Synthesis and Evaluation of New Bisphosphonates as Inhibitors for

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Synthesis and Evaluation of New Bisphosphonates as Inhibitors for Oilfield Carbonate and Sulfate Scale Control Mohamed F. Mady, Andrea Bagi, and Malcolm A. Kelland Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.6b02117 • Publication Date (Web): 17 Oct 2016 Downloaded from http://pubs.acs.org on October 20, 2016

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Synthesis and Evaluation of New Bisphosphonates as Inhibitors for Oilfield Carbonate and Sulfate Scale Control Authors: Mohamed F. Mady,a,b,* Andrea Bagi,a and Malcolm A. Kellanda,**

a

Department of Mathematics and Natural Science, Faculty of Science and Technology,

University of Stavanger, N-4036 Stavanger, Norway

b

Department of Green Chemistry, National Research Centre, 33 El Bohouth st. (former El Tahrir

st.), Dokki, Giza, Egypt, P.O. 12622.

Key words: oilfield scale, bisphosphonates, Moedritzer-Irani reaction, calcium compatibility, scale inhibitors, biodegradation

**

Corresponding author at:

Department of Mathematics and Natural Science, Faculty of Science and Technology, University of Stavanger, N-4036 Stavanger, Norway *

Corresponding authors, E-mail addresses [email protected] (M.A. Kelland),

[email protected] (M.F. Mady)

1

ACS Paragon Plus Environment

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Abstract: Most non-polymeric oilfield scale inhibitors contain aminomethylenephosphonate groups. They generally have poor biodegradability limiting their use in regions with strict environmental regions such as offshore Norway. From mono- and bis-nitrile starting materials we have synthesized and investigated compounds with one or two aminobis-phosphonate groups, C(NH2)(PO3H2)2, for seawater biodegradability, their calcium carbonate and barium sulfate scale inhibition and compatibility with Ca2+ ions. The distance between these groups was shown to affect biodegradability, with the aminobisphosphonate derived from adiponitrile, (1,6diaminohexane-1,1,6,6-tetrayl)tetraphosphonic acid (BP-7), giving the highest biodegradation of 25% in 28 days by the OECD306 seawater test. All the synthesized inhibitors exhibited both carbonate and sulfate scale inhibition properties. Compared to known commercial scale inhibitors, the scale inhibition performance was relatively poor for sulfate scale and moderate for carbonate scale. To improve the performance the amine groups were converted to aminobismethylenephosphonate groups, -N(CH2PO3H2)2, to give novel non-polymeric scale inhibitors with 4-8 phosphonate groups. The scale inhibition was much improved for carbonate and sulfate scale. One of these compounds, BP-9, was found to be the most potent scale inhibitor with fail inhibitor concentration (FIC) at 5ppm for carbonate scale and 20ppm for sulfate scale. The new bisphosphonates compounds showed moderate biodegradation activity. For example, compound BP-8 gave 40% seawater biodegradation over 28 days in the OECD306 test.

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1. Introduction Scale formation is the deposition of sparingly soluble inorganic salts from aqueous solutions. It is a major problem for the upstream oil and gas industry during the production of well fluids. Scale can deposit on almost any surface so that once a scale layer is first formed it will continue to get thicker unless treated. Scale can block pore throats in the near-well bore region or in the well itself causing formation damage and loss of well productivity.1,2 They can also deposit on equipment in the well causing it to malfunction. Scale can occur anywhere along the production conduit narrowing the internal diameter and blocking flow and can even occur as far along as the processing facilities. Alongside corrosion and gas hydrate formation, scale is probably one of the three biggest water-related oilfield production problems and needs to be anticipated in advance to determine the best treatment strategy.3,4 The four commonest scales encountered in the oil industry are calcium carbonate (calcite and aragonite), and sulfate salts of calcium (gypsum), strontium (celestite), and barium (barite). The commonest method of preventing scale formation in the oil industry is the use of scale inhibitors (SIs).4 SIs work by preventing either nucleation and/or crystal growth of the scale. Currently, scale is often treated by the addition of sub-stoichiometric levels of water-soluble organic scale inhibitors in the 1-500 ppm dosage range. These scale inhibitors are often referred to as threshold scale inhibitors, i.e. there is a threshold dose level below which they do not fully prevent scale formation. This limit is often referred to as the minimum inhibitor concentration (MIC).

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In order to deliver a required SI into a production well a downhole squeeze treatment is often performed. This is a method in which a SI solution is pumped directly into a formation, usually via the production well. An over flush of seawater is used to push the inhibitor further into the formation and into the region around a production well.4 The SI is then adsorbed or deposited on the formation rock in the near-well area. When oil is subsequently produced, scale inhibitor is released into the produced water where is now available for preventing scale formation during production. Many classes of commercial SIs for carbonate and sulfate scaling are typically polymeric e.g. polyphosphonates, polyacrylates, polymaleates, polysulfonates and copolymers thereof. There are also a range of small non-polymeric SI molecules with only a few phosphonate groups as shown in Figure 1.5-7 Nearly all the small phosphonate molecules contain aminomethylenephosphonate groups where the nitrogen atom can also ligate to divalent cations, increasing the chelate effect.

Figure 1. Common oilfield scale inhibitors containing phosphonate groups.

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Compounds containing one or more bisphosphonate groups (BPs) constitute an important class of biologically active compounds.8-10 BPs are bone-targeting agents used for decades in the therapy of bone-related disease.11,12 It is well-known that bisphosphonates are enzyme-resistant analogs of pyrophosphates, which normally inhibit mineralization in the bone.13 BPs are used to treat postmenopausal and glucocorticoid-induced osteoporosis, Paget's disease of bone and malignant hypercalcemia. Some well-known bis-phosphonate medicines available in the market are shown in Figure 2.14 Recently, BPs have shown interesting anticancer activity.15,16

Figure 2. Examples of osteoporosis medications incorporating bisphosphonates group.

In addition, BPs have been investigated for boiler water scale prevention17 and removal of toxic heavy metals from waste water, but do not appear to have been studied for oilfield scale inhibition.18,19 1-hydroxyethylidene diphosphonic acid (HEDP) and its tetrasodium or potassium

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salts are well-known SIs and corrosion inhibitors.4,20 The introduction of the hydroxyl group increases the binding affinity of the molecule as shown in Figure 3.

Figure 3. 1-hydroxyethylidene diphosphonic acid (HEDP) and its metal salts (M = H or Na).

Although phosphonate-based SIs can offer several advantages in squeeze treatments over other SI classes, one drawback is that they are not readily biodegradable. Recently, there have been several attempts to provide environmentally-acceptable biodegradable scale inhibitors, but rarely phophonate-based.4,21 The low toxicity of BPs encouraged us to design and synthesize a novel series of bis- and tetra-phosphonate derivatives that also contain primary amino groups and check their biodegradability and scale inhibition performance. Then, if necessary, methylenephosphonate moieties could be introduced onto the amines by the Moedritzer-Irani reaction to improve their inhibition performance.22 All synthesized compounds were also evaluated for biodegradability and calcium compatibility.

2. EXPERIMENTAL SECTION 2.1. Chemicals 6


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All chemicals were purchased from VWR, Nippon Chemical Industrial Co., Ltd., Tokyo Chemical Industry Co., Ltd. and Sigma-Aldrich. All solvents were used as purchased without further purification. The sodium salts of diethylenetriaminepentakis(methylenephosphonic acid) (DTPMP) and aminotris(methylenephosphonic acid) (ATMP) were obtained from Solvay.

2.2. Characterization of Scale Inhibitors Nuclear magnetic resonance (NMR) spectra were recorded on a 400 MHz Varian NMR spectrometer in deuterium oxide (D2O). 1H and 13C chemical shifts were obtained in D2O using TMS as an internal standard. Melting points were determined on a Bibby Sterilin Ltd. electrothermal melting point apparatus and are uncorrected.

2.3. Synthesis of Scale inhibitors (SIs) 2.3.1. (1-aminoethane-1,1-diyl)diphosphonic acid BP-4: A mixture of acetonitrile (10 g, 243.6 mmol) and phosphorous acid (59.92 g, 730.7 mmol) was added to a 500 ml two-necked Erlenmeyer flask fitted with a thermometer and additional funnel under vigorous stirring at room temperature. Phosphorous trichloride (66.9 g, 487.1 mmol) was added dropwise to the reaction mixture over a one-hour period under nitrogen. An exothermic reaction occurred causing the temperature to rise to 50oC. The reaction temperature was maintained at 50oC overnight. The mixture was carefully quenched slowly with H2O (50 mL) with vigorous stirring resulting in a temperature rise to 90oC. The reaction mixture was kept stirring at 90oC overnight. A white precipitate was formed during the hydrolysis, filtered off on a 7


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glass frit and washed with several portions of dry methanol to obtain the mono aminodiphosphonic acid BP-4 in a high yield compared to the literature (50% yield)23 as presented in Figure 4.

Figure 4. Synthesis of aminodiphosphonic acid BP-4.

(1-aminoethane-1,1-diyl)diphosphonic acid BP-4:23 White solid; Yield 80%; m.p. 260-262 oC; 1

H NMR (D2O, 400 MHz) δ 1.52 (2d, 3JP-H = 5.7 Hz, 3H); 13C NMR (D2O, 101 MHz) δ 53.2 (t,

1

JPC = 151.2 Hz, C-P2), 17.4; 31P NMR (D2O, 162.00 MHz) δ 13.23 ppm.

2.3.2. General procedure for synthesis of di aminotetraphosphonic acid derivatives (BP-6, 7): A mixture of bis-nitrile (1.0 equiv.) and phosphorous acid (6.0 equiv.) was added to a 250 ml two-necked Erlenmeyer flask fitted with a thermometer and additional funnel under vigorous stirring at room temperature. Phosphorous trichloride (4.0 equiv.) was added dropwise to the reaction mixture over a one-hour period under nitrogen. An exothermic reaction occurred causing the reaction temperature to rise to 50oC. The reaction temperature was maintained at 8


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50oC overnight. The mixture was carefully quenched slowly with H2O (50 mL) with vigorous stirring resulting in a temperature rise to 90oC. The reaction mixture was stirred at 90oC overnight. A white precipitate was formed during the hydrolysis, filtered off on a glass frit and washed with several portions of methanol to obtain the di aminotetraphosphonic acid derivatives BP-6 and BP-7 in a high yield as presented in Figure 5.

Figure 5. Synthesis of di aminotetraphosphonic acids BP-6 and BP-7. (1,4-diaminobutane-1,1,4,4-tetrayl)tetra phosphonic acid (BP-6): White solid; Yield 75%; m.p. 216-218oC; 1H NMR (D2O, 400 MHz) δ 2.9-2.44 (m, 4H); 13C NMR (D2O, 101 MHz) δ 66.3 (t, 1

JPC = 145.7 Hz, 2C-P2) 25.8; 31P NMR (D2O, 162.00 MHz) δ 15.08.

(1,6-diaminohexane-1,1,6,6-tetrayl)tetra phosphonic acid (BP-7):24 White solid; Yield 75%; m.p. 262-264oC; 1H NMR (D2O, 400 MHz) δ 2.11-1.90 (m, 4H); 1.49-1.42 (m, 4H), (D2O, 101 MHz) δ 58.4 (t, 1JPC = 148.0 Hz, 2C-P2), 37.1, 26.4; δ 12.71.

9


31

13

C NMR

P NMR (D2O, 162.00 MHz)

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2.3.3. General procedure for the synthesis of methylenephosphonates via the Moedritzer-Irani reaction. To a 100 ml two-necked Erlenmeyer flask fitted with a thermometer and additional funnel and a magnetic stirring bar were placed appropriate amines BP-4 and BP-7 (1.0 equiv.), H3PO3 ( 2.0 equiv. for compound 4, 4.0 equiv. for compound BP-7) and HCl (2 equiv. for compound BP-4, 4.0 equiv. for compound BP-7) in deionized water (20 ml), flushed with nitrogen for at least 10 min. Under the protection of nitrogen, the reaction mixture was allowed to heat stepwise from room temperature to 110oC, at which time HCHO (2 equiv. for compound BP-4, 4.0 equiv. for compound BP-7) was added dropwise. The reaction mixture was kept stirred at 125°C for 6 h. The mixture was cooled to room temperature, and ethanol was added to precipitate the product. The resulting solid was filtered and dried in vacuo. The new phosphonates were recrystallized from water and methanol to give methylenephosphonates BP-8 and BP-9 in a good yield. The route for the synthesis of all new SIs is summarized in Figure 6. It was found that BP-6 gave poor SI activity against carbonate and sulfate scale as presented in Table 9. In addition, the results of compatibility tests indicated that BP-6 showed poor compatibility with calcium ions (Tables 2 and 3). The purpose of this study is to check the turbidity of SIs with calcium ions as illustrated in section 2.4. Furthermore, the biological oxygen demand (BOD) for BP-6 showed poor biodegradation activity over 28 days in the OECD 306 test as shown in Figure 15. Therefore, we decided to disregard carrying out the MoedritziIrani reaction for compound BP-6.

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Figure 6. Synthesis of methylenephosphonates by Moedritzer-Irani reaction. (1-(dimethylenephosphonateamino)ethane-1,1-diyl)di phosphonic acid) BP-8: White solid; Yield 45%; mp. 270-272oC; 1H NMR (D2O, 400 MHz) δ 3.42-3.23 (m, 4H), 1.55 (2d, 3JP-H = 6.2 Hz, 3H) ; 13C NMR (D2O, 101 MHz) δ 54.8 (t, 1JPC = 152.0 Hz, C-P2), 52.2 (d, 1JPC = 135.0 Hz, 2CP), 17.4; 31P NMR (D2O, 162.00 MHz) δ 13.2, 9.7. (1,6-bis(dimethylenephosphonateamino)hexane-1,1,6,6-tetrayl)tetra phosphonic acid (BP-9): White solid; Yield 42%; 265-267oC; 1H NMR (D2O, 400 MHz) δ 3.40-3.25 (m, 8H), 1.86-1.84 (m, 4H), 1.46-1.42 (m, 4H); 13C NMR (D2O, 101 MHz) δ 58.6 (t, 1JPC = 153.5 Hz, 2C-P2), 57.0 (d, 1JPC = 136.1 Hz, 4C-P), 33.1, 25.14; 31P NMR (D2O, 162.00 MHz) δ 12.45, 7.12.

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2.4. Compatibility Tests The calcium compatibility activities of BP-6 and BP-7 were tested in-house to identify incompatibility between the scale inhibitor and brine. Compatibility tests were carried out in a mixture of deionized water and synthetic brine. The test procedure is as follows: (1) A total of 10 ml of deionized water and 30000 ppm (3.0 wt.%) sodium chloride is placed in a 50 ml glass bottle. (2) The scale inhibitor is dissolved in this solution to give the desired concentration; for example, 0.024 g of additive in 10 mL of solution gives a 1000 ppm solution of the SI at different concentration of calcium chloride dihydrate in a range of doses from 10-10000 ppm. (3) The bottles are placed in the oven at 100oC and the test time is generally 24 hours, viewing after 0.5, 1, 2, 4 and 24 hours to check the turbidity and/or precipitation of SIs with calcium ion in a synthetic brine solution. Tables 1 to 6 show compatibility data for BP-6 and BP-7. Table 1. Compatibility tests in 10 ppm of Ca2+ and 30000 (3.0 wt.%) NaCl for BP-6. Scale inhibitor BP-6 BP-6 BP-6 BP-6

Dose (ppm)

At Mixing

100 1000 10000 50000

Clear Clear Clear Clear

Appearance 30 mins 1 hour 4 hours Clear Clear Clear Clear



24 hours Clear Clear Clear Clear

Table 2. Compatibility tests in 100 ppm of Ca2+ and 30000 (3.0 wt.%) NaCl for BP-6. Scale inhibitor

BP-6 BP-6 BP-6

Dose (ppm)

100 1000 10000

Appearance At Mixing

30 mins

1 hour

4 hours

24 hours

Clear Haze Haze

Clear Haze Haze

Haze Haze Haze

Haze Haze Haze

Haze Haze Haze

12


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BP-6

50000

Haze

Haze

Haze

Haze

Haze

Table 3. Compatibility tests in 1000 ppm of Ca2+ and 30000 (3.0 wt.%) NaCl for BP-6. Scale inhibitor

BP-6 BP-6 BP-6 BP-6

Dose (ppm)

100 1000 10000 50000


30 mins

1 hour

4 hours

24 hours

Haze Haze Haze Haze

Haze Haze Haze Haze

Haze Haze Haze Haze

Haze Haze Haze Haze

Haze Haze Haze Haze

Table 4. Compatibility tests in 10 ppm of Ca2+ and 30000ppm (3.0 wt.%) NaCl for BP-7. Scale inhibitor BP-7 BP-7 BP-7 BP-7

Dose (ppm)

At Mixing

100 1000 10000 50000


Appearance 30 mins 1 hour 4 hours Clear Clear Clear Clear



24 hours Clear Clear Clear Clear

Table 5. Compatibility tests in 100 ppm of Ca2+ and 30000ppm (3.0 wt.%) NaCl for BP-7. Scale inhibitor

BP-7 BP-7 BP-7 BP-7

Dose (ppm)

100 1000 10000 50000


30 mins

1 hour

4 hours

24 hours

Clear Clear Clear Haze





Table 6. Compatibility tests in 1000 ppm of Ca2+ and 30000ppm (3.0 wt.%) NaCl for BP-7. Scale inhibitor

BP-7 BP-7 BP-7 BP-7

Dose (ppm)

100 1000 10000 50000


30 mins

1 hour

4 hours

24 hours

Clear Haze Haze Haze



Haze Haze Haze Haze

Haze Haze Haze Haze

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2.5. High-Pressure Dynamic Tube Blocking Test Methods Dynamic tube blocking tests to determine relative scale inhibitor performance were carried out on an automated rig (built by Scaled Solutions Ltd., Scotland) at 100oC and 80 bars using a 1mm internal diameter 316 steel test coil. (Figure 7). Both calcium carbonate and barium sulfate scale inhibition were investigated. Details of the test procedure have been given previously.25 The highest test scale inhibitor concentration, used in some but not all tests, was 100ppm and the lowest concentration investigated was 1ppm. The concentration at which rapid tube blocking occurs was taken as the fail inhibitor concentration (FIC) of the scale inhibitor. This is to avoid confusion with the operational use of the abbreviation MIC, which is the minimum inhibitor concentration which prevents scale formation.

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Figure 7. The rig used for high pressure tube blocking testing of scale inhibitors.

Figure 8 shows a typical graph obtained from a single run of the dynamic tube blocking rig, showing, in chronological order, a blank test with no inhibitor, a test to determine the FIC, a repeat FIC test and finally a repeat blank test. In the example in Figure 8, we injected scale inhibitor at 50 ppm, 20, and 10 ppm for 1 h each. After 40 min at 10 ppm (i.e. 194 min on the logger) rapid scale formation occurred. After cleaning of the coil, the repeat scale inhibitor test is carried out but starting from 20 ppm, which is at 214 min on the logger. After 34 min at 10 ppm (307 min on the logger), scale forms rapidly again. This shows that the reproducibility of the experiments is very good which was true for all experiments in this study. The final stage of the 15


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experiment was a new blank test without added inhibitor. In this case, the second blank scaling time was 19 min. We have found that the time for scaling in the second blank test is normally a little longer than the first blank test, both for carbonate and sulfate scaling. This may be due to the time needed to flush out the distilled water cleaning fluid in the system, which is not present in the first blank test. Before the first blank test, we normally flush the scaling brines, one at a time, to check for good flow in the system.

Figure 8. A pressure-time graph showing the four stages of a scale inhibitor test.

For this study, we chose to use model fluids based on production from the Heidrun oilfield, Norway. The composition of aqueous produced fluids from this field is given in Table 7. We 16


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used 50/50 volume mixture of formation water and synthetic seawater to produce barium sulfate scaling. Brines were degassed for 15 min using a vacuum pump to remove dissolve gas that might cause a pump to stop brine injection due to gas bubbles in the line.

Table 7. The composition of Heidrun formation water, seawater, and a 50/50 mixture.

Ion

Heidrun formation water

Seawater (ppm)

(ppm)

50/50 Mixed brine (ppm)

Na+

19,510

10,890

15,200

Ca2+

1020

428

724

Mg2+

265

1368

816.5

K+

545

460

502.5

Ba2+

285

0

142.5

Sr2+

145

0

72.5

SO42-

0

2960

1480

HCO3-

880

120

500

2.6. Scale Inhibitor Seawater Biodegradability Tests In order to determine marine biodegradability of the bisphosphonates of interest, a method based on OECD 306 guidelines was applied. Briefly, biological oxygen demand (BOD) of each BP was measured using the OxiTop ® Control manometric system (WTW, Germany) over a 28 day 17


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period of time and % biodegradability was determined based on comparing measured BOD and calculated theoretical oxygen demand (ThOD) values. Seawater was used as test medium (without added inoculum), and nutrients were supplied to ensure non-limiting conditions for microbial activity and growth. The experimental set-up was composed of test flasks, containing seawater, nutrients and the test chemicals, and three different types of control flasks. Control flasks included: (1) blanks with nutrient-amended seawater only, (2) negative controls with autoclaved (“killed”) seawater, nutrients and the test compounds at 60 mg/l final concentration, and (3) positive controls with nutrient-amended seawater and an easily biodegradable substrate, sodium-benzoate, at 100 mg/l final concentration. Three replicates of each test compound, positive control and blank were measured, while only one flask was prepared as a negative control for each tested chemical. The seawater sample (20 L) was collected at the International Research Institute of Stavanger (IRIS) in Mekjarvik (Stavanger, Norway) where water is supplied from Byfjorden via a pipeline system from the depth of 70 m (temperature was 12°C on sampling day). The sample was transported to our laboratory facilities immediately upon collection and was stored in the dark at 20°C overnight. The next day, seawater (297 ml) was distributed into 510 ml volume amber bottles and nutrient solutions were added as described earlier by our group.25 The OxiTop ® Control set-up was prepared according to manufacturers recommendations and bottles with measuring heads were incubated for 3 hours at 20°C prior to experiment start. After the 3 hr incubation, 1.8 ml of a 1.0 w/w % solution (in distilled water) of each test compound was added to the test and negative control flasks, while 1.0 ml of a 30 g/l sodium benzoate solution was 18


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added to the positive control flasks. The bottles were capped with measuring heads, placed on magnetic stirrers in an incubator cabinet and the measuring heads were started immediately. Oxygen consumption data was recorded over a 28 days period while all flasks were incubated in the dark at 20°C. After 28 days data was called up and raw results were collected. ThOD of each polymer was calculated as described in the OECD 306 guidelines, taking into account complete nitrification. Blank oxygen consumption values (BOD values representing background respiration in seawater) were deducted from each test compound’s BOD prior to determining % biodegradability according to the OECD 306 guidelines.

3. RESULTS AND DISCUSSION 3.1 Synthesis The synthesis of mono and di aminophosphonates BP-4, BP-6 and BP-7 involved the reaction between mono and bis-nitrile with phosphorous trichloride 2 and phosphorous acid 3 under reflux overnight, affording high yields of BPs. All synthesized compounds were characterized by spectroscopic techniques. 1H,

13

C and

31

P NMR spectroscopy are efficient methods to elucidate

the chemical composition of BPs in a liquid state. The

31

P NMR spectra of BP-6 and BP-7

displayed singlet signals at δ 12.71 and δ 15.08 respectively due to the equivalent –PO3H2 moiety indicating high purity. To further expand the novel BPs, two new BPs were synthesized by using the Moedritzer-Irani reaction.22 The synthesized key intermediates BP-4 and BP-7 were reacted with phosphorous acid and formaldehyde in the presence of HCl as a catalyst, affording 19


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good yields of methylene phosphonates BP-8 and BP-9. The structures of new BPs were confirmed on the basis of its spectral data. The 31P NMR spectra of BP-8 showed a distinct two signals at δ 13.2, 9.7 ppm for two different phosphonates. As discussed previously, we did not run any further reactions for Compound BP-6 because the low performance of scale inhibition and incompatibility with calcium ion. Furthermore, In order to introduce carboxylate or sulfonate groups into BP-4 or BP-7, we also investigated Michael addition reaction of the amine groups with vinylic monomers acrylic acid and vinyl sulfonic acid. However, even after long reflux periods with an excess reagent, we found no sign of the desired addition products by NMR spectroscopic analysis. Aqueous sodium chloroacetate was also reacted with BP-4 and BP-7 in an attempt to form aminomethylenecarboxylate groups. Again, no signs of addition products were detected after long reflux periods. We suggest that the primary amines may be deactivated in the amino bisphosphonates in reaction with vinylic monomers or chloroacetate ions, possibly due to internal hydrogen bonding, which is less present at very low pH in the Moedritzi-Irani reaction.

3.2 Calcium compatibility and high-pressure scale inhibitor experiments The detection of the calcium compatibility for the scale inhibitors in industrial oilfield applications is well recognized.4 Most of the phosphonate compounds prevent scale formation by adsorbing onto crystal growth sites but the precipitation of them with calcium ion can cause many problems in the oil production. Herein, metal ion tolerance towards SIs was detected by monitoring turbidity. It was found that the all tested concentrations of BP-7 except 50000ppm 20


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(5wt.%) showed compatibility with Ca2+ at 10 and 100 ppm over the 24 hours test period. Moreover, BP-7 was not compatible with Ca2+ at 1000 ppm as presented in Table 5. Compound BP-6 showed poor compatibility with calcium ion under the same experimental conditions. pH plays an important role in scale inhibition by its effect on the protonation of the scale inhibitor. It was reported that the influences of pH on the inhibition efficiency of the optimal scale inhibitor were investigated.26 Results of this seeded growth study show that an increase in the pH of the crystal growth medium over a pH range of 4 to 9 shows an improvement in inhibitor performance and the poor inhibitor performance is exhibited at pH

Synthesis and Evaluation of New Bisphosphonates as Inhibitors for

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