Reppe Process- Process Description
Reppe Process- Process Description...
PROCESS DESCRIPTION I. Production of 1,4-Butanediol by Reppe Process The production process is divided in two parts: The reaction of formaldehyde & acetylene to form 1,4butynediol; and hydrogenation to form 1,4-butanediol. In the manufacture of 1,4-butanediol, acetylene is first converted with 10-30% aqueous formaldehyde at 100- 110°C and 5-20 bar in the presence of modified copper acetylide to produce 2-butyne-l ,4-diol: −24 kcal 100 kJ HC=CH +2 HCHO ( aq . ) → HOCH 2−C=C−CH 2 OH ( aq . ) (∆ H= ) mol The reaction is conducted in a trickle-column reactor containing the copper acetylide catalyst with Bi as promoter on SiO2 or magnesium silicate. The intermediate propargyl alcohol is recycled, together with formaldehyde, to the reaction. The butyne-diol selectivity amounts to 80% (C2H2) and > 90% (HCHO). In the second step, 2-butyne-1,4-diol is hydrogenated to 1,4-butanediol: −60 kcal 251 kJ HOCH 2 −C=C−CH 2 OH +2 H 2 → HOCH 2 ( CH 2 ) 2CH 2 OH (∆ H = ) mol The hydrogenation can be conducted in the liauid phase at 70- 100°C and 250-300 bar in the presence of Raney nickel catalyst. Alternatively, the hydrogenation can take place in the trickle phase at 180 - 200 °C and 200 bar employing Ni catalysts with Cu and Cr promoters. The selectivity to 1,4-butanediol reaches about 95% (based on 2-butyne-1,4-diol). This acetylene-based manufacturing method profits more from the increasing worldwide interest in 1,4butanediol than other processes based on C 4 feedstocks, especially in the USA and Western Europe. An additional industrially useful intermediate can be obtained from the acetylene process for 1,4-butanediol. If the hydrogenation of 2-butene-1,4-diol is conducted in the presence of catalysts whose activity has been reduced either by their manufacturing process or by additives, then the reaction stops at the 2-butene-1,4diol stage. Iron catalysts, nickel catalysts with iron additives and possibly amine inhibitors or palladium catalysts, usually partially poisoned with zinc, are employed industrially. The typical yield of the process is around 90% of the theoretical yield based on acetylene.
II. Production of 1,4-butanediol from Maleic Anhydride via Dimethyl Maleate Hydrogenation Process The synthesis is made up of three major stages. First is the production of maleic anhydride by vapor phase oxidation of a hydrocarbon feedstock, in this case, n-butane, followed by the esterification of maleic anhydride using methanol vapor to form dimethyl maleate, and finally, the hydrogenation of dimethyl maleate forming 1,4-butanediol and other byproducts.
For the production of maleic anhydride, n-butane is supplied at a pressure of from 1 to 3 bar and at a temperature of 400° C to a partial oxidation plantwhich is also supplied with air from another line.The partial oxidation reactor is operated at an air:n-butane feed ratio of 20:1. The reaction is catalyzed using vanadium pentoxide. The hot vaporous product stream recovered from partial oxidation is cooled by external cooling against boiler feed water to raise steam and then against cooling water to reduce its temperature to 138° C. This contains 2.9% w/w maleic anhydride, 5.8% w/w water, 1.3% w/w carbon dioxide, 1.0% w/w carbon monoxide, 0.01% w/w acetic acid, 0.01% w/w acrylic acid, 15.7% w/w oxygen, and the balance essentially comprising nitrogen and other inert gases. The following reaction takes place:
7 C 4 H 10 + O2=C 2 H 2 (CO )2 O+4 H 2 O 2 n-butane
This stream is then supplied to the bottom of a column which is divided by a bubble cap plate into a lower sectionand an upper section. The lower sectionof the columnis provided with a number of washing trays where the vaporous feed stream passes up against a downflowing spray of dimethyl phthalate vapor which is supplied at a temperature of about 68° C via spray nozzles positioned at the top of the lower section. The bottoms product, which is a liquid stream, comprises a solution of approximately 22% w/w maleic anhydride and 0.04% w/w acrylic acid in dimethyl phthalate. While the off gas from the lower sectionof the columnpasses up through bubble cap plateinto the upper sectionof column. The upper section of the column is also provided with a number of washing trays where the off gas containing some dimethyl phthalate vapor passes up against a downflowingstream of di-n-butyl phthalate sprayed through nozzles placed at the top part of the uppersectionin order to scrub dimethyl phthalate out of this off gas. A solution of dimethyl phthalate in di-n-butyl phthalate collects in the bottom part of upper sectionand is removed from the column in a side draw. The scrubbed gas exits upper sectionof the column through mist eliminator and is purged from the plant where it can be passed to a waste burner.
The solution of maleic anhydride in dimethyl phthalate obtained as bottoms products from the previous column is then supplied to the top of a column reactorfor esterification. The reactor comprises a number of esterification trays mounted one above the other, each containing a charge of a solid esterification catalyst, such as Amberlyst™ 16 resin or DPT1 ion exchange resin, and each having a vapor upcomer for upflowing vapor and a liquid downcomer to permit liquid to flow down the column from one esterification tray to the next lower one. The column reactor is operated at a temperature of from about 110° C to about 125° C and at a pressure of from about 1 bar to about 3 bar.The residence time in the column reactoris about 3 hours. Normally the temperature on the top tray will be somewhat higher (e.g. about 125° C) than that on the lowermost tray(e.g. about 115° C). Methanol vapor is supplied to near the bottom of the column reactor while water of esterification is removed in the vapor stream exiting the column reactor as the tops product. The esterification reaction that takes place is:
CH ¿2 COOCH ¿ C2 H 2 (CO)2 O+CH 3 OH =HOOC ¿ Maleic anhydride
The bottoms productfrom the column reactor is a solution containing about 250 g/l dimethyl maleate in dimethyl phthalate. The solution is sent to near the top of a stripping columnoperated at a temperature of 170° C and a pressure of 885 psia (61.02 bar). The column has a number of distillation trays above the point of injection of the dimethyl maleate solution in order to reduce carryover of dimethyl phthalate in the overhead stream. The solution of dimethyl maleate in dimethyl phthalate flows down through packingagainst an upflowing stream of hydrogen supplied at near the bottom of the stripping column. The stripped dimethyl phthalate obtained as bottoms product is sent as recycle to a line combining with fresh dimethyl phthalate solvent supplied to the first column while a purge stream of the recycled solvent can be taken into another line.
The tops product from the stripping column is a near saturated vapor mixture stream comprising dimethyl maleate in hydrogen, with a hydrogen:dimethyl maleate molar ratio of about 320:1. This vapor mixture stream is at a temperature of from about 180° C to about 195° C and at a pressure of 62 bar. It is mixed with hot hydrogen supplied at a temperature of from about 180° C to about 195° C to yield a vaporous stream with a hydrogen:dimethyl maleate molar ratio of about 350:1 and is at least about 5° C above its dew point. This vaporous mixture passes onwards to the hydrogenation plantwhich includes an adiabatic reactor packed with a reduced copper-based catalyst, for example, a reduced copper chromite catalyst, and operated at an inlet temperature of 173° C, an inlet pressure of 885 psia (61.02 bar), and an exit
temperature of 190° C. The dimethyl maleate feed rate corresponds to a liquid hourly space velocity of 0.5 h−1. CH ¿2 COOCH ¿ HOOC ¿ Dimethyl maleate
The plant also includes a purification section in which the crude hydrogenation product mixture is distilled in several stages to yield pure 1,4-butanediol. Other streams include γ-butyrolactone stream and tetrahydrofuran stream.
III. Production of 1,4-Butanediol by Hydrogenation of Bio-Succinic Acid
This chemical process begins with two feedstocks: hydrogen gas and bio-succinic acid. The hydrogen gas will be obtained from a pipeline at 150 atm and will be used in molar excess inside the reactor. The plant will require 63,000 metric tonnes of bio-succinic acid per year to meet the proposed plant capacity. First the bio-succinic acid feed is pumped up to 150 atm to match the hydrogen gas feed, and then it is mixed with the hydrogen gas prior to being sent into heat exchanger for heating. The heat exchanger brings the two feeds up to 110oC and sends them to the jacketed packed bed reactor. The hydrogenation reaction occurs inside of the reactor thanks to the packed catalyst bed. The catalyst used is 0.4% Fe, 1.9% Na, 2.66% Ag, 2.66% Pd, 10.0% Re on 1.5mm carbon support. With this catalyst, BDO is produced with over 90% selectivity and minimal side reactions of THF and GBL (Bhattacharyya and Manila, 2011). The reaction has an operating pressure of 2000-4000 psi and internal reactor temperature of 165°C. This temperature allows for about 99.7% conversion of succinic acid (Bhattacharyya and Manila, 2011). Due to the exothermic nature of the reaction, a cooling jacket is required which utilizes downstream cold streams to cool the internal bed to maintain the desired reaction temperature. The effluent of the reactor is sent back to heat exchanger as the hot stream. After exiting heat exchanger, the reactor product stream is sent to a secondary exchanger, where utility cooling water is used to reduce the temperature to an acceptable temperature prior to sending it to a pressure let-down valve. At this point the pressure of the stream is taken from 150 atm to 1 atm. This large pressure drop allows for the stream to split into its vapor and liquid portions in a gas-liquid separator. The vapor stream of the gas liquid separator is primarily hydrogen gas and sent to a flare for disposal. The liquid effluent is at approximately 45oC
leaving the separator and is therefore pumped to the reactor jacket for the reaction cooling mentioned previously. After running through the reactor jacket, the stream enters the separation processes. The first distillation column is a 10 stage column whose primary purpose is separating the THF from the product feed. Due to THF’s lower boiling point, the byproduct comes off of the top of the column with mostly water. This distillate is sent to the plant's THF waste storage tank that has the capacity of two weeks. The bottoms of the column is sent to the subsequent distillation column that separates the BDO from the GBL and water. The relatively close boiling points of BDO and GBL, 235oC and 204oC, respectively, create a difficult separation that requires a 15 stage column. The distillate of the column is approximately 23% GBL with balance water. This stream is sent to a storage tank with similar sizing parameters as the THF storage tank. The bottom stream is the final 99.5wt% BDO product. This stream is sent to the final product tank.
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