BIOSCIENCES BIOTECHNOLOGY RESEARCH ASIA, December 2014. Vol. 11(3), 1765-1779

International and Russian Methods of Synthesis and Use of Pyromellitic acid Dianhydride and Tendencies of Their Development (Review)

Anton S. Yegorov*, Vitaly S. Ivanov and Alyona I. Wozniak

Federal State Unitary Enterprise «State Scientific Research Institute of Chemical Reagents and High Purity Chemical Substances» (FSUE «IREA») 3,Bogorodsky Val, Moscow, 107076, Russia.

doi: http://dx.doi.org/10.13005/bbra/1583

(Received: 30 October 2014; accepted: 05 December 2014)

Annotation: Pyromellitic Dianhydride (PMDA) is a raw material for heat resistant polyimide resins, films and coatings.Methods of pyromellitic acid dianhydride synthesis, its properties, use in the industry are in detail considered and structured for the first time herein as well as a possible tendency of these method development is estimated.

Key words: Pyromellitic acid, Pyromelliticacid dianhydride, Tetraalkylbenzene, Durene, isodurene, , cumene, pseudocumene, tetramethylbenzol.

The fast development of aircraft industry, A huge range of polyimides, based on a rocket building, astronautics, nuclear power, great number of tetracarboxylicacid dianhydrides electronics industry, radio engineering and other is synthesized and characterized by the present technics fields demands polymeric materials of time, but polyimides of dianhydrides of high durability, thermal stability, resistance to pyromellitic(1), diphenyloxidetetracarboxylic(2), nuclear and radiation, elasticity and durability. benzophenonetetracarboxylic(3), perylene- 3,4,9,10 Intensive researches in this field resulted in a – tetracarboxylic (4) acids (Scheme 1) are used in synthesis of a new class of cyclopolymers– practice more often. This paper contains polyimides1, with the above physical and international and national methods of pyromellitic mechanical properties. acid dianhydride synthesis most used in practice 1. The main raw materials for high quality Pyromelliticdianhydride (PMDA) 1 is polymeric materials are dianhydrides of various colourless crystals with fusion temperature of aromatic, heteroaromatic and aliphatic acids, and 287ºC, boiling temperature of 397ºC; dissolved in also diamines with a similar structure2. acetone and dimethyl form amide; under moisture it turns into monoanhydride, and pyromellitic acid (PMA). Pure pyromellitic dianhydride1 is non- degradable at heating to 583-603 K 3. DuPont (USA) approved its semi- * To whom all correspondence should be addressed. industrial production for the first time in 1960. Later E-mail: [email protected] Hexagon (USA) approved the production of this 1766 YEGOROV et al., Biosci., Biotech. Res. Asia, Vol. 11(3), 1765-1779 (2014)

Scheme 1. Dianhydrides of pyromellitic(1), diphenyloxidetetracarboxylic(2), benzophenonetetracarboxylic(3), perylene- 3,4,9,10 – tetracarboxylic(4) acids product under the similar technology. In 1964 these second stage, oxidation is completed with two companies received 181 tons of dianhydride1. nitric acid7, 8, 9. Later other largest companies were involved to c) Liquid-phasep rocesses of oxidation of 1 the technology development and production . 3,3',4,4'- tetraalkylbenzene O2 - gas (air) in Now PMDA synthesis is based on 3 main the acetic acid with catalysts - heavy metal methods: salts of variable valency and a) Vapor phase processes of oxidation of halogencompounds at 120-220°C. Catalysts 3,3',4,4'– tetraalkylbenzenes (mainly durene) Co - Mn; Co - Mn - Zr, HBr promoters, at 390-450°C using vanadium - titanic and tetrabromethane, mixture of HBr - HCl10, 11 other catalysts4, 5, 6. are used more often. b) Two-phase processes of oxidation of 3,3',4,4' The most common industrial method of - tetraalkylbenzene (mainly durene). At the pyromellitic dianhydride synthesis is the process

first stage, oxidation is fulfilled with O2 - based on catalytic oxidation of durene(5) with air gas (air) in aliphatic carboxylic acid (Scheme 2):

(CH3COOH) with cobalt catalyst, at the

Scheme 2. Catalytic oxidation of durene(5) The process is usually spent at the present time. Vanadium pentoxide is used as temperature of 410ºC - 450ºC, durene concentration an active base in all cases. Usually an active base in mixture with air 0,1-0,2 % (v), volume speed of with vanadium pentoxide contains lowest durene supply - an air mix 6000-15000 hour-1. vanadium oxides. Oxides of tungsten, phosphorus, Catalysts of vapor phase oxidation of tin, titan, silver, molybdenum, copper, yttrium, durene of numerous types, consisting of an active niobium, and etc are used as co-catalysts. Poor- base, a co-catalyst and a carrier are developed by porous aluminium oxide, silicon carbide, titanium YEGOROV et al., Biosci., Biotech. Res. Asia, Vol. 11(3), 1765-1779 (2014) 1767 oxide, aluminium silicates, and et care used as reduced basically onlyby increasing the industrial carriers. This technology is constantly improved plant capacity. that decreases the productprice. Basing on the literature10, 11, liquid-phase Products of the reaction of vapor phase methods of PMDA synthesis testify that mostly oxidation of durene 5 include other than they are similar and different only by the catalyst pyromellitic dianhydride 1 compounds of partial compound at the oxidation phase (Co - Br; Co - durene oxidation and its deeper oxidation. Mn - Br; Co - Mn - Zr– Brandetc) and reaction Benzenecarboxylicacids, their anhydrides, methods maintaining acatalyst activity by adding derivatives of benzaldehyde, phthalide, phtalan, a proton acid(HBr)oran acid reagent(CCl3OOH) duroquinone are found among products of stronger than acids of tetraalkylbenzene oxidation incomplete oxidation with preserved carbon products. skeleton. Maleic, dimethylmaleic, citraconic and In general, a liquid-phase of PMDA phthalic anhydride, trimellitic acid, acetic acid, synthesis is promising as this technology can be formaldehyde, carbon oxides are found among the used by a single scheme for the synthesis of other deeper oxidation products. dianhydridesof aromatic acids. Basing onthe technology specifics and The two-stage PMDA synthesis by essence for PMDA synthesis by pseudocumene tetraalkylbenzene oxidation at the first phase of condensation with formaldehyde,product O2–with gas (air), at the second phase – with nitric condensation hydrocracking, followed by durene acid7, 8, 9 (Scheme 3) had been widely used before, release and durenevapor-phase oxidation to but in recent years because of competing vapor pyromellitic dianhydride1,the conclusion can be phase and liquid phase processes, its use made that currently the process almost reached decreased, however not stopped yet. perfection and the further product cost can be

O

OH + O HO 2 HO +

O O 5

HNO3

O O

HO OH

HO OH

O O

6 Scheme 3.The two-stage PMDA synthesis

Their use was decreased because of c) Formation of explosive compounds; certain disadvantages: d) Equipment destruction caused by a) Formation of large amount of intermediate corrosion; difficult-to-separate products; e) A complex process scheme associated with b) Formation of large amount (10%) of nitro the need of regeneration of two corrosive

compounds, leading to a product active reagents (CH3COOH and HNO3). coloration; However, an oxidation with a nitric acid 1768 YEGOROV et al., Biosci., Biotech. Res. Asia, Vol. 11(3), 1765-1779 (2014) quite successively competes with a vapor unacceptable due to the consumption of equimolar phaseoxidation because of higher yield of the amount of the latter (CH3COOH is formed). Some desired product. methods of thermal anhydridization were tested: Pyromellitic acid 6 can be anhydridized sublimation, heating under nitrogen and with high- by chemical dehydrating agents (usually, boiling solvents. An hydridization is more rational aceticanhydride) and thermally (Scheme 4). An in high-boiling solvents, improving heat hydridization with an acetic anhydrideis technically dissipation condition.

Scheme 4. Anhydridization of pyromellitic acid 6 Anhydridization begins at about 180- isomerization); 190°C, violently proceeds at220-240°C and finishes 2) High-boiling methylation (300-350°C) of p- within 20-30min.Water vapor are removed inthe xylene or pseudocumene by on form of pseudoazeotrope with diphenylseparated aluminosilicate catalysts; from water after condensation and recycled into 3) Catalytic alkylation of p-xylene or the process. PMDA is to be washed with pseudocumene by ethylene orpropylene; boilingdioxane (~4 weight parts per1 weight part 4) Pseudocumene condensation with of PMDA) and dried at 100-120°C and a residual formaldehyde and di-pseudocumene- pressure of 200-300 mm Hg for 10-15hours. PMDA methane formation and the further outputis 92-93% of theoretical.The obtained hydrocracking in to pseudocumene and dianhydrideis melted at 286-287°C,its acid number- durene; 1026 (calculated 1027), the content of nitro 5) Chloromethylation of p-xylene or compounds is in significant (traces)12. pseudocumene. Raw materials for the pyromelliticdianhydride The above methodsare complex and synthesis expensive. Especially it concerns to atechnology Now a days 3,3',4,4'-tetra-alkylbenzoles of the pure durene preparation from aromatic are used as raw materials to get PMDA, (mainly, concentrates of the petroleum refining with a high durene) released from petroleum refining products content of difficult-to-separate alkylaromatic or synthesized from hydrocarbonaceous raw hydrocarbons (, isodurene, materials by the following methods: isomersdiethyl -anddietylmethyl benzole et al). 1) Durene release from C10 and C9-C10 One of durene concentrate sources is a

fraction (after disproportionation or C10 aromatic fraction contained in benzene of YEGOROV et al., Biosci., Biotech. Res. Asia, Vol. 11(3), 1765-1779 (2014) 1769 catalystre forming (about1%). So up to 0.15 %wt. content in the reaction products up to 32.0%. This of durene can be released from high-aromatic is confirmed by experimental results shown in Table reforming benzene. A possibility of C9– 1 (% wt).

C10hydrocarbon fraction trans formation into The above allows to conclude that the durene by disproportionation13 and isomerization content of the side products (non-target) obtained was studied in order to increase the desired by the above-described method from the fraction product yield. However, since these reactions are boiling at 160-177ºC is large enough(% reversible, reactant concentrations are closerto the concentration, wt: isodurene 64,paraffin and thermodynamic equilibrium during these reactions naphthenic hydrocarbons 8.0, prenitol–4.0), which using specific catalysts. This phenomenon reduces the efficiency of the proposed method. complicates increasing in the durene isomerization Nevertheless, some foreign companiessawan yield. Thus, by the experimental data, the durene opportunity for the future increase the durene yield was increased twice and brought to 15.7%, release by his separation from heavy petrol. followed by extraction ofthe low-temperature Sothe installationlaunch to produce synthetic crystallization into theraw material (durene benzene by Synthetic Fuels Corp was reported in concentrate). 1982, inMontuno, New Zealand. Benzeneis derived During isomerization of the mother from natural gas via methanol, using a zeolite solution on the silica-alumina catalyst (T =370°C), technologyof Mobil Oil.The formed heavy petrol the durene concentration in the reaction products flow contains up to 50% of durene. Specialists can be increased from 2% to 13% of weight. But believe that up to 30% can be recovered without even usingthis combinedprocess, the durene yield significant investments that initially will be 5-10 does not exceed 33%. The fractionof aromatic thousand tons /year, and further 30 thousand tons hydrocarbons with adistillation temperature of160- /year[1]. 177ºCobtained from benzene of catalytic reforming, The Ministry of Energy of New Zealand consists of: negotiated with local and foreign companies a) Ethyltoluene-16% by weight; (including Mitsubishi, Mitsui, ICI) on cooperationin b) Mesitylene- 24% by weight; the field of technology for durene separation and c) Pseudocumene-48% by weight; pyromelliticdian hydride production. d) Hemimellitene -12% by weight. An agreementon project of durene The use of an alum-silicate-molybdenum separation from heavy petrol and commercial deals 2 catalyst (1% MoO2) at T = 425ºC, P = 80 kg/cm , with other companies was signed between the New WHSV of 1.0 hr - 1 and circulating of hydrogenous Zealand Government andICI Syntec Ltd,a gas of 1000 m3/m3 of raw materials increased durene subsidiary companyof ICI New Zealand Ltdand Applied Chemistry Ltd. In addition, the company Table 1. The result of the alum-silicate- planned toset up production of pyromellitic molybdenum catalyst use dianhydride (designedup to 40 thousand tons / Aromatic Raw Materials Product year). Data onits production have not been Hydrocarbons reported, but using these raw materials the cost price of pyromellitic dianhydride was assumed to C6 – 7 - 5,8 be significantly lower than other companies. C8 - 24,5 Similarly, the studies on durene synthesis C9 100 40,3 were conducted at the State Research Institute of C10 - 18,4 Chemical Technology, Severodonetsk (Ukraine). C11 - 3,0 Experimental durene batches were used by All- C 10 aromatic hydrocarbon Russian Research and Project of Monomers (Tula) compound - Durene - 32,0 to test the technology of pyromellitic acid bya Isodurene - 64,0 liquid-phase catalyticoxidation (180 - 210°C) in Prehnitene - 4,0 CH3COOH medium. Pyromellitic acid PMA was Paraffin and turned into PMDA with total yield of 88- 91% of naphthenehydrocarbons - 8,0 theory by thermal dehydration. 1770 YEGOROV et al., Biosci., Biotech. Res. Asia, Vol. 11(3), 1765-1779 (2014)

Durene synthesis by methylation using methanol product. A methyl group can be introduced in to The yield of tetra-substituted the aromatic ring by methylation reaction and thus benzeneisomersis increased due tothe it will synthesize various polymethyl benzenes. disproportionation reaction or the temperature Methanol, dimethyl ether, methyl halides and other rising to400°C or morefor convertingof penta- reagents can be used to add the methylgroup. andhexa-substituted benzene into tetra-substituted Usually methanol is an economically beneficent isomers due toa dealkylation reaction. ethylating agent. Complexity and multistaging of the The conditions and results of the studies process scheme, a relatively low yield of the desired of different catalysts to use them for the synthesis product–durene~ 70% and significant irreversible of tetra-alkyl-substituted benzenebymethylation methanol losses of 285kg per a ton of C9aromatic with pseudocumene methanol, xylene isomers and hydrocarbon suggest that the costsfor production other alkyl-substituted aromatic hydrocarbonsare of raw materials –durene for synthesis of stipulated in the papers14, 15. pyromelliticacid and its dianhydride will be high The authors of the paper [14]found that enough that will increase incost of PMDA and aluminosilicate catalyst was quite active for this polyimide based on it.This is confirmed by the reaction. Methylation goes onwith a significant production data. Thus, for example, a texisting speed at 300-450°C. The substitution in the production, the durene synthesis costs H”48-50% benzene ringis in accordancewith the of costs of PMDA synthesis. orientationrules in presence of alumino To reduce energy and raw material costs silicatecatalyst at arelatively low reaction in the durene production, All-Russian Research temperature (300°C) when a reaction rateof Institute of Organic Synthesis (Moscow) isomerization of initial and obtainedhydrocarbonsis developed a continuous process for synthesis of low[15]. durene and pseudocumene from p-xyleneby vapor- The following results were obtained phasemethylation of the latter with methanol at during pseudocumenemethylation(300°C, 0.5h, 430-440°Con the catalystIC–28–2–3.The molar ratio ofmethanol torawmaterials 2- 1:1): reactionunitis testedin the experimental conditions Tetramethylbenzoene yield21.1wt.% and formed in two versions: Tetramethylbenzene compound: a) A divided unit with different gas flow, each a) Durol58.4wt.%: section is a separatereactor, turned on b) Isodurene 23.7wt.%: sequentially forming a cascade; c) Prehnitene 17.9wt.%: b) Avertical shelf unit, each shelf is a section These data show that under these with coils-receivers located between, conditions, the yield of is very consuming the reaction heat. lowduring methylation and reaches 21.1%. Thus In the reactor according to the first option, the content of the desired product (durene) is the catalyst is located in an annularspace 58.4%. (“basket”). To mitigate the process conditions and The maximum dureneyield atthe above uniform temperature distribution, the catalyst is process of durene synthesis by catalytic diluted with inert material in a ratio of 1:3.P-xylene methylation of aromatic hydrocarbons C9reaches and methanol fresh and recycled are heated in a 73.8%. tube furnace to 400- 410°C under a pressure of 2.5- Disadvantages of the aboveprocess of 2.6 MPa. durene synthesis include fast coking of the A mixture of source reagent vapors catalyst, significant methanol losses (10-20% of passes through a catalyst layer in the sections at the original), formationof a large number of side 430-440°C.The methylation reaction proceeds and intermediates products of alkylation, under these conditions forming pseudocumene, isomerization, requiring their recycling or disposal. durene and byproducts of thermal-oxidative This in turn necessitates the use of a partitioning degradation. scheme (rectification) of complex mixtures, followed Alkylateis sequentially cooled to 165°Cin by separation (2-foldcrystallization) of the desired heat-recovery boilers and to 45°C in heat YEGOROV et al., Biosci., Biotech. Res. Asia, Vol. 11(3), 1765-1779 (2014) 1771 exchanger-refrigerators. The reaction mixture goes PMDA synthesis and its technical and economic under further staging separation with dividing of comparison to the above vapor phase processis liquid andgas-vapor products. obvious. Alkylateis separated in the rectification However, the polyimide production can unit consisting of four columns, sequentially be provided with monomer raw materials not only emitting light fraction of methanol and by an improved technology for raw material dimethylether followed by sequentially emitting production for PMDA (dureneor2,5-diisopropyl- of p-xylene, pseudocumene, durene and p-xylene), but also by replacing the high resinousside products. temperature vapor phase oxidation process(400- Durene is purified -raw product from 450°C) to PMDA, developed by All-Russian isodurene and other by products with similar Institute of Oil and Chemical Research fora more boiling temperature- by crystallizationin methanol economical liquid-phase oxidation process at 55-63°C. Durene suspensionin methanolis (T≤200°C), which provides higher PMDA yield separated in acentrifuge. The isolated wet from 65% to ≤ 90%. dureneresi due containing 7-10% of methanolis Preparation of 1,2,4,5-tetraalkylbenzene by melted and the residual methanol is distilled off. alkylation of p-xylene and pseudocumene The above process of combined Because of the durene deficiency, synthesis of durene and pseudocumene from p- syntheses of alternative petro chemicals used as xylene exceeds the earlier discussed synthesis of raw materials are developed for synthesis of aromatic fractions of durene C9using zeolite pyromellitic acid and dianhydride on its basis. catalysts by technological and economic These raw materials include products of alkylation indicators. of or pseudocumene with ethylene or

The advantage ofthe technology propylene in presence of anhydrous AlCl3, namely developed by All-Russian Research Institute of 5-etilpseudocumene; 2,5-diethyl-p-xylene; 5- Organic Synthesis is in the increased selectivity isopropyl pseudocumene; 2,5-diisopropyl-p- of the gas-phase methylation of p-xylene with xylene, respectively16. methanoltothree- and tetra-methylbenzenes Alkylation of p-xylene and pseudocumene (pseudocumene and durene). using olefins with Friedel - Crafts catalysts of An improved process fordurene and tetraalkylbenzene cause seem veryinteresting in pseudocumene synthesis developedby All- recent years. Russian Research Institute of Organic Synthesis This interest is associated with durene is characterized not only bytechno-economic deficiency, a high yield of tetraalkyl benzene andenvironmental benefits, but certain comparing to other processes (95%) containing disadvantages including high temperature of 85% of isomer 1,2,4,5, as well as with the fact that alkylation process(430-450°C) andpressure (2.5 - ethylene or propylene are considerably cheaper 3.0 MPa). than methyl chloride used in methylation of High temperature inevitably leads to aromatic hydrocarbons. thermal catalytic decomposition of raw materials Selective alkylation of p-xylene with (10%), formation of high (resinous) products that propylene forms 1,4 - dimethyl - 2,5 - diisopropyl reduce catalyst range and impede alkylate benzene 8,as shown in Scheme 5. separation. The process is going at low temperatures High pressure of alkylation process increases (-10 to -70°C) with aluminum trichloride(0.03 -0.3mol the equipment cost pera mol ofp-xylene) [17]. Alkylationmay be carried Oxidation reactor structures are designed outat higher temperatures(30-60°C)with aluminum in two variants and under a frequent catalyst oxide adding borontrichloride. M-xylene or regeneration cause complications during their itsconcentrate18 can be alkylated in the similar way. operation. As a result of alkylationof pseudocumeneorxylene, In connection with the above, the need 1,2,4,5-tetraalkyl benzeneare formed which give to develop more cost-effective, low-temperature PMC after oxidation. technology for production of raw materials for Some foreign companies have patented 1772 YEGOROV et al., Biosci., Biotech. Res. Asia, Vol. 11(3), 1765-1779 (2014)

Scheme 5. Selective alkylation of p-xylene methods for the synthesis of alternative sources propylbenzol. Dimethyldiisopropylbenzol of raw materials to solve the problem how to containsisomers and 1,2,4,5- simplify the technology and to reduce the cost of dimethyldiisopropylbenzol. Regardless of petrochemical raw materials for PMDAsynthesis thereaction solution compound, the desired instead of durene. product can be crystallized and purified tothe Thus, accordingto the U.S. Patent[19], a desired quality.But the concentration of1,2,4,5– method is offered to obtain 1,4- dimethyl -2,5 - dimethyldiisopropylbenzolin the reaction productis diisopropyl benzene 8 by alkylation of p-xylene 7 at least 60wt.%, indicating a need for increased with propylene using a catalyst based on costsat the product isolation andpurification. The heteropoly acid and/or its salts.The catalyst may reaction product is offered to be treated to separate contain any heteropolyacid or itssalt, e.g. the catalyst and other undesirable components, dodecasilicotungstic acid (H4SiW12O40) followed by crystallization anddistillationof the dodecaphosphotungstic acid (H3PW12O40) reaction solutionprior to crystallization. Distillation dodecaphosphomolybdic acid (H3PMo12O40) at a temperature of 150 -300°C should ensure dodecagermanotungstic acid (H3GeM12O40) separationof dimethyldiisopropylbenzol from other anddodecagermanomolybdic acid (”3Ge“>1240). factions. Compounds obtained by partial orfull Alkylation products content significant substitutionof hydrogen atoms in these amount of side compounds, indicating a low yield heteropoly acids with metals oramines can be of the desired product andcomplexity of its served examples of use of heteropolyacid salts. separation circuit. The lack of data about a Silica gel, titanium oxide, activated carbon, etc can possibility (if any) of regeneration orrecycling of be usedas a carrier. Impregnation can be used to the complexcatalyst based onheteropoly acidsor obtain the heteropoly acid-based catalyst and/ their salts does not allow to make an unambiguous orheteropoly acid salt-based catalyst.Quantityof conclusion about the effectiveness of the proposed heteropoly acid may vary from1 to 50% in the carrier catalyst and the method as a whole. of the total catalyst weight. As for the reaction AnotherU.S. patent[20] offers a method conditions, a molar ratio of propylene and p- for synthesis of pyromelliticdian hydride from xylenemay vary 1,0-5,0; a reaction temperature may pseudocumene by alkylation with propylenein vary from70 to 200°C; an operating pressure may presence of an hydrous HFat 150°C. A ratio of vary from normal pressure to10 kg/cm2.If a reactor pseudocumene to propyleneis 1: 1.1-2(better 1:1.5). is used for continuous reaction, initial materials A mixture of 2,4,5–trimethylcumene, 3,5 -and 3,6– can be fed into the reaction zone with a velocity of diisopropylpseu documene is prepared as a result -1 0.1-10 hour (wt. unit/hr). of alkylation. The mixture isoxidized with O2 -

The main reaction product –dimethyldiiso containing gasat 100-500°Cin presence of V2O5 propylbenzol. The reaction solution containsun catalyst, applied onan inorganic carrier- Al2O3. reacted initial materials and by products such as Benzenepolycarboxylic acid isomers are oxidation dimethyliso propylbenzol and dimethyltriiso products. An isomeric mixture can be turned YEGOROV et al., Biosci., Biotech. Res. Asia, Vol. 11(3), 1765-1779 (2014) 1773 intothe desired product – pyromellitic dianhydride undervapor phase oxidation (400-500°C) and thus by decarboxylation of by products at high significantly reduce the process efficiency. temperatureof 270-400ºCand a pressure below Furthermore, free(unbound) hydrofluoric acid atmospheric. (HF)in the reaction medium requires the expensive This method has advantages comparing equipment of alloy steels and alloys, and necessary to known processes (throughd urene) regarding measures to ensure safe operation conditions for the useof a new moreaccessible raw material - staff. pseudocumene. At the same time, the use of volatile A synthesis method for 1,3-dimethyl- 5 – hydrofluoric acid as a catalyst (aggressive product) isopropyl9 andtetraalkylbenzenebyalkylationof during the alkylation as well asan inevitable xylene isomer mixture with propylene in presence formation of isomeric mixtures of ofAlCl3at low temperatures of the alkylation polyalkylenebenzol acids partiallydecarboxylated process 45-55°C[21] is shown in Scheme 6.

Scheme 6.Alkylationof xylene isomer mixture

The proposed method includes: The end reaction product contains1.5÷0.4molof (a) contacting of xylene and dimethyldiisopropylbenzolper molof dimethyldiisopropyl benzolmixturein dimethylisopropylbenzol. presence of aluminum chloride for 7-12 A method forsimultaneous(combined) hours at 45-55°Cat a molarratio of xylene preparation of mono- anddiisopropyl-xylene anddimethyldiisopropylbenzolfrom65:35to isomers by alkylation of xylene fraction in presence 75:25 anda xylenemixture consisting of at of Friedel-Crafts reaction catalyst22 is the closest least 60 wt %of m-xylene, 0-2wt% o-xylene bythe technical nature. and the balance of p-xylene; The proposed method is based onthe (b) Adding of propylene intoa mixture (a) at a alkylation with propyleneof xylene fraction

molar ratioof propyleneandxylenedimethyl enriched to 68% with m-xylene, in presence ofAlCl3 diisopropylbenzolinitially added for astage with preparation of an isomeric mixture ofmono- (a) at a level of 0.85:1.0 – 1.05:1.0while anddiiso propylxylene. This method allows to maintaining the temperature between 45- regulate anisomer ratioin a mixture ofmono- and 55°C within 50-80 minutes; diisopropylxylene by additional prior separation (c) Separation of dimethylisopropyl of alkylation products into a fraction with a high benzolanddimethyldiisopropylbenzolfrom content of diisopropylxyleneisomers (fraction- the reactionmixture.At the stage (c) 2)and a fraction with a high contentof dimethylisopropylbenzolcontains atleast monoisopropylxylene isomers (fraction- 1). 97wt%1,3-dimethyl1-5of isopropylbenzol. Fraction 2is to be re-alkylated with xylene Xylene mixturemainly consists of 68wt. in presence of Friedel–Crafts catalyst for 7-12 hours %m-xylene and 32wt.%p-xylene. A partof at 45-55°C, followed by treatment of the obtained dimethyldiisopropylbenzol separated at the stage mixture with propylene for 50-80 minutes at 45- (c) is used as a reactantat the stage(a). At the stage 85°C. Alternatively fraction- 2 is mixed with xylene

(c) dimethyldiisopropylbenzol contains at least in a molar ratio of 40:60-60:40 in presence ofAlCl3at 80wt.%1,2,4,5-tetraalkylbenzene. 70-80°Cfor 3 hours, followed by an additional 1774 YEGOROV et al., Biosci., Biotech. Res. Asia, Vol. 11(3), 1765-1779 (2014) treatment of the obtained mixture with propylene documene or diisopropyl- p-xylene, subjected to at45-60°Cto themolar ratioof monoisopropylxylene exposurein inert gas atmosphere in presenceof > to diisopropylxylene45:55-35:65. AlCl2 • H2PO4at 60-90 C for2-6 hours to The main disadvantageof the proposed concentration of 5-isopropylpseudocumene or 2,5 methodis thatthe use ofxylene fraction complicates -di-isopropyl- p-xylene,at least 95%. an isomeric mixtureof alkylation products, its This methodcan simplifythe synthesisof separation to alkylbenzol (2,5- diisopropyl- p- two alternativepetrochemical products,their xyleneor 5-izopropylpseu documene) is quite oxidation leads to the formationof pyromelliticacid complex and requires considerable costs. andthe further thermaldehydration of the latter-to To separate pure 2,5 –diizopropylxylene obtain pyromelliticdianhydride. – an alternative raw material for PMDAsynthesis According to thesedata, the synthesis from this complex isomeric mixture is difficult, asthe of1,2,4,5-tetraalkylbenzene by alkylationof boiling point of isomeric components are very pseudocumeneor p-xyleneis believed to be one of close, so the method is complicated with additional the effective methods of raw material obtaining stagesof re-alkylation, isomerization, trans forPMDA synthesis. alkylation. Durenesynthesis by condensation The patent [23] stipulates a method of The industrialprocess fordurene 5 synthesis of tetraalkylbenzene(5-isopropylpseu synthesis by pseudocumene 10 condensation with documene and 2,5–diisopropyl- p-xylene) whereby formaldehyde, followed by hydrocracking of forme alkylatedpseudocumeneormonoisopropyl- p- dalkyldiphenylmethan 10 (dipseudocu methane) xyleneinone stage at 70-90>Cin the presence ofa designed by Shell Development Company24. catalystAlCl2 • H2PO4 until a conversion of The chemical processcan be represented initialhydrocarbon 40-90%, and accumulation bythe reactions shown in Scheme 7. inalkylateof individual5-mono-isopropylpseu The reaction of pseudocumene documeneor 2,5 -diisopropylbenzene,at least 50%, condensation with formaldehyde for dipseudocume followed by separation of alkylate and thane synthesis is studied inpresence of p- concentrateof isomers of monoisopropylpseu sulfonic acid(paraformaldehydewas used) and

Scheme 7. Durene5 synthesis by pseudocumene10 condensation with formaldehyde sulfuric acid (formaldehyde isintroduced in the sulfuricacid. form of formalin). P- toluenesulfonic acid is better as a catalyst Table 2 shows the yieldand compound of because the process proceeds with greater pseudocumenecondensation productsobtained selectivity and higher yield of dipseudocumethane inpresence of p-toluenesulfonic acidand than in presence of sulfuric acid. YEGOROV et al., Biosci., Biotech. Res. Asia, Vol. 11(3), 1765-1779 (2014) 1775

Table 2. Yields and compounds of the pseudocumene product condensation.

Reagents and Catalysts Paraformaldehyde and Formalin and toluene sulfonic acid 88% sulphuric acid

Synthesis conditions: Temperature, °! 90 90 Contact time, h 4 4 Molar ratio of pseudocumene and formaldehyde 2 : 1 2 : 1 Catalyst amount, wt. % perpseudocumene 12,5 25,0 The yield of hydrocarbon layer, wt. % per pseudocumene 105 108 Hydrocarbon layer compound, % Dipseudocumethane 78,0 50,0 Pseudocumene 21,0 42,6 Deep - condensated pseudocumene products – 7,0 Formaldehyde 0,4 0,3 P-toluenesulfonic acid 0,6 – Sulfuricacid – 0,1 Acid layer compound, wt.% P-toluenesulfonic acid 50,0 – Sulfuric acid – 49,0 Formaldehyde 7,0 8,0 Water 43,0 43,0

Dipseudocumethane is turned into durene 3) A large amount of waste(>1t /tdurene). and pseudocumene by hydrocracking over Preparation ofd urene by chloromethylation alumocobaltmolybdic catalyst. Dipseudocum Chloromethylation reactionof aromatic ethane decay reaction proceeds completely at 450°C hydrocarbons (benzene and its alkyl derivatives) and a partial pressure of hydrogen from 0.5 to 2.0 has long been known[25]as a methodof an aromatic 2 MPa (5-20 kgf /cm ); a molar ratio of hydrogen to ring substitution with H2Cl chloromethylgroup, it feed 5 - 6.5: 1, the contact time exceeds 20 seconds. was discovered byGrassy and Maselliin 1898(in The selectivity of the dipseudocumethane literature –Blancreaction)and its general scheme hydrocracking decreases while the contact time is can be represented as shown in Scheme 8. increasing. Increase in the contact timeleads to ZnCl2, H2SO4, AlCl38 SnCl3 are used as increased isodurene concentrations, prehnitene catalysts more often,and a mixture of hydrochloric concentration remains constant. acid and formaldehyde as a26-40% solution is

Tetramethylbenzene mixture obtained by usually used for forming CH2Cl-groups. dipseu docume than ehydrocrackingcontains (in wt.%): durene 80-87; isodurene 5-10;prehnitene8– 10. Becauseof asignificant content of isodurene and prehniteneintetramethylbenzenes, special methods are required to separate high purity durene: clearrectification or crystallization. The total (average) durene yield considering allprocess stages (condensation, where R: CH3, C2H5, C3H7, OCH3,OC2H5etc hydrocracking and rectification) makes 65% Scheme 8. Blanc reaction perinitial pseudocumene. The raw material synthesis to obtain The main disadvantages of durene pyromellitic acid bychloromethylation ofalkyl synthesis from pseudocumene by condensation aromatic hydrocarbonswas reported in the period methodand hydrocrackingare: of 1951-1968 years12. Firstlym-xylene, p-xylene and 1) High energy consumption; pseudocumene were used as alkylaromatic 2) A lowdureneyield(65%); hydrocarbon. A mixture of hydrochloricacid and 1776 YEGOROV et al., Biosci., Biotech. Res. Asia, Vol. 11(3), 1765-1779 (2014) form aldehy deserved as a chloromethylating onchloromethylatedxylenes, which excludes acetic reagent12. The yield of substituteddurene products acid andm-xylene. The process consists of the using p-xylene was 80%, while usingm-xylene- following stages: 70%. a) Chloromethylation of xyleneat 95-100°C, The yield of monochlormethyl pressure of 0.2-0.3MPaand separation pseudocumeneis 78% by pseudocumenechloro of1,2,4,5-isomersby recrystallization; methylation with paraformaldehyde in35-36% b) Hydrolysis of 1,2,4,5-isomers with an hydrochloric acid. aqueous alkaliforming corresponding According to the patent26 pseudo- glycols and polyethers; cumenechloro methylationis carried outat e”150°C c) Oxidationof hydrolysis products with 20% anda pressure of 0.5-1.5MPa.1 –chloromethyl- nitric acid at180°C, pressure of 2.0MPaand 2,4,5–trimethylbenzene obtained this wayis 12-fold molar excess. transformed into durene under the at the gaseous PMC yield at the oxidation stage is87-93 phase at150-200°C. mol%, and per xylenessource- 65mol%. Chloromethyl derivativecan also be Pseudocumene becomes widely available recovered with zinc inpresence of hydrochloricacid. technical product, which canbemore acceptable Also chloromethylderivatives canbe notrecovered comparing to xylenes for the three stage synthesis buthydrolyzed to alcohol which by oxidationis of PMC based on chlormethylation. transformed into pyromellitic acid. Though the durene synthesis technology M.I.Farberovshows in his paper[12] that using chloromethylation reaction has not been chloromethylderivatives are formed during developed very well because of significant raw chloromethylation of m-or p-xylenewhich, material costs, large amount of waste, a relatively afterhydrolysisto correspondinggly colsorpoly low efficiency of the process and, consequently, ethers can bedirectlyoxidized topyromellitic acid. higher costs of durene comparing to other The well-known German company” processes, however recently, this methodseems BergWerkSfer Band” produces PMDA using interesting because of its possible improvement chloromethylation of p-xylene with paraformaldehy to a level of competing technologies. deusinghydrochloricacid and acetic acids. The paper [27], published in 2010, This process consists of three main describes the synthesisof raw materials – bis stages: chloromethylation, hydrolysisand (chloromethyl) xylene 15, 16, 17 for the pyromellitic oxidation. At the first stage, p–xylene ischloro acid synthesis 6bychloromethylation of xylenes12, methylated using para formaldehyde and 13, 14in an aqueousmedium, using as a hydrochloric and acetic acids at 70-85°C and0.5 catalyst[C12mim] Br.bis (chloromethyl) MPa.At the second stage,the obtained xylenesbyaerobic oxidationin presence ofcatalyst dichloromethyl- p –xyleneis saponifiedat 70°C in VO (0A0A)2 / Cu(2 – Eth)2 /DABCOin [hmim]OTfis presence of alkali solution and methanol. The transformed into pyromellitic acid6, dehydratedby obtained methoxy derivativeis purified by heating in presence of aceticanhy dride (Scheme distillation. At the thirdstage, dimethoxy- p – 9).The yieldof pyromellitic dianhydrideis 76.7%. xyleneis oxidized with 20-25% -nitric acid at 190- The main disadvantage of durene 200°C and2.0MPa.The significant disadvantages synthesis by chloromethylationisa large amount of this process are the high unit costof raw materials of wastes (more thanone t/ tof durene). and reagents. The technical and economic comparison Duringthe “BergWerkSferBand”’s of durene synthesis by known methods from processto obtainone ton ofpyromellitic acidthe different sourcesof petrochemical raw materials, following is consumed: 0.59ton of p-xylene, 0.38 conducted earlier by scientific-research institutes tonof paraformaldehyde, 0.56 tonof hydrochloric and describedin b is shown belowin Tables 3 and4 acid, 0.25ton of acetic acid,0.45 ton of sodiumalkali, for anapproximate comparative assessment. 0.54 ton of methanol and 1.62 ton of nitricacid. According to the above, thealkylationof 12 M.I.Farberov et al developed the fraction C9 and higher and xylene fraction dis process of PMDA synthesis based proportionation are characterized by bestindicators YEGOROV et al., Biosci., Biotech. Res. Asia, Vol. 11(3), 1765-1779 (2014) 1777 and better efficiency. By these methods, durenecan development of new technologies and be synthesized at relatively low operation costs improvement of known processes, the comparative and capital expenditures. technical and economic assessment should be However, taking into account the reviewed and specified by the results achieved.

(I) (CH2O)n, 50% H2SO4. AcOH [C12mim]Br, HCl, 55°C, 12 hours;

(II) VO (acac)2 / Cu(2 – Eth)2 / DABCO hmimotf, O2, 120°C, 24 hours;

(III) (CH3CO)O2, boiling, 3 hours. Scheme 9.Three-stage synthesis of PMDA(using ionic solvents iLS). Table 3. Comparison of the main technical and economic indicators of durene synthesis by different methods,%

DureneSynthesis Methods Annual yield of Capital Operat in Cost price of 100%durene expenditures g costs gram of 100% durene

Alkylation by methanol of fraction

C9 and higher 100 100 100 100 Alkylation of aromatichydrocarbons concentrate of catalytic cracking 100 245 200 215 Isomerization of aromatic hydrocarbons by catalytic cracking 100 400 570 170 Pseudocumene condensation and hydrocracking of condensation products 100 190 240 290 Durene separation from the heaviest part of plat forming benzole 100 480 950 420 Disproportionation of xylene fraction 100 235 290 105 1778 YEGOROV et al., Biosci., Biotech. Res. Asia, Vol. 11(3), 1765-1779 (2014)

Table 4 . 1 g Durene Production Cost Structure,%

Expenditures Durene Production By alkylation Isomerization Pseudocumene By durene Bydisprop of separation ortionation With cracking aromatics condensatio from heavy of xylene Methanol Concentrate hydrocarbo n and part of fraction of of ns of hydrocracki benzoleplat fraction aromatics catalytic ng of forming

C9 hydrocarbons condensation forming and ofcatalytic products higher cracking

Raw materials and basic materials 44,9 76,4 102,3 54,1 180,4 45,2 Auxiliary materials 7,0 2,4 6,6 18,7 5,1 14,1 Process fuel 2,5 0,8 1,2 0,3 0,1 0,3 Energy costs 4,2 14,0 20,7 7,3 80,1 51,7 Semi-fixed expenses 34,7 27,0 44,5 15,4 21,6 67,8 Shop expenses 2,3 2,4 5,4 1,3 5,7 6,7 Works general expenses 6,0 6,1 13,8 3,3 14,6 17,2 Total 101,6 129,1 224,5 100,4 307,5 203 Byproducts 1,6 29,1 124,5 0,4 207,5 103 The cost price of one ton of marketable durene 100 100 100 100 100 100

CONCLUSION mentioned in the article. Applied researches arecarried outwith The results of the study ofthe existing state financial support represented bythe Ministry syntheses of pyromellitic acid dianhydrideshowed of Educationof Russia under the Agreement the following. ongranting subsidies No.14.625.21.0003of August 1. This monomeris notmanufactured in Russia. 25,2014. (Uniqueidentifier for Applied Scientific The unit for PMDA synthesis designed and Researches (project) RFMEFI62514X0003). builte arlier(1970-1980years) at OAO “Ufaneftekhim” in 1995ceased REFERENCES theproduction and was later liquidated. Currently, pyromellitic acid dianhydrideis 1. Bessonov,M.I.,Koton, M.M., Kudryavtsev,V.V., imported. Laius, L.A., Polyimides -a class of heat-resistant 2. Foreign manufacturersof PMDA(“Lonza polymers L.: Nayka, 1983. Liang Chemical Co. Ltd”,China, “Hamish 2. Borschenko, V.P., Mahiyanov, G.F., Pyromelliticdianhydride, synthesis and use, WerkeHüls”, “Gecher Halenge” Germany, M.:Nayka, 1974. “Dupont” USA,”Mitsubishi”, “Sumimoto” 3. Plate, N.A., Slivinskiy, Y.V., Fundamentals of Japan, “Hatcher” New Zealand) produce Chemistry and Technology of Monomers, M.: PMDA by vapor-phaseandliquid-phase Nayka 2002. methods of dureneoxidation using 4. Rafikov,S.R., Naletova,G.P., Varfolomeev,D.F., vanadium or vanadium-titanium catalysts at Tolstikov, G.A., Vshivtseva,N.S., Obukhov, the vapor phase oxidation and A.S., Yegorov, I.V., Karimov, A.T., metalbromide –at the liquid phase oxidation. SU956454.Institute of Chemistry,Bashkir 3. Currently,the source petrochemical raw Branch of the USSR Academy of Sciences, 1982. 5. Maximova, N.Ye.,Imashev,U.B., Zlotsky,S.S., materials in PMDA synthesis isdurene or Kantor,Ye.A., Sirkin,A.M., Rahmankulov,D.L., 5–isopropyl pseudocumene derived from Yegorov,I.V., Garbuz,A.I., Taymolkin,N.M., pseudocumene under the methods Rakhimov,M.G.,Mahiyanov, G.F.,Kukovitsky, YEGOROV et al., Biosci., Biotech. Res. Asia, Vol. 11(3), 1765-1779 (2014) 1779

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