Apparatus and method for gelling liquefied glasses

Abstract

The present invention is a method and apparatus for gelling liquid propane and other liquefied gasses. The apparatus includes a temperature controlled churn mixer, vacuum pump, liquefied gas transfer tank, and means for measuring amount of material entering the mixer. The method uses gelling agents such as silicon dioxide, clay, carbon, or organic or inorganic polymers, as well as dopants such as titanium, aluminum, and boron powders. The apparatus and method are particularly useful for the production of high quality rocket fuels and propellants.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a cut away view of a temperature controlled churn mixer.

FIG. 2 is a diagram showing components of the gelling method.

DETAILED DESCRIPTION OF THE INVENTION

Gelling Apparatus

In the example provided, LP is gelled using a one-liter, temperature controlled churn-mixer (FIG. 1). The mixer comprises a cylindrical vessel 10 with a heat exchange coil 12 located in the side and bottom walls of the vessel. The exterior surfaces of vessel 10 are thermally insulated with high density foam, polystyrene foam, or other high R value insulator (not shown). The heat exchange coil in this case comprises copper tubing in liquid communication with a cooling pump that circulates cooling liquid such as chilled ethylene glycol, ethanol, acetone, or freon to control temperature inside the mixer. The vessel volume 14 is set by positioning a piston-like closure lid, or follower plate, 20 at a set distance from the bottom of the vessel and securing it in place by compression of o-rings 24. Follower plate 20, comprises a heat exchange coil 22 or a void volume for circulating a cooling liquid. This arrangement provides temperature control on all surfaces in contact with vessel lumen volume 14. A rod 30, attached externally to a pneumatic actuator, goes through the center of the closure-lid and attaches to a perforated churn-plate 40. In this example, the churn-plate has thirty-six, 6 mm diameter holes and is pneumatically cycled up and down, through the entire mixer volume. Ports 50 and 60 are for connection to a liquefied gas transfer tank and vacuum pump, respectively. The ability to evacuate the mixing chamber before the introduction of liquefied gas prevents the formation of bubbles during the mixing process. A third port 70 is located at the bottom of the mixer for removing GLP or other gelled product from the mixer and can also be used to in some embodiments as a port for filling the chamber in a manner similar to filling a syringe. Pneumatically actuated zero void volume valves 52, 62, and 72 are used to regulate flow through ports 50, 60, and 70, respectively. Two thermocouples 80 and two pressure sensors, not shown, are used to monitor temperature and pressure inside the vessel.

The churn mixer may be scaled up or down to 500 liters, 200 liters, 50 liters, 10 liters, or 0.5 liters, for example. The mixing vessel components may be made of any material resistant to the chemicals, temperatures and pressures used in the gelling process. In the present example, the mixer and transfer tank are made of aluminum. Other materials such as stainless steel may and borosilicate glass may also be used. Pneumatically actuated zero void volume valves are preferred but other types of valves may be used.

EXAMPLE 1

Gelling Liquid Propane

A schematic of the components used in the gelling method is shown in FIG. 2 and comprises an aluminum storage tank 5 located on scale 15, vacuum pump 25, churn mixer vessel 10, connecting lines 35, cooling bath 45 for circulating ethanol chilled with dry ice, and valves 52, 62, 72, and 82. The outer surfaces of mixer vessel 10 and the follower plate (not shown) are insulated with a removable, high-density foam insulating material. Connecting lines 35 are flexible, stainless steel braided lines coated with Teflon®.

20 grams of Cabot M-5® fumed silica were placed in mixing vessel 10. The follower plate was lowered into the mixing vessel until the churn plate contacted the gellant. The vessel was sealed by compressing o-rings in the flower plate. Transfer tank 5 and mixing vessel 10 were evacuated using vacuum pump 25 with valve 72 closed and valves 52, 62, and 82 open. Valves 52, 62, and 82 were then closed and LP was transferred from an LP tank (not shown) into the evacuated transfer tank through a fill valve (not shown). Scale 15 was used to monitor the mass of the propane in the aluminum tank during transfer. The fill valve was then closed.

The temperature inside the transfer tank and mixing vessel was lowered to −45° C. to prepare the propane gel mixer for propane transfer. The mixer was cooled after vacuum was reached in order to prevent condensation inside the mixer. Valve 82 was slowly opened to fill connecting line 35 between the transfer tank and the mixer. The mass of LP lost from the transfer tank to the transfer line was recorded. Valve 52 was slowly opened to allow LP from transfer tank 5 into mixing vessel 10. The follower plate was pulled upward by a pneumatic actuator to draw liquid propane into the mixing vessel until 500 grams of propane was transferred into the mixer and valve 52 was closed. LP and gellant were mixed with a chum plate frequency of 1 Hz for 2 minutes. Valve 72 was opened and GLP was pressed from the mixer into a storage container by moving the follower plate to the bottom of the mixing vessel.

EXAMPLE 2

Gelling MON-30

The apparatus used is the same as for gelling liquid propane with the exception that the o-rings (24 in FIG. 1) were made of the MON-resistant material Kalrez®. Storage tank 5 was filled with MON-30 from a holding tank rather than LP and the temperature in the mixer was maintained between −1° C. and −8° C.

It is possible to gel liquefied gasses having lower boiling points and higher vapor pressures than LP as long as the combination of temperature and pressure in the mixing chamber maintain the liquefied gas in the liquid state. Extremely low temperatures can be achieved by using liquid nitrogen or liquid helium as the circulating fluid for heat exchange.

The above examples are presented for illustrative purposes to describe the present apparatus and method. Although particular embodiments of the present invention have been described, it is not intended that such references be construed as limitations upon the scope of this invention except as set forth in the following claims.

Claims

1. An apparatus for gelling a liquefied gas comprising a churn mixer comprising: a) a cylindrical mixing vessel open at one end and comprising a means of circulating heat exchange fluid in the walls of the vessel,b) a closure lid that fits inside the opening of the mixing vessel comprising o-rings capable of sealing the mixing vessel, the closure lid having an opening,c) a rod passing through the opening in the closure lid attached to a perforated plate located inside the mixing vessel,d) at least one valved port in the mixing vessel or closure lid for delivering liquefied gas into or removing gelled liquefied gas from the mixing vessel, ande) at least one valved port for in the mixing vessel or closure lid for evacuating the mixing vessel.

2. The apparatus of claim 1 further comprising a means of circulating a heat exchange fluid in the closure lid of the churn mixer.

3. The apparatus of claim 2 further comprising a refrigeration bath in liquid communication with the means of circulating a heat exchange fluid in the walls and closure lid of the churn mixer.

4. The apparatus of claim 1 wherein the means of circulating a heat exchange fluid is a heat exchange coil in liquid communication with a refrigeration bath.

5. The apparatus of claim 1 further comprising a transfer tank in liquid communication with the at least one valved port in the mixing vessel for delivering liquefied gas into the mixing vessel.

6. The apparatus of claim 5 wherein the transfer tank rests on a scale for measuring the mass of liquid transferred into and from the transfer tank.

7. The apparatus of claim 6 wherein the liquid communication between the transfer tank and the at least on valved port comprises a flexible tube.

8. The apparatus of claim 1 wherein the churn plate is connected to a pneumatic tank and is pneumatically cycled up and down, through the entire mixer volume.

9. The apparatus of claim 1 wherein the perforated plate comprises holes with diameters of between 4 and 8 mm.

10. The apparatus of claim 1 wherein the volume of the mixing vessel is between 0.1 liters and 500 liters.

11. A method for gelling a liquefied gas comprising: a) placing a gellant in a mixing vessel,b) applying a vacuum to the mixing vessel,c) cooling the mixing vessel to a temperature of less than 0° C.,d) introducing liquefied gas into the mixing vessel, ande) mixing the gellant with the liquefied gas.

12. The method of claim 11 wherein the mixing vessel is a churn plate mixer.

13. The method of claim 12 wherein the churn plate mixer comprises: a) a cylindrical mixing vessel open at one end and comprising a means of circulating heat exchange fluid in the walls of the vessel,b) a closure lid that fits inside the opening of the mixing vessel comprising o-rings capable of sealing the mixing vessel, the closure lid having an opening,c) a rod passing through the opening in the closure lid attached to a perforated plate located inside the mixing vessel,d) at least one valved port in the mixing vessel or closure lid for delivering liquefied gas into or removing gelled liquefied gas from the mixing vessel, ande) at least one valved port for in the mixing vessel or closure lid for evacuating the mixing vessel.

14. The method of claim 11 wherein the volume of the mixing vessel is between 0.1 liter and 500 liters.

15. The method of claim 11 wherein the liquefied gas is propane or a mixed oxide of nitrogen.

16. The method of claim 11 wherein the gellant is silicon dioxide, clay, carbon, or an organic or inorganic polymer.

17. The method of claim 16 wherein the gellant is doped with one or more dopants.

18. The method of claim 17 wherein the one or more dopants are selected from boron, carbon, lithium, aluminum, or titanium.