Patent Application
20120230882
The system and process of the present technology relate to alkylation of isobutane with olefin to make alkylate for gasoline blending, and more particularly to alkylation of isobutane with olefin utilizing a slurry reactor.
In alkylation of isobutane with olefin to make alkylate for gasoline blending, the stability of the catalyst and the quality of the alkylate product are strongly influenced by the local olefin concentration at the catalytic site. A very high ratio of paraffin, such as isobutane (iC4), to olefin, such as butene, is desirable to ensure that hydride transfer of a once-alkylated intermediate to release iso-octane from the catalytic surface occurs preferentially to alkylation with a second olefin. The latter reaction tends to result in the formation of heavier olefinic species that are difficult to remove from the surface of the catalyst, and eventually results in deactivation of the catalyst.
Existing commercial alkylation processes, such as Sulfuric Acid or HF alkylation, tend to operate at a ratio of reboiled isobutane to olefin feed (i/o) of from about 6:1 to about 12:1. One of the limiting factors is the cost of separating the excess isobutane from the alkylate product, which includes costs associated with both the size of the isostripper and the utility requirements to reboil the isobutane overhead. Thus, economic considerations normally limit the amount of reboiled isobutane that is available for olefin dilution. For effective solid catalyst alkylation, a local i/o ratio in excess of 100:1 and preferably in excess of 200:1 to 500:1 is desirable to provide sufficient catalyst stability for an economic operation. To get from an i/o ratio of from about 6:1 to about 12:1 to a more desired i/o ratio, existing alkylation technologies tend to use a combination of reactor effluent recycle and/or multiple reactor stages with separate olefin injection into each stage.
The system and process of the present technology relate to alkylation of isobutane with butenes utilizing a slurry reactor in which olefin is injected in a gas stream with gas diluent.
In one aspect, an alkylation system for alkylation of isobutane with olefin to make alkylate for gasoline blending is provided that includes a slurry reactor, a slurry vessel, a catalyst source, and an isostripper. The slurry reactor receives a reactor feed slurry including catalyst and liquid isobutane, an olefin feed that is in a vapor phase or vaporizes upon being injected into the slurry reactor, and a circulating reactor vapor stream. The circulating reactor vapor stream combines with the olefin in the reactor to form a combined reaction vapor. An alkylation reaction occurs in the reactor when the combined reaction vapor contacts the reactor feed slurry, and a reactor liquid effluent stream is produced. The reactor liquid effluent stream includes catalyst, isobutane, and a liquid alkylate product. The slurry vessel provides the reactor feed slurry to the slurry reactor. The catalyst source provides catalyst to the slurry vessel, and the isostripper provides a liquid isobutane feed stream to the slurry vessel.
In another aspect, an alkylation process for alkylation of isobutane with olefin to make alkylate for gasoline blending is provided. The method includes providing a slurry reactor, providing the reactor feed slurry to the slurry reactor from a slurry vessel, providing catalyst to the slurry vessel from a catalyst source, and providing a liquid isobutane feed stream to the slurry vessel from an isostripper. The slurry reactor receives a reactor feed slurry including catalyst and liquid isobutane, an olefin feed that is in a vapor phase or vaporizes upon being injected into the slurry reactor, and a circulating reactor vapor stream. The circulating reactor vapor stream combines with the olefin in the reactor to form a combined reaction vapor. An alkylation reaction occurs in the reactor when the combined reaction vapor contacts the reactor feed slurry, and a reactor liquid effluent stream is produced.
Specific examples have been chosen for purposes of illustration and description, and are shown in the accompanying drawings, forming a part of the specification.
The systems and processes disclosed herein conduct alkylation of isobutane with olefin, such as butene, utilizing a slurry reactor. The i/o ratio can be regulated and controlled during the alkylation reaction by supplying olefin at a rate that is less than the rate of reaction. In this manner the olefin concentration can remain depleted at the active sites of the catalyst. In the systems and processes disclosed herein, the olefin feed is in a vapor phase in the slurry reactor. The olefin can be injected into the reactor in a vapor stream, or can be injected into the slurry reactor as a liquid that vaporizes upon being injected into the slurry reactor. The olefin concentration can be controlled by diffusion resistance provided by an induced gas-liquid interface in the reactor. The olefin can be supplied in a manner that controls the diffusion of olefin into the liquid phase based upon the gas phase olefin concentration, bubble size and interfacial area.
It has been found experimentally that a physical diffusion barrier that provides diffusion resistance, and thus a reduction of olefin concentration at the active site of the catalyst, can occur indirectly during catalyst deactivation. An individual catalyst pellet deactivates from the outside to the inside in a “shrinking active core” mode. The deactivated outer layer provides a physical diffusion barrier that slows down the diffusion of olefin to the remaining active interior sites. The physical diffusion barrier helps to keep a lower olefin concentration at the interior sites and those interior sites deactivate less rapidly. Without being bound by any particular theory, it is believed that this phenomenon contributes to the observation that larger catalyst particles, while initially less active than small particles, experience a slower rate of deactivation and have a longer useful life before regeneration becomes necessary.
When such a physical diffusion barrier is allowed to happen naturally by deactivation of the outer catalyst layer, a portion of the catalyst becomes sacrificial, and feed must pass over already deactivated catalyst which tends to result in additional non-beneficial oligomerization. The overall reaction rate tends to become constrained by the diffusion rate because the physical diffusion barrier reduces both the rates of olefin diffusion into the catalyst and the diffusion of alkylate product out of the catalyst. More catalyst volume is ultimately needed to accomplish the same amount of reaction. Additionally, reduction of the diffusion of alkylate product out of the catalyst can result in increased cracking to lights and isomerization to lower TMP/DMH ratio. In contrast, diffusion resistance provided by the induced gas-liquid interface in the reactors of the present systems and processes results in control and limitation of the olefin diffusion rate to the catalyst, but the diffusion of alkylate from the catalyst to the bulk liquid is not affected.
One example of an alkylation system 100 utilizing a slurry reactor is illustrated in
As illustrated in
In the example illustrated in
Referring back to
An olefin feed stream 118 can be provided to the slurry reactor 102. Olefin feed stream 118 can include any suitable olefins, such as butene. Olefin feed stream 118 can also contain saturates such as isobutane (iC4) and n-butane (nC4), and limited amounts of propane (C3) or isopentane (iC5). The olefin feed stream 118 can include olefins and saturates in an amount sufficient to supply the stoichiometric isobutane needed for alkylation. Olefin feed stream 118 can be divided into a plurality of olefin injection streams 130. The olefin injection streams 130 can be injected into the space between the plurality of distillation trays 200 through a plurality of distributors 202.
The olefin feed stream 118 can be a liquid or a vapor when it is injected into the slurry reactor 102. For example, the olefin feed stream 118 can be a liquid feed stream, and spray nozzles can be utilized on the distributors 202 to introduce the olefin feed as a fine liquid spray that vaporizes in the slurry reactor 102. This example can utilize excess heat of reaction to vaporize the olefin feed, and can reduce the amount of heat utilized to vaporize the olefin external to the slurry reactor 102. In another example, as illustrated in
Referring back to
The combined reaction vapor bubbles up through the first distillation tray 200, which is located above the distributor 202 through which the vapor olefin ejection stream 130 was ejected into the slurry reactor 102, where it comes in contact with the reactor slurry on the first distillation tray 200. An alkylation reaction occurs on the first distillation tray 200 wherein olefin from the combined reaction vapor diffuses into the reactor slurry, reacts with the liquid isobutane in the presence of the catalyst, and produces a liquid phase alkylate product. In order to promote the alkylation reaction, the slurry reactor 102 can operate at a reaction temperature of from about 40 to 120° C. and preferably from about 60° C. to about 80° C. The slurry reactor can also operate at a bubble point pressure corresponding to such a reaction temperature, which can be at about 160 psig.
The rate of diffusion of the olefin out of the combined reaction vapor into the reactor slurry can be maintained at a desired rate that can be lower, and is preferably only slightly lower, than the rate of olefin reaction during alkylation. Maintaining the desired rate of olefin diffusion can be accomplished by controlling the interfacial area between the combined reaction vapor and reactor slurry based on bubble size, gas rate, and tray geometry. Without being bound by any particular theory, it is believed that the olefin concentration in the reactor slurry at the catalyst surface can be maintained at a level low enough to minimize deactivating oligomerization reactions.
The liquid alkylate product is carried downward through the slurry reactor 102 with the downward flowing reactor slurry, forming a reactor liquid that contains both the reactor slurry and the liquid alkylate product. The concentration of liquid alkylate product in the reactor liquid increases on each successive tray downwardly through the slurry reactor 102, and reaches a maximum value at the bottom of the slurry reactor 102. In one example, the amount of reactor slurry 114 provided to the slurry reactor 102 is sufficient to provide an amount of reactor slurry 114 in the reactor liquid at the bottom of the slurry reactor 102 that will prevent the maximum concentration of liquid alkylate product in the reactor liquid at the bottom of the reactor from building up to more than a threshold value. The threshold value of liquid alkylate product in the reactor liquid at the bottom of the reactor can be the amount of liquid alkylate product to which the catalyst can be exposed during the alkylation reaction before alkylate selectivity to undesirable C9+ products begins to hurt product quality and result in rapid catalyst deactivation. For example, when the catalyst is a Y type zeolite catalyst, the threshold value of liquid alkylate product can be about 15% by weight of the reactor liquid. In examples with some other types of catalyst, the threshold value of alkylate product can be up to about 25% by weight to about 30% by weight of the reactor liquid.
The slurry reactor 102 can also include one or more inter-cooling loops 204, which can remove heat of alkylation reaction from the slurry reactor 102 by removing reactor liquid from the slurry reactor, cooling it, and returning it to the slurry reactor 102. An inter-cooling loop 204 can include a draw-off tray 206, at least one pump 208, and at least one cooler 210. The draw-off tray 206 is located within the slurry reactor 102, and collects reactor liquid as it flows downwardly through the slurry reactor 102. The draw-off tray 206 can be sloped, which can direct collected reactor liquid to an outlet where a draw-off stream 212 can be removed from the slurry reactor 102. The at least one pump 208 can pass the draw-off stream 212 to the at least one cooler 210 to form a cooled draw-off stream 214. The cooled draw-off stream 214 can be injected back into the slurry reactor 102 through a draw-off stream distributor 216. The draw-off stream distributor 216 can be located in the slurry reactor 102 below the draw-off tray 206. Alternatively, cooling for the slurry reactor can also be supplied by other suitable means, such as, for example, a stabbed in heat exchanger.
As the reactor liquid flows downwardly to the bottom of the slurry reactor 102, the gases within the slurry reactor 102 flow upwardly to the top of the slurry reactor 102. A reactor vapor stream 132 can be removed from the top of the slurry reactor 102. Prior to being removed from the top of the slurry reactor 102, the reactor vapor stream 132 can pass through a finishing tray 218, in order to facilitate complete conversion of the vapor olefin injections streams 130. The reactor vapor stream 132 can also pass through a wash section 220 at the top of the slurry reactor 102, which can remove any entrained solids. Wash section 220 can be a disk-and-donut style wash section. Solids entrained in the reactor vapor stream 132 can be washed out of the gas in the wash section 220 by a recirculating stream of isobutane 222, and can be returned to the reactor in a solids return stream 224. An additive isobutane stream 226 can also be added to the recirculating stream of isobutane 222 from the isostripper 106. The reactor vapor stream 132 can be recycled to the bottom of the slurry reactor 102. For example, the reactor vapor stream can be provided to the bottom of the slurry reactor through a compressor 134.
The volume and pressure of the circulating reactor vapor stream 132 can be regulated by separating an excess portion 136 from the circulating reactor vapor stream 132, condensing the excess portion 136 in a condenser 138 to form a condensate to a receiver 140. A hot vapor bypass 142 an also be provided to maintain an interface in the receiver 140. A condensate stream 144 can be provided from the receiver 140, combined with the reactor slurry 114, and returned to the slurry reactor 102.
Alkylation system 100 can also provide for separating the catalyst in the reactor liquid from the liquid alkylate product, and regenerating the catalyst before the catalyst is reintroduced to the slurry reactor 102 in reactor slurry 114. The reactor liquid can be removed from the bottom of the slurry reactor 102 in a reactor liquid effluent stream 146. The reactor liquid effluent stream 146 can contain solid catalyst, liquid alkylate product, and isobutane. The reactor liquid effluent stream 146 can be provided to a at least one first stage liquid solid separation device. As shown in the illustrated embodiment, the at least one first stage liquid solid separation device can be hydroclone 148. It should be noted that any of the hydroclones disclosed herein with respect to the illustrated example could be replaced with other liquid solid separation devices if desired.
In an alternative example, a cold regeneration section (not shown) can be included between the slurry reactor 102 and the at least one first stage hydroclone 148, which can reduce the amount of solids load on the catalyst regenerator 104, which can be a hot catalyst regenerator. The cold regeneration section can be a liquid phase regenerator using hydrogen-saturated isobutane. In this alternative example, a smaller slipstream of catalyst could be sent to the catalyst regenerator 104. Such an example can reduce the energy requirements for heating and cooling of the catalyst between the alkylation reaction temperature, which can be from about 60° C. to about 80° C., to the hot regeneration temperature, which can be from about 250° C. to about 400° C., and could also reduce the heat of vaporization of residual liquid left in the catalyst pores after the hydroclone separation. However, there would likely be an increased usage of isobutane for both the cold regeneration and a flush to remove residual hydrogen.
Referring back to
The at least one first stage hydroclone 148 can separate the solid catalyst from the liquid alkylate product and isobutane in the reactor liquid effluent stream 146. As illustrated in
As illustrated in
A washed concentrated solids stream 162 can be provided from the at least one second stage hydroclone 158 to catalyst regenerator 104 through a slide-valve 164. Catalyst regenerator can be a fluidized bed regenerator. The washed concentrated solids stream 162 can contain isobutane, which can be desorbed from the pores of the catalyst in catalyst regenerator 104 to regenerate the catalyst. In the catalyst regenerator 104, the catalyst can be kept fluidized by a stream of regeneration gas 168, which can be hydrogen. In one example, the catalyst regenerator 104 can provide for a 30 minute catalyst residence time in the catalyst regenerator 104, and can operate at a temperature of about 400° C. and a pressure of about 200 psig.
Regenerator gas effluent stream 172 can pass through one or more cyclones 170 to remove entrained catalyst fines, and can exit the catalyst regenerator 104. Heat can be recovered from the regenerator gas effluent stream 172 by heat exchange of the regenerator gas effluent stream 172 with a recycle gas 174 and makeup hydrogen 176 in a regenerator gas heat exchanger 178. For example, the regenerator gas effluent stream 172 can pass downward through a tube side of the regenerator gas heat exchanger 178, and can be passed to a barrier filter 180 that can remove catalyst fines. The catalyst fines can be periodically removed from the barrier filter 180 in a dry fines stream 184 by using a small hydrogen blowback stream 182.
A filtered regenerator gas stream 186 can be removed from the barrier filter 180, and can be cooled in an isostripper auxiliary reboiler 188 and an air-trim cooler 190. Cooling the filtered regenerator gas stream 186 can cause condensation of heavier hydrocarbons that may be desorbed or cracked off the catalyst during catalyst regeneration, such as C5+ hydrocarbons. The condensed heavier hydrocarbons can be removed in a knock out (KO) drum 192, and a condensed heavier hydrocarbon stream 194 can be provided to a Butamer section stabilizer 196, along with a reactor effluent stream 244 from a Butamer section reactor 242, in a Butamer section stabilizer feed stream 246. A Butamer section stabilizer overhead stream 248 can contain C3− that can be utilized for fuel gas. A Butamer section stabilizer bottoms stream 250 can be returned to the isostripper 106. Alternatively, a portion of the Butamer section stabilizer bottoms stream 250 can be provided to the reactor effluent hydroclones 148 to function as wash liquid and reactor effluent filtration backwash liquid to 154, which can reduce isostripper reboiled i/o, as well as the associated capital and utility costs of the isostripper 106.
The gas stream from the KO drum 192 can be used as recycle gas 174. A compressor 198 can be used to provide the recycle gas 174 to the regenerator gas heat exchanger 178. The recycle gas 174 can be further provided from the regenerator gas heat exchanger 178 to a furnace 228 to be heated to regeneration conditions prior to being provided to the catalyst regenerator as regeneration gas stream 168.
Referring back to the catalyst regenerator 104, dried regenerated catalyst can flow from the catalyst regenerator 104 to a catalyst stripper 230. In catalyst stripper 230, a stripping stream 232 of isobutane can strip hydrogen out of the pores of the catalyst, so that it is not carried back to the reactor section where hydrogen could potentially saturate the olefin feed, leading to yield loss. The regenerated catalyst can then be passed to the catalyst cooler 234, where heat can be recovered from the regenerated catalyst by exchange with the olefin feed stream 116. Cooled regenerated catalyst can then be provided to the slurry vessel 110, and can be provided back to the slurry reactor 102 in reactor slurry 114. Flow of the catalyst from the catalyst cooler 234 to the slurry vessel 110 can be regulated by a side valve 236, which sets the overall catalyst circulation rate.
As discussed above, in the illustrated example, the olefin feed stream 116 can contain olefins and saturates such as iC4 and nC4 in an amount sufficient to supply the stoichiometric isobutane needs for alkylation. In an alternative example, a saturate feed stream can be provided separate from the olefin feed stream 116. In such an example, a saturate feed stream can be provided to the isostripper 106. The saturate feed stream can be up to about 10% by weight of the total reboiled isobutane removed from the isostripper 106 in isostripper overhead stream 238. To keep n-butane from building up in the isobutane loop, a separate n-butane draw 234 can be taken from the isostripper 106. The n-butane draw 234 can optionally be sent to the Butamer section reactor 242 where the normal butane can be isomerized to an equilibrium mixture of iC4 and nC4.
As further illustrated in
From the foregoing, it will be appreciated that although specific examples have been described herein for purposes of illustration, various modifications may be made without deviating from the spirit or scope of this disclosure. It is therefore intended that the foregoing detailed description be regarded as illustrative rather than limiting, and that it be understood that it is the following claims, including all equivalents, that are intended to particularly point out and distinctly claim the claimed subject matter.
This application is a Division of co-pending application Ser. No. 12/554,044 filed on Sep. 4, 2009, the contents of which are hereby incorporated by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 12554044 | Sep 2009 | US |
| Child | 13480626 | US |
