[0001] Ethyleneamines are used for a variety of purposes. One particularly useful ethyleneamine is triethylenetetramine (TETA), which is used, for example, as a curing agent for epoxy resins. In one commercially important method of making TETA, a complex mixture of products is formed when aqueous ammonia is reacted with ethylene dichloride (EDC). The complex mixture is neutralized and then distilled to separate the products. One cut (also called a "fraction") from the distillation, herein called the "TETA cut," is rich in the specific linear molecule L-TETA, and the most prevalent coproducts in that cut are other ethyleneamines that contain 4 nitrogen atoms in each molecule. This particular distillation cut is known as the "TETA congener." “Congener” is the term used herein to describe a family of ethyleneamines having the same number of nitrogen atoms, but not necessarily the same number of carbon and hydrogen atoms. Although the term "congener" can be applied to all ethyleneamines, including ethylenediamine (EDA) and piperazine, in reality it is normally only used for the distillation cuts such as TETA (i.e., the cut of ethyleneamines having 4 nitrogens), TEPA (i.e., the cut of ethyleneamines having 5 nitrogens), etc. For industrial use, TETA is commonly supplied as the TETA congener instead of the pure L- TETA. During the manufacture of the TETA congener, higher ethyleneamines, such as tetraethylenepentamine (TEPA), are produced as well.

[0002] Prior to the present invention, it was generally considered that it is not possible to increase the weight percentage of the TETA congener in the overall product mix without also disproportionally increasing the amount of the higher ethyleneamines. It is also, independently, desired to identify a process that could increase the weight percentage of the TETA congener in the overall product mix without also disproportionally increasing the amount of the higher ethyleneamines. Additionally, it has been independently desired to find inexpensive alternative raw materials, such as byproducts of industrial processes, where those byproducts could suitably be used as raw materials in the manufacture of TETA congener. Use of such byproducts, if suitable, in the manufacture of TETA congener, would improve the other industrial process by finding a use for otherwise- wasted byproduct, and such use would improve the manufacture of TETA congener by reducing the cost. Further, it is also independently desired to identify a process of manufacturing TETA congener that does not result in large amounts of unconverted EDA in the reactor effluent. [0003] US 3,462,493 discloses production of triethylenetetramine by reaction of excess ethylenediamine with ethylene halides. US 3,462,493 discloses that one of the byproducts of the reaction is piperazine.

[0004] Generally, when EDC is reacted with ammonia to form TETA congener, a byproduct is crude piperazine, which is a mixture that contains piperazine, water, EDA, and possibly one or more additional alkylamines, possibly among other compounds. Piperazine in the pure state is a useful industrial product. Prior to the present invention, the crude piperazine formed during production of TETA congener would require expensive purification before being suitable as an industrial product. It has been desired to find a use for this crude piperazine.

[0005] The present invention is a process for the production of TETA congener that uses piperazine, which may be crude piperazine.

[0006] The following is a statement of the invention.

[0007] A first aspect of the present invention is a process for producing products that comprise linear triethylenetetramine, wherein the process comprises forming a reaction mixture comprising ethylene dichloride and piperazine, wherein the weight ratio of piperazine to ethylene dichloride is 0.1 : 1 to 1 : 1.

[0008] The following is a brief description of the drawings. Figure 1 is an apparatus for performing one particular embodiment of the present invention, in which one feed stream containing EDA and piperazine is mixed with another feed stream containing EDC. Figure 2 shows an apparatus for another particular embodiment of the present invention, in which an apparatus similar to that shown in Figure 1 is combined with a parallel reaction process that reacts EDC with ammonia.

[0009] The following is a detailed description of the invention.

[0010] The following abbreviations for chemical compounds are used herein:

[0011] As used herein, the term alkylamine refers to compounds whose molecules meet the following criteria: each molecule contains only carbon, nitrogen, and hydrogen atoms; only single bonds between atoms are present; the number of carbon atoms is equal to or greater than the number of nitrogen atoms. As used herein, the plural term

"ethyleneamines" (EAs) refers to a class of compounds that includes the compound EDA and also includes any compound whose structure consists of ethylene units (i.e., -CH2CH2- ) linked together via amine groups. Examples of EAs include, for example, EDA, DETA, TAEA, PEEDA, DAEP, all congeners of TETA, TEPA, and all other heavier EAs. As used herein, the phrase "an ethyleneamine" (an EA) refers to any one of the EAs. "Heavier EAs" refers to EAs having 5 or more nitrogen atoms per molecule.

[0012] Ratios presented herein are characterized as follows. For example, if a ratio is said to be 3:1 or greater, that ratio may be 3: 1 or 5:1 or 100:1 but may not be 2:1. This characterization may be stated in general terms as follows. When a ratio is said herein to be X:1 or greater, it is meant that the ratio is Y:l, where Y is greater than or equal to X. For another example, if a ratio is said to be 15:1 or less, that ratio may be 15:1 or 10: 1 or 0.1:1 but it may not be 20: 1. In general terms, when a ratio is said herein to be W:1 or less, it is meant that the ratio is Z :1, where Z is less than or equal to W. Unless stated otherwise, ratios herein are weight ratios. Unless stated otherwise, percentages herein are weight percentages.

[0013] The process of the present invention includes forming a reaction mixture that contains ethylene dichloride (EDC) and piperazine. This reaction mixture is herein referred to as reaction mixture (1A). Preferably the weight ratio in reaction mixture (1A) of piperazine to EDC is 0.1:1 or higher; more preferably 0.2:1 or higher; more preferably 0.3:1 or higher; more preferably 0.4:1 or higher. Preferably the weight ratio in reaction mixture (1A) of piperazine to EDC is 1:1 or lower; more preferably 0.9: 1 or lower; more preferably 0.8:1 or lower.

[0014] The reaction mixture (1A) optionally also contains ethylenediamine (EDA). Preferably, the weight ratio of EDA to EDC is 0: 1 or higher; more preferably 1 : 1 or higher; more preferably 2: 1 or higher; more preferably 5: 1 or higher. Preferably, the weight ratio of EDA to EDC is 20: 1 or lower; more preferably 15:1 or lower; more preferably 10:1 or lower; more preferably 8:1 or lower.

[0015] The reaction mixture (1A) also optionally contains water. Preferably, the weight ratio of water to EDC is 0 : 1 or higher; more preferably 1 : 1 or higher; more preferably 2 : 1 or higher. Preferably, the weight ratio of water to EDC is 20:1 or lower; more preferably 10:1 or lower; more preferably 5 : 1 or lower. [0016] Preferably, the reaction mixture (1 A) has temperature of 40°C or higher; more preferably 50°C or higher; more preferably 60°C or higher; more preferably 70°C or higher; more preferably 75 °C or higher. Preferably, the reaction mixture (1A) has temperature of 200°C or lower; more preferably 185°C or lower; more preferably 170°C or lower; more preferably 160°C or lower; more preferably 150°C or lower.

[0017] The reaction mixture (1A) is preferably at a pressure at or above atmospheric pressure. Preferably, the reaction mixture is at a pressure of 100 kilopascal (kPa) or higher; more preferably 200 kPa or higher; more preferably 300 kPa or higher; more preferably 500 kPa or higher. Preferably, the reaction mixture is at a pressure of 20,000 kPa or lower; more preferably 10,000 kPa or lower; more preferably 5,000 kPa or lower; more preferably 2,000 kPa or lower.

[0018] At the beginning of the process of the present invention, before any significant amount of chemical reaction has taken place to produce L-TETA, the reaction mixture (1A) preferably contains little or no L-TETA. That is, preferably, the amount of L-TETA in the reaction mixture at the beginning of the process is, by weight based on the weight of the reaction mixture, 3% or less; more preferably 1% or less; more preferably 0.3% or less; more preferably 0.1% or less; more preferably 0%.

[0019] At the beginning of the process of the present invention, before any significant amount of chemical reaction has taken place to produce L-TETA, the reaction mixture (1A) preferably contains little or no ammonia. That is, preferably, the amount of ammonia (including both molecular ammonia Nth and the ammonium ion NHT) in the reaction mixture (1A) at the beginning of the process is, by weight based on the weight of the reaction mixture (1A), 3% or less; more preferably 1% or less; more preferably 0.3% or less; more preferably 0.1% or less; more preferably 0%.

[0020] The process of the present invention may be carried out in any type of apparatus, to promote the chemical reaction that produces L-TETA. Two suitable types of apparatus are batch reactors and plug flow reactors. In a batch reactor, all the ingredients are brought together to form the reaction mixture (1A), and the desired conditions of agitation (if any), temperature, pressure, etc. are established and/or maintained. At the end of the desired time, the contents of the reactor (the "crude product") may be subjected to additional processing and/or purification steps. In a plug flow process, reactants are brought together to form the reaction mixture (1A), which then flows through a tube, from the tube entrance to the tube exit. Each ingredient is brought into the entrance of the tube at its own characteristic rate, and these rates are adjusted in order to establish the desired ratios among the ingredients. The flow conditions in the tube may be adjusted to maintain the desired pressure in the reaction mixture, and the tube may be kept in a temperature-controlled chamber in order to maintain the reaction mixture at the desired temperature. Plug flow reactors are preferred.

[0021] The material that is present at the end of the batch reaction time or the material that exits the tube (the "crude product", products (IB)) may be subjected to additional processing and/or purification steps. Crude product is preferably subjected to a neutralization step. Neutralization is preferably performed by mixing the crude product with an aqueous solution of a base. A preferred base is sodium hydroxide. After neutralization, the neutralized crude product is preferably separated into a two streams: an aqueous salt stream and a mixed-EAs stream. The aqueous salt stream preferably contains chloride ion produced from the chemical reactions of EDC. The mixed-EAs stream preferably contains a mixture of a variety of EAs.

[0022] The mixed-EAs stream is preferably distilled to separate various EAs from each other. The distillation process produces multiple fractions. Preferably, one fraction from the distillation contains EDA and also contains piperazine, possibly also containing one or more additional compounds. Preferably, a separate fraction from the distillation contains L- TETA, possibly also contains one or more of DAEP, PEEDA, or TAEA, and possibly also contains one or more additional compounds. In some embodiments, the fraction that contains L-TETA is suitable as the TETA congener. In some embodiments, a fraction that contains piperazine is suitable as crude piperazine that may be used by reacting with EDC to form a mixture comprising L-TETA.

[0023] One embodiment of the present invention is shown if Figure 1. Feed stream 15 contains piperazine. Preferably, the feed stream 15 additionally contains EDA. Preferably, the feed stream 15 contains, optionally among one or more additional compounds, crude piperazine that had been produced as a distillation fraction from a process in which a separate distillation fraction contained L-TETA. The additional compounds in the feed stream 15 may include, for example, additional EDA, water, or both. Feed stream 15 preferably contains water. Feed stream 41 contains EDC. Reactor 13 is the location of the chemical reaction between EDC and the amines from feed stream 15. When reactor 13 is a plug flow reactor, the ratio of piperazine to EDC is controlled by adjusting the relative flow rates of feed stream 15 and feed stream 41. Effluent stream 16 is the crude product of the reaction that occurred in reactor 13. [0024] Also shown in Figure 1 is apparatus 14. In some embodiments, apparatus 14 includes two or more vessels (not shown separately in Figure 1). In a first vessel, the crude product is neutralized by the addition of an aqueous solution of a base via feed stream 7.

The neutralized crude product is transferred downstream within apparatus 14. From apparatus 14, two streams exit: effluent stream 9 and effluent stream 10. Effluent stream 9 comprises a chloride salt. Effluent stream 10 is a mixed-EAs stream, which enters distillation apparatus 3. Distillation apparatus 3 includes a train of multiple distillation columns, each of which produces an effluent stream. One of these distillation columns within distillation apparatus 3 produces aqueous effluent stream 11 that contains water. Preferably, the amount of water in effluent stream 11 is, by weight based on the weight of effluent stream 11, 50% or more; more preferably 75% or more; more preferably 90% or more. Another of the distillation columns within distillation apparatus 3 produces distillation effluent 12. Distillation effluent 12 represents a variety of distillation fractions, including a fraction that contains EDA, possibly along with additional compounds; a fraction that contains piperazine, possibly along with additional compounds; and/or a fraction that contains both EDA and piperazine, possibly along with additional compounds. Also included in distillation effluent 12 is another fraction that contains L-TETA, possibly along with additional compounds. Preferably, the fraction that contains L-TETA is suitable as the TETA congener. Additionally, distillation effluent 12 contains multiple further fractions, including, for example, a "DETA fraction," (which contains DETA and other compounds), an "AEP fraction," (which contains aminoethylpiperazine and other compounds, a "the TEPA fraction", (which contains L-TEPA and other compounds), and a "higher EA" fraction (which contains EAs having more than 5 nitrogen atoms in each molecule, along with other compounds).

[0025] The TEPA fraction typically contains approximately 7 different EAs, each having 5 nitrogen atoms in each molecule, along with other compounds. The TEPA fraction often additionally contains some L-TETA and some higher EAs having more than 5 nitrogen atoms per molecule, often along with other compounds.

[0026] Figure 2 shows an embodiment in which the process described in Figure 1 is used as part of process that also includes elements of a process that produces products that contain L-TETA by reacting an aqueous ammonia solution with EDC. Feed stream 5 contains aqueous ammonia, and is mixed with feed stream 42, which contains EDC, to form reaction mixture (2A). The mixture is fed into reactor 1, where the reaction between EDC and ammonia takes place. The crude product of this reaction (products 2B) is effluent stream 6, which exits reactor 1. Effluent stream 6 is combined with effluent stream 16, either before entering apparatus 14 or within apparatus 14. Excess ammonia (stream 8) is optionally recovered from apparatus 14 and is optionally fed back into feed stream 5.

Streams 7, 9, 10, 11, and 12, apparatus 14, and distillation apparatus 3 are the same as described in Figure 1.

[0027] In some embodiments, a function is performed that is not shown in Figure 1 or Figure 2. In these embodiments, some or all of the one or more distillation fractions that contain piperazine or EDA or both is removed from stream 12 and is fed back into feed stream 15.

[0028] The process of the present invention produces L-TETA. Preferably, the process produces a product mixture that contains compounds in addition to L-TETA. The productivity of the overall process, including the separation of the TETA congener, may be assessed by calculating the "TETA Congener Selectivity,", as follows:

(TETA Congener Selectivity) =

100 * (weight of TETA congener) / (weight of total EA output) where the total output includes all EAs except for EDA and Piperazine when these components are used as reactants instead of being formed in the reactor like it is the case for the process of Figure 1.

In embodiments like those shown in Figure 1 and Figure 2, the preferences for the TETA Congener Selectivity refer to the final products of the process, after the distillations are performed. Preferably, the TETA Congener Selectivity is 30% or greater; more preferably 40% or greater; more preferably 50% or greater. These preferences for the TETA Congener Selectivity refer to the output of the overall process of Figure 1. For a process like those shown in Figure 2, the TETA Congener Selectivity will be a weighted average of the TETA Congener Selectivity’s of the streams 16 and 6.

[0029] Another assessment of the products produced by the overall process is the "Linearity in the TETA Congener" (abbreviated herein "LTC"), which is calculated as follows: LTC = (Linearity in the TETA Congener) =

100 * (weight of L-TETA) / (weight of TETA Congener)

Prior to the present invention, the linearity in commercial TETA congeners has been approximately 60%, and it is desirable for the process of the present invention to produce a similar result. Preferably, the Linearity in the TETA Congener is 50% or more; more preferably 55% or more; more preferably 60% or more. Preferably, the Linearity in the TETA Congener is 80% or less; more preferably 75% or less; more preferably 70% or less. These preferences for the Linearity in the TETA Congener apply to the final output of the process, for example after the distillations shown in Figure 1 and Figure 2. Additionally, when a process like that shown in Figure 2 is used, these preferences for the Linearity in the TETA Congener apply independently to each of the streams 6 and 16. For example, in a process like that shown in Figure 2, if samples were taken from stream 16 and analyzed, the composition would preferably match the preferred levels of Linearity in the TETA

Congener as stated above.

[0030] Typically, prior to the present invention, processes involving reaction of ammonia with EDC were used to make TETA congener, and such processes typically produced TETA congener with significant amounts of DAEP and TAEA in addition to PEEDA and L-TETA. It has been discovered in the course of the present invention that the reaction among EDA, piperazine, and EDC produces a TETA congener having far less DAEP and TAEA, with the majority by weight of the TETA congener made up of L-TETA and PEEDA.

[0031] The following are examples of the present invention. Operations were performed at room temperature (approximately 23 °C) except where otherwise stated.

[0032] The crude product mixtures were neutralized with aqueous NaOH, and the products were analyzed by gas chromatography (GC).

[0033] The GC conditions were as follows:

Instrument: Agilent 6890 with Atlas 8.2 Chromatography Data System (Agilent

Technologies)

Carrier: Helium

Column: Rtx-35 Amine, 30 m x 0.320-mm i.d. x l.O-pm film thickness, Cat# 11354 Constant flow rate: 2.0 mL/min

Injection port: 295°C

FID detector: 300°C Hydrogen: 40 mL/min

Air: 450 mL/min

Makeup: 30 mL/min of helium

Injection: 0.2 pL

Split ratio: 30

Temperature programming: 60°C for 0 min, 20°C/min to 220°C, and hold for 17 min Internal standard was 5 wt% diglyme solution is isopropanol. Samples were diluted 1:20 by volume in the internal standard.

[0034] The following experiments were performed. Ratios shown are by weight.

Ratios are listed as the quotient of dividing the numerator by the denominator; that is, each ratio shown is equivalent to the number shown in a ratio to 1 ; for example, a ratio listed as 1.250 is equivalent to a ratio of 1.250:1. Each example is labeled with an "ID" number. ID numbers containing "C" are comparative. "Temp" is temperature. The column headed "LTC" shows the linearity in the TETA Congener, as defined above.

[0035] Example A: Experiments at small scale.

[0036] EDA, EDC, PIP, and water were mixed at the ratios and at the temperatures shown below in Tables AA through AP, and the mixtures were allowed to react. The products were analyzed by gas chromatography as described above.

Table A A- results of Example A

Table AB - results of Example A

Table AC - Results of Example A

Table AD - Results of Example A Table AE - Results of Example A

Table AF - Results of Example A

Table AG - Results of Example A Table AH - Results of Example A

[0037] The results of Example A were modeled using a best- fit polynomial model (including cross terms). This model identified the following trends:

[0038] higher EDA/EDC ratio resulted in the following:

- higher TETA Congener Selectivity (desirable)

- higher linearity of the TETA Congener (target = 60%)

- more unconverted EDA produced (undesirable)

[0039] higher PIP/EDC ratio resulted in the following:

- lower TETA Congener Selectivity (undesirable)

- lower linearity of the TETA Congener (target = 60%)

[0040] From these trends, it is possible to deduce the combination of PIP/EDC ratio and EDA/EDC ratio that would result in achieving the various desirable outcomes (i.e., higher TETA Congener Selectivity, level of Linearity of the TETA Congener near 60%, and lower unconverted EDA). Useful juxtapositions of these outcomes are expected to result when both the EDA/EDC ratio and the PIP/EDC ratio are chosen according to the preferred values discussed above. As examples, each of the following combinations of EDA/EDC ratio and PIP/EDC ratio is expected, according to model, to result in a preferred juxtaposition of the desired outcomes:

[0041] Example 1: Experiments Using Feed Streams

[0042] Experiments were performed with an apparatus similar to that shown schematically in Figure 1. Feed streams 15 and 4 were each regulated by a Gilson pump, and the streams were mixed in a low-dead-volume tee joint, where the pressure was monitored with a pressure gauge. The mixture passed through a coiled reactor tube that was immersed in an oil bath for temperature control. Crude product from the reactor was passed through a water cooling jacket for thermal quenching. A back pressure regulator controlled the reactor pressure. Reaction products were neutralized and analyzed as described above.

[0043] Also measured in the product mixture (but not shown in the tables below) were the amounts of EDC, EDA, aminoethylethanolamine (AEEA), PIP, DETA,

aminoethylpiperazine (AEP), DAEP, PEEDA, monoethanolamine (MEA),

triethylenediamine (TED A), and higher ethyleneamines that were produced.

Table 1A: Experimental Conditions and L-TETA produced (part 1)

Table IB: Experimental Conditions and L-TETA produced (part 2)

Table 1C: Experimental Conditions and L-TETA produced (part 3)

* In Examples 23C, 24, and 25 the amount of PIP shown was crude PIP, which was, by weight, 50% PIP, 25% water, and 25% various EAs.

[0044] Also measured but not shown in the above tables were the weight percents in the product of EDC, EDA, AEEA, PIP, DETA, AEP, DAEP, PEEDA, TEPA, MEA, TEDA and higher ethyleneamines.

[0045] When comparing data of various PIP/EDC ratios under fixed conditions of 120°C, EDA/EDC weight ratio of approximately 2.4:1, and water/EDC weight ratio of approximately 3.6:1, the productivity may be assessed by examining the "TETA Congener Selectivity," as defined above. [0046] This TETA Congener Selectivity remains at 50% or above for all ratios of PIP/EDC, as shown in Table ID below. This result shows that including PIP in the reaction mixture does not seriously reduce the productivity (which is assessed by the TETA

Congener Selectivity). Similarly, including crude PIP in the reaction mix does not seriously reduce the productivity. Therefore the crude PIP, which in the past would have been discarded (or would have required expensive purification prior to use), can be used as a raw material in the production of ethyleneamines without significant loss to productivity.

[0047] Also, the Linearity in the TETA Congener (as defined above) remains within the desirable range, as shown in Table ID below.

[0048] The TETA Congener Selectivity and the Linearity in the TETA Congener are illustrated by comparing the results of the experiments with ID numbers 5, 15, 16, and 17 (as defined in the table above). The difference in temperature among these experiments is considered to be unimportant.

Table ID: Selectivity Results

[0049] Example P: The following production-style examples are also present here, based on using an apparatus as shown in Figure 2.

[0050] Comparative example 31C: Based on well-known results published in open literature, it is easy to know the results of operating an apparatus for reacting EDC and aqueous ammonia, with no feedback stream. The apparatus would be like that of Figure 2, without reactor 13 and without the streams entering and leaving reactor 13. The result would be the product mixture as shown in Table 2.

[0051] Comparative example 32C: As in Comparative Example 31, the results can be known for a process in which EDC and aqueous ammonia are reacted under similar conditions as comparative example 1 , but simultaneously EDA is recycled to the reactor. The final product mixture would be as shown in Table 2.

[0052] Inventive example 33:

[0053] From the experiments shown in Tables 1A - 1C, the results are known of a process of reacting aqueous EDA and crude piperazine with ethylene dichloride, using a process that results in no net production of piperazine, using feed weight ratios of

EDA/piperazine/water/EDC of 51.4/12.1/28.5/7.9. A process like that shown in Figure 2 was envisioned, in which such a reaction was operated in parallel with a second reaction, in which EDC and aqueous ammonia were reacted under similar conditions as comparative example 31C, and the products of the two reactions were combined. The two streams combined would give an overall product mixture as shown in Table 2.

[0054] Inventive example 34:

[0055] A process was envisioned in which the reaction of crude piperazine and EDC, as described in Inventive example 33, was combined with a reaction as described in comparative example 32C. The two streams combined would give an overall product mix as shown in Table 2.

[0056] Comparative example 35C: Based on well-known results published in open literature, it is easy to know the results of operating an apparatus for reacting EDC and aqueous ammonia under similar conditions to those of comparative example 32C, but simultaneously EDA (a larger amount than was recycled in comparative example 32C) would be recycled to the reactor such that the final product mixture would be as shown in Table 2.

[0057] The following Table 2 summarizes the results of Examples 31C, 32C, 33, 34, and 35. Amounts shown are weight percent of the product mix. Each column represents a different cut from the distillation apparatus.

Table 2: Product Mixtures

(1) The TETA cut is the TETA congener (2) Sum of all EAs having 5 or more nitrogen atoms per molecule

(3) The piperazine cut is, in other experiments, used as crude piperazine

[0058] When comparing comparative example 31C to example 33, it is clear that inclusion of the crude piperazine in example 33 caused the following desirable results: the amount of TETA congener rose by 1%, the amount of crude piperazine dropped to 0%, and the amount of heavier EAs did not increase. That is, the productivity of making the TETA congener improved without increasing the amount of the undesirable heavy EA byproduct.

[0059] When comparing comparative example 32C to example 34, it is clear that inclusion of the crude piperazine in example 34 caused the following desirable results: the amount of TETA congener rose by 2%, the amount of crude piperazine dropped to 0%, and the amount of heavier EAs did not significantly increase. That is, the productivity of making the TETA congener improved without increasing the amount of the undesirable heavy EA byproduct.

[0060] When comparing comparative example 35C to comparative example 31C, it is clear that it is possible to raise the output level of TETA congener to 20% without using piperazine in the reactants, by increasing the EDA in the feedback stream. However, this method also raises the level of heavier EAs, which is undesirable.