WO2002055511A1

WO2002055511A1 - Purification of propylene oxide

Info

Publication number: WO2002055511A1
Application number: PCT/EP2001/015326
Authority: WO
Inventors: David Thorpe; David John Sparrow
Original assignee: Huntsman International Llc
Priority date: 2001-01-15
Filing date: 2001-12-27
Publication date: 2002-07-18

Abstract

A process for purifying propylene oxide containing an unacceptable quantity of poly(propylene oxide) contaminant having a molecular weight of at least 50,000 which comprises contacting the so-contaminated propylene oxide with a quantity of a substantially calcined diatomaceous earth for a time and under conditions sufficient to reduce the amount of such contaminant in such propylene oxide to acceptable levels, and recovering the purified propylene oxide product. Also, processes for making polyether polyols from such purified propylene oxide products, and for making high resilient flexible polyurethane foams from such polyols.

Description

PURIFICATION OF PROPYLENE OXIDE

The present invention relates to processes for the purification and/or separation of propylene oxide. The present invention relates more particularly to a process of the type described in United States Patent No. 4,692,535 to Larson et al. (hereafter, Larson), wherein a propylene oxide product suitable as an intermediate in the production of polyether polyols for high resilient flexible polyurethane foam applications is made by removing substantially all of a high molecular weight poly(propylene oxide) fraction from an otherwise commercially-acceptable propylene oxide. As disclosed in the Larson patent, propylene oxide of an otherwise commercially- acceptable purity was found to contain a certain nonvolatile impurity (namely, poly(propylene oxide) (or PPO) having a molecular weight of at least 50,000), which impurity made the propylene oxide unsuitable for making polyether polyols to be used with a polyisocyanate and blowing agent in the manufacture of acceptable high resilient flexible polyurethane foams. Polyether polyols prepared from propylene oxide having in excess of 0.1 parts per million by weight of the high molecular weight poly(propylene oxide) impurity were determined to lead to low foam rise and substantial blow hole formation in the polyurethane foams, whereas polyether polyols made from propylene oxide having reduced levels of the high molecular weight PPO impurity produced polyurethane foams with good foam rise and without substantial blow hole formation.

The solution proposed by Larson involved filtering or percolating either crude liquid propylene oxide of 95 percent or greater propylene oxide content or propylene oxide of otherwise commercially-acceptable, 99 percent purity or better through a fixed bed of an adsorbent material. The adsorbent materials suggested by Larson as suitable for this purpose are activated carbon, charcoal and attapulgite, and granular forms are said to be preferable to powdered forms of these materials. The quantities of adsorbent to be used per unit volume of propylene oxide to be treated are estimated at from about 0.001 to about 0.01 grams or more of solid adsorbent per gram of propylene oxide, with contact times ranging from about 1 to about 15 minutes, temperatures of from about 10 to about 100°C and pressures ranging from atmospheric to superatmospheric. In Bachman the use of non-calcined diatomaceous earth has been proposed for removing poly (propylene oxide). In comparative examples calcined diatomaceous earth did not show very good results in a slurry-based treatment. Surprisingly, we have found that calcined diatomaceous earth may be used advantageously in the purification of propylene oxide, provided the calcined diatomaceous earth is applied as a filter bed.

Therefore the present invention is a process for purifying propylene oxide containing an unacceptable quantity of a poly(propylene oxide) polymer contaminant having a molecular weight of at least 50,000, wherein the process comprises contacting the propylene oxide with a substantially calcined diatomaceous earth for a time and under conditions sufficient to reduce the amount of said contaminant to acceptable levels, and thereafter recovering the purified propylene oxide product; wherein the contaminated propylene oxide is passed through a bed of said calcined diatomaceous earth. "Unacceptable" and "acceptable" in this context refer to those levels of the poly(propylene oxide) contaminant which make the polyether polyols produced from propylene oxide containing such levels of such contaminant commercially unacceptable or acceptable, respectively, for making high resilient flexible polyurethane foams.

In another, related aspect, the invention provides a process for making polyether polyols from propylene oxide, wherein the propylene oxide has been purified according to the process described in the preceding paragraph. In still another aspect, a process for making high resilient flexible polyurethane foams from the just-mentioned polyether polyols is provided.

As summarized in Kirk-Othmer Encyclopedia of Chemical Technology, 3rd ed., Vol. 7 at pages 603-614 (1979), diatomaceous earth (sometimes also referred to as kieselguhr or diatomite) is a sedimentary rock of marine or lacustrine deposition, and consists mainly of accumulated shells or frustules of hydrous silica secreted by diatoms (microscopic, one- celled, flowerless plants of the class Bacillarieae).

Diatomaceous earth consists in chemical terms primarily of silicon dioxide, albeit in a different physical structure than typically encountered. Impurities typically include other aquatic fossils, sand clay, volcanic ash, calcium carbonate, magnesium carbonate, soluble salts and organic matter, while a typical spectrographic analysis on a dry basis may show SiO₂, CaO, MgO, Aι₂O₃, Fe O₃, Na₂O, V₂O₅, and TiO₂. The chemically combined water content can vary from 2 to 10 percent by weight.

In physical terms, most diatomaceous earths are powders, having mean particle diameters ranging from 20 to 0.75 micrometers, although aggregates can be obtained having 1.27 centimeter diameters down to fine powders.

The calcined diatomaceous earth may be selected from those which have been subjected to normal calcination and those which have been subjected to so-called white or flux calcination; useful calcined diatomaceous earth has a surface area by nitrogen adsorption (BET surface area, m²/g) of at most 12 m²/g, preferably of at most 10 m²/g and most preferably at most 7 m²/g. Examples of useful calcined diatomaceous earths are : Standard Super-Cel™, Celite™ 512, 501, 503, 535, 545 and 560 and Hyflo Super-Cel™ all from Celite Corporation.

The process of the present invention is readily adaptable to commercial industrial operations, and involves as indicated above the removal of high molecular weight poly(propylene oxide) (having a molecular weight generally of at least 50,000, for example) from crude propylene oxide of 95 percent or greater propylene oxide content or from propylene oxide of an otherwise commercially-acceptable purity.

The purified propylene oxide, containing preferably less than 100 parts per billion by weight of the high molecular weight poly(propylene oxide), more preferably less than 65 parts per billion and most preferably less than 50 parts per billion of such contaminant, is suitable for direct conversion (generally with one or more other organic oxides) to highly pure polyether polyols via reaction (normally catalyzed) with an initiator containing two or more active hydrogens. These polyols then react with an isocyanate in the presence generally of water and other conventional materials, for example, inorganic fillers, surfactants, catalysts, auxiliary blowing agents, and provide flexible, stable polyurethane resilient foams exhibiting high rise while being substantially free of blow-hole formation. The processes of producing polyether polyols from oxides including propylene oxide and of producing high resilient flexible polyurethane foams from such polyols are well-known in the art and are broadly summarized and described in "Flexible Polyurethane Foams", Herrington and Hock (Dow Plastics, 1991), so that no additional explanation or description need be offered herein.

The propylene oxide starting material of the purification process of the present invention may be obtained by any of the known routes for the production of propylene oxide. The purification process of the present invention is most conveniently effected at any time after propylene oxide of an otherwise suitable commercial purity has been obtained and the poly(propylene oxide) contaminant formed therein at unacceptable levels.

Preferably the inventive purification process is followed by prompt conversion of the purified propylene oxide product into the desired polyether polyols, or by shipment or storage of the purified product in a vessel which is made of a conventional carbon steel but which is kept at a low temperature (for example, 7°C) or in a vessel constructed of or lined with a suitable material which will not catalyze the polymerization of propylene oxide to poly(propylene oxide) (for example, a stainless steel such as is preferably used for constructing treatment vessels for performing the present process). In this regard, conventional carbon steels were found by Larson to catalyze over a period of time at a given temperature the formation of the undesired high molecular weight poly(propylene oxide)contaminant.

In an embodiment of the process, then, propylene oxide liquid is passed through a bed of diatomaceous earth, for example, by a conventional static-bed percolation process wherein the propylene oxide to be refined is passed through a stationary bed of the diatomaceous earth under controlled conditions. This purification process is continued until the product propylene oxide has attained the desired poly(propylene oxide) contaminant content. The treatment with the diatomaceous earth may generally be conducted at temperatures in the range of from -20°C to 35°C, and at atmospheric or superatmospheric pressures, for example, up to 7 kg/cm (gauge) (100 psig). Preferably the temperature of the propylene oxide is kept at a temperature below 10°C, preferably below 0°C.

It is expected that the beds will have an effective lifetime of at least 3 months before the diatomaceous earth requires replacement or regeneration, with replacement presently appearing to be a much more viable approach than regeneration. A preferred method of replacing the diatomaceous earth will comprise water-washing the diatomaceous earth until the total organic content (TOC) in the effluent is less than 50 parts per million, then refilling the column with water and heating the water-filled column to 100°C for 25 hours, for example, to convert any residual propylene oxide to propylene glycol. The column can then be flushed of the water, and the diatomaceous earth removed by vacuum truck and disposed of. Given the time involved in removing the diatomaceous earth by this process, it is again generally to be preferred for columns to be operated in a rotation rather than in series or parallel so that not all columns need to be taken off-line at any given time.

Those skilled in the art will appreciate however that the optimum parameters of operation for any given stationary bed arrangement will depend on, for example, the diatomaceous earth employed and on the degree of purification required, but it is considered that these persons will be well able to select those parameters given the present disclosure.

After the propylene oxide has been purified by passing it through the calcined diatomaceous earth bed, the propylene oxide may be further treated, e.g. filtered using a filter having a pore size of 0.2 μm or more to remove remaining particulate earth material.

Claims

1. A process for purifying propylene oxide containing an unacceptable quantity of poly(propylene oxide) contaminant having a molecular weight of at least 50,000, comprising contacting the so-contaminated propylene oxide with a quantity of a calcined diatomaceous earth for a time and under conditions sufficient to reduce the amount of such contaminant in such propylene oxide to acceptable levels, and recovering the purified propylene oxide product, wherein the contaminated propylene oxide is passed through a bed of said diatomaceous earth.

2. A process according to claim 1 wherein the diatomaceous earth has a surface area by nitrogen adsorption of at most 12 m /g.

3. A process for making a polyether polyol from propylene oxide, comprising the steps ofpurifying propylene oxide according to the process of claims 1 and 2; and reacting the purified propylene oxide with an initiator having two or more active hydrogens.

4. A process for making high resilient flexible polyurethane foam, comprising the step of reacting the polyether polyol of claim 3 with an isocyanate and water.