HK1056190B - Process for removal of odors from silicones - Google Patents

Description

Process for removing odor from silicones

Technical Field

The present invention relates to a method, and more particularly, to a method for removing odor components from a silicone anhydrous cleaning solvent.

Background

Current anhydrous cleaning technologies use Perchloroethylene (PERC) or petroleum-based materials as cleaning solvents. PERC has problems of toxicity and odor, and petroleum-based products are less effective than PERC in cleaning garments. Volatile silicones have been introduced into the anhydrous cleaning industry as a replacement for PERC. However, silicone solvents sometimes carry undesirable odors, and it is therefore desirable to remove the odor from the silicone solvent.

Methods for purifying organopolysiloxanes using elemental metals have been reported in recent years (see U.S. Pat. No. 5,245,067). Other patents also disclose the purification of polyether siloxanes by contacting with an aqueous acid and removing the odor species formed (see US5,118,764), or reacting with hydrogen and a hydrogenation catalyst (see US5,225,509). Hexamethyldisiloxane has been purified by successive treatment with a condensation catalyst, washing with water, phase separation, distillation of the siloxane, treatment with acidic clay, followed by treatment with activated carbon (see US4,774,346). Siloxanes have also been purified by contacting with steam and distilling off impurities (see EP 543665). A method for deodorizing using activated carbon has been reported in which a functional group is fixed to activated carbon by a silanol bond (see US5,238,899). Finally, a method for purifying silicone oils by adding a drying agent and an absorbent to the silicone and then passing a low-water-vapor inert gas through the system has been reported (see U.S. Pat. No. 4,661,612).

There is a need for a method to remove undesirable off-flavors in volatile silicones used in the field of anhydrous cleaning.

Summary of The Invention

In a first aspect, the present invention relates to a method of removing an odorous component from a silicone anhydrous cleaning solvent comprising contacting the silicone solvent with an absorbent to remove the odorous component and then separating the silicone solvent.

The process of the present invention is effective in removing or reducing malodorous elements such as propionic acid, propionaldehyde, butyric acid, and butyraldehyde from silicone solvents.

Detailed Description

Preferably, the first preferred embodiment of the method of the present invention comprises contacting the silicone anhydrous cleaning solvent, which may contain malodorous elements, with an absorbent to remove the malodorous elements, and then separating the silicone solvent. Preferably, the silicone anhydrous cleaning solvent is a volatile linear, branched, cyclic, or combination thereof silicone.

Suitable compounds for use as absorbents are those effective in removing malodorous components of silicone solvents. Examples of suitable absorbents include, but are not limited to, silica gel, fuller's earth, alumina, diatomaceous earth, magnesium silicate, granular activated carbon, molecular sieves, powdered decolorizing carbon, magnesium sulfate, corn cob grits, zeolites, and clays. Preferably, the absorbent is granular activated carbon, 4A molecular sieve, or 13X molecular sieve.

Compounds suitable as solvents for the linear or branched volatile siloxanes according to the invention are those which contain a polysiloxane structure comprising 2 to 20 silicon atoms. Preferably, the linear or branched volatile siloxane is a relatively volatile material, such as having a boiling point of less than about 300 ℃ at a pressure of 760 millimeters of mercury (mm Hg).

In a preferred embodiment, the linear or branched volatile siloxane comprises one or more compounds of formula (I):

M_2+y+2zD_xT_yQ_z (I)

wherein: m is R¹ ₃SiO_1/2；

D is R² ₂SiO_2/2；

T is R³SiO_3/2；

And Q is SiO_4/2；

R¹、R²And R³Each independently is a monovalent hydrocarbon group; and x and y are integers, respectively, wherein x is 0. ltoreq. x.ltoreq.10, y is 0. ltoreq. y.ltoreq.10, and z is 0. ltoreq. z.ltoreq.10.

Suitable monovalent hydrocarbon groups include acyclic hydrocarbon groups, monovalent alicyclic hydrocarbon groups, monovalent and aromatic hydrocarbon groups. Preferred monovalent hydrocarbon groups are monovalent alkyl groups, monovalent aryl groups, and monovalent aralkyl groups.

The term "(C) as used herein₁-C₆) Alkyl "means a linear or branched alkyl group containing from 1 to 6 carbon atoms per group, such as methyl, ethyl, propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, pentyl, hexyl, preferably methyl.

The term "aryl" as used herein refers to a monovalent unsaturated hydrocarbon ring system containing one or more aromatic rings per group, which may optionally be substituted on the aromatic ring or rings, preferably with one or more (C)₁-C₆) Alkyl is substituted, and in the case of two or more rings, it may be a fused ring, including, for example, phenyl, 2, 4, 6-trimethylphenyl, 2-isopropylmethylphenyl, 1-pentalenyl, naphthyl, anthracenyl, preferably phenyl.

The term "aralkyl" as used herein refers to an aryl derivative having one alkyl group, preferably (C)₂-C₆) Alkyl, wherein the alkyl part of the aryl derivative may optionally be interrupted by oxygen atoms, such as phenylethyl, phenylpropyl, 2- (1-naphthyl) ethyl, preferably phenylpropyl, phenoxypropyl, diphenoxypropyl.

In a preferred embodiment, the monovalent hydrocarbon group is a monovalent (C)₁-C₆) Alkyl, most preferably methyl.

In a preferred embodiment, the linear or branched volatile siloxane comprises one or more hexamethyldisiloxane, octamethyltrisiloxane, decamethyltetrasiloxane, dodecamethylpentasiloxane, tetradecylhexasiloxane or hexadecamethylheptasiloxane or methyltris (trimethylsiloxy) silane. In a more preferred embodiment, the linear or branched volatile siloxane of the present invention comprises octamethyltrisiloxane, decamethyltetrasiloxane, or dodecamethylpentasiloxane, or methyltris (trimethylsiloxy) silane. In a more preferred embodiment, the silicone component of the composition of the present invention consists essentially of decamethyltetrasiloxane.

Suitable linear or branched volatile siloxanes are prepared by known methods such as hydrolysis and condensation of one or more of tetrachlorosilane, methyltrichlorosilane, dimethyldichlorosilane, trimethylchlorosilane, or by separation of the desired fractions of an equilibrium mixture such as hexamethyldisiloxane and octamethylcyclotetrasiloxane, and are commercially available.

Compounds suitable as cyclic siloxane components in the present invention are those containing a polysiloxane ring structure, wherein the ring comprises from 2 to 20 silicon atoms. Preferably, the linear volatile siloxanes and cyclic siloxanes are relatively volatile materials, such as having a boiling point of less than about 300 ℃ at a pressure of 760 millimeters of mercury (mm Hg).

In a preferred embodiment, the cyclic siloxane component comprises one or more compounds of formula (II):

wherein:

R⁵、R⁶、R⁷and R⁸Each independently is a monovalent hydrocarbon group; and

a and b are each an integer of 0. ltoreq. a.ltoreq.10, 0. ltoreq. b.ltoreq.10, assuming that 3. ltoreq. a + b.ltoreq.10.

In a preferred embodiment, the cyclic siloxane comprises one or more of octamethylcyclotetrasiloxane, decamethylcyclopentasiloxane, dodecamethylcyclohexasiloxane, tetradecylcycloheptasiloxane. In a more preferred embodiment, the cyclic siloxane of the present invention comprises octamethylcyclotetrasiloxane or decamethylcyclopentasiloxane. In a more preferred embodiment, the cyclic siloxane component of the composition of the present invention consists essentially of decamethylcyclopentasiloxane.

Suitable cyclic siloxanes are prepared by known methods such as hydrolysis and condensation of dimethyldichlorosilane and are commercially available.

In a first embodiment of the process of the present invention, about 100 parts by weight (pbw) of a siloxane solvent are contacted with up to about 100, more preferably up to about 50, even more preferably up to about 25pbw of an absorbent in a batch mode at a temperature of from about 10 ℃ to about 100 ℃, more preferably from about 20 ℃ to about 60 ℃, for from about 0.1 to about 6 hours, more preferably from about 0.1 to about 2 hours, even more preferably from about 0.1 to about 0.5 hours.

In another preferred embodiment of the present invention, the silicone solvent is contacted with the absorbent bed in a continuous mode at a rate sufficient to provide effective absorption of the undesirable odor components, preferably in a ratio of from about 1pbw silicone solvent to about 1pbw absorbent (1: 1) to about 10pbw silicone solvent to about 1pbw absorbent (1: 1).

After the silicone solvent has been in contact with the absorbent for a suitable time and the odor has been removed, the silicone solvent may be circulated in the waterless cleaning apparatus. The method of the present invention is effective in reducing the amount of malodorous elements in the silicone solvent.

In a second embodiment of the method of the invention, the anhydrous cleaning solution is treated by the method of the invention.

The method of the present invention also includes a waterless cleaning method comprising the steps of: an article is contacted with a silicone solvent and the silicone solvent is then removed, followed by treating the removed silicone solvent by contacting the silicone solvent with an absorbent and separating the silicone solvent from the absorbent, and then reusing the treated silicone solvent in an anhydrous cleaning process.

The following examples illustrate the process of the present invention, they are illustrative, and the claims are not to be construed as being limited by these examples.

Example 1

Treatment of Cyclic siloxanes (D) which have been used as anhydrous cleaning solvents and have been recovered₅) To remove off-flavors. Approximately 100 grams of used odoriferous silicone solvent was mixed with 25 grams of a different absorbent to form a slurry. The slurry was mixed at room temperature for 6 hours. The absorbent was removed by filtration and the siloxane solvent was evaluated olfactively to determine the effectiveness of the purification process. The results and the absorbents used are shown in table 1 below.

The following absorbents were used in all examples.

Absorbent numbering	Absorbent type
		A	Diatomite (Celite)*545)
B	4A molecular sieve
		C	13X molecular sieve
D	Silica gel, 60-200 mesh
		E	Granular activated carbon
F	Acid clay
		G	Sodium bicarbonate
H	Sodium carbonate
		I	Bleaching earth
J	Powdered decolorizing charcoal (Norit)*)
		K	Powdery 13X molecular sieve

TABLE 1 removal of odor from Cyclic siloxanes- -Long contact time

Experiment number	Absorbent agent	Off-flavor 1	Peculiar smell 2	Peculiar smell 3	Average grade
						1	Is free of	1	1	1	1
2	A	1	1	2	1.3
						3	B	3.5	4.5	4	4
4	C	4.5	4	5	4.5
						5	D	3	2	3	2.7
6	E	5	5	5	5
						7	F	1	1	2	1.3
8	G	1	1	-1	1
						9	H	1	1	1	1
10	I	2.5	2	3	2.5

The grade ratios are as follows:

1-unchanged

2 is slightly improved

Some off-flavor still exists

4 is almost odorless

No peculiar smell 5 ═

Table 1 shows that the 4A and 13X molecular sieves and the granular activated carbon effectively removed the odor from the siloxane solvent.

Example 2

A second set of experiments was conducted using a simulated in-line purification method with reduced contact time and a siloxane anhydrous cleaning solvent flowing through glass tubes (approximately 1/2 inches in diameter) containing various absorbents. The purified siloxane solvent was again evaluated olfactively to determine the effectiveness of the purification process. The results and the absorbents used are shown in table 2 below.

TABLE 2 odor removal from Silicone solvents- -short contact time

Experiment of	Absorbent agent	Amount of absorbent	Amount of siloxane to be used	Contact time (minutes)	Peculiar smell
						11	E	58 g	200g	10	5
12	J	12 g (24 g filter aid)	200g	30	5
						13	B	35 g	200g	10	5

The same scale ratio as in example 1 was used.

Example 3

An experiment similar to example 1 was carried out using a linear siloxane solvent (MD)₂M) in place of the cyclic siloxane. MD₂M sample was spiked with 10% D containing an odorous component₅. Table 3 shows the treatment of 200g D spiked with various off-flavors (propionaldehyde (0.0145g), propionic acid (0.0330g), butyraldehyde (0.0210g) and butyric acid (0.0353g))₅And the results of the samples were subsequently analyzed olfactively and by GC (gas chromatography). Approximately 40 grams of the linear siloxane solvent with incorporated odor was mixed with 10 grams of a different absorbent to form a slurry. The slurry was mixed for 6 hours at ambient temperature, the absorbent was removed by filtration, and the siloxane solvent was then evaluated olfactively to determine the effectiveness of the purification process. The results and the absorbents used are shown in table 3 below.

TABLE 3 removal of odors from Linear siloxane solvents

Experiment of	Absorbent agent	Amount of absorbent	Amount of siloxane to be used	Contact time (minutes)	Peculiar smell
						14	E	10g	40g	6	3.3
15	J	10g	40g	6	4.7
						16	B	10g	40g	6	2.7
17	C	10g	40g	6	4.3
						18	D	10g	40g	6	3.0
16	"smelly" MD2M solvent (control)	Is free of	40g	-	1.0

The same scale ratio as in example 1 was used.

Example 4

Pure D₅Various components were blended (as shown in table 4). The sample was passed through the absorbent (10% absorbent loading, contact time 1 minute) and the sample was analyzed by GC to determine the effect of odor removal, with the results shown in table 4.

TABLE 4 doping with D₅Analysis result of the sample of (1)

Experiment of	Absorbent agent	Propionaldehyde	Propionic acid	Butyraldehyde	Butyric acid	Peculiar smell
							17	Is free of	73ppm	165ppm	105ppm	176ppm	1
18	J	＜10ppm	＜10ppm	＜10ppm	＜10ppm	4
							19	C	＜10ppm	＜10ppm	＜10ppm	＜10ppm	4
20	E	9ppm	46ppm	31ppm	53ppm	3

The odor value was determined using the same scale ratio as in example 1.

Results were obtained from GC/MC (gas chromatography/mass spectrometry) data and expressed in ppm and compared to the initial loading of the control sample. From the GC/MC data, powdered decolorizing carbon and powdered 13X molecular sieve removed substantially all impurities, and the same conclusion was also drawn in terms of smell from an odor grade of 4, granular activated carbon was less effective, an odor grade of 3, and some residual acid and aldehyde residues remained after treatment.

Claims (4)

1. A method for removing malodorous elements from silicone anhydrous cleaning solvents comprising contacting the silicone solvent with an adsorbent at a temperature of 10-100 ℃ for 0.1-6 hours in a ratio of from 1 part by weight solvent: 1 part by weight of adsorbent to 10 parts by weight of solvent: 1 part by weight of an adsorbent, and then separating the siloxane solvent from the adsorbent, wherein the adsorbent is selected from the group consisting of 4A molecular sieves and 13X molecular sieves, and the malodorous component removed from the solvent is propionic acid, propionaldehyde, butyric acid, or butyraldehyde,

and the solvent is a linear or branched volatile siloxane of the formula:

M_2+y+2zD_xT_yQ_z

wherein:

m is R¹ ₃SiO_1/2；

D is R² ₂SiO_2/2；

T is R³SiO_3/2；

Q is SiO_4/2；

R¹、R²And R³Are each independently C₁-C₆An alkyl group; and x, y and z are each an integer, where x is 0. ltoreq. x.ltoreq.10, y is 0. ltoreq. y.ltoreq.10, and z is 0. ltoreq. z.ltoreq.10,

or the solvent is a cyclic siloxane with the following structural formula:

wherein:

R⁵、R⁶、R⁷and R⁸Are each independently C₁-C₆An alkyl group; and

a and b are respectively integers, wherein a is more than or equal to 0 and less than or equal to 10, b is more than or equal to 0 and less than or equal to 10, and the condition is that (a + b) is more than or equal to 3 and less than or equal to 10.

2. The process of claim 1, wherein the process is a batch process.

3. The process of claim 1, wherein the process is a continuous process.

4. The method of claim 1, wherein the cyclic siloxane consists of decamethylcyclopentasiloxane.