pump 68 to the first recrystallisation 
as suspension mixed in stirrer tank 67 with methanol (material flow 4.3 in 
FIG. 4, material flow 3.3 in FIG. 3). 
The filtrate is conducted into the collecting tank 69 and from there by 
means of the pump 70 to the vaporiser 71 in which the methanol is 
evaporated off completely (material flow 4.5, Table 4). The remaining 
mixture consists predominantly of DMI (37% by weight) and DMO (26% by 
weight)-and contains only relatively small amounts of valuable products, 
in particular DMT (16% by weight), TAE (10% by weight) as well as 5% by 
weight each of p-TA and HM-BME so that they are discharged completely 
without great losses via the pump 72 (material flow 4.4), in particular to 
undergo combustion. 
Processing of residue 
"Residue A" according to FIG. 1 (material flow 1.14, Table I=material flow 
2.1, Table II) is stored in tank 15 (FIG. 2). Residue A contains, in 
addition to DMT (about 52% by weight), predominantly high boiling 
substances (37% by weight) as well as the catalyst (about 1% by weight). 
The acids still present in Residue A are afterwards esterified in the 
two-step methanolysis according to FIG. 2, a part of the high boiling, in 
particular binuclear aromatic, compounds are cleaved and the valuable 
products (DMT, HM-BME, methoxymethylbenzoic acid methylester [MM-BME] and 
p-TE) are separated from the remaining undesired high boiling substances. 
The valuable products are fed back into the oxidation while the undesired 
high boiling substances are discharged from the process. 
Among the distillable high boiling substances found in residue A are 
substances which, insofar as they are fed back into the oxidation, 
influence yields or selectivity of the oxidation disadvantageously since 
they influence the effectiveness of the catalyst system. Moreover such 
substances can, during the oxidative treatment, form cleavage products 
e.g. CH.sub.3 -DMT isomers, which are disadvantageous for the quality of 
the crude DMT, can only be removed distillatively with difficulty .from 
the crude ester and require additional purification expenditure in the 
subsequent crystallisation if high purity polyester crude substances are 
to be produced. The feeding back of such high boiling substances into the 
oxidation must therefore be avoided. 
The following reaction guidance is given in the illustrated exemplifying 
embodiment: 
Residue A from the crude ester distillation is run from the tank 15 by 
means of the pump 16 into a circulating system which consists of pump 18, 
heat exchanger 17 and reactor 19. At the same time, methanol in the form 
of vapour (material flow 2.10) is pumped into the circulation. As a result 
of the presence of the methanol, residual amounts of esterified high 
boiling acids which are still contained are esterified and to some extent 
taken up by the high methanol vapour excess and flashed in the form of 
vapour into the vapour space of the reactor 19. The amount of liquid which 
is not vaporised remains in the sump part of the reactor 19 and is treated 
afresh with methanol vapour and cleaved methanolytically again. The esters 
being produced remain in the methanolic vapour phase and are conducted 
together with the distillable constituents of the residue and the flash 
product into the distillation column 20. The temperature in the reactor 19 
chosen in the exemplifying embodiment amounts to 265.degree. to 
270.degree. C., whereas the temperature in column 20 is at about 
250.degree. C., so that a part of the high boiling constituents can be 
withdrawn at the sump of the column 20. The high boiling by-products are 
concentrated in the operating part of the distillation column 20, and 
withdrawn at the sump of the column. A part of the high boiling product is 
discharged, while the rest, mixed with methanol vapour, is fed back via 
pump 22 and vaporiser 21 to the sump of the column. Until the distillable 
high boiling substances, which do not represent valuable products and 
therefore, as mentioned above, leave the sump of the column 20 as high 
boiling substances, all valuable products are directed with the methanol 
vapour to the dephlegmator 23 and condensed. A part of the condensate is 
used as reflux, whereas the rest is discharged (material flow 2.5) and is 
mixed with the p-TE flow for the oxidation. The methanol excess (material 
flow 2.4) is directed together with the water being produced in the 
methanolysis and postesterification to a methanol dewatering column (not 
shown). 
A part of the circulating flow from the reactor 19 is discharged from the 
circuit and subjected to a further methanolysis step in the reactor 24 
with heat exchanger 25, circulating pump 26 and dephlegmator 27. This 
second methanolysis step is carried out at a temperature of &gt;275.degree. 
C., so that further high molecular compounds of Residue A are split off. 
The products leaving the reactor 24 in gaseous form are condensed 
completely in the dephlegmator 27, with the exception of the methanol, 
while the methanol (material flow 2.7) together with the methanol from the 
dephlegmator 23 is discharged for reuse in the general process. The 
products condensed in the dephlegmator 27 are for the largest part fed 
back together with the p-TE flow into the oxidation, while a small part is 
fed back as reflux to the head of the column of the reactor 24. The 
constituents which have not vaporised are withdrawn at the sump of the 
reactor 24 and discharged partly for catalyst recovery (material flow 2.3) 
while the remainder is led back by means of pump 26 via vaporiser 25 to 
the reactor. In addition methanol in the form of vapour is supplied to the 
reactor circulation. 
EXAMPLE 2 
The washing of the DMT crystalysate can possibly be dispensed if not 
especially high requirements are placed on the purity of the DMT 
intermediate product, e.g. for the production of medium pure terephthalic 
acid (MTA). In FIG. 3, this alternative for the production of DMT 
intermediate product is shown in broken line. The DMT intermediate product 
(product flow 3.7) withdrawn from the melter still contained about 150 ppm 
of TAE and HM-BME as well as 580 ppm of isomers DMI and DMO. 
EXAMPLE 3 
The simultaneous production of fibregrade DMT (DMT-p) and DMT-intermediate 
products for terephthalic acid production is shown to a further extent in 
FIG. 3. For this purpose, the crystalysate flow from the centrifuge is 
distributed to mixing tanks 36 and 54. The DMT crystalysate is mixed -with 
methanol from the intermediate tank 52 in the mixing tank 54 and supplied 
via the pump 55 to the centrifuge 56. The filtrate being produced is 
supplied to the methanol intermediate tank 39, while the crystalysate in 
the mixing tank 57 is mixed with pure methanol and is supplied via the 
pump 58 and heat exchanger 43 to the intermediate tank 44. The DMT 
dissolved in methanol is further purified in the second recrystallisation 
consisting of crystallyser 45, heat exchanger 47 and pump 46. The crystal 
suspension is then supplied via the pump 48 to the washing centrifuge 49 
where it is distributed into a filtrate and a crystalysate flow. The 
crystalysate is then melted in melter 50 and freed from residual mother 
liquor while the filtrate is directed via the condensation head of the 
melter 50 to the intermediate tank 52. The filtrate consisting almost 
exclusively of methanol is fed back via the pump 53 to the mixing tank 54 
(countercurrent). The DMT-p produced is withdrawn by means of the pump 51 
to the melter 50. It contains less than 10 ppm of isomers and only about 2 
ppm TAE and HM-BME (material flow 3.6) and represents accordingly a 
fibregrade DMT with--for large scale industrial plants--hitherto 
unachieved purity. 
EXAMPLE 4 
Hydrolysis (PTA) 
The hydrolysis of the DMT intermediate product according to FIG. 3 
(material flow 3.5) to fibre pure terephthalic acid (PTA) is explained 
more precisely with reference to FIG. 5. 
The DMT intermediate product (material flow 5.1) coming from the first 
recrystallisation (FIG. 3) is mixed in mixing tank 73 with water from the 
stripping steam producer 74 in the ratio 1:1 and partially hydrolysed. The 
suspension is pumped into the hydrolysis reactor 76 by means of the pump 
75, in which the mixture is treated ,with stripping steam from the 
stripping steam producer 74. In this way the methanol being freed in the 
hydrolysis together with steam and the dimethylether formed is driven off 
in the hydrolysis column 77 with condenser 78 and heat exchanger 79. By 
suitable choice of the reflux ratio, the result is attained that a 
methanol free water can be withdrawn at the sump of the column 77 with the 
help of the pump 80 and can be fed back into the stripping steam producer. 
The condensed head product (material flow 5.2) consists chiefly of 
dimethylether (DME), methanol and water and can be supplied to a methanol 
rectification (not shown) after distillative separation off of the DME. 
The dimethylether is burned off while the methanol is fed back into the 
esterification (FIG. 1). From the reactor 76, the terephthalic acid being 
produced is crystallised out in a three-step expansion crystallisation 
(crystallisers 81, 82 and 83) and conveyed to the centrifuge 85 by means 
of pump 84. The crystal slurry is supplied to the drier 86 and dried there 
to form pure terephthalic acid (PTA) (material flow 5.5). The mother 
liquor running out from the centrifuge 85 into the collecting tank 87 is 
discharged, partially as waste water (material flow 5.4) for removal of 
still dissolved isomers (ITA, OTA) and of foreign substances which arise 
for example by wear of the mechanically moved parts like slide ring seals 
etc. The largest part of the filtrate is however fed back by means of the 
pump 88 to the stripping vapour producer with heat exchanger 89. The water 
used in the hydrolysis and withdrawn in the distillate (material flow 5.2) 
as well as in the waste water (material flow 5.4) is replaced by fresh 
deionised water (material flow 5.3). 
The temperature in the mixing tank 73 and in the hydrolysis reactor 76 
amounts in the illustrated exemplifying embodiment to about 265.degree. C. 
The expansion crystallisation was conducted at up to a temperature of 
95.degree. C. As is to be seen from Table V (material flow 5.5) the PTA 
has in addition to about 100 ppm MMT still only about 40 ppm of further 
impurities and is accordingly suitable for almost all usages. 
EXAMPLE 5 
Hydrolysis (PTA-p) 
Should a terephthalic acid with hitherto unachieved low content of MMT and 
p-TA (PTA-p) be desired, the PTA in the connection to the crystallisation 
can optionally be washed once again with deionised water. The combined 
production of PTA and PTA-p according to FIG. 6 is especially 
advantageous. The arrangements 73 to 89 and the procedure correspond 
moreover largely to FIG. 5. Only in the crystallyser 82 is a part of the 
crystal slurry withdrawn by means of pump 90 and pumped into the 
countercurrent washer 91, e.g. according to DE-A1-36 39 958, where it is 
washed in countercurrent with deionised water (material flow 6.3). The 
washing takes place at a temperature of 190.degree. C. The washed crystal 
suspension is released into the crystalliser 92 and conveyed from there by 
means of the pump 93 to the centrifuge 94 for separating off of the mother 
liquor. The damp PTA is dried in the drier 95 and leaves the plant as high 
purity PTA-p with a total content of impurities inclusive of MMT and p-TA 
of &lt;50 ppm (material flow 6.6, Table 6) while the mother liquor running 
off from the centrifuge 94 is combined in the tank 96 with the mother 
liquor running off from the centrifuge 85 and is pumped by means of pump 
97 into the stripping stream producer 74. 
Pump 88 conveys the mother liquor from the countercurrent washing 91 back 
into the stripping stream producer 74. 
Abbreviations 
DME--Dimethylether 
DMI--Dimethyl isophthalate 
DMO--Dimethyl orthophthalate 
DMT--Dimethyl terephthalate 
DMT-p--Pure DMT (fibregrade DMT) 
HM-BME--Hydroxymethylbenzoic acid methyl ester 
ITA--Isophthalic acid 
MM-BME--Methoxymethylbenzoic acid methyl ester 
MMT--Monomethyl terephthalate 
MTA--Medium pure terephthalic acid 
OTA--Orthophthalic acid 
p-TA--para-Toluic acid 
p-TE--para-Toluic acid methyl ester (pT-ester) 
p-X--para-Xylene 
PTA--Pure terephthalic acid (fibregrade TA) 
PTA-p--Terephthalic acid of very high purity (content of MMT and p-TA&lt;50 
ppm) 
TA--Terephthalic acid 
TAE--Terephthalaldehydic acid methyl ester 
TAS--Terephthalaldehydic acid (4-CBA) 
Definitions 
In the description, % and ppm amounts used relate, unless otherwise 
indicated, to parts by weight 
______________________________________ 
Legend 
______________________________________ 
1 - Oxidiser 
2 - Stripper 
3 - High pressure pump 
4 - Heat Exchanger 
5 - Esterification column 
6 - Intermediate tank 
7 - Crude ester rectification 
(high boiler column) 
8 - Evaporator 
9 - Condenser 
10 - Pump 
11 - Crude ester rectification 
(low boiler column) 
12 - Vaporiser 
13 - Condenser 
14 - Pump 
15 - Tank 
16 - Pump 
17 - Hear Exchanger 
18 - Pump 
19 - Reactor 
20 - Distillation column 
21 - Vaporiser 
22 - Pump 
23 - Dephlegmator 
24 - Reactor 
25 - Heat Exchanger 
26 - Circulating pump 
27 - Dephlegmator 
28 - Mixing Tank 
29 - Crystallizer 
30 - Circulating Pump 
31 - Condenser 
32 - Pump 
33 - Centrifuge 
34 - Tank 
35 - Pump 
36 - Tank 
37 - Pump 
38 - Centrifuge 
39 - Methanol-inter- 
mediate tank 
40 - Pump 
41 - Melter 
42 - Pump 
43 - Heat exchanger 
44 - Intermediate tank 
45 - Crystalliser 
46 - Pump 
47 - Heat Exchanger 
48 - Pump 
49 - Washing centri- 
fuge 
50 - Melter 
51 - Pump 
52 - Intermediate 
tank 
53 - Pump 
54 - Mixing tank 
55 - Pump 
56 - Centrifuge 
57 - Mixing tank 
58 - Pump 
59 - Evaporator 
60 - Separator 
61 - Tank 
62 - Pump 
63 - Crystalliser 
64 - Condenser 
65 - Pump 
66 - Centrifuge 
67 - Stirring Tank 
68 - Pump 
69 - Collecting Tank 
70 - Pump 
71 - Evaporator 
72 - Pump 
73 - Mixing Tank 
74 - Stripping Vapour producer 
75 - Pump 
76 - Hydrolysis reactor 
77 - Hydrolysis column 
78 - Condenser 
79 - Heat Exchanger 
80 - Pump 
81 - Crystalliser 
82 - Crystalliser 
83 - Crystalliser 
84 - Pump 
85 - Centrifuge 
86 - Drier 
87 - Collecting Tank 
88 - Pump 
89 - Heat Exchanger 
90 - Pump 
91 - Countercurrent washer 
92 - Crystalliser 
93 - Pump 
94 - Centrifuge 
95 - Drier 
96 - Tank 
97 - Pump 
______________________________________ 
3 TABLE I 
Stream No. 1.9 1.1 1.2 1.3 1.4 1.5 1.6 1.7 P1 1.8 Methanol 
Xylene to oxid. Process air Catalyst p-TE Discharge gas from Vapour from 
Steam to Oxidation product Methanol to vapour (after separation) to 
oxidation to oxidation to oxidation oxidation stripper stripper upstream 
stripper oxidate heater to esterification Components kg/h wt % kg/h wt % k 
g/h wt % kg/h wt % kg/h wt % kg/h wt % kg/h wt % kg/h wt % kg/h wt % 
kg/h wt % 
High boilers -- -- -- -- -- -- 2062.5 2.51 DMT + DMI + DMO 
191.8 0.58 11244.6 22.48 118.7 0.12 11101.4 13.51 MM-BME 
379.2 0.76 -- -- MMT 516.1 1.03 18466.4 22.47 HM-BME 
499.1 0.99 164.3 0.20 TA -- -- 8307.6 10.11 TAE 
15.8 0.05 1144.2 2.29 15.8 0.02 394.4 0.48 p-TE 5189.0 15.63 
32473.3 64.92 2137.1 2.21 616.2 9.34 19722.3 24.00 TAS -- -- -- -- 
-- -- 714.9 0.87 p-TA 102.9 0.31 -- -- 102.9 0.11 14330.8 
17.44 BME 2239.5 6.75 3556.6 7.11 1266.4 1.31 308.1 4.67 4839.9 
5.89 Benzoic acid -- -- -- -- -- -- 82.2 0.10 p-X 25318.5 76.28 
5960.1 6.17 1232.4 18.68 1232.6 1.5 Acetic acid 441.8 
0.46 164.3 2.49 164.3 0.20 Cobalt 32.08 6.91 -- -- -- -- 10.7 
0.013 Manganese 7.76 1.68 -- -- -- -- 2.5 0.003 Formic acid 
220.9 0.23 82.2 1.25 82.2 0.10 Carbon dioxide 1850.8 1.92 
Methanol 136.9 0.27 474.9 0.49 3613.0 100.00 32154.0 
100.00 Oxygen 21720.4 22.86 2732.3 2.83 Nitrogen 71902.1 
75.69 71902.1 74.51 Carbon monoxide -- -- 462.7 0.48 
Water 133.5 0.40 1377.5 1.45 424.16 91.41 69.0 0.15 7915.2 8.20 4193.8 
63.57 3921 100.00 493.0 0.6 Light ends -- -- -- -- -- -- -- -- 900.3 
0.94 -- -- -- -- .SIGMA. Total 33191 100.00 95000 100.00 464 100.00 
50019 100.00 96502 100.00 6597 100.00 3921 100.00 82172 100.00 3613.0 
100.00 32154.0 100.00 
Stream No. 1.10 1.11 1.12 1.13 1.15 1.16 1.17 1.18 Vapour from Vapour 
from p-TE distillate crude DMT to 1.14 Vacuum gas from Vacuum gas from 
Feed to Reflux to esterification crude ester flash from crude DMT still 
recrystallisation Residue A crude DMT still crude ester still crude 
ester still crude ester still Components kg/h wt % kg/h wt % kg/h wt % 
kg/h wt % kg/h wt % kg/h wt % kg/h wt % kg/h wt % kg/h wt % 
High boilers -- -- -- -- -- -- -- -- 2261.6 36.83 -- -- -- -- 2261.6 
3.41 -- -- DMT + DMI + DMO 73.1 0.26 1602.3 7.50 4789.8 18.16 29641.7 
99.80 3167.0 51.57 47.5 2.19 265.9 13.13 37911.9 57.21 17079.1 59.29 
MM-BME -- -- -- -- -- -- -- -- -- -- -- -- MMT 516.1 2.42 -- -- 
-- -- 610.7 9.94 610.7 0.92 -- -- HM-BME 98.0 0.46 -- -- 14.8 0.05 
51.5 0.84 66.3 0.10 7.3 0.03 TA -- -- -- -- -- -- -- -- -- 
-- TAE 47.6 0.22 1053.2 4.00 29.7 0.10 26.5 1.22 16.9 0.83 1126.3 
1.70 549.5 1.91 p-TE 2435.7 8.81 10853.7 50.83 18788.8 71.34 -- -- 
1643.6 75.59 1107.7 54.71 21540.1 32.51 10121.2 35.13 TAS -- -- -- -- -- 
-- -- -- -- -- -- -- -- -- -- -- p-TA -- -- -- -- -- -- 14.8 0.05 -- 
-- -- -- 14.8 0.02 7.3 0.03 BME 665.0 2.41 1539.4 7.21 1704.2 6.47 
352.4 16.21 262.0 12.94 2318.6 3.50 1018.8 3.53 Benzoic acid 
-- -- p-X -- -- Acetic acid -- -- Cobalt 
40.4 0.66 40.4 0.06 Manganese 9.8 0.16 9.8 0.02 
Formic acid -- -- Carbon dioxide -- -- 
Methanol 18562.9 67.15 6501.4 30.45 41.1 1.89 290.2 14.33331.5 
0.50 20.4 0.07 Oxygen -- -- -- -- -- -- -- -- Nitrogen 
56.0 2.58 56.0 2.77 -- -- -- -- Carbon monoxide -- -- -- -- 
-- -- -- -- Water 5825.6 21.07 194.5 0.91 6.9 0.32 26.3 1.29 33.2 
0.05 3.4 0.01 Light ends 82.7 0.30 -- -- -- -- -- -- -- -- .SIGMA. 
Total 27645 100.00 21353 100.00 26336.0 100.00 29701.0 100.00 6141.0 
100.00 2174.0 100.00 2025.0 100.00 66265.0 100.00 28807.0 100.00 
Stream No. 1.19 1.20 Distillate of Reflux to crude ester still crude 
DMT still Components kg/h wt % kg/h wt % 
High boilers -- -- -- -- DMT + DMI + DMO 34479.0 59.29 7350.03 18.19 
MM-BME -- -- -- -- MMT -- -- -- -- HM-BME 14.8 0.03 -- -- TA -- -- -- -- 
TAE 1109.4 1.91 1616.28 4.00 p-TE 20432.4 35.13 28826.35 71.34 TAS -- -- 
-- -- p-TA 14.8 0.03 -- -- BME 2056.6 3.53 2614.34 6.47 Benzoic acid p-X 
Acetic acid Cobalt Manganese Formic acid Carbon dioxide Methanol 9,841.4 
0.07 Oxygen -- -- Nitrogen -- -- Carbon monoxide -- -- Water 6.9 0.01 
Light ends -- -- .SIGMA. 
Total 58155.0 100.00 40407.0 100.00 
3 TABLE II 
Stream No. 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 Residue A from Methanol from 
Residue B to Vapour from re- Distillate from re- Reflux to re- Vapour 
from Distillate from crude ester still filtrate evaporation catalyst 
recovery esterification column esterification column esterification 
column reactor column reactor column Components kg/h wt % kg/h wt % kg/h w 
t % kg/h wt % kg/h wt % kg/h wt % kg/h wt % kg/h wt % 
High boilers 2261.6 36.83 876.1 91.73 -- -- -- -- -- -- -- -- -- -- 
DMT + DMI + DMO 3167.0 51.57 28.7 3.01 436.6 6.04 3063.0 96.93 2322.5 
96.93 204.3 3.15 834.6 53.95 MM-BME -- -- -- -- -- -- -- -- 34.0 
0.52 345.1 22.31 MMT 610.7 9.94 -- -- -- -- -- -- -- -- -- -- HM-BME 
51.5 0.84 2.7 0.04 44.5 1.21 33.7 1.41 38.6 0.60 313.6 20.27 TA 
-- -- -- -- -- -- -- -- -- -- TAE -- -- -- -- -- -- -- -- -- -- 
p-TE 1.7 0.02 1.7 0.05 1.3 0.05 50.1 0.77 26.2 1.69 TAS 
p-TA BME Benzoic acid p-X Acetic 
acid Cobalt 40.4 0.66 40.4 4.23 Manganese 9.8 0.16 9.8 
1.03 Formic acid Carbon dioxide Methanol 
13238.0 100.00 6766.6 93.55 50.3 1.59 38.1 1.59 6142.0 94.73 27.5 1.78 
Oxygen -- -- -- -- -- -- -- -- Nitrogen -- -- -- -- -- -- -- 
-- Carbon monoxide -- -- -- -- -- -- -- -- Water 25.4 0.35 
0.5 0.02 0.4 0.02 15.0 0.23 Light ends -- -- -- -- -- -- -- -- 
.SIGMA. Total 6141.0 100.00 13238.0 100.00 955.0 100.00 7233.0 100.00 
3160.0 100.00 2396.0 100.00 6484.0 100.00 1547.0 100.00 
Stream No. 2.9 2.15 2.16 Reflux to Residue from re- Sump product 
of re- reactor column esterification reactor esterification column 2.10 
2.11 2.12 2.13 2.14 Components kg/h wt % kg/h wt % kg/h wt % kg/h kg/h 
kg/h kg/h kg/h 
High boilers -- -- 1966.9 78.58 142.5 95.00 1530 4580 795 4743 1590 DMT 
+ DMI + DMO 1733.4 53.95 474.6 18.96 7.5 5.00 .BHorizBrace. MM-BME 716.8 
22.31 -- -- Methanol vapour MMT -- -- -- -- see stream no. 2.2 
HM-BME 651.3 20.27 7.4 0.30 TA -- -- TAE -- -- p-TE 54.3 1.69 TAS 
p-TA BME Benzoic acid p-X Acetic acid Cobalt 
40.4 1.61 Manganese 9.8 0.39 Formic acid -- -- Carbon dioxide -- 
-- Methanol 57.2 1.78 3.9 0.16 Oxygen Nitrogen Carbon monoxide 
Water Light ends .SIGMA. Total 3213.0 100.00 2503.0 100.00 
150.0 100.00 
TABLE III 
__________________________________________________________________________ 
Stream No. 
3.1 3.2 3.3 3.4 3.5 
crude DMT for 1st 
Pure methanol for 
Crystal slurry from 
Filtrate A to 
Intermediate product 
recrystallisation 
recrystallisation 
isomers discharging 
isomers discharging 
for hydrolysis 
Components 
kg/h wt % 
kg/h wt % 
kg/h wt % kg/h wt % 
kg/h wt % 
__________________________________________________________________________ 
DMT 29463.4 
99.2 1172.9 
35.16 
1219.4 
2.05 
21917.0 
99.991 
DMI 104.0 0.35 21.95 
0.66 125.07 
0.21 
0.85 39 ppm 
DMO 74.3 0.25 15.55 
0.47 89.22 0.15 
0.61 28 ppm 
HM-BME 14.8 0.05 3.15 0.09 17.78 0.03 
0.15 6 ppm 
TAE 29.7 0.10 6.30 0.19 35.75 0.06 
0.24 11 ppm 
p-TA 14.8 0.05 3.15 0.09 17.78 0.03 
0.15 6 ppm 
Methanol 
-- -- 55873 
100.00 
2113.0 
63.34 
57986.0 
97.47 
-- -- 
.SIGMA. Total 
29701.0 
100.00 
55873 
100.00 
3336.0 
100.00 
59491.0 
100.00 
21919.0 
100.00 
__________________________________________________________________________ 
Stream No. 
3.6 3.7 
DMT-p from 
Intermediate product 
melter for hydrolysis 
Components 
kg/h 
wt % kg/h wt % 
__________________________________________________________________________ 
DMT 7499.9 
99.999 
21902.14 
99.92 
DMI 0.03 
4.3 ppm 
7.38 337 ppm 
DMO 0.02 
3.1 ppm 
5.27 240 ppm 
HM-BME traces 
0.7 ppm 
1.05 48 ppm 
TAE traces 
1.2 ppm 
2.11 96 ppm 
p-TA traces 
0.7 ppm 
1.05 48 ppm 
Methanol 
-- -- -- -- 
.SIGMA. Total 
7500.0 
100.00 
Only for MTA 
production 
__________________________________________________________________________ 
TABLE IV 
__________________________________________________________________________ 
Stream No. 
4.1 4.2 4.3 4.4 4.5 
Filtrate A from 1st 
Methanol vapour from 
Crystal slurry to 1st 
Isomers to 
Methanol vapour from 
recrystallisation 
filtrate A evaporation 
recrystallisation 
burning isomer evaporation 
Components 
kg/h wt % 
kg/h wt % kg/h wt % kg/h 
wt % 
kg/h wt % 
__________________________________________________________________________ 
DMT 1219.4 
2.05 1172.9 
35.16 
46.5 
16.49 
DMI 125.07 
0.21 21.95 
0.66 103.12 
36.57 
DMO 89.22 0.15 15.55 
0.47 73.67 
26.12 
HM-BME 17.78 0.03 3.15 0.09 14.63 
5.19 
TAE 35.75 0.06 6.30 0.19 29.45 
10.44 
p-TA 17.78 0.03 3.15 0.09 14.63 
5.19 
Methanol 
57986.0 
97.47 
54387.0 
100.00 
2113.0 
63.34 
-- -- 1486.0 
100.00 
.SIGMA. Total 
59491.0 
100.00 
54387.0 
100.00 
3336.0 
100.00 
282.0 
100.00 
1486.0 
100.00 
__________________________________________________________________________ 
TABLE V 
__________________________________________________________________________ 
Stream No. 
5.1 5.2 
DMT intermediate 
Distillate from hydro- 
5.3 5.4 5.5 
product to hydrolysis 
methanol distillation 
Deionised water 
Waste water 
PTA 
Components 
kg/h wt % kg/h wt % kg/h wt % 
kg/h 
wt % kg/h wt % 
__________________________________________________________________________ 
DMT 21917.0 
99.991 
DMI 0.85 39 ppm 
DMO 0.61 28 ppm 
HM-BME 0.15 6 ppm 
TAE 0.24 11 ppm 
p-TA 0.15 6 ppm 0.1 15 ppm 
0.05 &lt;3 ppm 
Methanol 6927.0 
51.84 -- -- -- -- 
ITA 0.53 
78 ppm 
0.21 11 ppm 
OTA 0.37 
54 ppm 
0.12 6 ppm 
TA 1.8 264 ppm 
18747.44 
99.98 
TAS -- -- 0.3 16 ppm 
Water 5995.0 
44.87 
17000.0 
100.00 
6799.30 
99.87 
-- -- 
DME 439.0 3.29 -- -- -- -- -- -- 
MMT -- -- -- -- 5.9 867 ppm 
1.88 100 ppm 
.SIGMA. Total 
21919.0 
100.00 
13361.0 
100.00 
17000.0 
100.00 
6808.0 
100.00 
18750.0 
100.00 
__________________________________________________________________________ 
TABLE VI 
__________________________________________________________________________ 
Stream No. 
6.2 
6.1 Distillate from 
6.3 
DMT intermediate 
hydromethanol 
Deionised 
6.4 6.5 6.6 
product to hydrolysis 
distillation 
water Waste water 
PTA PTA-p 
Components 
kg/h wt % kg/h wt % 
kg/h 
wt % 
kg/h 
wt % kg/h wt % kg/h 
wt 
__________________________________________________________________________ 
% 
DMT 21917.0 
99.991 
DMI 0.85 39 ppm 
DMO 0.61 28 ppm 
HM-BME 0.15 6 ppm 
TAE 0.24 11 ppm 
p-TA 0.15 6 ppm 0.128 
18 ppm 
0.03 2 ppm 
&lt;0.01 
0.4 ppm 
Methanol 6927.0 
51.84 -- -- -- -- -- -- 
ITA 0.59 
87 ppm 
0.14 10 ppm 
&lt;0.01 
2.4 ppm 
OTA 0.38 
46 ppm 
0.07 5 ppm 
&lt;0.01 
1.4 ppm 
TA 1.8 264 ppm 
14048.14 
99.98 
4699.8 
99.996 
TAS -- -- 0.22 16 ppm 
0.07 
16 ppm 
Water 5995.0 
44.87 
17000.0 
100.00 
6799.21 
99.87 
-- -- -- -- 
DME 439.0 
3.29 
-- -- -- -- -- -- -- -- 
MMT -- -- -- -- 5.9 867 ppm 
1.4 100 ppm 
0.11 
25 ppm 
.SIGMA. Total 
21919.0 
100.00 
13361.0 
100.00 
17000.0 
100.00 
6808.0 
100.00 
14050.0 
100.00 
4700.0 
100.00 
__________________________________________________________________________