KR20230037591A - Pitch process and product - Google Patents

Abstract

The present invention relates to a process for making mesophase and/or isotropic pitch. The aromatic rich liquid is charged into the first thermal polymerization reactor at high temperature and pressure to produce an isotropic pitch rich liquid that is flashed. The remaining liquid is charged to the second thermal reactor to produce mesophase pitch. The reactor may be a tubular reactor or a CSTR. Carbonized or graphitized fibers, foams, blocks, sheets or spheres can be produced from mesophase pitch.

Description

Pitch process and product

Cross-References to Related Applications

Applicant's two recent patents, US 9,222,027 and US 9,376,626, are related and incorporated herein by reference.

field of invention

The present invention relates to the formation of isotropic or mesophase pitch.

Many studies have been conducted to prepare isotropic or mesophase pitch. Applicant's two recent patents mentioned above relate to making isotropic and mesophase pitches, respectively.

Although the method in this patent is considered the most available technology for producing isotropic and mesophase pitch, the inventors continued their research with the aim of improving this process. The inventors have developed an improved two stage process and also provided a better one stage process.

Accordingly, the present invention provides a first method operating the feed under thermal polymerization conditions comprising a temperature high enough to induce thermal polymerization and a pressure high enough to maintain at least a portion of the two and three ring aromatics in the liquid phase. At least a portion of the two and three ring aromatics are converted by charging in a stage reactor to convert at least 20% by weight of the two and three ring aromatics to isotropic pitch and to light, usually gaseous hydrocarbons, and discharging the first stage reactor effluent. thermally polymerizing an aromatics liquid feed comprising removing at least a majority of the light, typically gaseous, hydrocarbons in a flash zone having an absolute pressure less than or equal to one-half the absolute pressure in the first stage thermal polymerization reactor. flashing the first stage reactor effluent to produce a flash effluent liquid stream, at least 1/2 of the flash effluent liquid by weight and at a pressure less than or equal to 1/2 the absolute pressure in the first stage reactor. forming mesophase pitch from the flash effluent liquid stream in a second stage reactor at mesophase formation conditions comprising a temperature to convert 3 to mesophase pitch, and recovering mesophase pitch as a product from the second stage reactor. A two-stage process for producing mesophase pitch from an aromatics liquid, comprising:

In another embodiment, the present invention provides liquid aromatics feed to thermal polymerization conditions comprising a temperature high enough to induce thermal polymerization and a pressure high enough to maintain at least a portion of the two and three ring aromatics in the liquid phase. converting at least 20% by weight of said two and three ring aromatics to isotropic pitch and to light, usually gaseous hydrocarbons by charging a first stage reactor operating in thermally polymerizing an aromatics liquid feed comprising at least a portion of the compounds, in a flash zone having an absolute pressure of less than one-half the absolute pressure in the first stage thermal polymerization reactor; flashing the first stage reactor effluent to remove at least a majority thereof to produce a flash effluent liquid stream, wherein the flash effluent liquid at a pressure and weight basis of less than half the absolute pressure in the first stage reactor. forming mesophase pitch from the flash effluent liquid stream in a second stage reactor at mesophase formation conditions comprising a temperature that converts at least one third of the mesophase pitch to mesophase pitch, and recovering mesophase pitch from the second stage reactor; The mesophase pitch is converted to at least one of carbonized or graphitized fibers, foams, blocks, sheets or spheres by conventional processing of the mesophase pitch, and any of the carbonized or graphitized fibers, foams, blocks, sheets or spheres Recovering at least one of them as a product of the process provides carbon fibers, graphite fibers or carbon foam made from the mesophase pitch.

The Figure is a simplified diagram of an embodiment of a two-stage process for producing mesophase pitch from an aromatics liquid. Fresh feedstock consisting of filtered aromatics liquid (1) is fed to feed tank (2), then charged to line (103) via pump (3) and recycled in line (4), with heavy aromatics stream and It is mixed and discharged to the mixed feed drum (5). The mixed feed is discharged through line 106 and pump 7 increases the pressure for discharge to heated heater 8. The heated mixed feed is then charged via line 108 to a first stage tubular reactor 9 where the feed is partially converted to a mixture of isotropic and mesophase pitch. The reactor effluent is withdrawn from the first stage reactor through line 10 and passed through a pressure reducing valve 11 to reduce the pressure. The flashed partially converted mixture is then mixed with superheated steam added via line 12, produced by passing boiler feed water through steam boiler/superheater 13 in line 113. The molar ratio of steam to hydrocarbon is generally greater than 1:1, for example 3:1. The resulting mixture in line 14 is fed to a second stage tubular reactor 15, where additional intermediate phases are formed. The second stage reactor effluent exits via line (16) to a vapor/liquid separator (17). The liquid stream 18 leaving this separator contains between 85 and 90 weight percent mesophase pitch, the balance being mainly isotropic pitch, representing an 88 weight percent yield on fresh feedstock. Stream 18 is recovered for storage and distribution by feeding it to a pitch cooling and solidification system 19. Vapor 20 from vapor/liquid separator 17 is cooled to 155° C. in shell and tube heat exchanger 21 using glycol/water cooling stream 22 from glycol cooling system 23. Any other conventional cooling means may be used, such as feed/product exchange, air cooling via a fin-fan cooler, or cooling water from a cooling tower. The cooled vapor stream 24 passes to a vapor/liquid separator 25 where a heavy aromatics stream 26 is withdrawn from the bottom and temporarily stored in a heavy aromatics tank 27. These heavy aromatics are then recovered via line 127 and pump 28 and recirculated via line 29 to supply drum 5 or cooled with air cooler 30 and line 131 for storage. to heavy aromatics tank 31 and pumped through line 133, pump 32 and line 132 for sale as a valuable by-product, e.g., an aromatics-rich solvent. Overhead vapor removed from vapor/liquid separator 25 via 33 is cooled to 49° C. in air cooler 34 and discharged via line 134 to three-phase separator 35. The vapor phase is removed overhead via line 36. Water from the steam condensate is removed from the bottom of the separator via line (37). A light hydrocarbon stream is removed via line 38 and discharged to light hydrocarbon storage tank 39, where it is pumped through line 140, pump 40 and line 141.

Details of the feeds, products and reaction conditions in the tubular reactor are described in the inventor's relevant prior patents, incorporated herein by reference, and not repeated herein.

first stage

Tubular reactors and relatively high pressures are preferred. What is different from the present inventors' previous studies is that it promotes the conversion of aromatic compounds to pitch molecules. In our previous patents, we attempted to limit the mesophase content in the isotropic pitch product to preferably 1% by weight or less. While this is a good and effective method when isotropic pitch is the desired product, it is not always optimal when some or all of the isotropic pitch product is converted to mesophase pitch. When mesophases are the ultimate goal, an isotropic pitch "contaminated" with more than 1 wt% mesophase, preferably more than 2-5 wt% mesophase, and ideally more than 10-25 wt% mesophase or more mesophases. It may be advantageous to operate the first stage of the process to produce

This contaminated product from the first stage is "neither fish nor fowl" and has little or no value as an isotropic pitch product, but it is further thermally polymerized into a second reaction to produce a salable intermediate phase product. It is the ideal charge stock for the stage. The first stage flashing removes light gases formed as by-products of thermal polymerization and thermal dealkylation, and also preferably removes two and three ring aromatics. In the second stage reactor, lower pressure facilitates mesophase formation. Two- and three-ring aromatic compounds are removed as they are believed to interfere with mesophase formation.

When the first stage is performed in a continuous stirred tank reactor (CSTR), the chemistry and general process are similar, but with different constraints and concerns.

Although the thermal reactions to form isotropic pitch and, to a limited extent, mesophase pitch are the same, the reactants are somewhat different, and the amount of mesophase that can be tolerated is often significantly reduced.

The reactants in a CSTR can be different because a CSTR typically consists of an agitated vessel with an agitated liquid at the bottom and a vapor space at the top. Vapor-phase materials have a harder time reacting with liquid-phase materials because the contact is greatly reduced compared to the intense vapor-to-liquid contact in a tubular reactor.

The amount of mesophase in the first stage product that can be tolerated will generally be less than that which can be tolerated in a tubular reactor. The tubular reactor keeps everything moving and is mostly wiped clean by fluid flowing through its walls. The situation is similar to that experienced by refiners trying to use cooling water from the high solids Mississippi River. Dirty cooling water can be used, but only in tubular heat exchangers and when the flow rate is kept high. In a conventional CSTR, the walls of the vessel and the paddles of the impeller or other mixing device may tolerate some mesophases, but generally not as much as can be tolerated in a tubular reactor.

In the first stage the pressure must be high to keep more of the two and three ring aromatics in the liquid phase. These aromatics can be converted to isotropic pitch, but generally only when they are in the liquid phase.

2nd stage

The second stage can be operated as described in our previous patents on mesophase production when tubular reactors are used.

The pressure in the second stage must absolutely be reduced by at least 50% compared to the pressure in the first stage. When maximum mesophase formation and concentration is the goal, preferably the pressure is low enough and the temperature is high enough to vaporize at least a majority of the moles of the two- and three-ring aromatic compounds. These two- and three-ring aromatics tend to interfere with mesophase formation, so they are best removed.

When a CSTR reactor is used, greater care is required in design and operation to avoid clogging of the thermal reactor. The mesophase content will generally be greater than 50% by weight, and this material is hot enough to readily form coke and tacky enough to easily clog a vessel or impeller. CSTR operation can be extended to some extent by using higher impeller speeds and/or swing reactors.

One advantage CSTRs have over tubular reactors is that they are cheaper to build and require only a small footprint.

Preferably, there is little or no external heating of the flash effluent to the second stage reactor. Preferably there is no external heating of the second stage reactor. This is because coke-prone materials rich in these mesophases tend to coke on hot surfaces.

thermal equilibrium

The heat demand of the second stage of the process is preferably and predominantly supplied by the feed. The feed to the first stage reactor and products therefrom may accept significant conventional heating, for example in a heated heater or immersion in a molten metal or molten salt bath. The thermal reaction occurring in the first reactor is highly dependent on time and temperature. Since the reaction rate approximately doubles for every 10° C. temperature increase, the size of the reactor can be reduced by operating the first reactor at a higher temperature.

The first stage reactor effluent will cool significantly when flashed to remove hard ends and 2 and 3 ring aromatics. The residual liquid from this flash is still very hot and, in many cases, hot enough to induce thermal polymerization in the second stage reactor.

Additional heat may be added to the second stage reactor in the form of superheated fluid, preferably superheated steam. Since the second stage reactor operates at a much lower pressure than the first stage, construction costs can be significantly reduced due to lower pressure operation. Reactor residence time can be increased by using a larger inside diameter and/or longer length tube reactor or by using a larger CSTR.

Additional residence time may be achieved by using multiple reactors in series or by recycling a portion of the second reactor effluent back to the first reactor. Once through operation is preferred because it generally reduces capital and operating costs and because the liquid effluent from the second reactor is mesophase rich and easily coked.

When a CSTR reactor is used, heat may also be added by mixing or mechanical energy. Energy can be added by a conventional mixing impeller. There is no free energy, rather an electric or steam driven pump transfers the energy to the second reactor by intensive mixing.

Other forms of energy may be added, for example ultrasonic or microwave energy, such as the use of microwaves to heat coal as disclosed in US 3,503,865 (COAL LIQUEFACTION PROCESS, Stone).

Exemplary Embodiments

The data and discussion below are based on limited laboratory experiments on different parts of the process with significant extrapolation and extrapolation. These are reasonably reliable estimates, but not real experiments.

Case 1 - Two Tubular Reactors

This is the reactor design illustrated by the drawing. Although the discussion in relation to the figure is primarily for the mesophase product, the design permits the recovery of relatively pure isotropic pitch as either an intermediate or final product. Relatively pure isotropic pitch can be recovered as an intermediate product when conversion in the first tubular reactor is limited by the amount of intermediate phase that can be tolerated in the product. In this example, the first stage reactor is operated to convert most of the feed to isotropic pitch, but the intermediate pitch product has less than 2 wt% mesophase, or 1 wt% mesophase, or less than 0.5 wt% mesophase or less. and limiting the conversion to have a mesophase of This will not maximize mesophase production as a whole, but will allow recovery of some isotropic pitch product from the middle separator and some mesophase pitch product downstream of the second thermal reactor.

It will also be possible to obtain a relatively pure isotropic pitch product as product from the second thermal reactor. The first thermal reactor converts the desired amount of aromatic feed to isotropic pitch, generally from 10 to 60% by weight, preferably less than 50% by weight, to isotropic pitch, and in the second thermal reactor the desired isotropic pitch content, Typically about 70%, or 80%, or 90% by weight. It will generally be necessary to flash the intermediates in both thermal reactors as the second thermal reactor will be designed for lower pressure operation than the first thermal reactor, but in the second thermal reactor to facilitate their conversion to the liquid phase. It is advantageous to retain more of the two and three ring aromatics. A good flash method is to reduce the pressure enough to remove most of the lighter byproducts and most of the two ring aromatics while retaining at least most of the moles of three ring aromatics in the residual liquid phase removed from the flash. This residual liquid phase can then be charged to the second thermal reactor, preferably with superheated fluid injection after flash.

Case 2 - Tubular Reactor for CSTR

This method may be similar to the Case 1 method. The first thermal reactor is a tubular reactor while the second thermal reactor is a CSTR. The pressure will be lower in the CSTR to favor vaporization of the two- and three-ring aromatics and mesophase formation.

Case 3 - CSTR for tubular reactor

The first thermal reactor is a stirred tank reactor. A robust reactor design will be required to handle operation at high pressures, but the reactor will operate relatively easily, at least in terms of coking issues. Since the first reactor can leave most of the feed unconverted, it is fairly easy to agitate the fluid. The tendency of a material to coking increases with increasing percent pitch, particularly percent mesophase pitch. Thus, most of the coke problem is moved downstream to the second thermal reactor, which is a tube operating in fully developed turbulence.

The first reactor should operate at a relatively high pressure sufficient to keep at least a majority of the three ring aromatics in the liquid phase and preferably a majority of the two ring aromatics in the liquid phase. These aromatic compounds can be converted to pitch, but liquid phase operation is preferred. Flashing or some pressure drop means will be necessary to remove at least most of any remaining unconverted two- and three-ring aromatics, usually in the middle of the first and second reactors.

This method of CSTR for tubular reactors allows for a relatively compact and simple first reactor with increased fluidity largely offsetting the risk of coking, and tubular reactors can rely on turbulence to reduce coking.

Case 4 - 2 CSTRs

In this method, a stirred tank reactor is used for both the first and second thermal reactors. The pressure is relatively high in the first reactor, keeping the two and three ring aromatics in the liquid phase. The flashing step removes most of the 2- and 3-ring aromatics which favor thermal conversion to the mesophase in the second thermal reactor. Since the mesophase is close to coke, the coking problem is important in these methods. For this reason, it may be advantageous to have multiple CSTRs so that when one CSTR is being coked, they can be swapped out for decoking.

Residence time effect on product properties

In some applications it will be important to have a final mesophase or isotropic pitch product with a relatively narrow range of molecular weights. The use of tubular reactors with precisely controlled residence times in the thermal reactor will produce products with the narrowest molecular weight range. In some applications, it may be advantageous to have some distribution of molecular weight. To facilitate mesophase pitch processing, it is often advantageous to have an amount of isotropic pitch as a softening agent, i.e., 5, 10 or 15% by weight. CSTR reactors will have varying liquid residence times, but tubular reactors will not.

The process of the present invention provides what is believed to be the most cost effective method of making mesophase pitch from aromatics liquids. Most of the benefits are achieved by the tight coupling of the first reactor stage and the second reactor stage. There is no need to cool the isotropic pitch material and little or no preheating of it upstream of the second stage of the reactor is required.

Also, the process is flexible and can be used to recover isotropic pitch from a flash vessel in the middle of the two stages.

The process also provides a way to produce pure isotropic pitch from two thermal reactors in a single stage or even from an aromatics-rich liquid. The process can also be used to produce mesophase pitch from an isotropic pitch feed if desired.

Tubular reactors with good mixing properties, the ability to resist fouling, and the ability to add some heat through electrically heating the tube walls have proven to work well in the inventor's laboratory. In some applications, the relatively large footprint and relatively low capacity and careful manufacturing required when some type of electrical heating is used may suffice for use of a CSTR in either the first reactor or the second reactor, or both.

A CSTR will likely be slightly less chemically efficient than a tube reactor when used in a first stage reactor. 2 and 3 ring aromatics will be concentrated in the vapor phase above the liquid in the CSTR. These aromatics can potentially be converted to isotropic pitch, but to do so they must be in close contact with the larger aromatics in the liquid phase. Thus, the CSTR is at a slight disadvantage in the first reactor for this reason. In the second stage reactor forming mesophase pitch, we find that the presence of two- and three-ring aromatics tends to hinder the formation of large mesophase molecules, so that the vapor space above the stirred liquid is somewhat advantageous in the second stage reactor. found that it did.

discussion/optimization

The discussion and claims sometimes refer to two- and three-ring aromatic compounds, but in many applications only one of these may be helpful in optimizing the process. Thus, it may be sufficient to design and maintain the first thermal reactor at a pressure sufficient to keep the tricyclic aromatics primarily in the liquid phase, preferably at least 60, 70, 80, 90% of them in the liquid phase. The process will still work if the two ring aromatics are in the vapor phase from time to time or continuously. Alternatively, a refiner may use at least a majority of the two ring aromatics, preferably 60, 70, 80, 90 % or more can be focused on keeping it in the liquid phase. Oversimplifying considerably, it would generally be advantageous to have a pressure high enough to keep most of the two-ring aromatics in the liquid phase in the first reactor and low enough to reject most of the three-ring aromatics in the vapor phase in the second reactor. .

The inventors prefer to operate the reactor to achieve conversion of the majority of the feedstock to isotropic pitch in the first thermal reactor and to convert the majority of the first reactor effluent to mesophase pitch in the second thermal reactor. If there is a market for by-products or sufficient capital and working capital to recycle unconverted materials, profitable operations can be achieved with much lower conversions. The threshold for a viable commercial plant is probably around 20% conversion of the liquid aromatic feed to isotropic pitch. Similarly, it is not necessary to convert most of the feed to the second thermal reactor to mesophase pitch, and conversions of 20, 30, 40% or more are satisfactory.

A preferred method is to push the first reactor fairly hard and feed the majority of the aromatics liquid feed into an isotropic pitch, preferably at least 1% by weight, preferably 2, 3, 4, 5, 7, 10, 15, 20% by weight. % or more of the mesophase to convert to heavily “soiled” pitch. This method will ensure that most of the readily convertible molecules in the feed are converted to the pitch product. Generally, aromatics liquid feeds contemplated for use herein will contain significant amounts of two- and three-ring aromatics of relatively low value/cost. The economics of the process are better if these lower cost feeds can be converted to higher value mesophase pitch.

Conditions in the first thermal reaction zone will preferably include temperatures from 455 to 540°C, preferably from 480 to 510°C, and ideally from 495 to 500°C. The pressure should be sufficient to maintain the desired amount of two or three ring aromatics in the liquid phase, preferably between 7 and 210 bar, more preferably between 35 and 170 bar, and ideally between 70 and 140 bar. The residence time will depend primarily on the temperature and conversion desired, but will typically range from 10 seconds to 10 minutes, preferably from 0.5 to 5 minutes, and ideally from 2 to 3 minutes.

The conditions in the second thermal reaction zone will typically involve significantly lower pressures and shorter residence times. The pressure should be less than half of the absolute total pressure in the first thermal reactor, and will typically be less than 7 bar, preferably less than 3.5 bar and ideally less than 2 bar or even atmospheric or subatmospheric pressure. The residence time required to achieve the desired conversion of the feed to the mesophase will normally be less than 1 minute, preferably 0.1 to 10 seconds, ideally 0.2 to 2 seconds.

The pressures and temperatures of the first and second zones are suitable for relatively simple commercial process designs in which all or essentially all of the heat and pressure energy is added at the inlet of the first reactor. There will be a lot of pressure to get the reactants through the first stage reactor and into the flash or second thermal reactor. The temperature in the first reactor may be selected to be high enough such that, after flashing, the liquid phase is at or near the required temperature in the second stage reactor. In this way, any heat required can be added to the feed to the first reactor. Any pressure required to get the reactants through the process may be applied upstream of the first reactor.

The flash zone is a necessary concept to allow vaporization of two and three ring aromatics from an isotropic pitch "product", but a flash vessel is not a requirement per se. Preferably with enlarged bore tubes in the second reactor section, it is possible to flash the isotropic pitch liquid relying solely on hydrodynamics in the tubular reactor. The isotropic pitch-rich liquid discharged into the tubes forming the second thermal reactor will flash in the tubes such that the liquid phase is depleted of 2 and 3 ring aromatics. It is possible to have the flash drum at a sufficiently low, relatively high pressure to be able to remove most of the 2 and 3 ring aromatics from the isotropic pitch discharged with this high pressure flash. The liquid phase from the high-pressure flash can then be charged to a second thermal reactor. It is possible to have a flash drum at a relatively low pressure to facilitate the removal of increased amounts of two and three ring aromatics.

Direct contact heating/stripping

A superheated fluid, preferably superheated steam, may be added to supply any heating or stripping needs of the process. Superheated steam may be added in small amounts, for example 1 to 10% by weight of the liquid, when little heating is required and adequate stripping or removal of the two and/or three ring aromatics is desired. There is no upper limit on the addition of superheated steam, and amounts up to 50%, 100%, 200% or more by weight are contemplated when some heating of the liquid is desired. Steam is preferred, but other superheated fluids such as hydrogen, usually gaseous hydrocarbons, may be used if desired.

Our process has several applications. The process preferably consists of two plug flow reactors in series, with a pressure drop in the middle of the two reactors produced by thermal polymerization in the first stage reactor or sufficient to vaporize most of the two ring aromatics in the feed. can be used to produce mesophase pitch from an aromatic oil feed.

In another embodiment, the process can be used to produce isotropic pitch and mesophase pitch using two thermal reactors in series. The first thermal reactor is a mixture of tricyclic aromatic compounds in the liquid phase feed in the first reactor to produce a first reactor effluent comprising isotropic pitch and mesophase pitch of up to a predetermined amount, typically less than 1% by weight. It should be operated at a pressure sufficient to retain at least a majority and at a temperature sufficient to thermally polymerize at least a majority of the tricyclic and heavier aromatics. The first reactor effluent is flashed to a flash drum operating at a pressure low enough to vaporize at least a majority of the two ring aromatics present in the first reactor effluent. A portion of the flash drum liquid is recovered as the isotropic pitch product of the process, the remainder being at least a majority of the liquid feed on a weight basis to the second reactor and at a pressure low enough to vaporize at least a majority of the two ring aromatics present. It is charged to a second thermal reactor operated at a temperature sufficient to convert to mesophase pitch. In a preferred embodiment, a superheated fluid such as steam or hydrocarbon is charged to the second reactor for heating. The first thermal reactor may be a continuous stirred tank reactor or a tubular reactor. The second thermal reactor may be a continuous stirred tank reactor or a tubular reactor.

Preferably, the pressure in the first stage reactor is between 14 bar and 210 bar, more preferably between 35 bar and 140 bar, and ideally between about 68 bar and 70 bar. Preferably, the pressure of the second stage reactor is less than 1/10 the pressure of the first stage reactor, more preferably 7 bar to less than atmospheric pressure, ideally atmospheric pressure to 5 bar.

For maximum production of mesophase pitch, the first stage reactor preferably produces a first stage reactor isotropic pitch intermediate product contaminated with an amount of mesophase pitch sufficient to make said intermediate unsuitable for use as isotropic pitch. is carried out under thermal polymerization conditions sufficient to do so. Preferably, the first stage reactor effluent isotropic pitch intermediate product contains greater than 1.0, 1.5, 2, 5, 10, 15, 20, 25, or 30 weight percent mesophase pitch.

In some cases, the "flash zone" is simply a pressure drop valve without any removal of vapor. In this case, the two-phase flow will be fed to the second stage reactor. In other cases, a vapor/liquid separator may be used to remove the vapor, then only the liquid is sent to the second stage reactor. In plants operated with flash separators, overhead vapor from the first or flash vapor/liquid separators and vapor recovered from the second stage reactor effluent will be combined for use as fuel or other product recovery.

Recycling of heavy liquids will often be beneficial. When the conversion in the first stage reactor is relatively low, for example between 20 and 50 weight percent, it will generally be advantageous to recycle a portion of the first stage reactor effluent for mixing with the reactor feed. In the second reactor, where the conversion to the middle phase is low, for example, 35 to 60%, the heavy distillate from the second reactor can be recycled. Preferably all of the liquid recycle is to the first reactor, but in some cases it may be desirable to recycle the reactor 1 effluent to reactor 1 and the reactor 2 effluent to mix with the feed to the second reactor. Recycling may be necessary to improve the economics of the process, particularly when conversion per pass is relatively low.

It may be necessary to add steam or some other steam, preferably superheated steam, to the feed entering the second stage reactor. The presence of these vapors reduces the partial pressure, provides added thermal inertia, produces high velocities, and provides better dispersion of pitch droplets. Any vapor may be used, but we prefer a low molecular weight, condensable gas that is non-reactive and has very low solubility in the mesophase pitch. Steam is most preferred. The amount of steam, as a percentage of the weight of the liquid feed, may vary from 10 to 1000%, preferably from 150 to 400%, more preferably from 250 to 350%.

In some applications it will be advantageous to have two second stage reactors (in series) or a second stage and a third stage reactor. This allows the mesophase pitch leaving the second stage reactor to be "annealed" to a small CSTR, or even another tubular reactor, before or after light gas removal to provide additional residence time for "fine tuning" of the final mesophase pitch product. make it possible to supply

The pressure drop can be high across the second stage reactor. In our experiments and simulations, the outlet pressure is about 2.75 bar plus the downstream equipment pressure drop. If desired, it may be possible to draw a vacuum on the final vent gas to further reduce the outlet pressure. Recommended inlet pressures for the second reactor may range from 3.5 to 70 bar, preferably less than 35 bar, more preferably from 7 to 14 bar.

Suitable operating temperatures for both the first and second stage reactors may range from 400°C to 595°C, preferably from 425°C to 525°C and more preferably from 482°C to 510°C.

In our mesophase process, the gas phase is continuous and the liquid phase is discontinuous. At high specific flowrates in the tubular reactor forming the mesophase, the shear rate in the reactor is very high. Typically, the pressure drop in the 9.5 mm (3/8") reactor tube was 4 to 6 bar (60 to 90 psi). At these high shear rates, only small (< 20 micron) droplets are present. Multiphase In flow analysis, this flow region can be described as a mist annular: this relatively small spherical size combined with very turbulent flow (Reynolds number > 5 × 10 ⁵ ) results in a very fast mass between the liquid and vapor phases. and heat transfer.There may be some collision of these spheres with other spheres, resulting in fusion, but they quickly decompose back into smaller spheres as a result of high shear.Vapor fraction is greater than 99% by volume In most cases, volatilization of the lighter hydrocarbons and subsequent organization of the larger polycondensed aromatics into mesophases appears to occur in isolated globules.

When the second or mesophase formation process is coupled with the first stage or isotropic pitch formation process, significant advantages also arise. The heavy distillate by-products of the mesophase formation process are not suitable for recycling to the mesophase formation process because in most cases they will only evaporate and little conversion to the mesophase will be achieved. This heavy-distillate stream may be recycled as a feed to the isotropic pitch forming reactor, where a portion may be converted to isotropic pitch to be converted to mesophase pitch in the second stage of the process of the present invention. This additional conversion can be an important factor in having an economically viable process, especially when conversion per pass is low and maximum conversion is desired. Recycle of unconverted heavy aromatics liquids is generally counterproductive in the mesophase forming reactor, but recycling of these heavy liquids to the first reactor in a two stage process is very effective.

We prefer tubular reactors to continuously stirred tank reactors (CSTRs) because CSTRs are not efficient at converting isotropic pitch to mesophase pitch. A CSTR can be useful for adjusting the final mesophase content of a tubular mesophase forming reactor. A CSTR reactor to adjust the mesophase content and possibly other properties can be useful for quality control of the mesophase product.

The inventor's process methodology and results are surprising. We form an isotropic pitch in a first stage reactor, then produce a liquid mesophase pitch in a second stage reactor that is preferably 99 LV % vapor. We recover unconverted heavy aromatics from the mesophase forming reactor for recycling, but do not recycle to the mesophase forming reactor.

As noted in our related patent US 9,376,626, our mesophase pitch can be used to make carbon fibers, graphite fibers, carbon foam and the like using known conventional processes.

Claims (14)

As a two-step method for producing mesophase pitch from an aromatic compound liquid,
a. The feed is charged to a first stage reactor operated at thermal polymerization conditions comprising a temperature high enough to induce thermal polymerization and a pressure high enough to maintain at least a portion of the two and three ring aromatics in the liquid phase At least a portion of the two and three ring aromatics is prepared by converting at least 20% by weight of the two and three ring aromatics to an isotropic pitch and to light, usually gaseous hydrocarbons and discharging the first stage reactor effluent. thermally polymerizing an aromatics liquid feed comprising;
b. flash effluent by flashing the first stage reactor effluent to remove at least a majority of the light, typically gaseous, hydrocarbons in a flash zone having an absolute pressure of less than one-half the absolute pressure in the first stage thermal polymerization reactor. producing a water liquid stream;
c. The second stage reactor at mesophase forming conditions comprising a pressure of less than one-half the absolute pressure in the first stage reactor and a temperature to convert at least one-third by weight of the flash effluent liquid to mesophase pitch. forming mesophase pitch from the flash effluent liquid stream; and
d. recovering mesophase pitch as product from the second stage reactor. The method of claim 1 , wherein the first stage reactor is selected from the group of tubular reactors and continuously stirred tank reactors. The method of claim 1 , wherein the second stage reactor is selected from the group of tubular reactors and continuously stirred tank reactors. The method of claim 1 , wherein at least a portion of the flash effluent liquid is recovered as an isotropic pitch product. The method of claim 1 , wherein the pressure in the first stage reactor is between 15 bar and 350 bar. The method of claim 1 , wherein the pressure of the second stage reactor is less than 1/10 the pressure of the first stage reactor. The method of claim 1 , wherein the inlet pressure of the second stage reactor is between 3.5 and 70 bar. The process of claim 1 , wherein the pressure in the second stage reactor is sufficiently low to maintain at least a majority of the two and three ring aromatics by weight in the vapor phase. The process of claim 1 , wherein the pressure in the first stage reactor is high enough to maintain at least a majority of the two and three ring aromatics by weight in the liquid phase. The process of claim 1 , wherein conditions in the first stage reactor are sufficient to produce an isotropic pitch having a mesophase pitch of 1 to 20 weight percent. The method of claim 1 , wherein steam is added to the second stage reactor. 2. The method of claim 1 wherein sufficient steam is added to the second stage reactor, wherein the second stage reactor is a tubular reactor to maintain a vapor continuous dispersed liquid droplet flow in the second stage reactor. 13. The method of claim 12, wherein the second stage reactor exits into a cyclone separator. a. The feed is charged to a first stage reactor operated at thermal polymerization conditions comprising a temperature high enough to induce thermal polymerization and a pressure high enough to maintain at least a portion of the two and three ring aromatics in the liquid phase An aromatic compound comprising at least a portion of said two and three ring aromatic compounds by converting at least 20% by weight of said two and three ring aromatic compounds to isotropic pitch and to light, usually gaseous hydrocarbons and discharging the first stage reactor effluent; thermally polymerizing the liquid feed;
b. flash effluent by flashing the first stage reactor effluent to remove at least a majority of the light, typically gaseous, hydrocarbons in a flash zone having an absolute pressure of less than one-half the absolute pressure in the first stage thermal polymerization reactor. producing a water liquid stream;
c. The second stage reactor at mesophase forming conditions comprising a pressure of less than one-half the absolute pressure in the first stage reactor and a temperature to convert at least one-third by weight of the flash effluent liquid to mesophase pitch. forming mesophase pitch from the flash effluent liquid stream; and
d. recovering mesophase pitch from the second stage reactor as a product, converting the mesophase pitch to at least one of carbonized or graphitized fibers, froths, blocks, sheets or spheres by conventional processing of the mesophase pitch; recovering at least one of the graphitized or graphitized fibers, foams, blocks, sheets or spheres as a product of the process,
Carbonized or graphitized fibers, foams, blocks, sheets or spheres made from mesophase pitch.

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