Method and Apparatus for Continuous Production of Mesophase Pitch

Abstract

A process and apparatus for the continuous conversion of isotropic carbonaceous materials into anisotropic mesophase pitch is disclosed. The invention disclosed herein addresses the need for lower production costs compared with traditional batch mesophase conversion of isotropic pitch. A unique thermal processing and in-process separation of reacted mesophase from the continuous matrix of fresh or partially reacted isotropic pitch is provided. Potential uses are for further continuous processing into carbon fibers or carbon form densification.

Claims

1. An apparatus for continuous production of mesophase pitch comprising: a generally cylindrical reactor vessel having an outer vessel wall, a top end and a bottom end, said vessel having an upper controlled temperature zone and a lower controlled temperature zone; a reactor head mounted on said top end of the vessel; a cylindrical tube baffle centered and mounted along said central axis of said vessel and spaced inwardly from said outer vessel wall; an inlet for feeding isotropic pitch into the upper controlled temperature zone; flow control means for circulating fluid in said vessel downwardly inside said tube baffle and upwardly outside said tube baffle; a mesophase separator located between said upper temperature zone and said lower temperature zone; a first heating element for heating said upper temperature zone; a second heating element for heating said lower temperature zone; and an outlet for providing mesophase pitch for further processing.

2. An apparatus for continuous production of mesophase pitch according to claim 1 wherein said flow control means comprises a mechanical agitator powered by a motor.

3. An apparatus for continuous production of mesophase pitch according to claim 2 wherein said mechanical agitator further comprises an axial flow impeller at a top and bottom of said tube baffle to promote liquid flow down through tube baffle and high-shear impellers mounted between the axial flow impellers to promote dispersion of mesogens that shear into smaller domains as well as back-mixing of the isotropic pitch feed.

4. An apparatus for continuous production of mesophase pitch according to claim 1 wherein said flow control means comprised at least one sparge ring to dispense an inert gas to promote upward flow and collect lower molecular weight molecules that are the products of thermal cracking but do not take part in a subsequent polycondensation reaction.

5. An apparatus for continuous production of mesophase pitch according to claim 1 wherein said inlet is located near said top end of said vessel wall.

6. An apparatus for continuous production of mesophase pitch according to claim 1 wherein said inlet has a branch line to feed isotropic pitch to a second reactor vessel in parallel to said vessel.

7. An apparatus for continuous production of mesophase pitch according to claim 1 wherein said reactor head is flanged for inspection, cleaning and maintenance.

8. An apparatus for continuous production of mesophase pitch according to claim 1 wherein said bottom end of said outer vessel wall has a conical bottom in which said lower temperature zone is located.

9. An apparatus for continuous production of mesophase pitch according to claim 8 wherein said conical bottom is flanged for inspection, cleaning and maintenance.

10. An apparatus for continuous production of mesophase pitch according to claim 8 wherein higher density mesophase domain shed off said mesophase separator accumulate in said conical bottom of said vessel.

11. An apparatus for continuous production of mesophase pitch according to claim 8 wherein said outlet is in the bottom of said conical bottom of said vessel.

12. An apparatus for continuous production of mesophase pitch according to claim 1 wherein said heating element for said upper temperature zone and said heating element for said lower temperature zone is selected from the group comprising contact resistance heaters, induction heaters and molten salt or metal when an external jacket is employed.

13. An apparatus for continuous production of mesophase pitch according to claim 1 wherein said upper temperature zone is maintained at a temperature necessary to maintain reaction conditions.

14. An apparatus for continuous production of mesophase pitch according to claim 1 wherein said lower temperature zone is maintained at a temperature below that necessary to maintain reaction conditions by above that necessary to maintain mesophase pitch in a liquid state.

15. An apparatus for continuous production of mesophase pitch according to claim 1 further comprising one or more additional temperature zones to control reaction conditions more precisely.

16. An apparatus for continuous production of mesophase pitch according to claim 1 further comprising a transfer pump to promote mesophase pitch to exits said outlet.

17. An apparatus for continuous production of mesophase pitch according to claim 1 wherein mesophase pitch exits said outlet by reactor operating pressure.

18. An apparatus for continuous production of mesophase pitch according to claim 1 wherein said flow control means continuously cycles unreacted isotropic pitch which reaches the lower temperature zone back to said upper temperature zone for further reaction.

19. A method for continuous production of mesophase pitch comprising the steps of: feeding isotropic pitch into an upper temperature zone of a vessel; heating and maintain said upper temperature zone to a reaction temperature needed to produce mesophase pitch from said isotropic pitch; allowing said mesophase pitch to drop into a lower temperature zone of a vessel and separating said mesophase pitch from unreacted isotropic pitch; cycling unreacted isotropic pitch which reaches said lower temperature zone back to said upper temperature zone for further reaction; maintaining the temperature of said lower temperature zone into which the mesophase pitch has dropped below a reaction temperature and above a temperature needed to maintain the mesophase pitch in a liquid state; and removing mesophase pitch from the vessel for further processing.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0025] FIG. 1 is a photomicrograph under polarized light showing round mesophase nematic liquid crystal domains in a continuous isotropic pitch.

[0026] FIG. 2 is a schematic diagram showing the method and apparatus of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0027] The process as described herein comprises a reactor and its feed, product, inert gas, vapor handling and instrumentation systems for the conversion of isotropic pitch from carbonaceous sources into mesophase pitch. Carbonaceous sources include, but are limited to, those derived from coal by high temperature metallurgical coke production, coal liquefaction or coal gasification, petroleum sources and other high molecular weight organic liquids.

[0028] Referring to FIG. 1, isotropic pitch stream 1 is circulated from an intermediate storage tank or process vessel with a pump through an in-line filter(s) to the reactor feed take-off to the reactor. The feed stream further supplies additional reactors in a larger multi-reactor facility and then returns the excess isotropic pitch to the intermediate storage tank or vessel. As required, a back pressure control valve or orifice restriction is installed to provide the appropriate pressure to feed the reactor system.

[0029] The reactor feed rate is controlled as measured by the feed flow meter. The reactor product is removed at a constant rate so the reactor level instrument (12), will set the feed rate into the reactor. The reactor is comprised of an external vessel of a size and construction that is required by the carbonaceous material to be converted and its reaction process conditions. Reaction temperatures are typically 300 to 500 degrees Celsius, and pressures are typically less than 5 bar gage. This coupled with reactor residence times of typically less than six hours make the vessel economical to construct and install. The reactor head and optionally the bottom cone are typically flanged (10) for inspection, cleaning and maintenance.

[0030] Internal to the reactor is a mechanical agitator driven by a motor (1) using AC or DC electric current, hydraulic or pneumatic energy. The motor can be magnetically coupled to the agitator shaft or has a seal that is packed or mechanical to prevent the escape of the reactor process vapor (4). The agitator sits inside a tube baffle (8) whose dimensions are set by the size of the reactor. The agitator blades, or impellers, have an axial flow impeller (6) at the top and bottom to promote liquid flow down through the tube baffle and upward on the outside of the tube baffle. There are high-shear impellers (7) between the axial flow impellers. This promotes dispersion of mesogens that shear into smaller domains as well as back-mixing of the isotropic pitch feed. The motor can be variable speed to adjust the rate at which the reacting liquid is circulated downward through the tube baffle and upwards on its exterior surface.

[0031] The internal reactor flow exits the tube baffle and impacts an internal cone mesophase separator (9). Both the tube baffle and mesophase separator are affixed to the vessel's top flange for stability and ease of removal for maintenance. The higher density mesophase domains shed off the cone and accumulate in the conical bottom section of the reactor under the conical separator. The continuous phase isotropic pitch turns upward on the outside of the tube baffle. Inert gas (3) is released on the outside at the tube baffle's base using a sparge ring (11) to promote upward flow and vaporization, or “stripping”, the lower molecular weight molecules that are products of the thermal cracking but do not take part in the subsequent polycondensation reaction. The inert gas flow is controlled to optimize this light vapor stripping without overcooling or disturbing the heat transfer efficiency from the reactor shell. The inert gas may be externally preheated so as not create a region of high liquid viscosity upon its exit from the sparge ring. Oils in the vapor are condensed and the non-condensable gas is appropriately treated. The rising liquid is heated as described below and re-enters the top of the tube baffle where is combines with fresh isotropic pitch feed. Maintaining an even reaction zone temperature is key to controlling the extent of the reaction.

[0032] The reactor is heated externally by a means that can provide the energy necessary to reach reaction conditions. In this example exterior radiant heat is used but this could also be contact resistance heaters, induction heating or molten salt or metal when an external jacket has been employed. It is essential that the method of heating be closely controlled so as not to provide an area that is overheated by developing hot spots. Hot spots can lead to over-reaction and coking. The spacing between the tube baffle and the internal vessel wall in conjunction with the agitator design will provide sufficient upward liquid velocity to meet the required heat transfer efficiency to prevent overheating.

[0033] As shown in FIG. 1, at least two zones of heating are employed. Depending on the length of the reactor, more zones can be employed with individual controls. In FIG. 1 with radiant heating mantles (16), the temperature of the exterior shell, or skin, of the reactor is controlled. The temperature of the skin is controlled by one or more exterior temperature measurement device(s) or probes (14). To ensure efficient heat distribution around the shell, a reactor heat spreader wrap (15) holds the probe in place against the reactor exterior skin. The heating mantle is insulated to prevent the outward loss of heat. Each heating zone temperature is set by the internal reactor liquid temperature measure by another probe (13).

[0034] The conical bottom of the reactor is separately temperature controlled at a lower temperature to cease further reaction of its contents while remaining above the mesophase pitch softening point. This has a separate skin temperature probe (17), heat spreader wrap (18) and exterior heating coils or mantle (19). The setpoint of this temperature zone is 20 to 50 degrees Celsius below the controlled reaction conditions.

[0035] Mesophase pitch is removed from the reactor by a transfer pump or, alternatively, by the reactor operating pressure, for further processing such as carbon fiber spinning, carbon artifact densification or solidification for sale and transport. Alternatively, during equipment start-up, shutdown or a pause in forward feeding the mesophase pitch can be returned to the reactor where it mixes with the reactor liquid contents. In the case of starting the system, the precursor will be recirculated until the reaction progresses.

[0036] It is to be understood that while certain forms of the present invention have been illustrated and described herein, the present invention is not to be limited to the specific forms or arrangements of parts described and shown.