FIELD OF THE INVENTION

[0001] in the manufacture of butanediol from feedstock comprising acetylene, formaldehyde and hydrogen, costs associated with recycle of unreacted formaldehyde are critical for commercial petrochemical plant operation. The present invention relates to an improved method for optimizing energy use in the recycle of unreacted formaldehyde from butynediol reactor product. More particularly, the method involves feeding a stream comprising unreacted formaldehyde downstream from a butynediol synthesis reactor to a column maintained at specific conditions, removing a top stream from the column comprising formaldehyde, water and methano!, for recycle and treatment to remove some methanol, and removing a bottom stream from the column comprising butynediol, water, methanol and less than 1 wt % by weight formaldehyde, for further processing to create butanediol of the required quality. Energy optimization is achieved by raising steam from steam condensate, which has been generated in the column reboiler, in a column overheads product condenser/steam raiser unit, and passing the steam from the condenser/steam raiser unit through a compressor for use in the column reboiler, or by simply raising steam from steam condensate generated in the column reboiier in the column overheads product

condenser/steam raiser unit, and passing the steam generated in the condenser/steam raiser unit for use in other processes as required.

BACKGROUND OF THE INVENTION

[0002] In current processes for manufacturing butanediol, acetylene and formaldehyde are converted into butynediol, which is in turn hydrogenated to form butanediol. The synthesis of butynediol from acetylene and formaldehyde has been described, for example, in K. Weisserme!, H.-J. Arpe, industrielie Organische Chemie [Industrial Organic Chemistry], 5th Edition, 1998, Wiley-VCH, pages 110 and 111). in addition to copper, the catalysts typically used in this synthesis may, if appropriate, comprise bismuth and also silica (Si0 ₂ ) or alumina (Ai ₂ 0 ₃ ). The hydrogenation of butynediol to butanediol has been described many times. For instance, U.S. Pat. No, 5,068,468 discloses the hydrogenation of butynediol over solid supported nickel-copper catalyst, while U.S. Pat. No. 4,153,578 describes a two-stage process for hydrogenating butynediol over suspended Raney nickel-molybdenum catalyst at a particular pressure. Patent publication DD-A 272 644 discloses the suspension hydrogenation of aqueous butynediol over nickel-Si0 ₂ catalyst, and EP-B 0 319 208, DE-A 19 41 633 and DE-A 20 40 501 disclose general hydrogenation processes which may be applicable to butynediol. [0003] Butynedioi may be manufactured from a reaction mixture comprising an aqueous solution containing formaidehyde, acetylene and suspended catalyst in a reaction vessel. For example, U. S. Pat. No. 4,584,418A describes a means for making a copper acetyiide cataiyst for synthesis of butynedioi in a single vessel wherein acetylene is bubbled through the reactor at 90 °C and atmospheric pressure. In a further example, U. S. Pat. No.

5,444, 169A discloses a process for synthesizing butynedioi from an aqueous solution containing formaldehyde by reaction with acetylene in the presence of a suspended catalyst, wherein the solution is conveyed in a cascade by several reactors, the solution drawn off from the first through the penultimate reactor of the cascade being fed to the next reactor in the cascade, acetylene being introduced into each of the reactors, and a butynedio!-rich solution being drawn off only from the last reactor in the cascade. The catalyst is separated from the solution in each individual reactor of the cascade above the last reactor to prevent the catalyst from escaping the reactor.

[0004] In each instance of the butynedioi manufacturing step of a butanediol

manufacturing process, unreacted formaldehyde is a valuable component which should be recovered and recycled to make the overall process more commercially advantageous. This is typically done by feeding the butynedio! synthesis reactor effluent ultimately to a distillation column in which methanol, formaldehyde and water are removed from the top, while butynedioi, water and methanol and a small amount of formaldehyde are removed from the bottom. This can be an energy intensive operation; particularly if the butynedioi reactor is operated at a comparatively low formaldehyde conversion. To achieve low concentrations of formaldehyde requires longer residence times and requires use of large butynedio! reactors or even trains in series of such reactors which results in very high capital cost. To use higher concentrations of formaldehyde, requiring much shorter reactor residence times, results in high energy costs to recycle the formaldehyde. A simple economical method for such recovery and recycle is needed.

SUMMARY OF THE INVENTION

[0005] The present invention provides an economical improved method for recovering and recycling unreacted formaldehyde from a butynedioi synthesis reaction product stream. An embodiment of the invention method involves the steps of: a) feeding the reaction product comprising unreacted formaldehyde to a column maintained at specific conditions, the column associated with a reboiler, b) removing a vapor phase top stream comprising formaldehyde, water and methanol from the column of step a), and passing at least a portion thereof to a condenser/steam raiser maintained at specific conditions, wherein steam is raised from steam condensate or boiler feed water by heat interchange with the vapor phase top stream and a process condensate stream is generated from the vapor phase top stream, c) removing a liquid phase bottom stream comprising butynediol, water, formaldehyde and methanol from the coiumn of step a), d) removing the process condensate stream of step b), and passing at least a portion thereof back to the coiumn of step a) as reflux, e) removing steam from the condenser/steam raiser of step b), and passing the steam through a compressor and to the reboiler of the column of step a), and f) passing a portion of steam condensate from the reboiler of the column in step a) to the condenser/steam raiser of step c).

[0006] Another embodiment of the invention method involves the steps of: a) feeding the reaction product composition comprising unreacted formaldehyde to a coiumn maintained at specific conditions including a top temperature of from 115 to 150 °C, and a bottom temperature of from 130 to 170 °C, the column associated with a reboiler, b) removing a vapor phase top stream comprising water, methanol and at least 25 wt % formaldehyde, from the column of step a), and passing an 80 to 100 wt % portion thereof to a

condenser/steam raiser maintained at specific conditions, wherein steam is raised from steam condensate or boiler feed water by heat interchange with the vapor phase top stream and a process condensate stream is generated from the vapor phase top stream, c) removing a liquid phase bottom stream comprising butynediol, water, methanol and at most 1 wt % formaldehyde from the column of step a), d) removing the process condensate stream of step b), and passing a 50 to 70 wt % portion thereof back to the column of step a) as reflux, e) removing steam from the condenser/steam raiser of step b), and passing the steam through a compressor and to the reboiler of the coiumn of step a), and f) passing a portion of steam condensate from the reboiler of the coiumn in step a) to the

condenser/steam raiser of step c).

[0007] Another embodiment of the invention involves the above steps wherein the compressor of step e) increases the pressure of the condenser/steam riser product by a factor of from 2 to 10.

[0008] Another embodiment of the invention involves the above steps preceded by reacting a mixture comprising an aqueous solution containing formaldehyde, acetylene and suspended catalyst in a reaction vessel at reaction conditions to yield the reaction product composition comprising unreacted formaldehyde. Therefore, another embodiment of the invention comprises the steps of: 1) reacting a mixture comprising an aqueous solution containing formaldehyde, acetylene and suspended catalyst in a reaction vessel at reaction conditions to yield a reaction product comprising butynediol, water, unreacted formaldehyde and methanol, 2} feeding the reaction product of step 1) comprising butynediol, water, unreacted formaidehyde and methanol to a column maintained at specific conditions, the column associated with a reboiler, 3) removing a vapor phase top stream comprising formaldehyde, water and methanol from the column of step 2), and passing an 80 to 100 wt % portion thereof to a condenser/steam raiser maintained at conditions, wherein steam is raised from steam condensate or boiler feed water by heat interchange with the vapor phase top stream and a process condensate stream is generated from the vapor phase top stream, 4) removing a liquid phase bottom stream comprising butynediol, water, formaldehyde and methanol from the column of step 2), 5) removing the process condensate stream of step 3), and passing a 50 to 70 wt % portion of the process condensate stream back to the column of step 2) as reflux, and the remainder of the process condensate stream back to the reaction vessel of step 1) as recycle, 6) removing steam from the condenser/steam raiser of step 3), and passing the steam through a compressor and to the reboiler of the column of step 2), and 7) passing a portion of condensate from the reboiler of the column in step 2) to the condenser/steam raiser of step 3).

BRIEF DESCRIPTION OF THE DRAWING

[0009] Fig. 1 shows a diagrammatic flow of an embodiment of the present method. DETAILED DESCRIPTION OF THE INVENTION

[000101 As a result of intense research in view of the above, we have found that we can - economically and effectively recycle unreacted formaldehyde from a butynediol synthesis reaction product composition downstream from a butynediol synthesis reactor. The method involves feeding the reaction product composition comprising unreacted formaldehyde to a column maintained at specific conditions, the column associated with a reboiler, removing a vapor phase top stream from the column comprising formaldehyde, water and methanol, and passing at least a portion of the recovered top stream to a condenser/steam riser maintained at specific conditions, removing a liquid phase stream from the column condenser/steam raiser comprising butynediol, water, methanol and unreacted formaldehyde for recycle to the butynediol reactor and providing column reflux, raising steam in the condenser/steam raiser by heat interchange with the column vapor phase top steam, removing the steam from the condenser/steam raiser and passing it through a compressor to increase the steam pressure prior to passing it to the column reboiler, and then passing the higher pressure steam condensate from the reboiler back to the condenser/steam raiser for further steam raising.

[00011] An embodiment of this method comprises feeding the reaction product composition comprising unreacted formaldehyde to a column maintained at specific conditions, removing a vapor phase top stream comprising formaldehyde, water and methano!, and passing at ieast a portion of the recovered top stream to a condenser/steam riser maintained at specific conditions, removing a liquid phase bottom stream from the column comprising butynediol, water, methanoi and unreacted formaldehyde, and passing at ieast a portion thereof to a reboiier maintained at specific conditions, removing steam product and condensate from the condenser/steam riser, and passing the steam product from the condenser/steam riser through a compressor and to the reboiier, removing a top stream from the condenser/steam riser, and passing at ieast a portion thereof to the top of the column as reflux, passing condensate from the reboiier to the top of the

condenser/steam riser, and passing a top stream from the reboiier to the column.

[00012] The term butynedioi ("BYD") represents the compound structure

HOCH ₂ C≡CCH ₂ OH. The term butanediol ("BDO") represents the compound structure HOCH ₂ CH ₂ CH ₂ CH _z OH. Pressures are in kPa.A, wherein 98.7 kPa = 1 bar = 0.987 atmosphere, and "A" denotes absoiute pressure, uniess otherwise indicated.

[00013] In addition to the processes for manufacturing BYD noted above, an embodiment of such a process involves manufacturing BYD from a reaction mixture comprising an aqueous solution containing formaldehyde, acetylene and suspended catalyst in a single or series of reaction vessels containing internal filters, such as candle filters, for separation of suspended catalyst from reaction product. In such reaction vessels, catalyst solids build up on the fi!ters as cake which can be removed by back flushing each filter reguiar!y to avoid plugging the reactor vessel From the reaction vessels is recovered product comprising BYD, water, unreacted formaldehyde and methanol. Another embodiment of such a process involves manufacturing BYD from a reaction mixture comprising an aqueous solution containing formaldehyde, acetylene and suspended catalyst in a reaction vessel whereby a product slurry stream comprising BYD, water, unreacted formaldehyde, methanol and suspended catalyst is passed from the reaction vessel to a filter external from the reaction vessel where the suspended catalyst is removed, allowing for recovery of product comprising BYD, water, unreacted formaldehyde and methanol.

[000 4] The BYD synthesis reaction product composition downstream from a BYD synthesis reactor for use herein typically comprises from 30 to 50 wt % BYD, 40 to 60 wt % water, 1 to15 wt % unreacted formaldehyde, and 2 to 7 wt % methanol, on a solids free basis. [00015] The reaction vessel for use in a process for manufacturing BYD may comprise one of current use in such a process. Such a reaction vessel may be a bubble column wherein acetylene and other gases are injected at the base of the reactor both to conduct the reaction and to maintain the catalyst solids in suspension, or a stirred tank reactor which uses an agitator to maintain catalyst soiids in suspension and to assist in gas dispersion, or some combination thereof. Reaction conditions in such a reaction vessel include a temperature of from 40 to 1 10 °C, for example, from 60 to 1 10 °C, pressure from 0 to 200 kPa.A, for example from 9 to 1 10 kPa.A, and pH from 3 to 9. Contents of the reaction vessel are agitated by either or both of mechanical means, for example a stirrer, or gaseous injection.

[00016] Catalyst for use in the reaction vessel for manufacturing BYD and suspended as solids in the product slurry stream comprising BYD, water, unreacted formaldehyde and methanol may be added to the reaction zone or produced in the reaction zone. The catalyst may comprise copper, and a catalyst precursor may comprise a compound of copper, such as, for example, copper carbonate.

[00017] The new improved method of this invention involves recovering unreacted formaldehyde from a BYD synthesis reaction product composition downstream from a BYD synthesis reactor using a formaldehyde recycle column ("column") in a method designed to reduce the variable costs associated with such an effort. The column used is a conventional distillation column with steam heating applied at the base of the column by way of a reboiler, and water cooling applied at the top of the column by way of a condenser/steam riser. This method utilizes the heat available in the column overheads using water as an external working fluid. The working fluid is vaporized by exchanging heat with the overheads in the condenser/steam riser. This low pressure steam is then compressed in a compressor and subsequently used as the heating medium for the column reboiler. The high pressure condensate from the column reboiler is then sent back to the condenser/steam riser to be vaporized and recompressed. This vapor recompression scheme (loop) results in significant reductions in consumption of high pressure steam and cooling water usage.

[00018] The column used herein may comprise one of current use in such a unit operation, such as, for example, a trayed or packed column. The conditions maintained for the column include a top temperature of from 1 15 to 50 °C, and bottom temperature of from 130 to 170 °C. The column top pressure will be from 100 to 600 kPa.A. [000191 (n this new method, most of the column energy demand is supplied by the loop described above; however, when the heat available in the condenser/steam riser is lower than that required by the reboi!er, for examp!e if a vapor purge is taken from the column, the difference between the two duties is provided by utility steam supplied directly to the reboi!er. The use of water as the working fluid allows direct injection of utility steam in the same heat exchanger. This not only eliminates the need for having a separate auxiliary reboiler, it also increases the degrees of freedom in control and operation of the heat pump loop.

[00020] To maximize the efficiency of the present method, we can use a standard shell and tube heat exchanger as the condenser/steam riser. The formation of paraformaldehyde, and thus exchanger fouling, is expected to be promoted when formaldehyde vapor is in contact with coid surfaces (for example, when condensing against cooling water). The present method involves condensation of the column overheads in the absence of cold surfaces and hence leads to reduced exchanger fouling.

[00021] The condenser/steam riser used herein may comprise one of current use in such a unit operation, such as, for example, a shell and tube heat exchanger with steam generation in the shell side. The conditions maintained for the condenser/steam riser for use herein include a pressure from 0 to 400 kPa.A raising saturated steam.

[00022] The coiumn reboiler used herein may comprise one of current use in such a unit operation, such as, for example, a vertical thermosyphon or a forced circulation heater. The conditions maintained for the reboiler for use herein include a pressure from 400 to 1400 kPa.A.

[00023] The compressor of step e) used herein may comprise one of current use in such a unit operation, such as, for example, a reciprocating or axial compressor or a steam ejector or thermocompressor. The compressor increases the pressure of the steam raised in the condenser/steam raiser by a factor of from 2 to 10, such as, for example from 3 to 5.

[00024] The top stream recovered from the column in the present method comprises at least 25 wt % formaldehyde and the bottom stream recovered from the column comprises at most 1 wt % formaldehyde. More specifically, the top stream recovered from the column comprises from 25 to 35 wt % formaldehyde, 50 to 60 wt % water, and 5 to 15 wt % methanol; and the bottom stream recovered from the column comprises 50 to 60 wt % BYD, 40 to 50 wt % water, from 0 to < 0.1 wt % methanol, and 0.2 to 1 wt % formaldehyde. [00025] in step b) of the present improved method, an 80 to 100 wt % portion, for example a 93 to 100 wt % portion, of the top stream removed from the column of step a) is passed to the condenser/steam riser, where steam is raised by heat interchange with the condensing stream. This may be accomplished by, for exampie, flow split control using a simple control ioop. Raising steam in the condenser/steam riser may be accomplished by, for example, utilizing a shell and tube heat exchanger to raise steam on the shell side. Further, in step e) of the present improved method, a 0 to 100 wt % portion, for example an 80 to 100 wt % portion, of the steam raised in the condenser/steam raiser is compressed for use in the reboiler of the column of step a). This may be accomplished by, for example, a reciprocating or turbo compressor and a thermosyphon or forced circulation reboiler.

[00026] Referring more particularly to the drawing, and as an example of the present method, Fig. 1 shows an embodiment of the present invention wherein a liquid phase effluent from a BYD manufacturing step of a BYD manufacturing process comprising 37 wt % BYD, 10 wt % unreacted formaldehyde, 49 wt % water and 4 wt % methanol (on a soiids free basis) is passed via line 1 to a formaldehyde recycle column 00 maintained at a top temperature of 148 °C and a bottom temperature of 160 °C. A vapor phase product comprising 30 wt % formaldehyde, 58 wt % water and 12 wt % methanol is removed via line 2 from the top of column 100, whereby a 7 wt % portion thereof is removed via line 4 by way of a flow split control using a simple control ioop (not shown), and the remainder is passed via line 5 to the condenser/steam raiser 1 10 maintained at 250 kPa.A on the steam raising side. A liquid phase bottoms stream comprising approximately 54 wt % BYD, 45 wt % water, < 0.1 wt % methanol and < 1 wt % formaldehyde is recovered from column 100 via line 6. With a small bleed of < 1 wt % thereof to reboiler 130 by way of a flow split control using a simple control ioop (not shown), the remainder of the liquid phase bottoms stream, i.e. 95 to 00 wt %, for example 98 to 100 wt %, is recovered as refined butynediol for further processing to butanediol. Considering the column side (process side) of the reboiler 130 as integral with column 100, as accepted engineering practice, the reboiler 130 provides sufficient steam to maintain the column 100 base temperature at 160 °C.

[00027] Any required fresh boiler feed water at about 800 kPa.A at its bubble point temperature is fed to condenser/steam raiser 1 10 via line 14. A steam product is removed from condenser/steam raiser 10 via line 8 at a pressure of about 250 kPa.A, and steam condensate purge is removed from condenser/steam raiser 1 10 via line 13. A process condensate stream comprising 30 wt % formaldehyde, 58 wt % water and 12 wt % methanol from condenser/steam raiser 1 10 is withdrawn via line 10, whereby a 35 wt % portion thereof is removed via line 1 1 for recycle by way of a flow split control using a simple control loop (not shown), and a 65wt % portion thereof is passed via tine 12 to the top of column 100 as reflux.

[00028] The steam product of !ine 8 at a pressure of about 250 kPa.A is passed to compressor 120 and withdrawn therefrom via line 9 at a pressure of about 1000 kPa.A. The product of line 9 is passed to reboiler 130, and fresh make-up high pressure steam is passed to reboi!er 130 via line 15. Condensate from reboiler 130 is passed to the condenser / steam raiser 10 via line 17.

[00029] All patents, patent applications, test procedures, priority documents, articles, publications, manuals, and other documents cited herein are fully incorporated by reference to the extent such disclosure is not inconsistent with this invention and for ail jurisdictions in which such incorporation is permitted.

[00030] When numerical lower limits and numerical upper limits are listed herein, ranges from any iower limit to any upper limit are contemp!ated.

[00031] While the il!ustrative embodiments of the invention have been described with particularity, it will be understood that various other modifications will be apparent to and may be readily made by those skii!ed in the art without departing from the spirit and scope of the invention. Accordingly, it is not intended that the scope of the c!aims hereof be limited to the examples and descriptions set forth herein but rather that the claims be construed as encompassing all the features of patentable novelty which reside in the present invention, inciuding ail features which would be treated as equivalents thereof by those skilled in the art to which the invention pertains.