Patent Application
20090198088
The present invention relates generally to a process for purifying crude glycerin, such as that formed as a by-product of biofuels production, as well as to the product of such a process. The process broadly includes the purification of crude glycerin by ion exclusion chromatography, fractionation, and one or more dewatering steps utilizing moderate temperatures and pressures.
In the search for secure sources of transportation fuels, much effort has been directed towards bioethanol and biodiesel. These agriculturally based fuels lessen the dependence on petroleum from foreign sources and have been embraced worldwide. In the production of these biofuels, organic by-products such as crude glycerin are produced. This by-product must be either disposed of or used for other purposes. The magnitude of the volume of crude glycerin produced as a result of biodiesel production makes disposal undesirable and ultimately uneconomical. Crude glycerin from agricultural sources will contain pure glycerol, the valued component in the solution/mixture, water, low boiling organic compounds, non-volatile salts and low volatility organic compounds. There are several well documented uses of refined glycerin as a replacement for petrochemicals but in general, the glycerin quality must be upgraded to remove contaminants.
The traditional method of upgrading crude glycerin involves evaporating glycerol from non-volatile inorganic salts in one or multiple stages then further evaporating the de-ashed glycerin solution from other higher boiling organics. (The terminology for these other organics is MONG—matter, organic, non-glycerin.) The traditional process to purify crude glycerin starts with the evaporation of lower boiling contaminants such as methanol and water. This is a relatively simple unit operation that involves heating the crude glycerin above the atmospheric boiling points of methanol and water (100° C. and 65° C., respectively) and reducing pressure. Moderate heat to supply heat of vaporization is used.
After low boiling volatile contaminants are removed, the remaining glycerin solution can be evaporated so as to reduce non-volatile inorganic salts in a wiped film evaporator. At atmospheric pressure, pure glycerol boils at 290° C. To initiate boiling, a heat source of at least 300° C., such as very high pressure steam or recirculation hot oil, is required. To reduce the high temperature required to boil the glycerin solution, vacuum is applied to lower the boiling point. At 40 mmHg absolute pressure, the boiling point of pure glycerol is 198° C. and high pressure steam, or hot oil, is still required. Because of the solution colligative property of boiling point elevation caused by the salt contaminants in the glycerin solution, the boiling point of glycerol will be higher than the temperatures stated above. To maintain reasonable heat transfer and to remove accumulated salt solids, a wiped film evaporator is required. The wet salt solids are mechanically wiped from the heat transfer surface and directed out a rotating lock valve at the base of the evaporator. The rotating compartment valve is required because of the physical condition of the salt solids. The wiped film evaporator is a complex heat transfer device that is relatively expensive to purchase and install. Additionally, a wiped film evaporator can be expensive to maintain due to complex system of moving parts and mechanical seals.
Following salt removal, the glycerin solution is evaporated from contaminants to obtain desired purity. Again, high temperatures and deep vacuum are required. This heat transfer operation may be carried out in a long tube, thin-film evaporator since the purged contaminants are liquid.
Following thin film evaporation, the glycerin solution product may require additional purification to remove color body contaminants. This decolorization can be accomplished with activated carbon or ion exchange resin.
There is broadly contemplated, in accordance with at least one presently preferred embodiment of the present invention, a process for purifying crude glycerin comprising one or more of the steps of: a) providing crude glycerin, said crude glycerin comprising glycerol, water, and at least one of methanol, free fatty acids, FAME, and salts; b) fractionating the crude glycerin thereby forming at least a first fraction comprising glycerol and water and a second fraction comprising water and at least one of methanol, free fatty acids, FAME, and salts; c) a first dewatering of the first fraction thereby producing an industrial grade glycerin solution product, said industrial grade glycerin solution product comprising glycerol and water where the glycerol weight percent is 60 to 90 wt %; and d) a second dewatering of the industrial grade glycerin solution product thereby producing a purified grade glycerin solution product comprising glycerol and water where the glycerol weight percent is between 95 to 100 wt %.
Further, in another embodiment of the invention, said fractionation step b) comprises ion exclusion chromatography (hereinafter “IEC”) as a means of separating glycerol from the salts and other by-products of the crude glycerin, where said other by-products include at least one of methanol, free fatty acids, and FAME.
In a further embodiment of the invention the IEC is performed with the use of a single column fixed bed process, a moving bed process, and/or simulated moving bed process.
In another embodiment of the present invention there is contemplated that the second dewatering step comprises adding the industrial grade glycerin solution to a glycerin water stripper apparatus having a bottom, a middle, and a top area, in which recirculating nitrogen gas and/or air is introduced into the bottom and wherein water of the industrial grade glycerin solution is removed from the middle and/or top of the apparatus while the purified grade glycerin solution product is collected and removed from the bottom of the glycerin water stripper apparatus.
Further the second dewatering step may alternatively comprise evaporation of an industrial grade glycerin solution via the use of one or more of a multi-effect vacuum evaporation apparatus, a thermal recompression apparatus, and a reboiled distillation apparatus. 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.
It shall be understood that as used throughout the specification and the claims crude glycerin, industrial grade glycerin, purified grade glycerin, recycled glycerin, glycerin product, and glycerin solution shall be understood to mean a solution comprising glycerol. Glycerol shall be understood to mean the chemical compound 1,2,3-Propanetriol.
It has now been found that in at least one embodiment of the present invention crude glycerin from sources such as biofuels production can be purified in a novel manner via the use of ion exclusion chromatography (“IEC”) for chromatographic separation fractionation in combination with glycerin solution dewatering/concentration. The use of IEC produces a glycerin solution in water that is substantially salt free. The glycerin solution product from ion exclusion chromatography can be concentrated by evaporating water to produce a valuable high volume petrochemical feedstock more economically than traditional crude glycerin purification processes.
Referring to the drawings in
Referring now to
The crude glycerin described above may comprise the following by-products: water, salts, MONG including free fatty acids (e.g., stearic acid and oleic acid), and fatty acid methyl esters (“FAME”). IEC utilizes a specific ion exchange resin designed for removing the by-products from the crude glycerin. For example, such ion exchange resins may include macroporous cation exchange resin such as Lewatit® GF303 available from LANXESS Deutschland GmbH. The ion exchange resin is more selective towards glycerol over the other crude glycerin by-products. Various methods for IEC are possible, for example, single column fixed bed processing, moving bed processing, or simulated moving bed processing may be used. In one embodiment, a single column fixed bed process is employed. Via the above mentioned ion exclusion chromatographic separation process the salts and other by-product of the crude glycerin are reduced.
More specifically, in the preferred embodiment a pulsed amount of crude glycerin is provided to the ion exclusion vessel, the resin bed thereof is then washed with demineralized water provided from the demineralized water storage tank. The demineralized water first carries a majority of the crude glycerin by-products out of the bed leaving behind the majority of glycerol. Further flow of demineralized water then elutes the remaining glycerol with little residual salt contamination. A graph of the ion exclusion chromatographic separation of the crude glycerin is shown in
The resin bed effluent is fractionated and monitored by refractive index and conductivity. Refractive index indicates the presence and concentration of glycerol in the fraction solution. Similarly, conductivity indicates the presence and concentration of ionic salts in the resin bed effluent. It will be appreciated that a number of fractions may be obtained via the IEC separation, which will then be further processed. In the preferred embodiment, up to four fractions of resin bed effluent are detected, segregated, and processed as described below. It should be appreciated that other fractionation monitoring and controlling methods may be employed, for example by means of on-line gas and/or ion chromatography or sequential events logic controllers.
Various fractions can be obtained as part of process of the invention. As part of the preferred embodiment, a faction (A) may be collected, which comprises demineralized water with elevated salt content. This fraction may be characterized by high conductivity and a low refractive index. As shown in
Further another fraction (B), according to the preferred embodiment, comprises demineralized water with small amounts of salt, other crude glycerin by-products, and glycerol. This fraction may be characterized as having reduced conductivity and measurable refractive index as compared to the preliminary fraction above. This fraction (B) can be recycled back to the crude glycerin storage, as shown in
A further fraction (C), of the preferred embodiment, comprises demineralized water containing the majority of glycerol from the IEC separation process of the crude glycerin and has a significantly reduced amount of salt and other crude glycerin by-products as compared to fraction (B) and as can be appreciated with reference to the graph at
In one embodiment, as shown in
As indicated above, in the preferred embodiment a fraction (D) may also be collected from the IEC process step (
Fraction (C) of the preferred embodiment, whether being additionally purified or not, comprises glycerol and water, wherein the glycerol weight percent is about between 10 and 50 wt %. As illustrated in
As shown in
The industrial grade glycerin solution product of the preferred embodiment is further concentrated to purified grade glycerin solution product by an additional water removal step. As shown in
In the preferred embodiment, the glycerin water stripper is a vertical pressure vessel with one or more beds of mass transfer packing to improve vapor liquid contact. Said pressure vessel may be divided into various areas such as, in ascending order, a bottom, middle, and top. Hot, dry recirculating nitrogen gas and/or air is introduced into the bottom of the glycerin water stripper. In one embodiment of the invention nitrogen gas is introduced. As the dry nitrogen flows upward through the packing and contacts the wet glycerin, the nitrogen is humidified with water from the glycerin solution and separated therefrom. The humidified nitrogen gas and water is then removed from the middle or top of the vessel. As the glycerin solution flows down through the packing, the water content continuously decreases. From the bottom of the vessel purified grade glycerin solution product is obtained and subsequently collected. It should be appreciated that the amount of water removal is a function of the design of the glycerin water stripper apparatus and can, therefore, be varied as desired.
In the preferred embodiment, the wet nitrogen leaves the glycerin water stripper through the top of the vessel and is sent to a glycerin stripper condenser to be cooled against air or cooling water (
In the preferred embodiment, United States Pharmacopeia (USP) quality purified grade glycerin solution product is obtained from the purified grade glycerin solution dewatering step via the glycerin water stripper apparatus and has a glycerol weight percent of about between 95 to 100 wt % and in at least one embodiment about 99 wt %. In one embodiment, the purified grade glycerin solution product comprises less than 1 ppm salts and other crude glycerin by-products.
To illustrate the current invention, examples of the purification of biodiesel derived crude glycerin are given below. The first comparative example describes the traditional thermal processes for the separation of glycerol from the major contaminants. The subsequent examples describe the processes according to the current invention.
The examples below were developed from computer models generated 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. In all examples, a crude glycerin feed stream, typical of that from a biodiesel plant, was utilized and was defined to be 82 wt % glycerol, 7 wt % inorganic ash, 6 wt % MONG (matter organic, non glycerin), 4 wt % water and 1 wt % methanol. The target quality of refined glycerin was greater than 99.5 wt % glycerol, under 1000 wt ppm MONG, under 100 wt ppm inorganic ash and the balance being water.
As depicted in
With reference to
The liquid stream from the lights removal FLSH01 step is further heated at heat exchanger HX02 and directed to a wiped film evaporator (WFE) modeled as FLSH02 to eliminate salts and other non-volatile contaminants. The WFE is an agitated thin film evaporator where the feed is introduced into the top of the evaporator and is spread into a thin film by rotating wiper blades as it flows down the conical sides of the evaporator. Vapor generation takes place as the thin film moves down the walls. As the remaining liquor thickens and becomes more viscous, the wiper blades direct the liquor to a bottom drain. Heat transfer area is limited to the walls and the heat transfer medium is usually high pressure steam or hot oil. Mechanical seals are required for the rotating shaft of the wiper blades which with the bearings of the shaft represent high maintenance components of the system. Depending upon the fluid nature of the bottoms salt purge, the bottoms flow will be controlled by either a flow control valve or, it the salt is sufficiently dry, a lock hopper or rotary valve assembly. The bottoms flow also carries with it appreciable amounts of glycerin that again contributes to the overall yield loss of the thermal process as well as amounts of high boiling compounds designated as MONG. This second purge stream is designated PRG02. The product as vapor generated from the WFE can be condensed in heat exchanger HX02 against the feed stream to reduce heat requirements.
The stabilized, de-ashed product from the WFE is sent to a high temperature, low pressure distillation column designated and modeled as FRCT01 to remove residual lights in an overhead purge stream designated PRG03 and MONG in a bottom draw purge stream designated PRG04 to produce a high quality glycerin product. Each of the two purge streams carries appreciable amounts of glycerol that further reduce purified glycerol yield.
In the Example 1 provided, the yield loss of contained glycerol is between 5% and 6% of the incoming crude glycerin. The net heat consumption is calculated to be 1170 BTU per pound of glycerol product.
As depicted in
With reference to
The first step of water removal utilizes a multiple effect evaporation process that utilizes successively decreasing pressure and temperature to make the optimal use of heat needed to vaporize water. Temperatures within the various sections of the multiple effect evaporator are maintained less than 240° F. to allow the use of low pressure steam.
To reduce water content further, several means of fractionation can be considered. In this example of the current invention, a stripping column designated STRP01 operating at slightly above atmospheric pressure with suitable internals such as trays or packing is used to enable intimate contact between stripper feed stream ST20 and a re-circulating nitrogen stream that enters STRP01 as ST25. Stream ST20 enters the stripper through suitable designed liquid distribution equipment within the stripper and flows onto the top section of the column internals. Design of the mass transfer internals and liquid distribution equipment is left to those familiar with the art. Stream ST25 is a gaseous steam that enters the stripper below the column's internal mass transfer equipment. The re-circulating nitrogen stream ST25 is humidified predominantly with water and to a very small extent glycerol that is removed from the liquid feed stream ST20. The overhead vapor stream, designated ST21, from STRP01 is cooled and dehumidified in the combined heat exchanger and phase separator FL02. This unit may exist as either a single piece of equipment such as condenser with large liquid holdup or could be a condenser and separate liquid surge drum with liquid de-entrainment internals. The liquid generated from the dehumidification step is designated ST26 and is recycled to recover any glycerol that is vaporized in STRP01. The nitrogen recirculation stream ST22 from phase separator FL02 is compressed in blower CMP01 and heated against steam or another heat source in heat exchanger HX03. Product glycerin exits STRP01 as a bottom stream designated ST30 with less than 0.5 wt % water. The glycerin product stream may be cooled against various process streams to recover heat. In the example, heat is transferred from the glycerin product to the liquid recycle stream from FL02.
According to Example 2, operated in the manner taught in this invention, overall glycerol yield loss is less than 3%. The net heat consumption is calculated to be 2390 BTU per pound of glycerin product. This value includes a calculated conversion of electrical power consumed by CMP01 into a heat load.
It is readily apparent that glycerol recovery has been improved and energy utilization efficiency has been reduced. With respect to heat provided by steam, this aspect of the current invention can utilize low level steam to reduce costs relative to high pressure steam required for the thermal process. A financial analysis may show that using greater amounts of low level waste heat can be more cost effective than expensive high pressure steam required in the traditional purification process described in Example 1.
Although a fixed bed operation of ion exclusion chromatography (IEC) will produce the required product quality, it is readily apparent that the water content of the intermediate glycerin product stream is great and contributing to high energy consumption. Fortunately, there exists technology that raises the operating efficiency of EC with respect to water usage and energy consumption.
Traditionally, continuous operations impart a degree of efficiency that batch operations can not. The efficiency of fixed bed chromatography could be improved by converting to a continuous mode of operation with fluids flowing in one direction and the ion exclusion resin flowing counter current to the liquid. In practice, this is impractical, if not essentially impossible. But this mode of operation can be approached by having liquids flowing continually and simulating the movement of the bed, which actually remains stationary. Such technology, designated Simulated Moving Bed (SMB) may therefore be utilized in another embodiment of the present invention.
For glycerin purification the use of SMB along with ion exchange will produce a dilute glycerin product similar to the fixed bed process previously described with the exception of having a much lower water content. Whereas the glycerin effluent of the fixed bed EC was 82 wt % water, the water content from SMB, in comparison, is only 46.4 wt % water for this example. Water content of the glycerin product leaving the SMB segment of the process may be varied depending upon technical and economic considerations. The exact water content of the glycerin product leaving the SMB segment does not affect the lessons taught in the present invention.
The unit operations for the dewatering system for this Example 3 are identical to those of Example 2. This Example 3 can utilize the process flow shown in
Operations according to Example 3, result in an overall glycerol yield loss of less than 3%. The net heat consumption as a result of using SMB is calculated to be 824 BTU per pound of glycerin product. This provides a great improvement over Examples 1 and 2. Additionally, the process equipment required for water removal in Example 3 will be substantially smaller and less expensive than the comparable equipment in Example 2
The use of a re-circulating nitrogen stream to strip water from wet glycerin takes advantage of low level waste heat. If higher pressure steam is available and economics can justify its use, the stripping column and its auxiliary heat exchangers and compressors can be replaced by a vacuum drying column that utilizes a reboiler and condenser. One embodiment of the water removal process according to the invention is depicted in
Multi effect evaporation is used to reduce the water content of the process glycerin stream from 46.4 wt % to 85 wt % in the same manner as Example 3.
In the present embodiment there is utilized either a tray or packed column with heat exchangers for preheat, reboil and condensation. The fractionation column, instead of operating at slightly above atmospheric pressure, requires vacuum conditions to keep temperatures in a more moderate range. Even with substantial vacuum, the process side of the reboiler must operate over 300° F. which is 70° F. hotter than the bottom of the stripping column in Example 3.
Operated in accordance with Example 4, the overall glycerol yield loss in is less than 3%. The net heat consumption is calculated to be 753 BTU per pound of glycerol product. This provides some improvement over Example 3 but requires higher pressure steam for the reboiler and preheater.
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.
This application claims priority to provisional U.S. Application No. 61/063,235, Filed Feb. 1, 2008, entitled A PROCESS FOR THE PURIFICATION OF CRUDE GLYCERIN UTILIZING ION EXCLUSION CHROMATOGRAPHY AND GLYCERIN CONCENTRATION, incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 61063235 | Feb 2008 | US |
