Terephthalic acid, production toluene

Production of terephthalic acid from toluene 13.13.1 Henkel 2 process... 

In addition to the use of p-xylene as a raw material in the production of tere-phthalic acid, processes were also operated in the past to produce terephthalic acid from toluene and phthalic anhydride. 

The alkylation of toluene with methanol has been investigated for many years as a potential alternative route to / - Qflene, ethylbenzene, and styrene. Conventional / -xylene production from petroleum reformate requires costly purification and separation from jQ lene isomers and other aromatics. A process that selectively produces /)-xylene could have a significant commercial impact by eliminating the need for p-xylene separation. Furthermore, styrene or ethylbenzene production from methanol and toluene is desired as part of the development of processes based on Cl feedstocks rather than ethylene or propylene feedstocks [48], Para- xyl ae is used primarily in terephthalic acid production, a major component of polyester manufacture. 

Toluene (methyl benzene) QH5CH3 Automotive fuels additive, organic solvent, production of benzene, styrene, and terephthalic acid... 

Toluene, formaldehyde, HC.1, calcium hydroxide, and UNO , comprise the chargestock. In step 1 of this process, the toluene is reacted with concentrated HC1 at about 70°C along with paraformaldehyde. This accomplishes chloromethylation of approximately 98% of the toluene. In step 2, saponification of the chloromethyltoluene is effected with lime and H20 under pressure and at about 125°C. The product is methylbenzyl alcohol. In step 3. the methylbenzyl alcohol is oxidized with HNO3 (dilute) under a pressure of about 20 atmospheres and at a temperature of about 170°C. The main products are o-phthalic acid in HNO3 solution and insoluble terephthalic acid. 

Homolytic liquid-phase processes are generally well suited to the synthesis of carboxylic acids, viz. acetic, benzoic or terephthalic acids which are resistant to further oxidation. These processes operate at high temperature (150-250°C) and generally use soluble cobalt or manganese salts as the main catalyst components. High conversions and selectivities are usually obtained with methyl-substituted aromatic hydrocarbons such as toluene and xylenes.95,96 The cobalt-catalyzed oxidation of cyclohexane by air to a cyclohexanol-cyclohexanone mixture is a very important industrial process since these products are intermediates in the manufacture of adipic acid (for nylon 6,6) and caprolactam (nylon 6). However, the conversion is limited to ca. 10% in order to prevent consecutive oxidations, with roughly 70% selectivity.97... 

Toluene also provides an alternative source for the manufacture of the xylene isomers, especially /uxylene. The last two products provide routes respectively to terephthalic acid and /uxylene without the need for an isomer separation, a very appealing use for toluene that is often in excess supply, unlike the xylene isomers. 

Benzoic Acid. Benzoic acid can be produced by the LPO of toluene using a catalyst such as cobalt or manganese. Domestic production of benzoic acid was about 130 million lb in 2000. Of this amount, about one half went to make phenol or phenolic derivatives. Other uses are in the synthesis of caprolactam and terephthalic acid, and as food additive, and as a plasticizer and resin intermediate. 

In 1999, the total demand for the xylenes (12.3 billion lb) was roughly comparable to that for toluene. The volume of o-, m- and /7-xylene were approximately 1.1, 0.27, and 9.9 billion lb, respectively. The principal uses of the three xylene isomers are the production of terephthalic acid (or di-methyl terephtha-late), phthalic anhydride, and isophthalic acid, respectively. 

The oxidation of / -xylene to terephthalic acid is by far the most important process based on the oxidation of methyl aromatics. However other similar processes are also operated industrially and oxidize toluene to benzoic acid or m-xylene to isophthalic acid. The latter is used as comonomer with terephthalic acid in bottles for carbonated drinks, and for special polyesters, and its production is roughly 2% of that of the terephthalic derivatives. 

About half of the benzene produced as a chemical feedstock is for styrene production, followed by large fractions for phenol and cyclohexane-based products. As much as half of the toluene produced is converted to benzene, depending on the price and demand differential. The largest use of toluene itself is as a component of gasoline. Much smaller amounts are used as a solvent, or in the manufacture of dinitrotoluene and trinitrotoluene for military applications. Xylenes are also used in gasoline formulations and function as octane improvers like toluene. para-Xylene and o-xylene are the dominant isomers of value as chemical feedstocks, for the production of terephthalic acid (and dimethyl terephthalate) and phthalic anhydride, respectively. Polyester and the synthetic resin markets, in turn, are major consumers of these products. meto-Xylene is oxidized on a much smaller scale to produce isophthalic acid, of value in the polyurethane and Nomex aramid (poly(m-phenylene isophthalamide)) technologies. 

These are benzene, toluene and xylenes, which are some of the basic feedstocks of the chemical industry. The products that can readily be made from them can be found in most industrial chemical texts. The synthetic gasoline has certain advantages, e.g. the yield of p-xylene (the feedstock for terephthalic acid) is enhanced relative to that normally found in petrochemical feedstocks but the overwhelming requirement for octane in the synthetic gasoline stream may make it economically unattractive to attenpt to remove these components. 

The best approach to improving separations is to work toward reactions that achieve 100% yields at 100% conversions. Frequently, this will require more selective catalysts. The previous chapter contained an example moving in this direction. Toluene was disproportionated to benzene and xylenes using a silica-modified zeolite catalyst.23 After removal of benzene and unchanged toluene by distillation, the xylene remaining was a 99% para-isomer. It was clean enough to put directly into the process of oxidation to terephthalic acid. This avoided the usual separation of xylenes by crystallization or by a molecular sieve. There are times when an equilibrium can be shifted by removal of a product or by-product continuously to give 100% conversion. The familiar esterification with azeotropic removal of water or removal of water with a molecular sieve is an example. 

The molar selectivity of terephthalic acid in the metathesis reaction is 97 per cent for a once-through conversion of potassium terephthalate of about 85 per cent The potassium terephthalate molar selectivity of the disproportionation reaction is 85 per cent for a conversion of 90 per cent This process, despite the improvements made to the Henkel 2 technology, and the value it offers by starting with toluene, which is cheaper than p-xylene, and co-production of easily marketable benzene, has nevertheless not yet been employed industrially. 

Cobalt compounds are useful chemical catalysts for the synthesis of fuels (Fi-scher-Tropsch process), the synthesis of alcohols and aldehydes from olefins, hydrogen and carbon monoxide at elevated temperatures and pressures ( oxo process , hydroformylation ). They are also used in petroleum refining and the oxidation of organic compounds. In the oxo process, cobalt carbonyl, Co2(CO)g, is employed or generated in situ. For the selective production of n-butanol from propylene, hydrogen and CO, an organophosphine-modified cobalt carbonyl complex is used as the catalyst. Cobalt salts are proven oxidation catalysts examples include the production of terephthalic acid by the oxidation of p-xylene, and the manufacture of phenol by the oxidation of toluene. 

There arc numerous examples of product selectivity, many of which involve mono-and disubslituted aromatics formed over ZSM-5 (MFI) catalysts (22-24). One of the early examples was xylene isomerization. Xylene can be formed over MFI catalysts via the acid-catalyzed reaction between methanol and toluene (see Fig. 10.3). According to thermodynamics the equilibrium distribution of o-, m-, and p-isomers is 26 51 23, which is different from the industrial demand as the p-isomer is a feedstock for terephthalic acid, a monomer for PET. However, very high selectivities of p-xylene can be obtained over MFT materials primarily because the diffusion of p-xylene is faster in the MFI pores compared to the other two isomers. 

Whereas benzene and toluene serve as the raw materials for a wide range of products, applications for the three xylene isomers, o-, m- and p-xylene, are basically limited to chemicals arising through oxidation, i.e. phthalic anhydride (PA) from o-xylene, isophthalic acid from m-xylene and terephthalic acid from p-xylene. 

The Henkel Il-process was also preferably operated in Japan. In this process, toluene is oxidized with air over cobalt catalysts to yield benzoic acid which is then transformed into potassium benzoate by subsequent neutralization. In the presence of cadmium oxide or zinc oxide, at temperatures of 450 °C and under CO2 pressure, disproportionation to dipotassium terephthalate occurs this is then converted into terephthalic acid. Benzene is a by-product of the disproportionation. 

Another alternative to the production of terephthalic acid is the process developed by Mitsubishi Gas Chemical, in which a complex generated from toluene, HF and BF3 is made to react under pressure with carbon monoxide (Gattermann-Koch). After decomposition of the complex, p-methylbenzaldehyde can be recovered by crystallization and may then be oxidized to terephthalic acid. 

After the oxidation process, the reaction mixture is separated by filtration, into products that are recycled in the same process (toluene, p-tolualdehyde, monomethyltoluate) and removed from this process (HjO, Og and byproducts) and into products that are passed to the esterification reactor (toluic acid, terephthalic acid, monomethylterephthalate and methyl ester of p-benzaldehyde carbonic acid). The latter product does not participate in the esterification reaction, but is passed to this reactor because, being a soUd substance, it remains on the filter at normal temperatures with all the other oxidation products and is passed with them to the esterification cycle, where it circulates as ballast. 

Within the aromatics e.g. benzene, toluene and xylene) the xylenes are used as a feedstock for the production terephthalic acid and dimethyl terephthalate, both monomers that are used for the production of polyethylene terephthalate (PET), which is the main constituent of plastic bottles and polyester clothing. There are three very close boiling isomers of xylene ortho-, meta- and para-) and it is mainly p-xylene that is used for PET production. The fractionation processes for all existing xylene isomers (crystallization or simulated moving bed) are expensive technologies and it is of interest to study the potentials of membranes for such a separation. 

The monomeric imidazole-blocked 1,4-phenyIenediisocyanates with n-alkoxymethyl substituents were prepared from 2,5-bis(n-alkoxymethyI) terephthalic acids by chlorination with oxalyl chloride in DM Ac at 0 C[19 - 21] followed by reaction with aqueous NaN3 as shown in Scheme 1. The isolated azido products were rearranged to isocyanates in the presence of excess imidazole at 85 °C in toluene. On cooling were precipitated the DIS-IBDIs, which were thoroughly purified by recrystallization from acetone. The substituted terephthalic acids were prepared by basic hydroysis of 2,5-bis(n-alkoxymethyl)-terephthalonitriles[17 - 18]. 

Mitsubishi Chemical Industries, Ltd. practiced a Henkel II technology starting with toluene to produce benzoic acid. Reaction of benzoic acid with potassium hydroxide resulted in potassium benzoate, which was subjected to a disproportionation reaction to produce dipotassium terephthalate and benzene. Dipotassium terephthalate reacted with sulfuric acid, and the resulting terephthahc acid was recovered by filtration and drying (65,66). Here, dipotassium sulfate was the by-product. 

The Cg alkylaromatics fraction is formed by ethylbenzene and the three xylene isomers. Ethylbenzene is used as a raw material to produce styrene by dehydrogenation, or oxidative dehydrogenation. Para-xylene and ortho-xylene are catalytically oxidized to give terephthalic and phthalic acid. The meta-xylene isomer can also be oxidized to give isophthalic acid. The major industrial source of these products is the catalytic reforming of naphthas. The Cyclar process, can also produce xylenes from propane and butane. However, using this process, xylenes are formed less selectively than toluene or benzene in the BTX. 

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