Industrialization and Expansion of Green Sustainable Chemical Process

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Industrialization and Expansion of Green Sustainable Chemical Process: A Review of Non-Phosgene Polycarbonate from CO2 Shinsuke Fukuoka, Isaburo Fukawa, Takashi Adachi, Hiroya Fujita, Naoki Sugiyama, and Toshiaki Sawa Org. Process Res. Dev., Just Accepted Manuscript • DOI: 10.1021/acs.oprd.8b00391 • Publication Date (Web): 04 Jan 2019 Downloaded from http://pubs.acs.org on January 6, 2019

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Organic Process Research & Development

Industrialization and Expansion of Green Sustainable Chemical Process: A Review of NonPhosgene Polycarbonate from CO2 Shinsuke Fukuoka,*† Isaburo Fukawa,‡ Takashi Adachi,* § Hiroya Fujita,∥ Naoki Sugiyama,∥ and Toshiaki Sawa∥ *†Fukuoka-Shin Professional Engineer Office, Yoshioka 359-11, Kurashiki-City, Okayama-Ken 710-0842, Japan. (Former: Research & Development Department, Asahi Kasei Corporation) ‡

Asahi Research Center, 1-1-2 Yurakucho, Chiyoda-ku, Tokyo 100-0006, Japan. (Former:

Research & Development Department, Asahi Kasei Corporation) *§Technology Licensing Department, Asahi Kasei Corporation, 2767-11 Niihama, Shionasu, Kojima, Kurashiki-City, Okayama-Ken 711-8510, Japan ∥

Technology Licensing Department, Asahi Kasei Corporation, 1-1-2 Yurakucho, Chiyoda-ku,

Tokyo 100-0006, Japan

ACS Paragon Plus Environment

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Organic Process Research & Development 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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Abstract Graphic.

Green sustainable non-phosgene polycarbonate process from CO2, wherein high materials-saving, energy-saving are attained, has been industrialized and expanded worldwide.


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ABSTRACT: World’s first Non-Phosgene Polycarbonate Process from CO2 has been developed and industrialized by Asahi Kasei Corporation (Japan). Hitherto, all polycarbonates (PC) have been produced using CO as a raw material. Among them, most PCs have been produced by socalled “Phosgene Process” using highly toxic phosgene (COCl2) and large amount of solvents (probable human carcinogen CH2Cl2 and water). The phosgene process has many environmental and safety problems. However, the technological hard barriers have hindered from realizing the non-phosgene PC process. The Asahi Kasei Process has not only solved the problems of the phosgene process, but also contributed to sustainability (reduction of CO2 emission, materialssaving and energy-saving). High-quality PC and high-purity mono-ethylene glycol (MEG) are produced in high yields, respectively, without waste and waste water, starting from CO2, ethylene oxide (EO), and bisphenol-A (BPA). In the monomer (diphenyl carbonate: DPC) production process, innovative reactive distillation process and in the melt polymerization process, Gravity-Utilized Non-Agitation Reactor had been developed, respectively. The Asahi Kasei Process has been expanding to worldwide, and 1.07 million tons of PC will be produced in 2019. The Green Sustainable Chemical Process has been changing the PC production world. In this review, the Asahi Kasei Process and perspective of the present PC production processes together with discriminating and detailed comparisons are described.

KEYWORDS: Non-Phosgene Polycarbonate (PC), CO2, Dimethyl Carbonate (DMC), Diphenyl Carbonate (DPC), Reactive Distillation, Gravity-Utilized Non-Agitation Melt Polymerization


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1. INTRODUCTION The aromatic polycarbonate (PC) having the linkages of carbonate group (-O-CO-O-) and bisphenol-A (BPA) residue is an indispensable plastic in our daily lives, looking around, smart phones, CD/DVDs, TV, car parts, camera, personal computers, sheet, construction materials, etc. PC is one of the engineering thermoplastics, which have excellent mechanical and thermal properties. PC, polyamide (PA), polybutylene terephthalate (PBT), polyoxymethylene (POM), polyphenylene oxide (PPO) modified by high impact polystyrene are called the five commodity engineering plastics, because they are widely used in large quantities, respectively. Among them, PC has been consumed in the largest quantity and maintained the top position as the engineering plastic since the demand of PC exceeded that of polyamides (PA) in 1995. The worldwide demand of PC exceeded about 3.6 million tons in 2016. The reasons for the largest demand of PC in the engineering plastics is owing to the excellent properties, such as outstanding impact resistance, good transparency, high heat resistance, high flame retardancy.1-14 PC based on BPA was invented independently by Dr. H. Schnell 1 (Bayer) and Dr. W. Fox5 (GE). Bayer and GE started the commercial production of PC by the phosgene process in 1958 and 1960, respectively. After that, Teijin Chemicals (1960; now Teijin), Idemitsu Petrochemicals (1960), Mitsubishi Gas Chemical (1961), Mitsubishi Chemical (1975; The process was transferred from Idemitsu Petrochemicals), and Dow Chemical (1985) started the commercial production of PC. Since then, only these seven companies’ groups have been producing PC by the phosgene process using highly toxic phosgene produced from CO and Cl 2 and large amounts of solvents (CH2Cl2: probably human carcinogen, H2O). In addition to these phosgene processes, only GE (now SABIC I. P.) group has been producing PC by the non-phosgene PC process from


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CO in Spain (1999), which was developed and industrialized by GE Plastics Japan in 1993. In any case, all PC had been produced using CO as a raw material. World’s first Non-Phosgene Polycarbonate Process from CO2 has been developed and industrialized (2012) by Asahi Kasei Corporation (Japan), and expanded to worldwide by licensing.15-19 This process had been developed via basic research of the flask scale and development by bench and pilot stages. The success of the industrialization is owing to develop the innovative processes both in the monomer production process and the melt polymerization process. 2. OUTLINES OF THE PHOSGENE PC PROCESS AND THE DRAWBACKS The nominal PC production capacity was about 4.89 million t/y in 2016. Until Asahi Kasei Process reveals, all PC processes have been using CO as a raw material. Among them, most PCs have been produced by “Phosgene Process” using highly toxic phosgene (COCl2) and large amount of solvents (CH2Cl2 and water). The insertion of CO part into BPA for making carbonate bond is very difficult. Therefore, highly active phosgene has been using, although it is highly toxic. Figure 1 shows the reaction scheme of the phosgene PC process.

Figure 1. Reaction scheme of the phosgene PC process.


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The polymerization is carried out under vigorous stirring of the reaction medium to occur the phosgenation of BPA and polycondensation at the interface between CH2Cl2 layer containing COCl2 and H2O layer containing disodium salt of BPA. Amine or quaternary ammonium compound is used as a polycondensation catalyst. The polymerization is a kind of neutralization. Produced PC dissolves into CH2Cl2 layer and by-produced NaCl dissolves into H2O layer. Figure 2 shows the steps of the phosgene PC process, which consists of many steps; (1) CO production step by the partial oxidation of cokes or lower hydrocarbons and purification, (2) Cl 2 and NaOH production step by the electrolysis of aqueous NaCl, (3) Phosgene production step by the reaction of CO with Cl2, (4) Interfacial polymerization step by the phosgenation and polycondensation of phosgene with BPA, (5) PC solution purification step by washing using a large amount of water, (6) PC separation step from the CH2Cl2 solution by adding a large amount of poor solvent such as hexane or toluene to precipitate PC particles, (7) PC particles drying step, (8) PC particles pelletizing step using melt pelletizer, (9) Solvents (CH2Cl2 and poor solvent) recovery step, and (10) Waste water disposal step. In the drying step, it is hard to remove CH2Cl2 completely from the powder form PC, because PC has strong affinity for CH2Cl2.

Figure 2. PC production steps of the phosgene process.


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The phosgene process has many problems in terms of environmental and safety, a large amount of waste water disposal, highly-corrosiveness, high cost, and quality (containing Cl-impurities). The drawbacks of the phosgene PC process except for the cost and quality are as follows; (1) A large amount (> 0.43ton / PC 1ton) of highly toxic and corrosive phosgene must be used. The permissible exposure limit of phosgene is 0.1 ppm. Phosgene was used as a chemical weapon in World War Ⅰ.20-21 Now, more than about 8 million t/y of phosgene has been used for PC, isocyanates, pesticides. The production and use of phosgene have been severely restricted by Chemical Weapons Convention. However, unfortunately, fatal accidents by phosgene leak have occurred in even 2000s.22-30 Even in the big chemical companies, phosgene leak accidents have occurred.25-26, 31 (2) As a polymerization solvent, a very large amount (>10 tons / PC 1 ton) of CH2Cl2 must be used. The boiling point of CH2Cl2 is low (40 °C) and the exposure limit is 25 ppm (OSHA)32 reflecting its carcinogenic properties (probable human carcinogen).33-34 (3) A very large amount of waste water disposal is necessary. The phosgene process uses a very large amount of water in the polymerization step (> 10 tons/ PC 1 ton), and purification step (10100 tons/ PC 1 ton) to remove NaCl, unreacted sodium salt of BPA, catalyst (amines). The water layer contains dissolved CH2Cl2 (20g/l) along with above contaminants. (4) Complete prevention of CH2Cl2 (b.p. 40 °C) release into the atmosphere is very difficult. (5) In all steps, Cl-compounds and H2O are co-existing, which circumstance is highly corrosive. 3. TECHNOLOGICAL HARD BARRIERS TO THE NON-PHOSGENE PC PROCESS


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Many attempts to develop the non-phosgene PC process from diphenyl carbonate (DPC) and BPA as shown in Figure 3 have been carried out for long years by the current PC manufacturers and several companies aiming to enter the PC business as new comers.

Figure 3. Reaction scheme of the Non-Phosgene PC Process. However, almost all of those attempts have not succeeded. Thus, until now, the phosgene process has been continued to produce PC as a main process. The reason why those attempts have been unsuccessful is owing to the technological hard barriers difficult to overcome for the industrialization. In the non-phosgene PC process, DPC is necessary as a safe monomer instead of highly toxic phosgene and the polymerization reaction of DPC with BPA is carried out in the molten state under reduced pressure to remove the by-produced phenol (PhOH). There are two technological hard barriers preventing from industrialization of the non-phosgene PC process: 3.1. Technological hard barrier in producing ultra-highly pure DPC at low cost. Ultrahighly pure DPC (Cl 99%). 76 5.2. DMC and MEG Production Process (Reaction 2: Figure 6). The reaction of EC with MeOH is governed by the small equilibrium constant (K = about 0.07). Hence, EC conversion using current reaction method has been low.77 The innovative reactive distillation process has broken this barrier.57, 78-79 Into the multi-stage distillation column, EC is continuously fed from


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the upper portion and MeOH is continuously fed from the lower portion, and the reaction and distillation of the products are simultaneously carried out in the column in the presence of a catalyst. Preferable catalyst is anion exchange resin78d or alkali metal hydroxide.79b The produced DMC (b.p. 90°C) and MEG (b.p. 198°C) are continuously withdrawn from the top and the bottom of the column, respectively.

Figure 6. Reaction schemes of EC and DMC/MEG productions from EO, CO2 and MeOH. 5.2.1. An Example of Industrial Reactive Distillation Process for Producing DMC/MEG. Industrial reactive distillation process for producing DMC/MEG has been disclosed. 79 According to the patent79a, a continuous multi-stage distillation column having number of stages = 60 was used, wherein the sieve trays were used as the internals. 3.27 Ton/hr of EC in a liquid form was continuously fed to the distillation column from an inlet at the 55th stage from bottom. 3.238 Ton/hr of MeOH in a gaseous form (containing 8.96 % by weight of DMC) and 7.489 ton /hr of methanol in a liquid form (containing 6.66 % by weight of DMC) were respectively continuously fed to the distillation column from inlets at the 31st stage from the bottom. The catalyst solution (KOH in EC) was continuously fed to the distillation column from an inlet at the 54th stage from


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the bottom (K concentration: 0.1 % by weight based on EC fed in). Reactive distillation was carried out at 98°C of the bottom temperature, about 1.118 x 105 Pa of the top pressure, and a reflux ratio of 0.42. The low boiling point reaction mixture was continuously withdrawn from top of the distillation column at 10.678 ton/hr, contained 4.129 ton/hr of DMC, and 6.549 ton/hr of MeOH. The liquid continuously withdrawn from the bottom of the column at 3.382 ton/hr comprised of 2.356 ton/hr of MEG, 1.014 ton/hr of MeOH and 4 kg/hr of unreacted EC. The actual produced amount of DMC excluding the DMC contained the starting material was 3.340 ton/hr, and the actual produced amount of MEG excluding the MEG contained in the catalyst solution was 2.301 ton/hr. The EC conversion was 99.88 %, the DMC selectivity was not less than 99.99 %, and the MEG selectivity was not less than 99.99 %. The yields of DMC and MEG were both more than 99.87%. This world’s first process enables to produce DMC and MEG in high yields (>99%), respectively.78-79 This process is best not only for DMC production, but also for MEG production. Because this process solves the two remaining important problems of the current EO hydration process,71-72 which are low MEG yield of about 90% using H2O/EO = 25 in molar ratio; and high energy consumption for separation of the remaining H2O in the reaction mixture. 5.3. DPC Production Process (Reaction 3). The reaction of DMC with PhOH to produce DPC has many difficulties, extremely small equilibrium constant, low reaction rate, easily occurrence of decarboxylation to produce anisole (PhO-CH3).80-81 In the production of DPC by the transesterification reaction of DMC with PhOH, the first replacement of MeO-group by PhO-


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group to produce methyl phenyl carbonate (MPC) (Reaction 3-1) has extremely small equilibrium constant of about K = 10-4. MeO-CO-OMe + PhOH → PhO-CO-OMe (MPC)

+ MeOH (Reaction 3-1)

5.3.1. MPC Production by Batch-Column Process. The reaction having a low reaction rate has been thought that the batch-wise reaction method is preferable. Thus, all attempts had been carried out batch-wisely. The conventional batch-column process for producing MPC from DMC and PhOH is shown in Figure 7. The yield and selectivity of MPC and DPC were low.82-84 One “Greenness metrics” describes batch-column process is inferior to the phosgene DPC process.157

Figure 7. Batch-column process. PhOH, DMC and a catalyst are charged in the bottom reactor, and the reaction is carried out under heating. The upper part column fitted on the reactor works to separate the low boiling point product (MeOH, b.p. 64°C) from the vapored reactants (DMC, b.p. 90°C; PhOH, b.p. 182°C) by distillation. The reaction is carried out only in the bottom reactor existing the catalyst,


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and in the column part, only distillation is carried out. Thus, in the batch-column process, the reaction and distillation are carried out in the separate zones respectively. 5.3.2. MPC Production by the Reactive Distillation Process (Principle). Figure 8 shows the principle of the reactive distillation process for producing MPC from DMC and PhOH.

Figure 8. Reactive distillation process The high boiling point reactant PhOH (b.p. 182°C) is continuously fed into the multi-stage distillation column from the upper portion of the column, the lower boiling point reactant DMC (b.p. 90°C) continuously fed into the column from the lower portion of the column. The homogeneous catalyst is continuously fed into the column from the upper portion. The continuously flowing down liquid PhOH reacts with the continuously rising gaseous DMC in the stages of the column existing the catalyst to produce MeOH and MPC. The low boiling point product MeOH (b.p. 64°C) is continuously withdrawn from the upper portion of the column by distillation, and the high boiling point product MPC (b.p. 213°C) is continuously withdrawn from the lower portion of the column. An example using 4 m height column packed with 6 mm


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Dixon packing (column bottom 204°C, top 7.8x105 Pa, reflux ratio 0.8) showed that the yields (based on the reacted PhOH) of MPC, DPC and anisol were 97%, 2% and 0.8%, respectively. The reaction and the separation of the products by distillation are carried out simultaneously in the same column. This is the reason why this method is called “reactive distillation process.” 5.3.3. Comparison of the Reactive Distillation Process with the Batch-Column Process. Figure 9 shows the results of the reactive distillation process and the batch-column process.

Figure 9. Comparison of the Reactive Distillation with Batch Column. The reactive distillation process enables to attain the higher conversion of PhOH than that of the current batch-column process, further, can produce MPC in high productivity since the selectivity is also high. The results of the plots A and B in the reactive distillation process are based on the data obtained using different height column of the pilot facilities constructed to examine the effect of the residence time of the liquid materials in the distillation column. Anisol is the decarboxylation by-product, PhO-CH3. The innovative reactive distillation process has overcome the hard barrier of MPC production process.


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5.3.4. DPC Production via MPC.

In the production of DPC by the transesterification

reaction of DMC with PhOH, the first replacement of MeO-group by PhO-group to produce methyl phenyl carbonate (MPC) (Reaction 3-1) has extremely small equilibrium constant of about K = 10-4. Further, the second replacement of MeO-group of MPC by PhO-group to produce DPC has small K < 10-4. The disproportion reaction of MPC to DPC and DMC (Reaction 3-2) has small K = about 10-3. Therefore, the disproportion reaction has been adopted. PhO-CO-OCH3 + PhOH → PhO-CO-OPh + CH3OH

(K< 10-4 )

2 PhO-CO-OCH3 → PhO-CO-OPh + CH3O-CO-OCH3 (K= about 10-3 ) Figure 10 shows the reaction schemes of DPC production process via MPC production (Reaction 3-1) and the disproportion reaction of MPC (Reaction 3-2). By-produced MeOH in the Reaction 3-1 is recycled to the DMC production process, and by-produced DMC in the Reaction 3-2 is recycled to the Reaction 3-1, respectively. Both the Reaction 3-1 and the Reaction 3-2 are carried out by the reactive distillation process. This innovative reactive distillation process enables to produce ultra-highly pure DPC in a high production rate with high selectivity.49, 85-86

Figure 10. Reaction schemes of DPC production from DMC and PhOH via MPC.


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5.3.5

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An Example of Industrial Reactive Distillation Process for Producing DPC.

Industrial reactive distillation process for producing DPC has been disclosed.86 Reactions 3-1 and 3-2 are continuously carried out using two continuous multi-stage distillation columns connected with each other (Figure 11).

Figure 11. Two Reactive Distillation Columns for producing DPC from DMC and PhOH. According to the patent,86f the first continuous multi-stage distillation column having number of stages = 80 was used for producing MPC, wherein the sieve trays were used as the internals. The second continuous multi-stage distillation column having number of stages = 30 was used for producing DPC, wherein, two sets of Mellapak (total number of stages 11) were installed in the upper portion, and the sieve trays were used in the lower portion as the internals. The mixture of PhOH and DMC (PhOH/DMC = 1.9 in weight) was introduced continuously at a flow rate of 50 ton/hr from an upper inlet of the first column. The mixture of DMC and PhOH (DMC/ PhOH = 3.6 in weight) was introduced continuously at a flow rate of 50 ton/hr from a lower inlet of the first column. Pb(OPh)2 as a catalyst was introduced from the upper inlet of the first column such that a concentration thereof in the reaction liquid was approximately 100 ppm.


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Reactive distillation of the first column was carried out at 225 °C of the bottom temperature and 7x105 Pa of the top pressure. The low boiling point reaction mixture of the first column containing MeOH, DMC, PhOH was continuously withdrawn from the top of the first column at a flow rate of 34 ton/hr. The high boiling point reaction mixture of the first column containing MPC, DMC, PhOH, DPC, catalyst was continuously withdrawn from the bottom of the first column, and was fed continuously into the second column at a flow rate of 66 ton/hr from the inlet installed between the Mellapack and the sieve tray. The liquid fed into the second column contained 18.2 % by weight of MPC and 0.8 % by weight of DPC. Reactive distillation of the second column was carried out at 210 °C of the bottom temperature and 3x104 Pa of the top pressure, and a reflux ratio of 0.3. The low boiling point reaction mixture of the second column containing DMC and PhOH was continuously withdrawn from the top of the second column at a flow rate of 55.6 ton/hr, and was continuously fed into the first column from the lower portion. The high boiling point reaction mixture of the second column containing 38.4 % by weight of MPC and 55.6 % by weight of DPC was continuously withdrawn from the bottom of the second column. The amount of DPC produced per hour was 5.74 tons. The selectivity for the DPC based on the PhOH reacted was 98 %. Prolonged continuous operation was carried out under these conditions. The amounts of DPC produced per hour at 500 hours after attaining stable state (excluding the DPC contained in the starting material) were 5.74 tons, and the selectivity were 98 %. The DPC produced substantially did not contain halogens (1 ppb or less). This is the worlds’ first reactive distillation technology for producing DPC.49 Success of the development for the above three reaction processes (EC, DMC/MEG, DPC) enabled to produce ultra-highly pure DPC (Cl

Industrialization and Expansion of Green Sustainable Chemical Process

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