Process for making biofuel from spent coffee grounds

Abstract

A system and process for producing biofuel from spent coffee grounds (SCGs) comprises the steps of performing a first operation comprising the steps of obtaining spent SCGs from a source, washing the SCGs, mixing the washed SCGs with an inorganic acid and heating and stirring the washed SCGs to form a SCG slurry without separating coffee oil, drying the SCG slurry, mixing the dried slurry with a solvent and heating the dried slurry and solvent mixture to create a reaction to produce biofuel and residual grounds, and separating the biofuel from the solvent and the residual grounds. The process further includes the step of using an activation agent and heating the residual grounds and the activation agent to create activated residual grounds. Biochar is also produced without activation and heating de-oiled SCGs at lower temperatures without oxygen.

Claims

1. A process for producing biofuel from spent coffee grounds (SCGs) comprises the steps of: performing a first operation comprising the steps of obtaining spent SCGs from a source; washing the SCGs; mixing the washed SCGs with an inorganic acid and heating and stirring the washed SCGs to form a SCG slurry without separating coffee oil; drying the SCG slurry; mixing the dried slurry with a solvent and heating the dried slurry and solvent mixture to create a reaction that produced biofuel and residual grounds; and separating the biofuel from the solvent and the residual grounds.

2. The process of claim 1 wherein the inorganic acid is sulfuric acid.

3. The process of claim 1 wherein the inorganic acid is 20 wt. % sulfuric acid.

4. The process of claim 1 further comprising the steps of using the residual grounds to produce biochar and/or activated carbon.

5. The process of claim 1 wherein the inorganic acid is selected from the list consisting of hydrochloric acid (HCl), nitric acid (HNO.sub.3), and organic acidic heterogeneous catalysts.

6. The process of claim 1 wherein the dried slurry and solvent is heated in the reactor of about 70 C. for about 6-about 20 hours.

7. The process of claim 1 wherein the solvent is methanol.

8. A process for producing biofuel from spent coffee grounds (SCGs) comprising the steps of: obtaining spent SCGs from a source; washing the SCGs; mixing the washed SCGs without separating coffee oil from the SCGs with sulfuric acid and stirring and heating to form a slurry; drying the slurry; mixing the dried slurry with methanol as a solvent and heating to create a reaction for producing biofuel and residual grounds; separating the biofuel from the methanol and residual grounds; and purifying the biofuel.

9. The process of claim 8 further comprising the step of heating the residual grounds to produce activated residual grounds.

10. The process of claim 8 further comprising the steps of removing the solvents from the residual grounds using natural evaporation, heating or by use of blowing air.

11. The process of claim 8 further comprising the step of heating an activation agent and the residual grounds in a non-oxygen gas environment to remove any solvents from the residual grounds to create a pyrolysis environment and then cooling to produce activated residual grounds.

12. The process of claim 9 further comprising the step of using an activation agent to produce the activated coffee grounds.

13. The process of claim 9 wherein the activation agent is one or more activation agents selected from the list consisting of carbon dioxide, water vapor and nitrogen, zinc chloride, phosphoric acid, nitric acid and hydrochloric acid.

14. The process of claim 8 wherein the residual grounds are heated to produce biochar.

15. A process for producing biofuel from spent coffee grounds (SCGs) comprises the steps of: performing a first operation comprising the steps of obtaining spent SCGs from a source; washing the SCGs; mixing the washed SCGs with an inorganic acid and heating and stirring the washed SCGs to form a SCG slurry without separating coffee oil; drying the SCG slurry; mixing the dried slurry with a solvent and heating the dried slurry and solvent mixture to create a reaction that produced biofuel and residual grounds; and separating the biofuel from the solvent; wherein said solvent is methanol; and wherein the inorganic acid is selected from the list consisting of sulfuric acid, hydrochloric acid, nitric acid, and organic acidic heterogeneous catalysts.

16. The process of claim 15 wherein the inorganic acid is 20 wt. % sulfuric acid.

17. The process of claim 15 wherein the inorganic acid is a 20 wt. % sulfuric acid and the mixture of SCGs and inorganic acid is heated to about 70 C. for about 6-about 20 hours.

18. The process of claim 15 further comprising the step of using an activation agent and heating the residual grounds and the activation agent to cause a chemical reaction to create activated residual grounds.

19. The process of claim 15 wherein the activation agent is one or more activation agents selected from the list consisting of carbon dioxide, water vapor and nitrogen, zinc chloride, phosphoric acid, nitric acid and hydrochloric acid.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) These and other features, aspects, and advantages of the present invention will become better understood with regard to the following description, appended claims, and accompanying drawings where:

(2) FIG. 1 is a flow diagram illustrating the prior art method of the three-step process of solvent extraction for producing biofuel using hexane or a hexane/isopropanol mixture to extract oil and whereby after oil extraction, a two-step process of acid esterification is followed by alkaline transesterification to convert the oil into biofuel;

(3) FIG. 2 is a graph showing the effect of reaction temperature on coffee biofuel yield and acid value, 20 wt. % H.sub.2SO.sub.4 mixing applied to SCGs with a reaction time of about 17 hours;

(4) FIG. 3 is a graph showing the effect of various sulfuric acid concentrations and different reaction times on the yield of coffee biofuel, the dotted line represents a mark/maximum point of coffee oil yield (17.32 wt. %);

(5) FIG. 4 is a graph showing the acid value of coffee biofuel influenced by the concentration of sulfuric acid and reaction time, the dotted line represents the ASTM standard of 0.5 mg KOH/g biofuel;

(6) FIG. 5 is a graph showing coffee biofuel yield from 20 wt. % H.sub.2SO.sub.4 mixed with SCGs with a reaction temperature of 70 C., the dotted line represents a mark point of coffee oil yield (17.32 wt. %);

(7) FIG. 6 is a graph showing acid value of coffee biofuel made from 20 wt. % H.sub.2SO.sub.4 mixed with SCGs with a reaction temperature of 70 C., the dotted line represents the ASTM D6751 standard of 0.5 mg KOH/g biofuel;

(8) FIG. 7 is a flow diagram showing the direct esterification process of the subject invention for creating biofuel from SCGs;

(9) FIG. 8A is a flow diagram showing the system of the subject invention having a first operation for obtaining a lipid content from SCGs to produce biofuel;

(10) FIG. 8B is a flow diagram showing the system of the subject invention having a first operation for obtaining a lipid content from SCGs to produce biofuel;

(11) FIG. 9A is a flow diagram showing the process of the subject invention, showing the steps of a first operation for producing biofuel from SCGs;

(12) FIG. 9B is a flow diagram showing the process of the subject invention showing the steps of a second operation for producing activated residual grounds for creating carbon products, such as biochar or activated carbon specialized for mercury control;

(13) FIG. 10 is a flow diagram showing the system of the subject invention having a second operation for creating activated grounds (SCG-activated carbon); and

(14) FIG. 11 is a flow diagram showing the system of the subject invention having a second operation for creating biochar.

DETAILED DESCRIPTION OF THE INVENTION

(15) The subject invention is a new and novel process of producing biofuel from spent coffee grounds (SCG) that does not require the steps of producing coffee oil thereby saving processing time and expense. Unlike prior systems and processes that first use esterification of the free fatty acids in SCG using acid catalysts, such as sulfuric acid, to convert the free fatty acids into esters and then uses transesterification of the glycerides into esters (biofuel) using alkaline catalysts (NaOH, KOH, or methoxides), the system and process of the subject invention does not require producing coffee oil thereby uses only one reaction step of acid catalyzed transesterification. Further, the subject invention includes the step of coating the SCG solids with sulfuric acid which functions to add sulfate thereby enhancing the produced biochar or activated carbon produced. In describing this and the other preferred embodiments and the various elements of the invention described herein and illustrated in the drawings, specific terminology will be resorted to for the sake of clarity. However, the invention is not intended to be limited to the specific terms so selected, and it is to be understood that each specific term includes all technical equivalents that operate in a similar manner to accomplish a similar purpose. As used herein, the terms biofuel includes biodiesel or any other fuel that meets the specifications of the biofuel produced using the subject invention.

(16) The process and system of the subject invention was developed by using spent coffee grounds (SCGs) collected from a locally owned coffee shop. The process and system also applied to SCGs collected from other sources, such as instant coffee producers, restaurants, etc. Solvents used for free fatty acid titration, such as hexane, and isopropyl alcohol were all HPLC grade (Fisher Scientific). Titration indicator, 1 w/v % phenolphthalein solution, was prepared from a phenolphthalein powder in a laboratory. Potassium hydroxide pellets were used for titration.

(17) The process of the subject invention was conducted using a Soxhlet apparatus, and both the distillation flask and extractor were wrapped with heating tapes to maintain the desired reaction temperature. The process of the subject invention can also be carried out in other devices that can enable acid catalyzed transesterification of the SCGs. SCGs were first impregnated (mixed) with the solvent (catalyst) for direct esterification. Since the acid value of coffee oil was higher than 2 mg KOH/g oil (6.18-6.94 mg KOH/g oil), sulfuric acid (95.0 to 98.0 wt. %) was selected as the catalyst to avoid the saponification between free fatty acids and the alkaline catalyst. SCGs (100 g dry weight) were impregnated (mixed) with various concentrations of sulfuric acid (5, 10, 15, and 20% of dry SCGs weight) diluted by de-ionized water. The slurry was heated to 70 C. and stirred for 3 hours, after which the slurry was dried in an oven at 105 C. for 24 hours to remove moisture.

(18) Fifty (50) grams of impregnated SCGs were measured and loaded into a cellulosic thimble. Two hundred fifty (250) ml of methanol was measured and placed in a distillation flask. Scale-up operations are possible with similar SCG to solvent ratios. After transesterification, the reaction mixture (methanol, glycerin, and coffee biofuel) was transported into a rotary evaporator for methanol recovery at 70 C. and moderate vacuum. Thereafter, coffee biofuel was moved into a separatory funnel and 20 ml of pre-heated (80 C.) de-ionized water was then added to the funnel and the mixture was settled for at least 30 minutes for glycerin separation. Afterwards, the bottom glycerin layer and mid layer of washing water were drained out. More pre-heated de-ionized water was used to wash the coffee biofuel until the pH of the washing water became the same as that of the initial de-ionized water. As a final step, after the washing water was drained, the washed biofuel was placed into a centrifuge (5000 rpm for 30 minutes) to separate any remaining impurities, such as trace amounts of water and fine SCGs particles. Parametric studies were performed based on the reaction temperature (60 C., 70 C., and 80 C.), reaction time (3, 4, 5, 6, 7, 10, 12, and 17 hours), and the catalyst (H.sub.2SO.sub.4) dosage (5 wt. %, 10 wt. %, 15 wt. %, 20 wt. %) to determine the optimum operating conditions.

(19) Soxhlet extraction of coffee oil with hexane and isopropyl alcohol (1:1 v/v, 250 ml) was performed to determine the maximum available oil content within the SCGs, which was used as an indicator for reaction completion. Various coffee oil extraction conditions were tested and the optimum extraction condition was 6 hours at 70 C. The AOCS titration method Cd 3d 63 was performed to determine the acid value of both coffee oil and biofuel.

(20) The biodiesel yield was calculated via Equation 1,
Biofuel Yield %=(M.sub.B/M.sub.SCGs)100%
Where,
M.sub.B: mass of biofuel, g
M.sub.SCGs: mass of dried spent coffee grounds, g
Also, the oil to biofuel conversion rate was calculated via Equation 2,
Conversion Rate %=(M.sub.B/M.sub.Oil)100%
Where,
M.sub.B: mass of biofuel, g
M.sub.Oil: mass of available coffee oil, g
Results

(21) The maximum available oil content within the SCGs was 17.320.93 wt. %. The moisture content of the SCGs ranged from 40.93 wt. % to 50.32 wt. %. The acid values of the coffee oil ranged from 6.18 to 6.94 mg KOH/g oil, which suggested that alkaline transesterification alone is not sufficient to make it into biofuel.

(22) FIG. 2 indicates the effect of temperature on the yield of biofuel and its acid value. All samples were impregnated with 20 wt. % H.sub.2SO.sub.4 and reacted for 17 hours to ensure complete reaction. An increase of biofuel yield from 60 C. (16.190.16 wt. %) to 70 C. (17.080.27 wt. %) was observed with a p value of 0.053. However, biofuel yield between 70 C. and 80 C. were not statistically different (p value of 0.559). At 70 C., the average acid value (0.790.18) was also the lowest among the three temperatures. Therefore, 70 C. was determined as the optimum reaction temperature of the acid impregnation process of SCGs.

(23) FIG. 3 shows the effect of sulfuric acid concentration (ranging from 5 wt. % to 20 wt. %) on the coffee biofuel yield. Ail the samples were reacted at 70 C. and the dotted line represented the coffee oil yield. When impregnating SCGs with higher concentrations of sulfuric acid, the coffee biofuel yield increased. The effect of various sulfuric acid impregnated concentration on the coffee biofuel yield with different reaction time was also studied in FIG. 3. Although the effect of reaction time played an important role in converting coffee oil to coffee biofuel when the impregnated concentration of sulfuric acid was low (5 and 10 wt. %). The effect of reaction time was negligible when the impregnated concentration reached 20 wt. %.

(24) The acid value of coffee biofuel decreased as the concentration of sulfuric acid increased as shown in FIG. 4. Although the acid value of both 7-hour sample and 17-hour sample decreased as the impregnated concentration increased, 17-hour sample resulted with a lower acid value at every impregnated concentration point. At the same time, 12-hour sample had a similar acid value with the 17-hour sample, but the reaction time was much shorter. As noticed, all samples did not meet the ASTM D6751 acid value requirement of 0.5 mg KOH/g (doffed line).

(25) Improvements such as alkaline wash could be applied to decrease the acid value. Based on the analysis of FIG. 3 and FIG. 4, 20 wt. % sulfuric acid was chosen to be the best impregnated concentration.

(26) FIG. 5 shows the effect of reaction time on the biodiesel yield from the samples of 20% impregnated SCGs with a reaction temperature of 70 C. The increase in yield with the extended reaction time leveled off after the reaction time reached 7 hours. The difference in the average biofuel yield between 7-hour sample and 12-hour sample was 0.76 wt. % (p-value: 0.32). However, as shown in Table 1, the concentration of total glycerol of 7-hour sample was well above the limit (0.24%) of the ASTM D6751 standard, which indicated that the conversion of coffee oil to biofuel was incomplete. Table 1 also demonstrates that both 12-hour and 17-hour samples met the selected ASTM D6751 requirements except the acid value. The figure also shows that the conversion rate of the coffee oil to the coffee biofuel was 98.50 wt. % (coffee oil yield was 17.32 wt. %, which was the dotted line in the figure).

(27) TABLE-US-00001 TABLE 1 Summary of the selected ASTM D6751 test results. The coffee biofuel results of 20 wt. % H.sub.2SO.sub.4 impregnated SCGs with a reaction temperature of 70 C. and a reaction time of 7, 12, and 17-hour were presented in the table. Reaction ASTM Time (hours) 7 12 17 D6751 Mono- 2.14% 0.06% 0.05% glycerides Di-glycerides 40.47% 0.45% 0.04% Tri-glycerides 34.74% 0.08% 0.03% Total Glycerol 10.03% 0.02% 0.02% 0.24 max. (mass %) Free Glycerol 0.000% 0.000% 0.001% 0.02 max. (mass %) Kinematic 5.36 5.27 1.9-6.0 viscosity (40 C.; mm.sup.2/s) Oxidation 6.62 33.42 3 min. stability (110 C. h; Rancimat; h) Acid value 1.90 0.80 0.79 0.5 max. (mg KOH/g)
In addition, the acid values of the resulted coffee biofuel with various reaction time were displayed in FIG. 6. Based on concurrently analyzing of FIG. 5 and FIG. 6, while the biofuel yield tended to stay unchanged after 7 hours, the acid value continued to decline. According to ASTM D6751, the maximum allowable acid value in the biofuel should be less than 0.5 mg KOH/g. Although the acid value did not meet the regulation, it could be easily solved by washing the coffee biofuel with the alkaline solution. In addition, the coffee biofuel could mix with a low acid value biofuel so that the mixed product could fulfill the requirement. In order to lower the acid value, 1% NaOH solution was used to wash the 12-hour biofuel sample and the acid value reduced to 0.31 mg KOH/g, which met the requirement.

(28) Biofuel yield and acid value of three critical time points (7, 12, and 17 hours) are summarized in Table 2. The results are shown in FIGS. 2, 3, and 4, show that 20 wt. % H.sub.2SO.sub.4 at 70 C. provides the best transesterification reaction. Table 2 illustrates the yield of coffee biofuel between 12-hour and 17-hour samples were close, while the 7-hour sample was lower than the other two samples. Also, the acid value of the 7-hour sample was close to 2.0 mg KOH/g biofuel while 12-hour and 17-hour samples were similar and both of them were approximately 0.80 KOH/g biofuel. Based on the coffee biofuel yield, acid value, and time consuming, it was determined that 12 hours is the optimized reaction time.

(29) TABLE-US-00002 TABLE 2 Comparison of the biofuel yield and acid value between three critical time points. The reaction temperature was set to be 70 C. for all samples. 20 wt. % H.sub.2SO.sub.4 impregnated SCGs were used. Biodiesel Yield Acid Value (mg Samples (wt. %) KOH/g biodiesel) 7 hours 14.66 0.12 1.90 0.04 12 hours 17.06 0.70 0.80 0.01 17 hours 17.08 0.27 0.79 0.07
The FAME (fatty acid methyl ester) composition of the coffee biofuel obtained from the optimum condition including the following: C16:0 (44.3%), C18:0 (8.8%), C18:1 (6.1%), C18:2 (30.8%), C20:0 (3.3%), C22:0 (0.3%). Coffee biofuel produced through the subject process contained mainly C16:0 and C18:2.

(30) The total biofuel production time of the subject process is comparable with the total biofuel production time of conventional methods. Also, the yield of coffee biofuel gives a 17.060.70 wt. % coffee biofuel yield and equals to a 98.50 wt. % coffee oil to coffee biofuel conversion rate under 70 C. and 12 hours via 20 wt. % H.sub.2SO.sub.4 impregnated SCGs. It was found that the produced coffee biofuel has a FAME profile that mainly contained C16:0 and C18:2. In a preferred embodiment of the invention the reaction condition is at 70 C. and about 6-about 20 hours using 20 wt. % sulfuric acid (H.sub.2SO.sub.4) mixed with the SCGs. It was found that the yield of coffee biofuel using the process of the subject invention reached 17.060.70 wt. % with an acid value of 0.31 mg KOH/g after alkaline washing. The corresponding conversion rate of coffee oil to coffee biofuel was found to be 98.50 wt. % under the preferred reaction condition.

(31) Referring to FIGS. 7-9, the first operation 100 of the process for producing bio-products from spent coffee grounds (SCGs) is shown comprising the steps of obtaining SCGs 102 from a source 104 (Step 200) and delivering the them to a conversion facility 106. The delivered SCGs 102 are washed (Step 202), such as by a water wash 107, and are placed within a mixing vessel 108 and are mixed (impregnated) with an inorganic acid 110 (Step 204), such as sulfuric acid, to form a slurry 112 of coated SCGs. Preferably, the sulfuric acid is diluted such as by de-ionized water to form a 20 wt. % sulfuric acid. It should be understood that other inorganic acids 110 may be utilized from the list consisting of hydrochloric acid (HCl), nitric acid (HNO.sub.3), and other organic acidic heterogeneous catalysts. The slurry 112 is heated (Step 206), such as in a heating vessel 114, and then dried (Step 208). Preferably, the slurry 112 is heated in the heating vessel to about 70 C. for a period of about 3-about 4 hours and then dried at a temperature of about 105 C. for about 24 hours to remove moisture from the slurry 112. After the slurry 112 has been dried, the dried slurry is placed into a reaction chamber 116 and mixed with a reaction solvent 118 (Step 210), such as methanol, for transesterification, to create a reaction mixture 120 of methanol 122, glycerin 124 and biofuel 126. The reaction mixture 120 is then transported to a recovery vessel 128, such as a rotary evaporator, for methanol recovery (Step 212). Preferably, the reaction vessel 128 operates to heat the reaction mixture to a temperature of about 70 C. and provide a moderate vacuum environment for evaporating the methanol 122 which is then cooled and reclaimed for reuse. After the methanol 122 has been removed from the reaction mixture 120, the remaining reaction mixture is then placed into a separation vessel 130 and is mixed with de-ionized water 132 allowed to settle for glycerin separation (Step 214). Preferably, the de-ionized water 132 is pre-heated to about 70 C. and allowed to settle for about 30 minutes. After sufficient time to settle, the glycerin 124 and de-ionized water 132 are drained out (Step 216). The biofuel 126 remaining in the separation vessel 130 is washed with an additional amount of de-ionized water 132 (Step 218) to wash the biofuel 126. It should be understood that the amount of additional de-ionized water 132 should be sufficient for ensuring that the pH of the additional de-ionized water is the same as the initial deionized water. The additional de-ionized water 132 is then removed (Step 220) and the washed biofuel 126 is transferred into a centrifuge 134 to separate any remaining impurities 136, such as any remaining de-ionized water and any fine SCG particles (Step 222).

(32) Referring to FIGS. 9B, 10 and 11 the second operation 140 of the process for producing biofuel from spend coffee grounds is shown for producing activated residual grounds for producing carbon products, such as biochar or activated carbon, specialized for mercury control. The residual grounds 138 (waste solidsthe material remaining after glycerin and biofuel is separated from the reaction mixture) are placed into a heating chamber 142, such as a tube furnace, for heating the residual grounds 138 and a non-oxygen gas 144, such as nitrogen, is blown into the heating chamber 142 to create a pyrolysis environment (to drive off oxygen) (Step 224). To produce activated residual grounds 148, as shown in FIG. 10, which is not required for producing biochar 150 (FIG. 11) an activation agent 146, such as carbon dioxide or water vapor, is injected into the heating chamber 142, such as by a carrier gas, and heated to cause chemical activation (Step 226) producing activated residual grounds (SCG-activated carbon) 148. It should be understood that in a preferred embodiment of the invention one or more activation agents selected from the list consisting of carbon dioxide (CO.sub.2), water vapor and nitrogen (H.sub.2o and N.sub.2), zinc chloride (ZnCl.sub.2), phosphoric acid (H.sub.3PO.sub.4), nitric acid (HNO.sub.3) and hydrochloric acid (HCl) may be utilized an activation agent. The heating chamber is preferably heated to about 800-1000 C. for about 30 minutes to about 2-4 hours. Preferably, higher temperature pyrolysis is used to produce larger surface area but with a lower yield. After chemical/physical activation, the activated residual grounds 148, and/or the biochar 150, are cooled (Step 228) and the cooled activated residual grounds (SCG-activated carbon) 148 and/or the biochar 150 are collected for use (Step 230).

(33) The process of the subject invention is a new and novel system and process that operates to produce biofuel from SCGs that does not require the need to produce coffee oil since the coffee oil is consumed for biofuel during the reaction steps thereby reducing time and expense. Unlike prior art processes where solvent extraction is followed by a two-step process of first esterification of free fatty acids in the SCGs using acid catalysts, such as sulfuric acid, to convert the free fatty acids to esters, and a second step of transesterification of the glycerides into esters (biofuel) using alkaline catalysts, NaOH, KOH, or methoxides. The process of the subject invention is an acid catalyzed transesterification process, using just an acid catalyst in a single step. Thus, the process of the subject invention significantly reduces the expense of the prior art processes. It should also be understood that the solvent extraction process, oil and solids are separated after solvent extraction, thus, solids remain. During the process of the subject invention, the solids have been mixed (coated) with sulfuric acid. The added sulfate operates to enhance its functions as biochar or activated carbon.

(34) It should also now be apparent to one skilled in the art that the three-step process (solvent extraction, esterification and transesterification) required in prior art systems to make biofuel from spent coffee grounds is relatively costly to utilize in large scale production. In contract the direct transesterification process of the subject invention produces biofuel from spent coffee grounds without the need of oil extraction by combining esterification, and transesterification into a two-step process to directly produce biofuel thereby significantly reducing production costs. The process, as shown in FIG. 7 directly uses a new and novel process using transesterification to directly obtain biofuel from SCGs without the solvent extraction and esterification steps to produce coffee oil of the prior art process, as shown in FIG. 1. Thus, solvent the step of solvent extraction and subsequent solvent recovery is eliminated.