Organic compounds -- part of the class 532-570 series – Organic compounds – Carboxylic acid esters
Reexamination Certificate
2000-01-11
2002-05-07
Killos, Paul J. (Department: 1623)
Organic compounds -- part of the class 532-570 series
Organic compounds
Carboxylic acid esters
Reexamination Certificate
active
06384268
ABSTRACT:
The present invention relates to a process for the treatment of formaldehyde-containing mixtures, especially for the treatment of methyl methacrylate streams which contain formaldehyde.
Conventionally, methyl methacrylate has been produced industrially via the so-called acetone-cyanohydrin route. The process is capital intensive and produces methyl methacrylate at a relatively high cost.
Other processes for the production of methyl methacrylate are disclosed in U.S. Pat. No. 3535371, U.S. Pat. No. 4,336,403, GB-A-1 107234 , JP-A-63002951 which require the condensation of propionic acid with formaldehyde or methylal in the presence of methanol. These references do not, however, describe how the methyl methacrylate product may be separated and recovered from the residual formaldehyde and other components which may be found in the reactor product stream.
It has now been found that the residual formaldehyde can be separated from a methyl methacrylate stream in a manner which may also allow the recycling of the formaldehyde to the initial condensation process. Although the invention has been found to be particularly useful for the separation of formaldehyde from a methyl methacrylate-containing stream, it will be understood that the process may also be applied to the removal of formaldehyde species from a variety of other organic mixtures.
Accordingly the present invention provides a process for the removal of formaldehyde species from a liquid organic mixture comprising at least a carboxylic acid or carboxylic acid ester and formaldehyde species and which forms a two-phase mixture with water, which comprises the step of subjecting the liquid organic mixture to at least one liquid liquid extraction stage wherein water is used as an extractant to produce an organic phase stream and an aqueous phase stream such that the organic phase stream contains a significantly reduced concentration of formaldehyde species compared to the liquid organic mixture.
By formaldehyde species we mean that the formaldehyde in the liquid stream is normally present in the form of adducts with water or polar organic compounds such as alcohols. Normally free formaldehyde is in the form of a light gas and would not therefore form part of the liquid mixture. References to formaldehyde are therefore taken to include formaldehyde species which are adducts of formaldehyde with components of the liquid mixture or with water.
Water is used to extract formaldehyde from the liquid stream, but this need not be pure water. The water used may contain small amounts of dissolved compounds which do not significantly affect the extraction of formaldehyde species into the aqueous phase. In operating a manufacturing process which incorporates the formaldehyde removal process of the invention, it may be convenient and economical to use an aqueous stream from another part of the process as the water extractant of the present process. The suitability of any particular aqueous stream for use as an extractant may be readily determined by analysis or experiment. Preferably the content of such an aqueous stream is known and comprises compounds which are present in the organic stream or which can be readily removed from the organic stream. Thus water as used in this specification should be taken to include such an aqueous stream which may contain a low level of dissolved compounds, e.g. traces of organic materials.
The concentration of formaldehyde in the organic phase stream output from the liquid extraction process is preferably <10%, more preferably <5%, and especially <1% of the concentration of formaldehyde in the untreated formaldehyde-containing mixture. The concentration of formaldehyde in the organic output will be largely determined by the equipment and method used, e.g. the number of stages, level of mixing or separation achieved, etc. A final concentration of much less than 1% of the starting concentration may be achievable by suitable processing.
The liquid organic mixture is subjected to at least one liquid-liquid extraction stage. Preferably more than one liquid-liquid extraction stage is performed, for example between one and twenty, preferably between one and ten liquid-liquid extraction stages may be performed, although the number of stages required will depend upon the nature and relative proportions of the compounds in the mixture. When we refer to separation stages, we mean theoretical stages. Certain process equipment, e.g. a rotating disc contactor column presents a continuum of one phase so that defined physical stages may not be evident although the theoretical stages present may be calculated.
Although the aqueous phase from the at least one liquid-liquid extraction stage may be disposed of, preferably the aqueous phase is subjected to a further at least one liquid-liquid extraction stage wherein it is mixed with a suitable organic liquid to extract (strip) from the aqueous stream organic compounds other than formaldehyde. Suitable liquids include non-polar organic solvents which are immiscible with water such as alkanes, e.g. petrol, hexane or heptane, other higher alkanes or ethers, or other organics. Preferably the liquid liquid extraction stage comprises a counter-current process in which an organic stream is run as a counter current to the water so that the extraction of formaldehyde into the aqueous phase and stripping of organics from the aqueous phase into the organic solvent may be accomplished in a single operation. Using this arrangement the formaldehyde-containing mixture is fed between the water feed and the organic stream, preferably approximately centrally between the two feeds which comprise the counter-current flow. The preferred counter-current flow can conveniently be established in well-known liquid-liquid extraction apparatus such as a rotating disk contactor or a cascade of mixer-settlers.
As discussed above the process of treatment according to the invention has been found to be particularly useful to remove formaldehyde from a formaldehyde-containing liquid organic mixture which is a product of a process for the production of an alkyl ester of an acrylic acid (e.g. methyl methacrylate) in which an alkyl ester of an alkanoic acid is reacted with methanol and formaldehyde in the presence of a catalyst. In particular, one useful application of the invention has been found to be the removal of formaldehyde from a methyl methacrylate containing stream in which formaldehyde is present, for example as produced by a process for the production of methyl methacrylate from the condensation reactions of methyl propionate with formaldehyde and methanol over a suitable catalyst.
Therefore, according to a further aspect of the invention, we provide a process for the production of methyl methacrylate comprising the steps of:
(i) reacting propionic acid or an ester thereof with formaldehyde or a precursor thereto in a condensation reaction stage to produce a gaseous product stream comprising methyl methacrylate, residual formaldehyde, residual propionic acid or an ester thereof and by-products;
(ii) liquefying at least a portion of the gaseous product stream to form a liquid product stream containing substantially all of the methyl methacrylate, the residual formaldehyde, the by-products and the remainder of the residual propionic acid or an ester thereof;
(iii) subjecting the liquid product stream to at least one liquid liquid extraction stage wherein water is used as an extractant to produce an organic phase stream which is substantially formaldehyde free and an aqueous phase stream which contains substantially all of the residual formaldehyde.
Preferably the methyl methacrylate is produced by the condensation of methyl propionate with formaldehyde or a precursor thereto, e.g. methylal, and particularly by the condensation of methyl propionate with formaldehyde. By-products from the reaction include water, diethyl ketone (DEK), propionic acid (PA), methacrylic acid (MAA) and methyl isobutyrate (MIB). The reaction is preferably carried out in the presence of methanol. Methanol may also be p
Harrison Stephen Patrick
Martin John Stuart
Parten William David
Ineos Acrylics UK Limited
Killos Paul J.
LandOfFree
Treatment of formaldehyde-containing mixtures does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Treatment of formaldehyde-containing mixtures, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Treatment of formaldehyde-containing mixtures will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2866092