Patent Application
20110076207
This invention relates to a procedure for monitoring the condition of a catalytic guard bed used in an adiabatic reactor mode to thereby protect a primary reaction catalyst. Application of the present invention may include a guard bed used prior to the heterogeneous catalyzed esterification of free fatty acids with low molecular weight monohydric alcohols, such as methanol, to produce fatty acid alkyl esters for biodiesel production.
Wide interest in renewable resources to replace petroleum-based transportation fuels led to a rapid increase in the production and number of producers of biodiesel. It is known that fatty acid alkyl esters may be used as a fuel for diesel engines. One method for the production of biodiesel utilizes oils having elevated levels of free fatty acid (FFA), which are less expensive than higher quality oil feeds. Such oils may be the result of degraded vegetable oils as well as mixtures of vegetable oil with animal fats. Sources of such typical oils are, for example, yellow grease which may contain up to 20% by weight FFA and brown grease that can contain even higher levels of FFA. Both have been considered as low cost feed oils for biodiesel production. Further examples of high FFA containing oils include pork and chicken fat, beef tallow, and lower purity vegetable oils. Such oils, however, are known to cause considerable operating problems in biodiesel transesterification reactors when used untreated including significant yield losses. High FFA containing feed oils can contain much higher levels of FFA (typically 5%-20%) and soaps than are contained in fresh refined, degummed and bleached vegetable based oils (RDB oils). They also generally contain varying amounts of phospholipids and other (in)organic contaminates and solids. By comparison RBD oils are clean, low in FFA content (generally about 0.5%), and suitable for direct introduction to a base-catalyzed transesterification process designed to produce biodiesel without expectation of major side reactions. However, with appropriate pretreatment, high FFA containing oils can also be used to efficiently produce biodiesel as well.
One process for pre-treating low cost, high FFA containing biodiesel feedstock utilizes a resin-based solid phase catalyst, such as Lewatit® GF-101 available from LANXESS Deutschland GmbH. This process is described in U.S. Pat. No. 4,698,186, which is hereby incorporated by reference. Lewatit® GF-101 is a strongly acidic, macroporous, polymer-based resin catalyst with sulfonic acid groups suited for esterification reactions. The heterogeneous catalyst can be used in a fixed bed mode and upon contact with a high FFA containing oil in the presence of a monohydric alcohol, such as methanol, sufficient FFA is converted to fatty acid alkyl esters so as to eliminate the negative effects of the high levels of FFA in the biodiesel transesterification reactor. The solid phase catalyst, however, is sensitive to poisons and contaminants that may be contained in low cost, high FFA biodiesel feedstock. Such contaminants and poisons include, for example, cations associated with saponified FFA soaps, which can exchange ions with the acidic catalyst sites of the resin, thereby deactivating the catalyst, along with various organic and inorganic materials including phospholipids which can be present as gummy material that blind the catalyst and reduces its activity.
A high FFA containing oil feedstock may be processed through a polishing step prior to FFA esterification with the use of a guard bed to remove trace residual soap, phospholipids and other fouling agents that would otherwise deactivate the solid phase catalyst. Broadly, such a guard bed may comprise sacrificial solid phase strongly acidic resin of the same or different type as the esterification catalyst that sorbs materials that would otherwise deactivate the primary esterification catalyst. As such, the guard bed can be placed upstream of the main reactor as depicted in
Once the protective capacity of the guard bed is exhausted, the poisons and contaminants of the feedstock will flow into the main esterification reaction vessel and begin to deactivate the catalyst of the main reactor. Thus, upon exhaustion, the guard bed esterification catalyst material must be replaced or regenerated. Regeneration of the guard bed may include backwashing to remove solids and acid washing to drive cations from the bed and replace them with hydrogen ions.
Surprisingly, it has now been found that where a guard bed reactor, employing guard bed esterification catalyst, is used to protect high value esterification catalyst in a primary chemical reactor (e.g., FFA esterification) via the guard bed esterification catalyst's ability to reduce and/or eliminate poisons and containments from entering the primary esterification reactor vessel housing the high value esterification catalyst, a monitoring system can be utilized to monitor the guard bed esterification catalyst's kinetic performance so as to determine the protective capacity of the guard bed reactor for eliminating poisons and contaminants from the primary esterification reactor and thereby allow for the further useful and protected employment of the primary esterification catalyst.
In such a monitoring process, the guard bed reactor vessel can be converted to a smaller version of the primary reactor vessel. Thereafter by directing the full or partial flow of reactants (e.g., high FFA oil feedstock and monohydric alcohol) to this guard bed reaction vessel, while being operated adiabatically under designated conditions of temperature and pressure, the guard bed reactor will act as a highly responsive version of the primary esterification reactor. Any loss of catalytic activity or accumulation of solid materials by the guard bed esterification catalyst will result in changes in temperature and pressure across the guard bed reaction vessel. For example, the observation of an increase in deferential pressure across the guard bed reactor is indicative of contaminant solids build up and catalyst blinding. In addition, a reduction in differential temperature across the guard bed reactor would be indicative of catalyst poisoning and/or blinding.
In a preferred embodiment of the invention there is disclosed an apparatus for protecting a primary esterification catalyst, comprising: a) a guard bed reaction vessel having a first inlet, a first outlet, an first interior region, and a guard bed esterification catalyst, wherein said guard bed esterification catalyst is disposed within said first interior region between said first inlet and said first outlet so as to thereby enable a first fluid stream comprising FFA and catalyst-contaminants to enter the guard bed reaction vessel through said first inlet, contact the guard bed esterification catalyst, thereby forming an effluent stream, and allowing said effluent stream to exit the guard bed reaction vessel via the first outlet; b) a primary reaction vessel having a second inlet, a second outlet, a second interior region, and the primary esterification catalyst, wherein said primary esterification catalyst is disposed within said second interior region between said second inlet and said second outlet so as to thereby enable the effluent stream to enter the primary reaction vessel through said second inlet, contact the primary esterification catalyst, thereby forming a final stream and allowing said final stream to exit the primary reaction vessel via the second outlet; c) a reactor preheater for heating the first fluid stream; d) a conduit, interposed between the reactor preheater, the guard bed reaction vessel, and the primary reaction vessel, thereby allowing the flow of a fluid between them; e) a guard bed temperature monitor connected to the guard bed reaction vessel for measuring the temperature differential across a portion of the guard bed; and f) a guard bed pressure monitor connected to the guard bed reaction vessel for measuring the pressure differential across a portion of the guard bed. In a further embodiment, said primary esterification catalyst is a solid phase strongly acidic resin-based catalyst that may be macroporous. In a further embodiment, a solid phase strongly acidic resin-based catalyst comprises a sulfonated styrene-divinylbenzene based polymeric resin.
In another embodiment of the invention there is disclosed a process for protecting a primary esterification catalyst in which an apparatus for protecting a primary esterification catalyst in accord with that described above is used to heat a first fluid stream prior to its introduction into the guard bed reaction vessel and in which the temperature differential across a portion of the guard bed esterification catalyst is measured with or without the measuring of the pressure differential across all and/or a portion of the guard bed esterification catalyst. In a further embodiment the primary esterification catalyst used in the disclosed process is a solid phase strongly acidic resin-based catalyst that may be microporous and may include the use of a sulfonated styrene-divinylbenzene based polymeric resin. For a better understanding of the present invention, together with other and further features and advantages thereof, reference is made to the following description, taken in conjunction with the accompanying drawings, and the scope of the invention will be pointed out in the appended claims.
Although the instant description pertains to the esterification reaction of free fatty acids (FFA) with alcohol to thereby form fatty acid alkyl esters (FAME), the present invention can be extended to other variations of esterification reactions, as well as other chemical reactions having both positive and negative heats of reaction. The following description pertains to a process of treating a triglyceride containing oil having appreciable levels of free fatty acids in an esterification reactor whereby FFA is reacted with methanol to form fatty acid methyl esters. Such an esterification reaction can be conducted in the presence of a solid sulfonic acid resin catalyst, however, it should be appreciated that the esterification reaction is applicable to other heterogeneous catalysts such as, for example, immobilized enzymes and solid phase organo-metallic esterification catalysts, such as, for example, tin impregnated resins.
The esterification reaction combines an organic acid, such as a free fatty acid, with an alcoholic compound, such as methanol or ethanol, to form an ester compound and a byproduct, such as water as shown by the following reaction:
R1—COOH+R2—OH→R1—CO—OR2+H2O (1),
where R1 is straight chain or branched, saturated or unsaturated, substituted or unsubstitued, acyclic, C4-C28 alkyl; and R2 is an aliphatic hydrocarbon. R1 may include synthetic and naturally occurring free fatty acids, for example R1 may include those fatty acids naturally occurring in animal and vegetable fats, the latter of which may include coconut oil, palm oil, cottonseed oil, wheat germ oil, soya oil, olive oil, corn oil, sunflower oil, safflower oil, hemp oil, rapeseed oil, canola oil, and/or palm oil. R2 may include C1-C4 alkyl, including methyl and ethyl groups. Furthermore, one skilled in the art will recognize that R1 and R2 can represent a myriad of chemical compounds that would fit within the concept of an esterification reaction.
For commercial purposes, the esterification reaction of FFA is too slow without the aid of high temperature and catalysts. The use of acid catalysts to increase the reaction rate of esterification reactions is well documented. As shown in
In the typical reactor system of
The problems described above for the typical system as shown in
Further, to monitor the filtering capacity of the guard bed, differential pressure across the guard bed reaction vessel RCTR 01 can also be measured. As long as the flow rate of the fluid flowing into the guard bed reaction vessel RCTR 01 and temperature either into or out of the guard bed reaction vessel RCTR 01 are controlled, any increase in the differential pressure measured across the guard bed material and/or the guard bed reaction vessel RCTR 01 will be indicative of pluggage and/or degradation of the contents of the guard bed esterification catalyst material.
As shown in
As shown in
Prior to the introduction of the first fluid stream into the guard bed reaction vessel RCTR 01, as shown in
Housed within the guard bed reaction vessel RCTR 01 is the guard bed esterification catalyst. As discussed infra, the guard bed esterification catalyst in the preferred embodiment is a strongly acidic, polymeric resin being in a substantially spherical bead form and having sulfonic acid groups as part thereof. For example such a polymeric resin may be based on a sulfonated styrene-divinylbenzene bead polymer. Furthermore, the strongly acidic resins of the present invention can have a gel-type or macroporous structure and are preferably monodispersed.
The entry of the first fluid into the guard bed reaction vessel RCTR 01 allows for contact to occur between the guard bed esterification catalyst and the first fluid stream and, moreover, between the guard bed esterification catalyst and the FFA and other contaminants of the first fluid stream. In turn the catalyzed esterification reaction of the FFA occurs whereby FAME is produced. As more fully discussed supra, both the differential pressure and differential temperature is monitored to thereby determine the exhaustion of the guard bed esterification catalyst as indicated by the decrease in differential temperature and/or increase in differential pressure. It should be understood, however, that without the use of temperature indicator and controller TIC 01, the measurements of the deferential temperature and pressure across the entire guard bed reaction vessel and/or a portion thereof could not be performed with sufficient accuracy necessary to monitor the state of exhaustion and blinding of the guard bed esterification catalyst, since the reaction rate of the FAA esterification reaction is well known to be dependent upon temperature and, to a lesser degree, pressure.
The FFA esterification reaction produces an effluent in which a portion of the FAA has been reacted to produce FAME, but more importantly, an effluent stream in which containments harmful to the primary esterification catalyst have been entirely or substantially removed from the stream. This purified effluent stream then flows from a first outlet of the guard bed reaction vessel RCTR 01 to the primary esterification reaction vessel RCTR 02 via an inlet thereto. The effluent stream is then allowed to contact the primary esterification catalyst so as to enable the reaction of the remaining FFA to FAME.
As is known to the skilled artisan, appropriate conduit can be used to enable the transfer of the fluid, gas, and/or steam streams between pumps, vessels, storage tanks, and other components of the system.
As shown in
Unlike the embodiment of
As the activity of the guard bed esterification catalyst decreases due to catalyst deactivation, the extent of reaction across the guard bed reaction vessel will decrease with a corresponding decrease in the differential temperature. In this embodiment, the first indication of the loss of activity will be a rise in temperature of the guard bed reaction vessel outlet. The temperature controller regulating the guard bed outlet temperature will respond by reducing heat input to the reactor preheater HX01 thereby decreasing the inlet temperature of the first fluid stream to the guard bed reaction vessel RCTR 01; thereby, maintaining the desired guard bed reaction vessel outlet temperature of the effluent stream. The result of this control action will be indicated by reduced differential temperature sensed by differential temperature indicator dT01. Differential pressure may be monitored as well according to the manner provided in the embodiment of
It should be understood that appropriate conduit can be used to enable the transfer of the fluid, gas, and/or steam streams between pumps, vessels, storage tanks, and other components of the system.
It should also be appreciated that more than one guard bed could be employed (not shown). For example, it may be preferable to employee two guard beds having the same or different catalyst material. Upon the exhaustion of the first guard bed, the high FFA containing feed stream could be transitioned to the second guard bed. This would allow for the replacement or regeneration of the first guard bed catalyst material without interruption to the overall reactive processing.
The catalyst material, for use as the guard bed esterification catalyst and/or primary esterification reaction catalyst, in at least one embodiment comprises a strongly acidic, polymeric resin being in a substantially spherical bead form and having sulfonic acid groups as part thereof, for example, such a polymeric resin may be based on a sulfonated styrene-divinylbenzene bead polymer. The strongly acidic resins can have a gel-type or macroporous structure and can be monodispersed. The formation of such resins according to the present invention is generally known. Monodispersed as used herein means a polymeric bead resin in which at least 90 vol. or wt. % of the particles have a diameter which lies in the interval around the most frequent diameter with width of +10% of the most frequent diameter. For example, a polymeric bead resin with most frequent bead diameter of 0.5 mm, at least 90 vol. or wt. % lie in a size interval between 0.45 mm and 0.55 mm; for a substance with most frequent diameter of 0.7 mm, at least 90 vol. or wt. % lie in a size interval between 0.77 mm and 0.63 mm.
A monodispersed bead polymerizate required for the production of monodispersed polymeric bead resin can be produced according to the methods known from the literature. For example, such methods and the monodispersed polymeric bead resins made from them are described in U.S. Pat. No. 4,444,961, U.S. Pat. No. 4,419,245, whose contents are fully incorporated by reference. According to the invention, monodispersed bead polymerizates and the monodispersed polymeric bead resins prepared may be obtained by jetting or seed/feed processes.
The terms microporous, macroporous or gel-like have already been described fully in the technical literature related to polymeric bead resins. Preferably the polymeric bead resin according to at least one embodiment of the invention has a macroporous structure. The formation of macroporous bead polymerizates for the production of macroporous polymeric bead resins can take place, for example, by adding inert materials (pore-forming agents) to the monomer mixture during the polymerization. Suitable as such pore-forming agents are, for example, organic substances that dissolve in the monomer, dissolve or swell the polymerizate slightly (precipitating agents for polymers), such as aliphatic hydrocarbons.
As provided above, the use of a strongly acidic, sulfonated, monodisperse, macroporous, styrene-divinylbenzene bead polymer is contemplated as the FFA esterification catalyst of the invention. An example of such a polymer bead resin is Lewatit® GF-101 commercially available from LANXESS Deutschland GmbH.
Illustrative of a preferred embodiment of the present invention, reference is hereby made to Table 1. The data used to generate Table 1 was developed from computer models created with the Aspen Plus steady state simulation software available from AspenTech. The NRTL property system within Aspen Plus was utilized to generate physical and thermodynamic properties.
As provided in Table 1 there is shown an example of how the relative capacity of the guard bed catalyst can be monitored directly from the relative differential temperature measured across the guard bed reaction vessel. Four cases of various FFA content of the feed are provided in the first column (Feed FFA in): 25%, 50%, 75% and 100%, respectively. For each of these concentrations, five levels of catalyst activity are selected and listed in the second column (Guard Bed RCTR01 Relative Capacity): 100%, 75%, 50%, 25%, and 0%. The next four columns pertain to the guard bed operation (inlet temperature (T in), inlet FFA flow rate (FFA in), outlet temperature (T out) and outlet FFA flow rate (FFA out)) and are determined from material and energy balance calculations utilizing a Langmuir-Hinschelwood kinetic model of the guard bed performance. The seventh column designated Conv % is the relative conversion of FFA as the process stream flows across the guard bed catalyst and can be calculated by dividing the change in FFA (FFA in minus FFA out) by the amount of FFA entering the guard bed. The eighth column, differential temperature designated δT, is the temperature difference across the bed (T in minus T out). The final column is the relative differential temperature calculated by dividing δT by the inlet temperature (T in). This information is depicted graphically in
Although the preferred embodiment of the present invention has been described herein with reference to the accompanying drawings and examples, it is to be understood that the invention is not limited to that precise embodiment or examples, and that various other changes and modifications may be affected therein by one skilled in the art without departing from the scope or spirit of the invention.
