Patent Publication Number: US-2002000009-A1

Title: Process for stabilization of dry cleaning solutions

Description:
TECHNICAL FIELD  
       [0001] The present invention is directed to a process, more specifically, to a process for stabilizing silicone dry cleaning solvents containing basic impurities.  
       BACKGROUND  
       [0002] Current dry cleaning technology uses perchloroethylene (“PERC”) or petroleum-based materials as the cleaning solvent. PERC suffers from toxicity and odor issues. The petroleum-based products are not as effective as PERC in cleaning garments. Volatile siloxanes are being introduced into the dry cleaning industry as an alternative to PERC. However, there exists a need to stabilize the siloxane solvents to prevent undesirable cyclic siloxane (D 4 ) formation and polymerization.  
       [0003] Methods for the purification of organopolysiloxanes have previously been reported, but they have not been reported for the purification of certain cyclic siloxanes (D 5 ). Methods for purifying organopolysiloxanes utilizing elemental metals has been reported (see U.S. Pat. No. 5,245,067). Other patents disclose the purification of polyether silicones by contacting with an aqueous acid and removing the odorous materials formed (see U.S. Pat. No. 5,118,764), or the reaction with hydrogen and a hydrogenation catalyst (see U.S. Pat. No. 5,225,509). Hexamethyldisiloxane has been purified by successive treatments with a condensation catalyst, washing with water, separating the phases, distilling the siloxane, treating with acid clay and then treating with activated carbon (see U.S. Pat. No. 4,774,346). Siloxanes have also been purified by contacting with steam and distilling out the impurities (see EP 543 665). A deodorization method utilizing active carbon to which a functional group has been fixed through a silanol bond has been reported (see U.S. Pat. No. 5,238,899). Finally, a method was reported for purifying silicone oil by adding a drying agent and an adsorption agent to silicone and passing a low water vapor inert gas through the system (see U.S. Pat. No. 4,661,612).  
       [0004] There is a need for stabilizing the siloxane and suppressing reequilibration and polymerization of the volatile siloxane containing basic impurities that is used in dry cleaning applications.  
       SUMMARY OF THE INVENTION  
       [0005] In a first aspect, the present invention is directed to a method for stabilizing silicone dry cleaning solvents that may contain an undesirable basic impurity capable of causing cyclic siloxane formation, comprising contacting the silicone solvent with an adsorbent, neutralizing agent, or combination thereof, and separating the silicone solvent.  
       [0006] The process of the present invention is effective in preventing formation of certain cyclic siloxanes (i.e., D 4 ) that are undesirable in the silicone solvent.  
       [0007] As used herein, the terms “D 4 ”, “D 5 ” and “D 6 ” refer to cyclic siloxanes having the formula: —(R 2 SiO) x — where x is 4, 5 or 6 (i.e., D 5  is decamethylcyclopentasiloxane).  
       DETAILED DESCRIPTION OF THE INVENTION  
       [0008] Preferably, the first preferred embodiment of the method of the present invention comprises, contacting a silicone dry cleaning solvent that may contain an undesirable basic impurity capable of causing cyclic siloxane formation with an adsorbent, neutralizing agent, or combination thereof, and separating the silicone solvent.  
       [0009] Impurities that have been successfully neutralized by the method of the present invention include, for example, potassium silanolate, potassium hydroxide, and tetramethylammonium hydroxide. The amount of these impurities that may be present in the siloxane solvent without preventing reequilibration may be up to about 1 parts by weight. The impurities may be introduced into the silicone solvents during the dry cleaning operation, and if they are not removed, reequilibration and polymerization of the solvent may take place, and undesirable cyclics are formed.  
       [0010] Compounds suitable as the adsorbent are those that effectively prevent gelling and formation of undesirable cyclics in the siloxane solvent. Examples of adsorbents suitable for use include, but are not limited to, granular activated carbon, powdered decolorizing charcoal, diatomaceous earth, magnesium sulfate, cob powder, clays, silica gel, fullers earth, molecular sieves, and alumina. In a preferred embodiment, the adsorbent is a chosen from granular activated carbon, silica gel, acid clay, fullers earth, diatomaceous earth, 4A molecular sieves, 13X molecular sieves, powdered decolorizing charcoal, and more preferably, 4A molecular sieves, 13X molecular sieves, powdered decolorizing charcoal and fullers earth.  
       [0011] Preferably, the silicone dry cleaning solvent is a volatile linear, branched, cyclic or a combination thereof, siloxane.  
       [0012] Compounds suitable as the linear or branched, volatile siloxane solvent of the present invention are those containing a polysiloxane structure that includes from 2 to 20 silicon atoms. Preferably, the linear or branched, volatile siloxanes are relatively volatile materials, having, for example, a boiling of below about 300° C. point at a pressure of 760 millimeters of mercury (“mm Hg”).  
       [0013] In a preferred embodiment, the linear or branched, volatile siloxane comprises one or more compounds of the structural formula (I): 
       M 2+y+2z D x T y Q z   (I) 
       [0014] wherein:  
       [0015] M is R 1   3 SiO 1/2 ;  
       [0016] D is R 2   2 SiO 2/2 ;  
       [0017] T is R 3 SiO 3/2 ;  
       [0018] and  
       [0019] Q is SiO 4/2    
       [0020] R 1 , R 2  and R 3  are each independently a monovalent hydrocarbon radical; and x and y are each integers, wherein 0≦x≦10 and 0≦y≦10 and 0≦z≦10.  
       [0021] Suitable monovalent hydrocarbon groups include acyclic hydrocarbon radicals, monovalent alicyclic hydrocarbon radicals, monovalent and aromatic hydrocarbon radicals. Preferred monovalent hydrocarbon radicals are monovalent alkyl radicals containing from 1 to 6 carbons per group, such as, for example, methyl, ethyl, propyl, iso-propyl, n-butyl, iso-butyl, sec-butyl, tert-butyl, pentyl, hexyl, preferably methyl, monovalent aryl radicals, such as, for example, phenyl, 2,4,6-trimethylphenyl, 2-isopropylmethylphenyl, 1-pentalenyl, naphthyl, anthryl, preferably phenyl, and monovalent aralkyl radicals such as, for example, phenylethyl, phenylpropyl, 2-(1-naphthyl)ethyl, preferably phenylpropyl, phenyoxypropyl, biphenyloxypropyl.  
       [0022] In a preferred embodiment, the monovalent hydrocarbon radical is a monovalent alkyl radical containing from 1 to 6 carbons per group, most preferably, methyl.  
       [0023] In a preferred embodiment, the linear or branched, volatile siloxane comprises one or more of, hexamethyldisiloxane, octamethyltrisiloxane, decamethyltetrasiloxane, dodecamethylpentasiloxane, tetradecamethylhexasiloxane or hexadecamethylheptasiloxane or methyltris(trimethylsiloxy)silane. In a more highly preferred embodiment, the linear or branched, volatile siloxane of the present invention comprises octamethyltrisiloxane, decamethyltetrasiloxane, or dodecamethylpentasiloxane or methyltris(trimethylsiloxy)silane. In a highly preferred embodiment, the siloxane component of the composition of the present invention consists essentially of decamethyltetrasiloxane.  
       [0024] Suitable linear or branched volatile siloxanes are made by known methods, such as, for example, hydrolysis and condensation of one or more of tetrachlorosilane, methyltrichlorosilane, dimethyldichlorosilane, trimethylchlorosilane, or by isolation of the desired fraction of an equilibrate mixture of hexamethyldisiloxane and octamethylcyclotetrasiloxane or the like and are commercially available.  
       [0025] Compounds suitable as the cyclic siloxane component of the present invention are those containing a polysiloxane ring structure that includes from 2 to 20 silicon atoms in the ring. Preferably, the linear, volatile siloxanes and cyclic siloxanes are relatively volatile materials, having, for example, a boiling point of below about 300° C. at a pressure of 760 millimeters of mercury (“mm Hg”).  
       [0026] In a preferred embodiment, the cyclic siloxane component comprises one or more compounds of the structural formula (II):  
                 
 
       [0027] wherein:  
       [0028] R 5 , R 6 , R 7  and R 8  are each independently a monovalent hydrocarbon group; and  
       [0029] a and b are each integers wherein 0≦a≦10 and 0≦b≦10, provided that 3≦(a+b)≦10.  
       [0030] In a preferred embodiment, the cyclic siloxane comprises one or more of, octamethylcyclotetrasiloxane, decamethylcyclopentasiloxane, dodecamethylcyclohexasiloxane, tetradecamethylcycloheptasiloxane. In a more highly preferred embodiment, the cyclic siloxane of the present invention comprises octamethylcyclotetrasiloxane or decamethylcyclopentasiloxane. In a highly preferred embodiment, the cyclic siloxane component of the composition of the present invention consists essentially of decamethylcyclopentasiloxane.  
       [0031] Suitable cyclic siloxanes are made by known methods, such as, for example, hydrolysis and condensation of dimethyldichlorosilane and are commercially available.  
       [0032] It is believed that those dry cleaning solvents useful in the present invention that lack a cyclic siloxane component would be more stable than those which include a cyclic siloxane component, in that cyclic siloxanes are known to ring open and polymerize under acidic and basic conditions.  
       [0033] In a first embodiment of the method of the present invention, approximately 100 parts by weight (“pbw”) of siloxane solvent contacts up to about 100, more preferably up to about 50, even more preferably up to about 10 pbw of adsorbent, neutralizing agent or a combination thereof, for about 0.001 to about 6 hours, at a temperature of from about 10° C. to about 80° C. After the siloxane solvent has contacted the adsorbent for the appropriate time and has been purified, the siloxane solvent can be recycled in the dry cleaning apparatus. The method of the present invention effectively reduces the level of impurities in the silicone solvent.  
       [0034] In a second embodiment of the method of the present invention, a dry cleaning fluid is treated by the method of the present invention.  
       [0035] The method of the present invention also comprises a dry cleaning process comprising the steps of: contacting an article with a silicone solvent, and removing the silicone solvent, then treating the silicone solvent that has been removed by contacting the silicone solvent with an adsorbent, neutralizing agent, or combination thereof, and separating the silicone solvent form the adsorbent, then reusing the treated silicone solvent in the dry cleaning process.  
       [0036] The following examples illustrate the process of the present invention. They are illustrative and the claims are not to be construed as limited to the examples. 
     
    
    
     EXAMPLE 1  
     [0037] Decamethylcyclopentasiloxane (D 5 ) was mixed with a base catalyst (potassium silanolate with a potassium hydroxide equivalence of approximately 4%) to make a stock solution containing 80 parts per million (“ppm”) potassium hydroxide. Aliquots of the stock solution were heated to 75° C. and 120° C. to determine if the mixture would undergo reequilibration and polymerization (increased D 4  and D 6  levels as well as increased viscosity). The results of the control experiments are shown in Table 1 below.  
     [0038] The following adsorbents were used throughout the examples:  
                                   Adsorbent Number   Type of Adsorbent                  A   acid clay (Filtrol ® F-20)       B   acid clay (Filtrol ® F-25)       C   diatomaceous earth (Celite ® 545)       D   granular activated carbon       F   fullers earth       F   silica gel 60-200 mesh       G   powdered decolorizing charcoal           (Norit ®)       H   4A molecular sieves       I   13X molecular sieves       J   powdered 13X molecular sieves                  
 
     [0039]               TABLE 1                          Polymerization and Reequilibration of D 5  with KOH                                                                         Rxn               Rxn                           Temp   KOH   Time               Time               Visc.       Exp#   (° C.)   (ppm)   (h)   % D 4     % D 5     % D 6     (h)   % D 4     % D 5     % D 6     Increase                                                                     Control   25   None   0   &lt;0.2   99.46   0.47     0**   —   —   —   —       1   75    80   7   &lt;0.2   99.44   0.51   24   0.35   98.71   0.58   yes       2   75   400   8   2.41   89.16   2.67   24   —   —   —   gel*       3   120   400   3.4   4.09   87.38   3.65    5   —   —   —   gel*                                    
     [0040] The base catalyst readily initiated polymerization and reequilibration of the D 5 . As shown in Table 1, at 75° C. and 80 ppm potassium hydroxide equivalents, only a small amount of D 4  was generated. At higher temperatures and base levels, a substantial amount of D 4  was formed in less than 8 hours, and in less than 24 hours, a gum was formed.  
     EXAMPLE 2  
     [0041] The same stock solution from Example 1 was then treated with a variety of absorbents and neutralizing agents. Approximately 1 gram of adsorbent was added to 10 grams of solution (10% loading) for 15 minutes, and then the absorbent was removed. The solution was heated to 120° C. for 2 hours and cyclic levels were measured. Heat was continued until 18 hours, and cyclic levels were again measured. Table 2 shows the results of cyclic formation.  
               TABLE 2                          10% Adsorbent with 15 minutes contact time.                                                                                 amt                                                           D 5     KOH   contact   120 ° C.               Rxn               amt   mix   equiv.   time   Rxn time               time       Exp. #   Adsorb.   (g)   (g)   (ppm)   (min)   (h)   % D 4     % D 5     % D 6     (h)   % D 4     % D 5     % D 6                                                                               4   A   1   10   80   15   2   0.54   98.88   0.53   18   0.52   98.96   0.51       5   B   1   10   80   15   2   0.46   98.97   0.45   18   0.4   99.01   0.51       6   C   1   10   80   15   2   &lt;0.2   99.46   0.46   18   &lt;0.2   99.48   0.47       7   D   1   10   80   15   2   &lt;0.2   99.5   0.45   18   &lt;0.2   99.48   0.46       8   E   1   10   80   15   2   &lt;0.2   99.49   0.46   18   &lt;0.2   99.45   0.45       9   F   1   10   80   15   2   &lt;0.2   99.44   0.46   18   &lt;0.2   99.46   0.45                                                             control   none   —   10   80   —   2   &lt;0.2   99.47   0.49   gelled in &lt;2 hours                      
 
     [0042] Table 2 indicates that using a high loading (10%) and long contact time (15 minutes), diatomaceous earth, granular activated carbon, fullers earth and silica gel all effectively prevented polymerization from occurring when compared to the control sample. The two acid clay substances were less effective, but they also significantly suppressed D 4  formation.  
     EXAMPLE 3  
     [0043] The same experiment as Example 2 was conducted using a lower loading (1%) and a shorter contact time (1 minute). Cyclic levels were measured after 2 hours and after 20 hours. Results of the experiment are shown in Table 3.  
               TABLE 3                          1% Adsorbent with 1 min contact time                                                                                 amt                                                           D 5     KOH   contact   120° C.               Rxn               Amt   mix   equiv.   time   Rxn time               time       Exp. #   Adsorb.   (g)   (g)   (ppm)   (min)   (h)   % D 4     % D 5     % D 6     (h)   % D 4     % D 5     % D 6                                                                               10   A   0.1   10   80   1   2   0.69   98.67   0.64   18   1.14   97.9   0.91                                                                 11   C   0.1   10   80   1   2   2.11   94.99   1.91   18   gelled           12   D   0.1   10   80   1   2               18   gelled                                                                     13   E   0.1   10   80   1   2   &lt;0.2   99.54   0.46   18   &lt;0.2   99.51   0.47       14   F   0.1   10   80   1   2   0.46   98.56   0.62   18   1.48   96.43   1.07       15   G   0.1   10   80   1   2   &lt;0.2   99.53   0.46   18   &lt;0.2   99.48   0.47                                                                 16   H   0.1   10   80   1   2   2.76   94.22   2.28   18   gelled           17   I   0.1   10   80   1   2   2.76   94.15   2.38   18   gelled                                                                     18   J   0.1   10   80   1   2   &lt;0.2   99.54   0.46   18   &lt;0.2   99.46   0.49                  
 
     [0044] Table 3 shows that at the shorter contact time and the lower adsorbent loading, some of the adsorbents failed to prevent polymerization. The best adsorbents at these conditions were powdered 13X molecular sieves, fullers earth and powdered decolorizing charcoal.  
     EXAMPLE 4  
     [0045] Another experiment was conducted in the same manner as Examples 2 and 3, using the same contact time as Example 3, with a 10% loading. Cyclic levels were measured after 2 hours and after 20 hours. The results are shown below in Table 4.  
               TABLE 4                          10% Adsorbent with 1 min contact time                                                                                 amt                                                           D 5     KOH   contact   120 ° C.               Rxn               Amt   mix   equiv.   time   Rxn time               time       Exp. #   Adsorb.   (g)   (g)   (ppm)   (min)   (h)   % D 4     % D 5     % D 6     (h)   % D 4     % D 5     % D 6                                                                       19   A   1   10   80   1   2   0.4   99.09   0.42   20   very viscous                                                                     20   C   1   10   80   1   2   &lt;0.2   99.45   0.47   20   &lt;0.2   99.43   0.49       21   D   1   10   80   1   2   &lt;0.2   99.46   0.46   20   &lt;0.2   99.43   0.46       22   E   1   10   80   1   2   0.92   98.12   0.95   20   &lt;0.2   99.44   0.48       23   F   1   10   80   1   2   &lt;0.2   99.37   0.49   20   &lt;0.2   99.42   0.47       24   G   1   10   80   1   2   &lt;0.2   99.5   0.41   20   &lt;0.2   99.5   0.46                                                             25   H   1   10   80   1   2   2.25   93.95   2.3   20   very viscous                                                                     26   I   1   10   80   1   2   —   —   —   20   &lt;0.2   99.38   0.49       27   J   1   10   80   1   2   &lt;0.2   99.42   0.48   20   &lt;0.2   99.43   0.46                  
 
     [0046] Table 4 illustrates that with the higher adsorbent loading, many of the adsorbents were able to successfully prevent polymerization.  
     EXAMPLE 5  
     [0047] Different bases were compared using fullers earth, powdered decolorizing charcoal and powdered 13X molecular sieves as adsorbents. The solutions of D 5  and base catalyst were prepared in the same manner as described in Example 1, with 100 ppm of the base added to the D 5 . A 1% loading and 1 minute contact time was used. Sample were measured after 2 hours and after 18 hours. The results are shown in Table 5.  
               TABLE 5                          1% Adsorbent with 1 minute contact time using different bases                                                                                 amt                                                           D 5         contact   120 ° C.               Rxn               Amt   mix   Base   time   Rxn time               time       Exp. #   Adsorb.   (g)   (g)   used   (min)   (h)   % D 4     % D 5     % D 6     (h)   % D 4     % D 5     % D 6                                                                       28   None   1   10   Me 4 N + OH −     1   2   7.5   89.1   1.4   18   very viscous                                                                     29   E   1   10   Me 4 N + OH −     1   2   &lt;0.2   99.47   0.48   18   &lt;0.2   99.49   0.46       30   J   1   10   Me 4 N + OH −     1   2   &lt;0.2   99.48   0.46   18   &lt;0.2   99.48   0.46       31   G   1   10   Me 4 N + OH −     1   2   &lt;0.2   99.48   0.47   18   &lt;0.2   99.48   0.47                                                             32   None   1   10   KOH   1   2    3.6   92.0   2.9   18   very viscous                                                                     33   E   1   10   KOH   1   2   &lt;0.2   99.45   0.47   18   &lt;0.2   99.47   0.48       34   J   1   10   KOH   1   2   &lt;0.2   99.47   0.42   18   &lt;0.2   99.46   0.49       35   G   1   10   KOH   1   2   &lt;0.2   99.45   0.47   18   &lt;0.2   99.48   0.47       36   None   1   10   NaOH   1   2   &lt;0.2   99.48   0.47   18   &lt;0.2   99.27   0.68                  
 
     [0048] Table 5 illustrates that Me 4 N + OH— will also work as a base catalyst, and the adsorbents chosen will effectively prevent polymerization of cyclics.  
     EXAMPLE 6  
     [0049] Another experiment was conducted in the same manner as Example 4, except that the siloxane solvent was a linear siloxane (MD 2 M). Cyclic levels were measured after 2 hours and after 18 hours (21 hours for the control sample with no adsorbent). The results are shown below in Table 6.  
               TABLE 6                          10% Adsorbent with 1 minute contact time using MD 2 M                                                             contact   100° C.                                       time   Rxn       Rxn       Exp. #   Adsorb.   (min)   time (h)   % MD 2 M   time (h)   % MM   % MDM   % MD 2 M   % MD 3 M                                                             32   None   1   2   100   21   2.0   11.0   64.28   13.32       33   E   1   2   100   18   —   —   100   —       34   J   1   2   100   18   —   —   100   —       35   G   1   2   100   18   —   —   100   —                  
 
     [0050] Table 6 illustrates that MD 2 M contaminated with potassium silanolate base catalyst (200 ppm KOH equiv.) can be treated with 10% absorbent for 1 minute at room temperature and rendered unreactive.