Subnanoscale composite, N2-permselective membrane for the separation of volatile organic compounds

• US 5,789,024 A
• Filed: 05/15/1996
• Issued: 08/04/1998
• Est. Priority Date: 05/15/1996
• Status: Expired due to Fees

• Current Assignee: New Jersey Institute of Technology
• Original Assignee: New Jersey Institute of Technology
• Inventors: Levy, Roland A., Ramos, Emmanuel S.
• Primary Examiner(s): Fortuna, Ana
• Application Number:
  US08/648,316
• Time in Patent Office: 811 Days
• Field of Search: 210/490, 210/500.25, 210/500.26, 210/651, 96/4-11, 264/45.1, 264/45.5, 264/45.6, 264/64, 427/244, 427/243, 427/226, 427/245, 501/133, 247/255.1, 247/255.2, 247/255.3
• US Class Current: 427/244
• CPC Class Codes: B01D 2323/08 Specific temperatures applied
• CPC Class Codes: B01D 2323/081 Heating
• CPC Class Codes: B01D 2323/10 Specific pressure applied
• CPC Class Codes: B01D 53/228 characterised by specific membranes
• CPC Class Codes: B01D 67/0072 by deposition from the gaseous phase, e.g. sputtering, CVD, PVD
• CPC Class Codes: B01D 71/02 Inorganic material
• CPC Class Codes: B01D 71/0213 Silicon
• CPC Class Codes: B01D 71/0215 Silicon carbide; Silicon nitride; Silicon oxycarbide
• CPC Class Codes: B01D 71/027 Silicium oxide
• CPC Class Codes: C23C 16/045 Coating cavities or hollow spaces, e.g. interior of tubes; Infiltration of porous substrates
• CPC Class Codes: C23C 16/401 containing silicon

Abstract

A composite membrane is disclosed which operates as a filter for liquids, solids and gases and combinations thereof, having high permeability for the filtrate, e.g., nitrogen passing therethrough, and high selectivity for matter retained thereby, e.g., volatile organic compounds, so that the N₂ /VOC selectivity is at least about 50/1 or greater; prepared by a low pressure chemical vapor deposition process comprising: (a) providing as a first component thereof, a mesoporous membrane substrate having pore diameters greater than about 20 Å; (b) contacting surfaces, including pore surfaces, of the membrane with at least two reactant gas streams in an opposing reactant geometry, wherein the smallest reactant gas molecule has a kinetic diameter intermediate in size between that of the matter retained by said filter and the filtrate passing therethrough; the reactant gases are capable upon reaction of depositing thereon as a second component thereof, a reaction product which by coating the surfaces, including pore surfaces of said mesoporous substrate, substantially reduces the pore diameters thereof, resulting in a substantially uniform microporous film having pore diameters in the range of from about 4 Å to about 8 Å; the reaction product comprises predominantly silicon oxide, --Si--O--, and may optionally include for the purpose of optimizing the stress, and other mechanical, chemical and thermal properties of said film, minor amounts of one or more members, in any combination thereof, selected from the group consisting of polysilicon, --Si--Si--, silicon carbide, --Si--C--, and silicon nitride, --Si--N--; and wherein said reactant gas streams comprise: (1) as the source of silicon and optionally carbide, a di-alkylsilane of the formula R¹ (R²)SiH₂.

Claims

1. A self-terminating low pressure chemical vapor deposition process utilizing opposing reactant geometry, for microengineering the subnancoscale pore structure of a tubular composite membrane filter, comprising a mesoporous borosilicate glass substrate and deposited microporous film predominantly of silicon oxide and optionally silicon carbide or silicon nitride for the purpose of optimizing the stress and other mechanical, chemical, and thermal properties of said composite membrane filter, having high permeability for the filtrate passing therethrough, and a high selectivity for matter retained thereby, as well as having permeability for nitrogen and selectivity for volatile organic compounds which may be entrained with said nitrogen, comprising:

(a) providing a tubular, borosilicate glass, mesoporous substrate substrate having pore diameters in the range of from about 30 Å

to about 3000 Å

as well pore and other surfaces;

(b) maintaining said substrate as well as other surfaces, both inside and outside thereof, at a temperature in the range of from about 350°

C. to about 650°

C., and a pressure in the range of from about 400 mTorr to about 600 mTorr;

(c) contacting said inside surfaces, including pore surfaces, of said tubular mesoporous substrate with a reactant gas stream comprising an oxide of nitrogen having a kinetic diameter intermediate in size between the kinetic diameter of said matter retained by said composite membrane filter and the kinetic diameter of said permeant gas passing therethrough, said oxide of nitrogen comprising one or more members selected from the group consisting of nitrous oxide, nitric oxide, nitrogen dioxide, and nitrogen trioxide; and

optionally, ammonia or reactive nitrogen-containing gas; and

at the same time

(d) contacting said outside surfaces, including pore surfaces, of said tubular microporous substrate with a reactant gas stream comprising diethylsilane (DES), SiH₂ (C₂ H₅)₂ or di-t-butylsilane (DTBS), SiH₂ C(CH₃)₃ !₂ ;

(e) causing said reactant gas streams to meet within said pores of said tubular microporous substrate, to react, and to deposit thereon a reaction product which by coating the surfaces, including pore surfaces of said mesoporous substrate, substantially reduces the pore diameters thereof, until the pore diameters approach the size of the kinetic diameter of said oxide of nitrogen, at which time said reactant gas streams cannot make contact within the pores, and the reduction of the pore diameters of said tubular mesoporous substrate self-terminates, resulting in a substantially uniform microporous film having pore diameters determined by the kinetic diameter of said oxide of nitrogen in the rang of from about 4 Å

to about 7 Å

;

said reaction product comprising predominantly silicon oxide, --Si--O--, and optionally including for the purpose of optimizing the stress, and other mechanical, chemical and thermal properties of said film, minor amounts of one or more members, in any combination thereof, selected from the group consisting of polysilicon, --Si--Si--, silicon oxide, --Si--O--, silicon carbide, --Si--C--, and silicon nitride, --Si--N--.

2. A process according to claim 1 wherein said borosilicate glass tubular mesoporous substrate has an average pore diameter of about 40 Å

.

3. A process according to claim 1 wherein said tubular mesoporous substrate and an area about it are maintained at a temperature in the range of from about 400°

to about 500°

C., and at a pressure in the range of from about 450 mTorr to about 550 mTorr.

4. A process according to claim 1 wherein said substantially uniform microporous film has pore diameters in the range of from about 3.0 Å

to about 5.0 Å

.

5. A process according to claim 1 wherein said optional reactive nitrogen-containing gas is NH₃ ;

and said oxide of nitrogen is nitrous oxide, N₂ O.