HYDROXYETHYL CELLULOSE DERIVED FROM BIOMASS AND USE OF HYDROXYETHYL CELLULOSE IN BRINE TREATMENT

Abstract

The hydroxyethyl cellulose derived from biomass is made by preparing a biomass by extracting resins and waxes, acid leaching, and alkali treatment to obtain a cellulose-rich residue, and then bleaching the cellulose-rich residue, followed by hydroxyethylation of the cellulose to obtain hydroxyethyl cellulose. The use of hydroxyethyl cellulose in brine treatment include reacting concentrated brine and hydroxyethyl cellulose with an effluent gas stream to capture CO.sub.2 and reduce salinity of the concentrated brine. The reduced salinity brine may then be useful for enhanced oil recovery methods.

Claims

1. A method of making hydroxyethyl cellulose derived from biomass, comprising the steps of: providing a biomass, wherein the biomass is selected from the group consisting of plant waste biomass and date palm waste; extracting the biomass to produce an extractive-free biomass; acid leaching the extractive-free biomass to obtain a cellulose/lignin-rich residue; alkali treating the cellulose/lignin-rich residue with sodium hydroxide to produce a cellulose-rich residue; bleaching the cellulose-rich residue to obtain bleached cellulose, wherein the bleaching is at 75° C. with 15 wt. % acetic acid, 20 wt. % hydrogen peroxide, and 10 wt. % sulfuric acid; and hydroxyethylating the bleached cellulose with 7.5 wt. % sodium hydroxide and 11 wt. % aqueous urea to produce alkaline hydroxyethyl cellulose with pH between 8.0 and 9.50.

2. The method of making hydroxyethyl cellulose of claim 1, wherein said step of extracting the biomass comprises extracting the biomass with benzene/ethanol (2:1) solvent in a Soxhlet extractor for at least 5 hours.

3. The method of making hydroxyethyl cellulose of claim 1, wherein said step of acid leaching the extractive-free biomass comprises acid leaching the extractive free biomass with 0.1 M hydrochloric acid at 100° C. for at least 2 hours.

4. The method of making hydroxyethyl cellulose of claim 1, wherein said step of alkali treating the cellulose/lignin-rich residue comprises alkali treating the cellulose/lignin-rich residue with 0.1 M sodium hydroxide at 100° C. for at least 2 hours.

5-9. (canceled)

10. A method of treating brine, comprising the steps of: mixing concentrated brine with hydroxyethyl cellulose to produce an aqueous feed stream; feeding the aqueous feed stream through a bubble column reactor; introducing a gas stream into the bubble column reactor while feeding the aqueous feed stream through the bubble reactor, the gas stream comprising between 0.15 wt. % CO.sub.2 and 10 wt. % CO.sub.2, in order to produce treated brine.

11. The method of treating brine of claim 10, wherein the aqueous feed stream has a starting sodium chloride concentration of more than 50 g/L.

12. The method of treating brine of claim 10, wherein the aqueous feed stream has a starting sodium chloride concentration of between 50 g/L and 75 g/L.

13. The method of treating brine of claim 10, wherein the gas stream comprises between 0.03% and 10% CO.sub.2 by volume.

14. The method of treating brine of claim 10, wherein the gas stream comprises between 0.03% and 0.15% CO.sub.2 by volume.

15. The method of treating brine of claim 10, wherein the hydroxyethyl cellulose comprises between 1.0 wt. % and 5.0 wt. % of the aqueous feed stream.

16. Treated brine made according to the method of claim 10, wherein the concentrated brine in the aqueous feed has a concentration of more than 50 g/L sodium chloride and the treated brine has less than 50 g/L sodium chloride.

17. Treated brine made according to the method of claim 10, wherein the treated brine has a pH between 8.0 and 9.50.

18. A method of enhancing oil recovery, comprising the step of administering the treated brine of claim 10 to an oil well during an oil recovery procedure.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0021] FIG. 1A is a plot of the first derivative (DTG curve) of the thermogravimetric analysis (TGA curve) of lignocellulose fractions in date palm waste biomass.

[0022] FIG. 1B is a plot of the first derivative (DTG curve) of the thermogravimetric analysis (TGA curve) of cellulose fractions isolated from date palm waste biomass.

[0023] FIG. 2A is a photograph of cellulose prepared from date palm waste biomass before bleaching.

[0024] FIG. 2B is a photograph of cellulose prepared from date palm waste biomass after bleaching.

[0025] FIG. 3 is a 3-D plot of CO.sub.2 capture percentage and sodium reduction as a function of the pH level of the brine and hydroxyethyl cellulose mixture.

[0026] FIG. 4 is a chart showing interfacial tension of crude oil samples as a function of treatment with brine of different pH.

[0027] Similar reference characters denote corresponding features consistently throughout the attached drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0028] The hydroxyethyl cellulose derived from biomass and use of hydroxyethyl cellulose in brine treatment may include preparing a biomass by extracting resins and waxes, acid leaching, and alkali treatment to obtain a cellulose-rich residue, and then bleaching the cellulose-rich residue, followed by hydroxyethylation of the cellulose to obtain hydroxyethyl cellulose. The biomass may be extracted by Soxhlet extraction with benzene/ethanol (2:1) to produce extractive-free biomass. The extractive-free biomass may then be acid leached by heating and stirring the extractive-free biomass in the presence of hydrochloric acid to obtain a cellulose/lignin-rich residue. The cellulose/lignin-rich residue may then undergo alkali treatment by stirring and heating the cellulose/lignin-rich residue in the presence of sodium hydroxide to produce a cellulose-rich residue. The cellulose-rich residue may be bleached by treating dried cellulose-rich residue with acetic acid, hydrogen peroxide, and sulfuric acid to obtain bleached cellulose. The bleached cellulose may then undergo hydroxyethylation by reacting the bleached cellulose with sodium hydroxide and urea in aqueous solution under mild conditions.

[0029] The source of the biomass may be plant waste. Preferably, the source of the biomass is date palm waste biomass (Phoenix dactylifera L.).

[0030] Methods are provided to use hydroxyethyl cellulose to treat concentrated brine, such as the concentrated brine produced during desalination. This treatment may include injecting effluent gas (10% CO.sub.2 and 90% air) into a bubble column reactor containing a mixture of hydroxyethyl cellulose and concentrated brine. The reaction mixture may be adjusted to a pH above 11.0, in order to increase the rate of the CO.sub.2 dissociation reaction and reduce the sodium concentration by up to 32%. The resulting treated brine sample has a low interfacial tension value.

[0031] The use of hydroxyethyl cellulose in brine treatment may include mixing hydroxyethyl cellulose with waste brine to form an aqueous feed stream. The aqueous feed stream may include between 1 wt. % and 5 wt. % hydroxyethyl cellulose. The starting concentration of sodium chloride in the aqueous feed stream may be between 50.0 g/L and 75.0 g/L. The method further includes passing a gas stream through the aqueous feed in a bubble column reactor. The gas stream may include (by volume) between 0.03% CO.sub.2 and 10% CO.sub.2, between 0.03% CO.sub.2 and 0.15% CO.sub.2, between 0.15% CO.sub.2 and 3% CO.sub.2, or between 3% CO.sub.2 and 10% CO.sub.2. The method may result in reducing the sodium chloride in the aqueous feed to below 50.0 g/L. The method may further result in reducing the carbon dioxide in the gas stream by between 80% and 95%. The method may further result in reducing the pH of the aqueous feed stream from a starting pH of 11.5 to between pH 8 and pH 9.5.

[0032] The brine samples treated with hydroxyethyl cellulose may be used in enhanced oil recovery operations.

[0033] Hydroxyethyl cellulose is a commercially important polymer derived from cellulose and having the structural formula:

##STR00001##

[0034] where R is H or CH.sub.2CH.sub.2OH. Hydroxyethyl cellulose is a gelling and thickening agent used in cosmetics, cleaning solutions, household products, drug delivery (particularly for hydrophilization), and lubricants. It is also used extensively in the oil and gas industry as a drilling mud additive under the name HEC, and in various industrial applications, such as paint and coatings, ceramics, adhesives, emulsion polymerization, inks, construction, welding rods, pencils, and joint fillers.

[0035] NaOH/Urea aqueous solution is a stable system for cellulose esterification. Hydroxyethyl cellulose is a nonionic, water-soluble polymer, dissolved readily in water to form a highly viscous formulation. In addition, it enhances pH value greater than 9.5, which is desired for the combined reaction of CO.sub.2 capture and brine desalination. Based on the molecular structure of hydroxyethyl cellulose, the hydroxyl bond will be broken and attached to the carboxyl group to form a bicarbonate group, which, in turn, will attach to the cations in brine, such as Na, Ca, and Mg. The long structure of hydroxyethyl cellulose will also provide more surface area for ion exchange within a given reaction time. This hexagonal structure of hydroxyethyl cellulose will accommodate more CO.sub.2 as compared to conventional alkaline sources. The method described herein provides a simple pollution-free and homogeneous aqueous solution system for synthesizing hydroxyethyl cellulose.

[0036] A method for making hydroxyethyl cellulose derived from biomass may include sieving 10 g of the biomass and transferring it to a Soxhlet flask, and removing extractives (including but not limited to resins and waxes) by Soxhlet extraction with benzene/ethanol (2:1) for 5 hours to produce an extractive-free biomass (as used herein, the term “extractive-free biomass” means the biomass remaining after extraction of materials that are soluble in benzene or ethanol). Five grams of the extractive-free biomass is then acid leached in a beaker with 0.1 M hydrochloric acid and heating to 100° C. under stirring for 2 hours to produce an insoluble cellulose/lignin-rich residue. The insoluble cellulose/lignin-rich residue is then separated by filtration, washed with deionized water, and air-dried. The dried cellulose/lignin-rich residue is then treated with 0.1 M sodium hydroxide under constant stirring at heating at 100° C. for 2 hours to produce a cellulose residue. The cellulose residue is separated by filtration, washed with 0.1 M sodium hydroxide, and air-dried. The dried cellulose residue is then bleached at 75° C. with 15, 20, and 10 wt. % acetic acid, hydrogen peroxide, and sulfuric acid, respectively. The bleached cellulose was then hydroxyethylated using 7.5 wt. % NaOH and 11 wt. % urea aqueous solution under mild conditions.

[0037] The use of hydroxyethyl cellulose in brine treatment (including, but not limited to, brine produced as reject brine during desalination) may include reacting hydroxyethyl cellulose, effluent gas (CO.sub.2 and air), and high salinity brine at an elevated pH. The method may include using a mixture of 10% CO.sub.2 and 90% air, and reacting the mixture at 20° C. at a pH above 10. The method may include reacting the mixture at a pH above 11. The result of reacting the aqueous mixture with the CO.sub.2/air gas mixture may be a CO.sub.2 uptake value up to 1.6 g CO.sub.2/1 g hydroxyethyl cellulose. The result of treating high salinity brine with hydroxyethyl cellulose may be a treated brine with a reduced sodium concentration of up to 32%. The hydroxyethyl cellulose used to treat the high salinity brine may be hydroxyethyl cellulose produced using date palm biomass as described herein.

[0038] The treated brine resulting from reacting high salinity brine with hydroxyethyl cellulose may be used in enhanced oil recovery applications. The treated brine may have a low interfacial tension (as low as 4.95 mN/m), and thus may be particularly useful in forming water-oil emulsions and removing oil from within porous rocks. The treated brine may be used to supplement any known or yet to be developed method of enhanced oil recovery, which generally include injecting long chain polymers and surfactants into an oil reservoir in order to increase the percentage of oil contained in the reservoir that may be recovered.

[0039] The methods discussed herein provide a new technique for isolating cellulose (low concentration acid-base cellulose isolation) using a combination of 0.1 M NaOH and 0.1 M HCl, and this technique is found to be less expensive relative to the existing cellulose extraction techniques. Additionally, the new technique is more environmentally friendly than existing approaches. The methods disclosed herein may result in a yield greater than 74-76%, thus these methods offer a greater cellulose yield than the reported yield of the prior methods.

[0040] As described herein, hydroxyethyl cellulose is produced from a homogenous date palm cellulose using 7.5 wt % NaOH and 11 wt % urea aqueous solution under mild conditions. Hydroxyethyl cellulose is further utilized in the reaction of a gaseous mixture consisting of carbon dioxide and other gases and high saline water to increase the pH of the solution to 9.5 or greater. This results in the simultaneous capturing of carbon dioxide and reduction of salinity. In the initial step of this process, hydroxyethyl cellulose is mixed with a high saline water to form an aqueous feed stream, in which hydroxyethyl cellulose contributes to 1.0 to 2.0% by weight of the total aqueous feed stream. The gas stream may include about 0.03 to 0.15% carbon dioxide by volume and the aqueous feed stream includes 50-75 g/L sodium chloride.

[0041] As described herein, a new buffering agent extracted from biomass waste, namely, hydroxyethyl cellulose, was used instead of ammonia and calcium hydroxide, as in the Solvay and the modified Solvay processes, respectively. The processes described herein have many benefits, such as reduction in brine salinity and capturing carbon dioxide. Moreover, the methods discussed herein remove the ammonia recovery step of the Solvay process, which is a highly energy intensive step. Additionally, the methods discussed herein avoid the calcium hydroxide used in the modified Solvay process, whose manufacturing results in the production of CO.sub.2 as effluent gas if pure CaO is used instead of waste material containing high content of CaO. Thus, the methods discussed herein are more economical and environmentally friendly than the previously used Solvay and modified Solvay processes. Further, adding hydroxyethyl cellulose will increase the density of the brine feed after mixing with certain molar ratios. This effect will increase the residence time distribution for the CO.sub.2 gas inside the contactor system and accordingly will increase reaction efficiency. On the other hand, the treated brine may be used for enhancing oil recovery processes, such as those using the water flooding method. In this application, hydroxylethyl cellulose is used to reduce the interfacial tension of saline water, which ultimately leads to increased recovery of oil. Further, the use of hydroxylethyl cellulose synthesized from date palm waste biomass avoids the use of other, more expensive chemicals in these processes.

[0042] The following examples further illustrate the present embodiments.

Example 1

Characterization of Palm Biomass Composition

[0043] Palm biomass samples were provided by a local farm, collected from adult size (10-15 years old) date palm trees in Al-Ain, UAE (24122 N, 554441 E). The palm biomass was washed with deionized water to remove dust and any other form of physical impurities and later dried under the shade. Characterization of the palm biomass' composition, including Thermo Gravimetric Analysis (TGA), was performed to ascertain the fractions present in biomass. The TGA results are summarized in FIGS. 1A-1B.

Example 2

Preparation of Hydroxethyl Cellulose Using Palm Biomass

[0044] ACS grade solvents and all reagents were purchased from Sigma Adrich and used as delivered without further purification. Cellulose is physically and chemically surrounded by hemicellulose and lignin, all of which are linked together to form a matrix of lignocellulose. Therefore, pretreatment is needed prior to cellulose isolation. Ten grams of palm biomass was sieved through a predetermined size mesh, transferred to a weighed thimble, and then to a Soxhlet flask. The resins, waxes and other extractives were removed by Soxhlet extraction with benzene/ethanol (2:1) for 5 hours. Cellulose was then isolated from the pretreated/extractive free date palm waste (palm biomass) as follows. 5 g of the extractive free biomass sample was weighed into a 250 mL beaker, followed by acid leaching using 0.1 M hydrochloric acid (HCl) and heating at 100° C. under stirring for 2 hours. The mixture was then filtered, and the insoluble cellulose/lignin-rich residue was washed with 20 ml of deionized water and air-dried overnight. The cellulose/lignin-rich residue was then treated with 0.1 M Sodium Hydrochloride (NaOH) under constant stirring and heating at 100° C. for 2 hours. The mixture was filtered, and the cellulose-rich residue was further washed with 20 ml of 0.1 M NaOH. The cellulose residue was air-dried overnight prior to bleaching. For bleaching, the dried isolated cellulose sample was treated at 75° C. with 15, 20 and 10 wt %, acetic acid, hydrogen peroxide and sulfuric acid, respectively.

[0045] The amount of bleached sample (expressed as a percentage) was the amount of cellulose in the sample and was used for preparation of hydroxyethyl cellulose. Hydroxyethyl cellulose was prepared from the bleached cellulose using 7.5 wt % NaOH and 11 wt % urea aqueous solution under mild conditions.

Example 3

Use of Hydroxyethyl Cellulose to Treat Brine

[0046] A commercially available hydroxyethyl cellulose was mixed based on different weight ratios with high salinity brine at different pH levels. The pH level of the high salinity brine/hydroxyethyl cellulose mixture was adjusted by adding different weight percentages of hydroxyethyl cellulose to 500 ml brine samples (See Table 1). Specifically, weight percentages of hydroxyethyl cellulose between 0.25 wt. % and 2 wt. % were mixed with 500 ml samples of brine having a specific sodium choride concentration (23,710 ppm) for 60 minutes to adjust the pH of the resulting aqueous mixture to between 8.8 and 11.8. This mixture was then fed into a bubble column reactor, and then an effluent gas mixture (10% CO.sub.2 and 90% air by volume) was injected into a bubble column reactor at a flow rate of 700 ml/min., where it reacted with one of the aqueous mixtures. This experiment was conducted in semi-batchmode (batch for the aqueous mixture and continuous for the gas stream) for 120 minutes.

[0047] In order to determine the percentage of CO.sub.2 present in the effluent gas before and after the reaction, the effluent gas from the top of the reactor system was passed through a moisture trap and a CO.sub.2 gas analyzer (Model 600 series, Non-Dispersive Infrared NDIR analyzers, USA). The CO.sub.2 capture percentage with time was recorded and the CO.sub.2 capture efficiency was calculated based upon Equation 1.

[00001]$\begin{array}{cc}{\mathrm{CO}}_2\mathrm{capture}\mathrm{efficiency}=\frac{{\mathrm{CO}}_2\mathrm{captured}\left(\mathrm{mol}\right)}{{\mathrm{CO}}_2\mathrm{feed}\left(\mathrm{mol}\right)}\times 100\%& \left(1\right)\end{array}$

[0048] The CO.sub.2 uptake value was also used to indicate the mass of CO.sub.2 sequestered/mass of hydroxyethyl cellulose (HEC) and calculated according to Equation 2.

[00002]$\begin{array}{cc}{\mathrm{CO}}_2\mathrm{uptake}=\frac{\mathrm{flow}\mathrm{rate}\times \mathrm{flow}\mathrm{time}\times {\mathrm{CO}}_2\left(\mathrm{vol}.\%\right)\times {\mathrm{CO}}_2\left(\mathrm{mol}.wt.\right)}{{\mathrm{CO}}_2\left(\mathrm{mol}.\mathrm{vol}.\right)\times \mathrm{HEC}\left(\mathrm{mass}\right)}& \left(2\right)\end{array}$

[0049] In order to determine the starting and final sodium chloride concentration, the feed and treated brine sodium were diluted and measured with the aid of three reference values of known sodium concentration. The results were validated with an average error within ±10 to 100 ppm. Sodium concentration was analyzed using inductively coupled plasma spectrometry (Varian 710-ES ICP otical emission spectrometer, USA). The percentage reduction in sodium was calculated according to Equation 3, where X.sub.i=the initial sodium concentration in the feed brine (ppm) and X.sub.f=the final sodium concentration in the treated brine (ppm).

[00003]$\begin{array}{cc}\mathrm{Sodium}\mathrm{Reduction}\%=\frac{X_i-X_f}{X_i}\times 100\%& \left(3\right)\end{array}$

[0050] The results of these experiments are summarized in Table 1. The reaction demonstrated high CO.sub.2 capture efficiency at optimum conditions of temperature (around 20° C.) and pH level more than 11.0, and salinity reduction was shown. The peak CO.sub.2 capturing efficiency resulted in a CO.sub.2 uptake of around 1.6 g CO.sub.2 per gram of hydroxyethyl cellulose. The long chain structure of hydroxyethyl cellulose allows for a large number of hydroxyl groups. This structural feature of hydroxyethyl cellulose increases the pH above 10.0, ultimately increasing the rate of the CO.sub.2 dissociation reaction by more than 95%. This leads to a reduction in sodium concentration of up to 32%, as shown in Table 1 and FIG. 3.

TABLE-US-00001 TABLE 1 Resulting pH, CO2 capture, and sodium reduction Initial Final Initial Final Initial Final CO.sub.2 Na.sup.+ HEC pH aq. pH aq. CO.sub.2 CO.sub.2 [Na.sup.+] [Na.sup.+] capture reduction wt. % mix mix Vol. % Vol. % ppm ppm eff. % % 2 11.8 8.8 10 0.2 23,710 16,027 99.2 32.4 1.5 11.01 8.1 10 0.9 23,710 19,537 97.6 17.6 1 10.2 7.9 10 1.6 23,710 21,173 92.4 10.7 0.5 9.2 7.8 10 8.1 23,710 22,097 59.4 6.8 0.25 8.8 7.8 10 9.8 23,710 22,880 48.1 3.5

[0051] Treated brine samples after physical separation from the solid products were subjected to Tracker Tensiometer analysis. The analysis was performed for different crude oil samples with different pH levels to measure variations in interfacial tension over time. This instrument was also used to measure the contact angle between liquids and solids. The liquid drops are oscillated to find out the complex elastic modulus, including viscous and elastic components. The results are illustrated in FIG. 4, which demonstrates evidence that the use of hydroxyethyl cellulose to treat brine reduced the interfacial tension value to 4.95 mN/m. This low value of interfacial tension indicates the high potential of using the treated brine in enhancing oil recovery from reservoir rocks. The low interfacial tension indicates an increased ability to form water-oil emulsions, which assist in driving oil in a more spontaneous way out from rock pores.

[0052] It is to be understood that the system and method for doing something is not limited to the specific embodiments described above, but encompasses any and all embodiments within the scope of the generic language of the following claims enabled by the embodiments described herein, or otherwise shown in the drawings or described above in terms sufficient to enable one of ordinary skill in the art to make and use the claimed subject matter.